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EVOLUTION 93. S. D. Weatherbee and S. B. Carroll, Cell 97, 283 (1999).

94. W. G. M. Damen, M. Hausdorf, E.-A. Seyfarth, D. Tautz, Proc. Natl. Acad. Sci. U.S.A. 95, 10665 (1998).

95. M. J. Telford and R. H. Thomas, ibid., p. 10671.

96. M. Averof and N. Patel, Nature 388, 682 (1997).

97. M. Averof and M. Akam, ibid. 376, 420 (1995).

98. E. Mouchel-Vielh, C. Rigolot, J.-M. Gilbert, J. S. Deutsch, Mol. Phylogenet. Evol. 9, 382 (1998).

99. J. K. Grenier, T. L. Garber, R. Warren, P. M. Whitington, S. B. Carroll, Curr. Biol. 7, 547 (1997).

100. R. Warren, L. Nagy, J. Selegue, J. Gates, S. Carroll, Nature 372, 458 (1994).

101. S. D. Weatherbee et al., Curr. Biol. 9, 109 (1999).

102. A. Burke, C. Nelson, B. Morgan, C. Tabin, Development 121, 333 (1995).

103. J. R. Nursall, Nature 183, 1170 (1959); P. E. Cloud, Science 160, 729 (1968); R. A. Raff and E. C. Raff, Nature 228, 1003 (1970); K. M. Towe, Proc. Natl.

Acad. Sci. U.S.A. 65, 781 (1970).

104. A. Krogh, The Comparative Physiology of Respiratory Mechanisms (Univ. of Pennsylvania Press, Philadelphia, 1941); B. Runnegar, Alcheringa 6, 223 (1982).

105. G. J. Vermeij, Science 274, 525 (1996).

106. L. A. Derry, A. J. Kaufman, S. B. Jacobsen, Geochim.

Cosmochim. Acta 56, 1317 (1992).

107. In oxygenic photosynthesis, CO2 ⫹ H2O 3 CH2O ⫹ O2. Although photosynthesis provides the ultimate source of atmospheric oxygen, respiration essentially runs the photosynthetic equation backward, consuming oxygen. The potential for oxygen to accumulate in the atmosphere will arise only when photosynthetically derived organic matter is buried, limiting consumption by respirers. Oxygen not used in respiration may react with old organic matter released during erosion or with reduced species in minerals or in solution, but if rates of oxygen production exceed those of consumption, oxygen will increase in the ocean/atmosphere system. Carbon isotopes provide a proxy for organic C burial rates, with higher values of ␦13C indicating a higher burial ratio of organic to carbonate C. 108. D. E. Canfield and A. Teske, Nature 382, 127 (1996).

109. D. E. Canfield, ibid. 396, 450 (1998).

110. P. F. Hoffman, A. J. Kaufman, G. P. Halvorson, D. P. Schrag, Science 281, 1342 (1998).

111. G. Vidal and A. H. Knoll, Nature 297, 57 (1982).

112. H. Kimura, R. Matsumoto, Y. Kakuwa, B. Hamdi, H. Zibaseresht, Earth Planet. Sci. Lett. 147, E1 (1997).

113. J. K. Bartley et al., Geol. Mag. 135, 473 (1998).

114. J. A. Baud, M. Magaritz, W. T. Holser, Geol. Rundsch.

78, 649 (1989).

115. S. Bengtson, in Early Life on Earth, S. Bengston, Ed. (Columbia Univ. Press, New York, 1994), pp. 412– 425.

116. N. J. Butterfield, Paleobiology 23, 247 (1997).

117. K. J. Peterson, R. A. Cameron, K. Tagawa, N. Satoh, E. H. Davidson, Development 126, 85 (1998).

118. G. G. Miklos, Mem. Assoc. Australas. Palaeontol. 15, 7 (1993).

119. J. G. Gehling, Alcheringa 11, 337 (1987).

120. M. A. McCaffrey et al., Geochim. Cosmochim. Acta 58, 529 (1994).

121. M. D. Brasier, Geol. Soc. Spec. Publ. 70, 341 (1993).

122. We thank M. A. Fedonkin, S. Xiao, and J. P. Grotzinger for permission to photograph some of the specimens in Fig. 1; J. Grenier, L. Olds, and S. Paddock for help with illustrations; H. Bode, E. Davidson, K. Peterson, and G. Budd for pointers; S. Bengtson, N. Shubin, A. Adoutte, E. Davidson, J. Grenier, and G. Halder for comments on the manuscript; and J. Wilson for help with its preparation. A.H.K. is supported in part by the NASA Astrobiology Institute. S.B.C. is an investigator of the Howard Hughes Medical Institute.

REVIEW

The Evolution of Dinosaurs Paul C. Sereno The ascendancy of dinosaurs on land near the close of the Triassic now appears to have been as accidental and opportunistic as their demise and replacement by therian mammals at the end of the Cretaceous. The dinosaurian radiation, launched by 1-meter-long bipeds, was slower in tempo and more restricted in adaptive scope than that of therian mammals. A notable exception was the evolution of birds from small-bodied predatory dinosaurs, which involved a dramatic decrease in body size.

Recurring phylogenetic trends among dinosaurs include, to the contrary, increase in body size. There is no evidence for co-evolution between predators and prey or between herbivores and flowering plants. As the major land masses drifted apart, dinosaurian biogeography was molded more by regional extinction and intercontinental dispersal than by the breakup sequence of Pangaea.

During the past 30 years, intensified paleontological exploration has doubled recorded dinosaurian diversity (1) and extended their geographic range into polar regions (2). Exceptional fossil preservation has revealed eggshell microstructure (3), nesting patterns and brooding posture among predators (4), and epidermal structures such as downy filaments and feathers (5, 6). Analysis of bone microstructure and isotopic composition has shed light on embryonic and posthatching growth patterns and thermophysiology (7).

Footprint and track sites have yielded new clues regarding posture (8), locomotion (9), and herding among large-bodied herbivores (10). And the main lines of dinosaurian descent have been charted, placing the aforementioned discoveries in phylogenetic context (11).

Department of Organismal Biology and Anatomy, University of Chicago, 1027 East 57th Street, Chicago, IL 60637, USA.

The most important impact of this enriched perspective on dinosaurs may be its contribution to the study of large-scale evolutionary patterns. What triggers or drives major replacements in the history of life?

How do novel and demanding functional capabilities, such as powered flight, first evolve? And how does the breakup of a supercontinent affect land-based life? The critical evidence resides in the fossil record—in the structure, timing, and geography of evolutionary radiations such as that of dinosaurs.

Early Dinosaurs: Victors by Accident Did dinosaurs outcompete their rivals or simply take advantage of vacant ecological space? The ascendancy of dinosaurs on land transpired rather rapidly some 215 million years ago, before the close of the Triassic.

Herbivorous prosauropods and carnivorous coelophysoid ceratosaurs spread across Pangaea, ushering in the “dinosaur era”: a 150-

million-year interval when virtually all animals 1 m or more in length in dry land habitats were dinosaurs.

Dinosaurs, the descendants of a single common ancestor, first appeared at least 15 million years earlier but were limited in diversity and abundance (Fig. 1). Well-preserved skeletons discovered recently in 230-million-year-old rocks (mid-Carnian in age) provide a glimpse of a land radiation already underway (12). The most fundamental adaptations for herbivory and carnivory among dinosaurs had already evolved. A novel means for slicing plant matter, utilizing inclined tooth-to-tooth wear facets, is fully developed in the meter-long herbivore Pisanosaurus, the oldest known ornithischian (Fig. 1, left; Fig. 2, node 1; Fig. 3A, feature 4).

Jointed lower jaws and a grasping hyperextendable manus for subduing and eviscerating prey are present in the contemporary predators Eoraptor and Herrerasaurus, which are the oldest well-preserved theropods (Fig. 1, right; Fig. 2, node 41; Fig. 3B, features 11 and 12).

Traditional scenarios for the ascendancy of dinosaurs that invoke competitive advantage (13) have difficulty accommodating the substantial temporal gap (15 million years or more) between the initial radiation of dinosaurs and their subsequent global dominance during the latest Triassic and Early Jurassic (14). Opportunistic replacement of a diverse array of terrestrial tetrapods (nonmammalian synapsids, basal archosaurs, and rhynchosaurs) by dinosaurs is now the most plausible hypothesis (11, 14, 15). This pattern is broadly similar to the replacement of nonavian dinosaurs by therian mammals at the end of the Cretaceous. Recent

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Fig. 1. Temporally calibrated phylogeny of Dinosauria, showing known temporal durations (solid bars), missing ranges (shaded bars), and ranges extended by fragmentary or undescribed specimens (dashed bars). At left is tabulated the number of recorded nonavian dinosaurian genera per stage and an estimated curve of generic diversity, taking in to account available outcrop area (87). Basal or primitive taxa, in general, appear earlier in time than more

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derived members of a clade. Long missing ranges result from preservational bias against small body size (less than 2 m), which truncates the early record of many clades, and from intervals for which there is little corresponding exposed terrestrial rock (such as the Middle Jurassic). The shaded zone (bottom) indicates the initial stage of the dinosaurian radiation before their dominance of land faunas in taxonomic diversity and abundance.

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EVOLUTION evidence, moreover, has implicated similar primary agents of extinction, namely global climatic change (seasonal aridity) (16) and, possibly, flood basalts associated with the opening of the Atlantic Ocean and extraterrestrial impacts (17).

Although the timing of end-Triassic extinctions remains less resolved than events at the end of the Cretaceous (18), dinosaurian and mammalian radiations cannot be explained as the result of niche subdivision, increased com-

petition, or progressive specialization (escalation), or as taxonomic, taphonomic, or stochastic artefacts (19). These two great land radiations, the conventional signposts for the subdivision of Phanerozoic time, constitute opportunistic infilling of vacant ecospace after physical perturbation on a global scale.

Ornithischians: Bird-Hipped Croppers Ornithischians processed plant matter by novel means. Vegetation was cropped by a

Fig. 2. Phylogeny of Dinosauria, showing the relationships among ornithischians (left) and saurischians (right). Thickened internal branches are scaled to reflect the number of supporting synapomorphies (scale bar equals 20 synapomorphies). Phylogenetic structure and internal branch lengths are based on minimum-length trees from maximum-parsimony analyses of approximately 1100 characters under delayed characterstate optimization (Table 1). The evolution of hadrosaurids within Ornithopoda (nodes 11 through 18) and birds within Tetanurae (nodes 46 through 57) provide the best examples of sustained skeletal transformation. Numbered nodes are listed here, with normal and bold text indicating stem- and node-based taxa, respectively (88): 1, Ornithischia; 2, Genasauria; 3, Thyreophora; 4, Eurypoda; 5, Stegosauria; 6, Stegosauridae; 7, Ankylosauria; 8, Nodosauridae; 9, Ankylosauridae; 10, Neornithischia; 11, Ornithopoda; 12, Euornithopoda; 13, Iguan-

horny bill and then sliced by tooth rows composed of expanded overlapping crowns with inclined wear facets (Fig. 3A, features 1 through 4). The predentary, a neomorphic bone, provided a stable platform for the lower bill while allowing the dentaries to rotate during (isognathus) occlusion (20). A holding space, or cheek, lateral to the tooth rows also suggests increased oral processing of plant matter (21).

Ornithischians were extremely rare during

odontia; 14, Ankylopollexia; 15, Styracosterna; 16, Hadrosauriformes; 17, Hadrosauroidea; 18, Hadrosauridae; 19, Marginocephalia; 20, Pachycephalosauria; 21, Pachycephalosauridae; 22, Pachycephalosaurinae; 23, Ceratopsia; 24, Neoceratopsia; 25, Coronosauria; 26, Ceratopsoidea; 27, Ceratopsidae; 28, Saurischia; 29, Sauropodmorpha; 30, Prosauropoda; 31, Plateosauria; 32, Massospondylidae; 33, Plateosauridae; 34, Sauropoda; 35, Eusauropoda; 36, Neosauropoda; 37, Diplodocoidea; 38, Macronaria; 39, Titanosauriformes; 40, Somphospondyli; 41, Theropoda; 42, Neotheropoda; 43, Ceratosauria; 44, Ceratosauroidea; 45, Coelophysoidea; 46, Tetanurae; 47, Spinosauroidea; 48, Neotetanurae; 49, Coelurosauria; 50, Maniraptoriformes, 51, Ornithomimosauria; 52, Ornithomimoidea; 53, Tyrannoraptora; 54, Maniraptora; 55, Paraves; 56, Deinonychosauria; 57, Aves; 58, Ornithurae; 59, Ornithothoraces.

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EVOLUTION the Late Triassic; their remains consist largely of isolated teeth. The first well-preserved ornithischian skeletons are Early Jurassic in age (20, 22), by which time the major clades of ornithischians were already established (Fig. 1).

The small-bodied bipeds Pisanosaurus and Lesothosaurus constitute successive sister taxa to other ornithischians (Fig. 2, node 1). The “birdhipped” configuration of the pelvic girdle (with the pubis rotated posteriorly) characterizes Lesothosaurus and later ornithischians (Fig. 3A, feature 9). Possibly before the end of the Triassic, the remaining ornithischians split into armored thyreophorans and unarmored neornithischians, which include ornithopods and marginocephalians (Fig. 1; Fig. 2, nodes 3, 10, 11, and 19). This phylogenetic scheme is based on few characters, which may indicate that these early divergences occurred within a short interval of time.

Thyreophoran body armor was originally composed of parasagittal rows of keeled scutes as in Scutellosaurus (23), a small Early Jurassic thyreophoran from western North America. More advanced thyreophorans, such as Emausaurus (24) and Scelidosaurus (25) from the Lower Jurassic of Europe, appear to have reverted to a quadrupedal posture, as evidenced by hoof-shaped manual unguals. The larger bodied stegosaurs and ankylosaurs constitute the “broad-footed” thyreophorans (Eurypoda), named for the spreading (versus compact) arrangement of metatarsals in their elephantine hind feet (Fig. 1; Fig. 2, node 4).

The earliest and most primitive stegosaurs, such as Huayangosaurus from the Middle Jurassic of China (26, 27), have reduced the lateral osteoderm rows while elaborating the pair flanking the midline into erect plates (over the neck) that grade into pointed spines (over the tail) (Fig. 1; Fig. 2, nodes 5 and 6). Stegosaurs more advanced than Huayangosaurus have low narrow skulls and long hindlimbs as compared to their forelimbs (27, 28).

Ankylosaurs elaborated the dermal armor of the trunk in another direction, filling the spaces between scute rows with smaller ossicles to create a solid shield over the neck and trunk. Several skull openings are closed by surrounding cranial bones and accessory ossifications, as in the basal ankylosaurid Gargoyleosaurus, discovered recently in Upper Jurassic rocks in western North America (29) (Fig. 2, node 9). Before the close of the Jurassic, ankylosaurs had split into two distinctive subgroups—nodosaurids and ankylosaurids— both of which diversified for the most part on northern continents during the Cretaceous (30, 31). The nodosaurid skull is proportionately low and held with the snout tipped downward. Cranial sutures completely fuse with maturity, as in the North American genera Pawpawsaurus and Panoplosaurus

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(32). In most ankylosaurids, the skull is very broad, and the snout is gently domed. The wedge-shaped osteoderms that project from the back corners of the ankylosaurid skull are short in basal forms such as Gastonia, Shamosaurus, and Minmi (33) but form prominent plates in other ankylosaurids. A terminal tail club, composed largely of two pairs of wedgeshaped osteoderms, also distinguishes all known ankylosaurids.

Ornithopods split into three distinct clades during the Jurassic: heterodontosaurids, hypsilophodontids, and iguanodontians (Fig. 1; Fig. 2, nodes 11 through 13). Heterodontosaurids, named for their prominent lower canines, were small fleet-footed ornithopods that first appear in the Early Jurassic. Although undoubted herbivores, heterodontosaurids have elongate forelimbs with large grasping hands tipped with trenchant claws, as seen in the southern African genera Heterodontosaurus and Abrictosaurus (34).

Hypsilophodontids, the most conservative ornithopods, underwent little modification during their long fossil record from the Middle Jurassic to the end of the Cretaceous (35).

As a consequence, their monophyly is less certain (30, 36). Iguanodontians, in contrast, underwent marked transformation during the Late Jurassic and Early Cretaceous, from basal forms such as Muttaburrasaurus and Tenontosaurus to more derived genera such as Dryosaurus, Camptosaurus, Probactrosaurus, and Iguanodon (37) (Fig. 2, nodes 13 through 17; Fig. 3A, features 5, 6, and 8).

Ornithopods achieved their greatest diversity in the Late Cretaceous with the radiation of duck-billed hadrosaurids (38).

Marginocephalians, a group characterized by a bony shelf on the posterior margin of the skull, are composed of two distinct subgroups: the thick-headed pachycephalosaurs (39, 40) and frilled ceratopsians (41, 42). Both clades are known exclusively from northern continents and primarily from the Upper Cretaceous of western North America and Asia (Fig. 1; Fig. 2, nodes 20 through 27). In all pachycephalosaurs, the skull roof is thickened and ornamented with lateral and posterior rows of tubercles. In primitive forms such as Goyocephale, the skull roof is flat with open supratemporal fenestrae. In more derived forms, the frontoparietal portion of the skull roof thickens further into a dome, which eventually incorporates all elements of the skull roof. The largest of these domed forms, Pachycephalosaurus and Stygimoloch, have swollen tubercles or horns projecting from the posterior corners of the skull (40) and constitute the only ornithischians to maintain an obligatory bipedal posture at large body size (more than 1 ton) (11). Some researchers have united flat-headed pachycephalosaurs as a clade (43), but this condition is primitive, with some flat-headed genera being more closely related to domed forms (11, 30).

Psittacosaurids, the most primitive ceratopsians, are small-bodied parrot-beaked herbivores from Asia assigned to the single genus Psittacosaurus. As in all ceratopsians, the anterior margin of the psittacosaurid snout is capped by the rostral, a neomorphic bone sheathed by the upper bill. Although they show remarkably little skeletal variation, psittacosaurids persisted throughout most of the Early Cretaceous.

Remaining ceratopsians (neoceratopsians) also date back to the earliest Cretaceous of China and include Chaoyangsaurus and Archaeoceratops (42). Archaeoceratops and more derived neoceratopsians are distinguished by very large skulls relative to their postcranial skeletons and may have already reverted to a quadrupedal posture. In Late Cretaceous neoceratopsians, such as the abundant Asian form Protoceratops, the posterior margin of the skull extends posterodorsally as a thin shield pierced by a pair of fenestrae. Ceratopsids, a diverse subgroup of large-bodied neoceratopsians, were restricted to western North America, ranging from Mexico to the north slope of Alaska. Their many cranial and postcranial modifications include slicing dental batteries composed of stacked columns of two-rooted teeth and postorbital horns and frill processes of variable length and shape (41).

Sauropodomorphs: Long-Necked Titans Sauropodomorphs constitute the second great radiation of dinosaurian herbivores. Although their origin is as ancient as that of ornithischians, their diversification followed a different time course (44, 45). As a group, sauropodomorphs are united by only a few characteristics, such as an enlarged narial opening and an unusual position for the longest pedal claw— on the first digit, or hallux, rather than the middle toe (Fig. 3C, features 21 and 29).

Unlike ornithischians, there are no singleton genera at the base of the clade. By the Late Triassic, sauropodomorphs had already split into two distinctive groups: prosauropods and sauropods (Fig. 2, nodes 29, 30, and 34).

Prosauropods diversified rapidly with only minor skeletal modification to become the dominant large-bodied herbivores on land from the Late Triassic through the Early Jurassic. Sauropods, in contrast, were rare in the Early Jurassic, when ornithischians appear to have undergone their major radiation, but diversified rapidly during the Middle Jurassic after prosauropods had gone extinct (Fig. 1).

A succession of basal sauropods lies outside the main neosauropod radiation, which split during the Middle Jurassic into diplodocoids and macronarians, a clade composed of camarasaurids, brachiosaurids, and titanosaurs (Fig. 2, nodes 37 through 40). Neosauropods became the dominant large-bodied herbivores during the Middle and Late Jurassic and, on

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EVOLUTION southern continents, throughout the Cretaceous as well (44, 45).

Traditionally, prosauropods were viewed

as an ancestral (paraphyletic) assemblage that gave rise to sauropods, a hypothesis with some appeal given the absence of any record

Fig. 3. Skeletal innovation in the three major clades of dinosaurs (Ornithischia, Theropoda, and Sauropodomorpha) as shown by contemporaneous species from the Upper Jurassic (Kimmeridgian) Morrison Formation of North America. Labeled features evolved at various nodes as described in the text. Scale bar, 1 m. (A) Camptosaurus dispar, an ornithischian. (B) Allosaurus fragilis, a theropod. (C) Camarasaurus lentus, a sauropodomorph [after (44)]. Skeletal innovations are as follows: 1, horny beak for cropping; 2, predentary bone for lower bill support; 3, cheek depression for oral processing of plant matter; 4, leaf-shaped crowns with wear facets and asymmetrical enamel for shearing plant matter; 5, coronoid process for attachment of robust jaw-closing muscles; 6, opisthocoelous cervicals with reduced neural spines for flexibility; 7, ossified tendons to stiffen trunk; 8, rigid digit I with subconical ungual for defense; 9, pubis with prepubic process and posteroventrally directed postpubic process opening posterior trunk; 10, pendant fourth trochanter for enhanced caudal hindlimb retractors; 11, intramandibular joint for flexible bite; 12, metacarpal extensor depressions for manual raking; 13, hollow

of sauropods during the Triassic. Several unique features, however, unite all prosauropods, such as a twisted pollex (thumb) tipped

skeleton to reduce bone weight; 14, semilunate carpal simplifying wrist action to maneuver large hands; 15, manual digit II longest, emphasizing inner digits; 16, long penultimate phalanges enhancing grasping capability; 17, pubic foot for body support at rest; 18, astragalar ascending process uniting tibia and tarsus; 19, elongate prezygapophyses unite distal tail forming a dynamic stabilizer; 20, crowns with regular V-shaped wear facets indicate precise occlusion for slicing vegetation; 21, nares enlarged and retracted; 22, columnar limb posture for weight support at large body size; 23, 12 or more opisthocoelous cervical vertebrae composing a longer neck; 24, 11 or fewer dorsal vertebrae shortening the trunk; 25, bifurcate neural spines accommodating a robust median elastic ligament; 26, arched ligament-bound metacarpus for digitigrade manual posture; 27, manual/pedal phalanges reduced in number for a more fleshy foot pad; 28, manual digits I and V weight-bearing to broaden support; 29, manual digit I ungual enlarged possibly for intraspecific rivalry; 30, distal tarsals unossified increasing shock-absorbing cartilage in joints; 31, elephantine pes for weight support at large body size.

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EVOLUTION by a large claw that points inward (11, 46).

Riojasaurus, a Late Triassic prosauropod from South America, is one of only a few basal prosauropods that retain a short neck (47). Other contemporaneous prosauropods and younger genera from the Early Jurassic, such as Massospondylus, have proportionately longer cervical vertebrae, as does the well known European genus Plateosaurus (47).

Prosauropods were remarkably uniform in skeletal design despite their broad distribution across Pangaea. As a consequence, their interrelationships are poorly established.

The columnar posture of the limbs and the partial pronation of the forearm in the earliest known sauropod, Vulcanodon from southern Africa (48), suggest that moderate-sized early sauropods had already adopted an obligatory quadrupedal stance during locomotion (Fig. 3C, feature 22). Shunosaurus and Omeisaurus, from the Middle Jurassic of China, preserve the earliest complete sauropod skulls (49). The spatulate crowns show a regular pattern of V-shaped wear facets that is common among primitive sauropods. Regular wear facets are the product of precise toothto-tooth occlusion, a remarkable adaptation in animals that were continuously replacing their teeth (11, 44, 50). Mammals evolved sophisticated occlusal precision during this same interval but did so at the cost of nearly eliminating tooth replacement. Two notable features that evolved early in sauropod evolution include the retraction of the external nares to a position above the antorbital opening and the increase in the number of cervical vertebrae from 10 to at least 12 (Fig. 3C, features 21 and 23) (44).

Neosauropods and several genera that lie just outside this diverse radiation are easily recognized by the digitigrade (rather than plantigrade) posture of the manus, in which the ligament-bound metacarpals are arranged in a tight arc and oriented nearly vertically (Fig. 3C, feature 26). Within Neosauropoda, Diplodocoidea (Fig. 2, node 37) includes the highly modified diplodocids, which have retracted the external nares to a position above the orbits. The muzzle of the diplodocid skull is squared and lined with a reduced number of slender cylindrical crowns that are similar in form to those in derived titanosaurs (although truncated by high-angle wear facets rather than the near-vertical facets that characterize the narrow crowns of advanced titanosaurs) (50). North American representatives, such as Diplodocus, have particularly long necks and tails, the former composed of 15 elongate vertebrae and the latter composed of 80 vertebrae that taper to a whiplash end.

Other neosauropods include Camarasaurus, a basal genus with broad spatulate crowns and a relatively short neck; and brachiosaurids, a long-necked subgroup with proportionately long forelimbs (51). Titano-

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saurs, best known from Upper Cretaceous rocks in South America but present worldwide during the Cretaceous, are characterized by a particularly broad pectoral region and wide-gauge posture (8), stocky limbs that lack ossified carpals and phalanges, and a short tail composed of procoelous vertebrae (52). Titanosaur teeth are either weakly spatulate or cylindrical; and some advanced genera, such as Saltasaurus, have large scutes embedded in the skin over the trunk.

Sauropod phylogeny is marked by parallel evolution of narrow cylindrical crowns, bifid (forked) neural spines in the presacral column, and elongation of the cervical column (44, 45, 53). The traditional union of the narrow-crowned diplodocoids and titanosaurs (54) has been abandoned in the face of recent cladistic analyses, based on a broad selection of characters and taxa, that unite brachiosaurids and titanosaurs (44, 45).

Theropods: Bipedal Predators All theropods, including birds, are obligatory bipeds. Distinctive predatory adaptations arose in the earliest theropods, Eoraptor and Herrerasaurus. Foremost among these are the flexible lower jaw with a sliding joint midway along its length and an elongate hand reduced to three functional digits that are specialized for grasping and raking (Fig. 3B, features 11, 12, and 16) (12). These early predators constitute successive sister taxa to all later theropods, or neotheropods, which split into ceratosaurs and tetanurans before the close of the Triassic (Fig. 2, nodes 42, 43, and 46). During the Late Triassic and Early Jurassic, the great majority of theropods were ceratosaurs. By the Middle Jurassic, in contrast, tetanurans had diversified on all continents and had split into two major groups, the allosauroids and coelurosaurs, the latter giving rise to birds before the end of the Jurassic (11, 55–57) (Fig. 1).

Eoraptor (12), a 1-m-long cursorial biped, more closely approximates the common ancestor of dinosaurs than does any other taxon discovered to date. Its jaws and raptorial hands nevertheless exhibit modifications shared with other theropods (Fig. 2, node 41). Herrerasaurus, a medium-sized theropod (12), exhibits additional locomotor adaptations such as a balancing tail, the distal half of which is stiffened by overlapping vertebral processes (Fig. 3B, feature 19).

Although some question remains regarding their monophyly, ceratosaurs are united by features of the pelvic girdle and hindlimb, including some that are sexually dimorphic (58). Before the close of the Triassic, ceratosaurs split into two subgroups: the ceratosauroids and coelophysoids (Fig. 2, nodes 43 through 45). First recorded in the Late Jurassic, ceratosauroids (or “neoceratosaurs”) include the Late Jurassic genera Elaphrosaurus and

Ceratosaurus. The group persisted into the Cretaceous in Europe and on several southern continents (South America, India, and Madagascar), where they are represented by the unusual short-snouted, horned genera Carnotaurus, Indosuchus, and Majungatholus (58). Coelophysoids include the medium-sized Dilophosaurus and Liliensternus, as well as a diverse array of small-bodied predators (such as Procompsognathus, Segisaurus, and Syntarsus) that are similar to the common North American genus Coelophysis (59).

Nearly all basal tetanurans are large-bodied, large-headed forms, formerly grouped together (with large-headed ceratosaurs and tyrannosaurids) as “carnosaurs.” Torvosaurids and the piscivorous crocodile-snouted spinosaurids appear to constitute an early side branch within Tetanurae (60). The oldest tetanuran, the crested allosauroid Cryolophosaurus, was discovered in Lower Jurassic rocks on Antarctica and is quite similar to allosauroids from Upper Jurassic rocks on several continents (61). During the Cretaceous, allosauroids reached body sizes rivaling those of the largest tyrannosaurids (57, 62). Many skeletal features characterize tetanurans, such as the peculiar semilunate wrist bone that constrains movement of the manus and the tall plate-shaped ascending process on the astragalus that immovably unites the shin bone and proximal tarsals (Fig. 3B, features 14 and 18). Further clarification of basal relationships within Tetanurae is anticipated, as genera such as Afrovenator, Neovenator, and others formerly referred to as “megalosaurids” are restudied.

Nonavian coelurosaurs include a diverse array of small-to-medium-sized predators, such as the ostrichlike ornithomimids, deep-snouted oviraptorosaurs, and sickle-toed deinonychosaurs (63). Coelurosaurs also include two clades, the therizinosaurids and tyrannosauroids, whose more derived members grew to very large body sizes (64). Coelurosaurs are characterized by an increase in the number of sacral vertebrae, a reduction in thigh retraction during locomotion, and an increased stiffening of the distal half of the tail—features that are further developed in birds.

Coelurosaurian interrelationships have remained controversial because of conflicting distributions for several salient features and differences in character data and analysis.

Consensus has been reached that tyrannosaurids belong within Coelurosauria (56), but opinions differ on the monophyly of most, or all, coelurosaurs that have an especially narrow middle metatarsal (the “arctometatarsalian” condition). Other major points of controversy include the position of therizinosaurids, the monophyly of Deinonychosauria (dromaeosaurids plus troodontids), the position of the feathered Caudipteryx among nonavians, and the interpretation of alvarez-

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EVOLUTION saurids (65) as avians.

The phylogeny shown here (Fig. 2, nodes 49 through 57; Table 1) supports and extends the conclusions of an early cladistic survey (55). Except for a few basal genera, coelurosaurs are divided into ornithomimosaurs and tyrannoraptorans, the former including alvarezsaurids and, with less support, therizinosaurids (Fig. 2, nodes 51 and 52). Tyrannoraptorans, in turn, diversified as tyrannosauroids, oviraptorosaurs, deinonychosaurs, and birds (63). Caudipteryx is interpreted here as a basal oviraptorosaur rather than an immediate avian outgroup (6). Deinonychosauria, the monophyly of which is here maintained (Fig. 2, node 56), and birds are united by many synapomorphies, including a powerful sickle-clawed digit in the pes. This eviscerating digit, first described in Deinonychus, is present but considerably muted in Archaeopteryx and the basal ornithurine Confuciusornis (66) and is well developed in Rahonavis (67), a close relative of Archaeopteryx.

Evolution of Feathers, Perching, and Flight For use in understanding the evolution of vertebrate flight, the early record of pterosaurs and bats is disappointing: Their most primitive representatives are fully transformed as capable fliers. The early avian record, in contrast, provides the rare opportunity to tease apart the sequence of modifications that led to powered flight and its early refinement (Fig. 4).

In the past decade, spectacular fossil discoveries in lacustrine rocks in northern China and central Spain (5, 6, 66, 68) and in fluvial rocks elsewhere (67, 69) have provided critical new evidence for the evolution of avian flight and perching and the origin of feather structure and arrangement. Cladistic analyses of character data (55–57, 65, 68, 69) (Table 1) have endorsed Ostrom’s hypothesis (70) that birds are specialized coelurosaurs, a conclusion also supported by egg size, eggshell microstructure, and nesting patterns (3, 4).

There is no longer any morphological “gap” in skeletal data: The number of changes at Aves (Fig. 2, node 57) is fewer than occur at more basal nodes within Theropoda or at nodes within Aves. Flagging opposition to the understanding of birds as coelurosaurian descendants (71) has yet to take form as a testable phylogenetic hypothesis (72).

Cooptation of structures that originally evolved for another purpose (73) has played a larger role than was previously thought in early avian evolution. Features formerly understood as strictly avian, such as vaned feathers and their tandem arrangement on the manus and forearm as primaries and secondaries, are now known among flightless nonavian coelurosaurs (Fig. 4, node 4) (6). In the oviraptorosaur Caudipteryx (6), for example, the short symmetrical

primaries and secondaries clearly had no flight function, and the rectrices at the distal end of its bony tail are better suited for display than for any aerodynamic function. Given the absence of basic flight-related features in its skeleton (such as a laterally facing glenoid), there is no evidence of flight function in the ancestry of Caudipteryx. Vaned feathers and their arrangement as primaries, secondaries, and rectrices therefore must have originally evolved for other functions (such as thermoregulation, brooding, or display). Other features formerly associated only with birds are now known to have arisen deeper in theropod phylogeny, such as a downlike body covering (5, 74), a broad plate-shaped sternum, ossified sternal ribs and uncinate processes (Fig. 4, nodes 3 through 5), and substantial enlargement of the forebrain (75).

The refinement of flight capability and maneuverability and the evolution of a fully opposable digit for perching proceeded rapidly once primitive avians were airborne (Fig. 4, node 6). Within 10 million years after the appearance of Archaeopteryx, body size shrank to that of a sparrow, well below the size range of nonavian coelurosaurs (Fig. 4, node 8). Modifications during this interval had a major impact on flight and perching performance, such as the evolution of alular feathers on the first digit of the manus, a fully opposable hallux in the pes, and a fused pygostyle at the end of the tail (Fig. 4, nodes 7 and 8). The crow-sized basal ornithurine Confuciusornis (66), known from thousands of specimens from earliest Cretaceous sites in northern China, is destined to become the best-known basal avian. Slightly younger sparrow-sized birds, such as Sinornis (68), Concornis, and Iberomesornis (76), document the enantiornithine radiation that dominated avifaunas for the remainder of the Cretaceous (77).

Controversy surrounds two taxa that were initially proposed as avians more advanced than Archaeopteryx: Protoavis (78) and the alvarezsaurids (65). Protoavis is widely regarded as a composite of several nonavian species, and the short-armed flightless al-

varezsaurids, such as Mononykus and Shuvuuia, have been interpreted alternatively as the sister group to ornithomimids (Fig. 2, node 52).

Evolutionary Tempo and Morphologic Scope How does the land-based radiation of nonavian dinosaurs sketched above compare with its successor, the Cenozoic radiation of therian mammals? Several similarities make the comparison particularly enlightening: The most recent common ancestor for each radiation lay at the minimum end of the range in body size for the clade; that ancestor lived 15 million years or more before the clade’s domination of land habitats (79); each clade underwent significant taxonomic diversification before the clade’s domination of land habitats; and each clade rather suddenly inherited significant vacant ecospace in the aftermath of mass extinctions.

These similarities render the differences between these radiations all the more remarkable. The Cenozoic diversification of therian mammals was explosive: The rate of origination and standing diversity of species rose dramatically in the first few million years (80); the range of body size expanded by three orders of magnitude in the first few million years, approaching the maximum range attained within land mammals (81); substantial morphologic disparity quickly emerged, as two dozen distinctive adaptive designs (recognized as orders) appear in the fossil record within the first 15 million years (82); these adaptive designs included gliders, swimmers, burrowers, saltators, and cursors (excluding bats for fair comparison to nonavian dinosaurs) that invaded dry land, marshland, tropical, arboreal, freshwater, and oceanic habitats.

The radiation of nonavian dinosaurs, by comparison, was sluggish and constrained: Taxonomic diversification took place at a snail’s pace (Fig. 1, left); standing diversity, which may have totaled 50 genera or less during the first 50 million years, increased

Table 1. Summary of cladistic analyses (76) that support the calibrated phylogeny of Dinosauria shown in Fig. 2. Characters and taxon/character-state matrices are available at www.sciencemag.org/feature/ data/1041760.shl. Abbreviations: CI, consistency index; RI, retention index.

Analysis

Number of terminal taxa

Number of characters

Number of minimum-length trees

CI, RI

Basal Dinosaria Thyreophora Ornithopoda Marginocephalia Prosauropoda Sauropoda Ceratosauria Tetanurae Basal Aves

15 19 14 19 11 13 13 20 6

146 119 149 155 32 116 60 220 100

1 27 1 1 6 1 1 3 1

0.81, 0.89 0.87, 0.94 0.94, 0.97 0.90, 0.96 0.97, 0.98 0.80, 0.86 0.91, 0.94 0.85, 0.86 0.97, 0.98

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Fig. 4. Major stages in the evolution of modern avian skeletal design and function. Many skeletal innovations of critical functional importance for flight arose for other purposes among early theropods, including (1) the hollowing of all long bones of the skeleton (Theropoda) and removal of pedal digit I from its role in weight support; (2) evolution of a rotary wrist joint to efficiently deploy a large grasping manus; (3) expansion of the coracoid and sternum for increased pectoral musculature and plumulaceous feathers for insulation (89); (4) the presence of vaned feathers arranged as primaries, secondaries, and rectrices for display or brooding or both; (5) shortening of the trunk and increased stiffness of the distal tail for balance and maneuverability. Archaeopteryx remains a pivotal taxon, documenting (6) the acquisition of basic flight and perching function before the close of the Jurassic (laterally facing shoulder joint,

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split propulsion-lift wing with asymmetric feathers, and reversed hallux).

Key refinements of powered flight and perching in later birds include (7) the deep thorax with strut-shaped coracoid and pygostyle; (8) the triosseal canal for the tendon of the principal wing rotator (the supracoracoideus muscle), alular feathers for control of airflow at slow speeds, rectriceal fan for maneuverability and braking during landing, and fully opposable hallux for advanced perching; and (9) the elastic furcula and deep sternal keel for massive aerobic pectoral musculature (90). Ornithothoracine birds diverged early as Enantiornithes (“opposite birds”) (68, 77), which prevailed as the predominant avians during the Cretaceous, and Euornithes (“true birds”), which underwent an explosive radiation toward the close of the Cretaceous that gave rise to all living avians (Neornithes, or “new birds”).

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EVOLUTION slowly during the Jurassic and Cretaceous, never reaching mammalian levels; maximum body size for herbivores and carnivores was achieved more than 50 million years after the dinosaurian radiation began (Fig. 1); only 8 to 10 distinctive adaptive designs emerged (recognized as suborders), and few of these would have been apparent after the first 15 million years of the dinosaur radiation (Fig. 1); adaptive designs that never evolved include gliders, burrowers, saltators, or taxa specifically adapted to marshland, arboreal, freshwater, or oceanic habitats (excluding birds for the purpose of comparison).

The dinosaurian radiation differs from that of Cenozoic therians in other ways that may have influenced tempo and adaptive scope: (i) during the basal radiation, Earth’s land surface was united as a supercontinent rather than subdivided into smaller land masses; (ii) the ancestor was a terrestrial biped rather than a terrestrial (or arboreal or fossorial) quadruped; and (iii) during basal divergences, body mass was greater by at least an order of magnitude. An undivided supercontinent is difficult to invoke as a significant constraint on taxonomic diversification or morphologic disparity in dinosaurs,

Fig. 5. Dinosaurian paleobiogeography. (A) Temporally calibrated areagram showing the breakup of Pangaea into 10 major land areas by the end of the Cretaceous. Checkered bars indicate high-latitude connections that may have persisted into the Late Cretaceous. Five paleogeographic reconstructions (91) divide continental areas (outlines) into dry land (black) and shallow (epieric) seas (unshaded). (B) Continent-level vicariance hypothesis for the carcharodontosaurids Acrocanthosaurus, Giganotosaurus, and Carcharodontosaurus, which lived on North America, South America, and Africa, respectively, approximately 90 to 110 Ma. (C) Polar dispersal across Beringia (double-headed arrow) must be invoked to explain the geographic distribution of ceratopsians and other dinosaurian subgroups during the Late Cretaceous. Checkered branches show dispers-

given that all of the major dinosaurian subgroups had diverged before the onset of significant breakup in the earliest Cretaceous (Figs. 1 and 5A). Bipedal posture cannot be invoked as an evolutionary constraint, because early avians with this posture rapidly invaded arboreal, freshwater, and marine habitats before the close of the Cretaceous.

Greater body mass and its ecological, physiological, and life-history correlates, however, may well have played a major role in shaping the dinosaurian radiation. Larger body size in mammals is correlated with lower standing diversity, greater species longev-

al from Asia to North America in three lineages, which is one of two equally parsimonious dispersal scenarios for ceratopsians (given this cladogram and an Asian origin for Ceratopsia). Globe shows Maastrichtian (70 Ma) paleogeography divided into orogenic belts (inverted Vs), lowlands (black), and shallow and deep seas (gray and white, respectively). Internal branch lengths of the cladogram are scaled according to the number of supporting synapomorphies under delayed character-state transformation. Scale bar indicates 10 synapomorphies (with the long ceratopsid branch shortened). 1, Psittacosaurus; 2, Chaoyangsaurus; 3, Leptoceratops; 4, Udanoceratops; 5, Microceratops; 6, Bagaceratops; 7, Protoceratops; 8, Montanoceratops; 9, Turanoceratops; 10, Chasmosaurinae; 11, Ceratopsinae.

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EVOLUTION ity, and greater habitat specificity (83), which may account for the slower rate of taxonomic diversification and more restricted range of morphologic disparity among nonavian dinosaurs. In these regards, avians more closely resemble therian mammals.

Evolutionary Trends and Coevolution Recurring phylogenetic trends among dinosaurs include incorporation of osteoderms in the skull, narial enlargement and retraction, reduction and loss of teeth, increase in neck length and number of cervicals, increase in the number of sacrals, miniaturization of the forelimb, reduction and loss of external digits in the manus, and posterior rotation of the pubis.

Judging from the body size and trophic adaptations of dinosaurian outgroups, the ancestral dinosaur was a bipedal carnivore closely resembling the 1-m-long early theropod Eoraptor. Anagenetic trends (84) toward substantially greater body mass occurred within six clades, four of which assumed facultative or obligatory quadrupedal posture (Thyreophora, Ornithopoda, Ceratopsia, and Sauropoda) (11). For dinosaurs as a whole, these trends are accretive (84), with upper values being attained in different clades at different times during the Jurassic and Cretaceous.

The only sustained trend toward decreased body mass occurred during the evolution of birds. The ancestral neotetanuran was probably a predator the size of Allosaurus, weighing 3 to 5 tons (Fig. 4, node 2). Basal maniraptorans are considerably smaller (20 to 100 kg); crow-sized basal avians such as Archaeopteryx and Confuciusornis are smaller than any mature nonavian dinosaur; and sparrow-to-starling–sized ornithothoracines mark the bottom of the trend, which certainly played a key role in the evolution of avian perching and powered flight (Fig. 4, nodes 5 through 8).

The study of limb proportions in dinosaurian herbivores and contemporary predators, as in mammalian ungulates and their predators, suggests that pursuit predation was not a major influence in the evolution of locomotor capabilities (85); large dinosaurian herbivores are most often graviportal irrespective of the locomotor capability of contemporary predators. Study of the dentitions of dinosaurian herbivores during the angiosperm radiation of the Late Cretaceous likewise does not reveal any clear co-evolutionary pattern (11).

Dinosaurs and Drifting Continents The breakup of the supercontinent Pangaea provides an extraordinary case study for the operation of large-scale biogeographic processes. Before the close of the Jurassic, rifting opened the Tethyan Sea between the northern and southern land masses Laurasia and Gondwana. Further breakup occurred during the Cretaceous, with the opening of

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the Atlantic Ocean and the spread of shallow seas on the continental margins. Subdivision of the once continuous land surface of the supercontinent can be represented by a calibrated areagram (Fig. 5A).

The fossil record shows that the relatively uniform dinosaurian faunas of the Late Triassic and Jurassic gave way to highly differentiated faunas during the Cretaceous. Faunal differentiation is governed by three processes: vicariance and regional extinction enhance faunal differentiation, and dispersal reduces it (11).

Vicariance, or the splitting of lineages in response to geographic partitioning, is a plausible hypothesis when a three-taxon cladogram matches an areagram established independently on the basis of geologic evidence (Fig. 5A). Carcharodontosaurid predators from three continents, for example, show a pattern of relationships that mirrors the breakup sequence of Pangaea (Fig. 5B). The breakup events, in addition, predate the predators, which come from rocks of mid- to Late Cretaceous age [Albian to Cenomanian, 110 to 90 million years ago (Ma)]. Continent-level fragmentation of Pangaea thus could have generated this phylogenetic pattern, assuming that primitive carcharodontosaurids were broadly distributed before the breakup. Vicariance at this scale, however, does not appear to have been a major factor in the differentiation of Cretaceous dinosaurs, both because phylogenetic patterns among taxa of Cretaceous age are not consistent with the areagram and because the age of relevant taxa often predates the relevant breakup event (11).

Regional extinction, or the disappearance from one or more geographic regions of a taxon whose former presence is clearly demonstrated by fossils, seems to have played a major role in the marked differentiation of Late Cretaceous dinosaurian faunas. Ceratosauroid and allosauroid predators, for example, were present on both northern and southern continents during the Jurassic and Early Cretaceous, but by the Late Cretaceous were replaced in North America and Asia by large-bodied coelurosaurs (tyrannosauroids). Similarly, titanosaurian herbivores were present on northern and southern continents during the Early Cretaceous. During the Late Cretaceous, titanosaurs were almost completely replaced as large-bodied herbivores in North America and Asia by hadrosaurids.

Dispersal, or the crossing of geographic barriers, reduces faunal differentiation that might arise in response to geographic isolation. Intercontinental dispersal during the Cretaceous is best documented between western North America and Asia. A polar dispersal route between these land areas allowed periodic bidirectional exchange, as evidenced by the phylogenetic relation-

ships of clades with representatives on both land areas (Fig. 5C). Dispersal between northern and southern continents across the Tethyan Sea also occurred during the Cretaceous, as shown by phylogenetic patterns in spinosaurid predators and hadrosaurids (86 ). Intercontinental dispersal clearly contributed to biogeographic patterns during the latter half of the Mesozoic.

Future discoveries are certain to yield an increasingly precise view of the history of dinosaurs and the major factors influencing their evolution.

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Supported by the David and Lucile Packard Foundation, National Geographic Society, Pritzker Foundation, and NSF. I thank C. Abraczinskas for her contribution to the design of the figures and for executing the final drafts; A. Beck, J. Conrad, J. Hopson, D. Jablonski, H. Larsson, R. Sadleir, and J. Wilson for critical review of the paper; and D. Rowley and A. Zeigler of the Paleogeographic Atlas Project (University of Chicago) for paleogeographic reconstructions.

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www.sciencemag.org SCIENCE VOL 284 25 JUNE 1999

2147

The Evolution of Dinosaurs Paul C. Sereno

Supplementary Material The calibrated cladogram (Fig. 2) is based on the following nine cladistic datasets, which are summarized in Table 1 and described in more detail elsewhere (1). Dataset 1 provides the phylogenetic framework at the base of Dinosauria for datasets 2-9 that compare taxa within major dinosaurian clades. Dataset 9 covers characters at the base of Aves, a terminal taxon in dataset 8.

Missing data, inapplicable comparisons, and coding complexity are major limiting factors when considering a broad array of extinct terminal taxa at low taxonomic levels. Necessary assumptions include the proximity of outgroups and the monophyly of ingroups. These are made strategically in the following datasets to focus on major phylogenetic questions.

Character-states are coded as follows: 0 = primitive state; 1-4, derived states; ?, missing data; X = topological homolog absent. When the basal condition of a character for a terminal taxon is ambiguous, it is scored as polymorphic. All character-states are weighted equally, and most characters are binary and unordered.

Multistate characters are usually unordered; when states are linked by a known developmental or growth trajectory, as in the size of a cranial horn, a step matrix is used that allows 1-step truncation to any lower state. In each analysis (Table 1), two outgroups were used with topological constraints that ensured successively more remote placement relative to ingroup taxa. Minimum-length trees were determined by maximum-parsimony (2). The characters are listed below under ingroup clades under delayed-transformation optimization.

1--Basal Dinosauria

This dataset includes 146 characters. Successively more remote outgroups include Marasuchus and a dinosauromorph ancestor (the latter based on Lagerpeton, Pterosauria, and Crurotarsi) (3).

Ingroups include 13 dinosaurian subgroups.

Characters and Character-States Dinosauria 1. Postfrontal: present (0); absent (1).

2. Frontal participation in supratemporal fossa: absent (0); present (1).

3. Pterygoid-ectopterygoid articular relation: ectopterygoid ventral (0); ectopterygoid dorsal (1).

4. Quadrate head, lateral exposure: absent (covered by squamosal) (0); present (1).

5. Posttemporal opening, size: fenestra (0); foramen (1).

6. Dorsosacral (3 sacrals): present (0); absent (1).

7. Ossified, paired sternal plates: absent (0); present (1).

8. Deltopectoral crest, length: 30% or less (0), or 35 percent or more (1), of humeral length.

9. Manual digit IV, strength: subequal to digits II and III with terminal ungual (0); narrower than digits II and III without terminal ungual (1).

10. Brevis fossa: absent (0); present (1).

11. Femoral greater trochanter, shape: rounded (0); angular (1).

12. Femoral medial tuberosity, size: large (0); small (1).

13. Cnemial crest on tibia: absent (0); present (1).

14. Astragalar ascending process: absent (0); present (1).

15. Astragalar anterolateral process, orientation of contact with calcaneum: ventral (0); lateral (1).

16. Calcaneal medial process, size: broad (0); rudimentary (1).

17. Distal tarsal 4 heel, depth: deep (0); shallow (1).

18. Metatarsal IV shaft axis, curvature (anterior view): straight (0); sigmoid (1).

Ornithischia 19. Premaxillary tooth number: 4 (0); 3 (1); 5 (2); 6 (3); 7 (4).

20. Maxillary/dentary teeth, crown shape: recurved (0); subtriangular (1); lanceolate (2).

21. Maxillary/dentary teeth, marginal ornamentation: serrations (0); denticles (1).

22. Maxillary/dentary teeth, position of largest tooth: anterior end (0), or center (1), of tooth row.

23. Dentary coronoid process: absent (0); present (1).

24. External mandibular fenestra, length: more (0), or subequal to or less (1), than maximum depth of dentary ramus.

Lesothosaurus + Genasauria 25. First premaxillary tooth, position: adjacent to midline (0); inset posteriorly the width of one or more crowns (1).

26. Premaxillary palate, depth: deep and narrow (0); shallow and broad (1).

27. Premaxillary posterolateral process, length: short (0); long (1).

28. Ventral margin of antorbital fossa, inclination: posteroventral (0); horizontal (1).

29. Antorbital fossa and fenestra, size: large, fossa adjacent to maxilla-nasal suture (0); small, fossa separated from maxilla-nasal suture (1).

30. Palpebral: absent (0); present (1).

31. Predentary: absent (0); present (1).

32. Dentary symphysis, shape: V-shaped (0); spout-shaped (1).

33. Iliac preacetabular process, shape: tab-shaped (0); strap-shaped (1); subtriangular (2); semicircular (3); crescentic (4).

34. Iliac preacetabular process, length: distal end is posterior (0), or anterior (1), to distal end of pubic peduncle.

35. Pubic shaft orientation: anteroventral (0); vertical (1); posteroventral (2).

36. Pubic shaft shape: blade-shaped (0); rod-shaped (1).

37. Pubic symphysis length: along entire pubic blade (0); at distal end only (1).

38. Puboischial symphysis: absent (0); present (1).

39. Puboischial contact below acetabulum, depth: deep (0); shallow (1).

40. Obturator opening in pubis, form: foramen (0); notch (1).

41. Prepubic process: absent (0); present (1).

42. Ischial blade shape: tapering (0), or expanding (1), distally.

43. Femoral anterior trochanter, form: prominent crest (0); vertical flange (1); vertical ridge (2).

44. Fourth trochanter, shape: aliform (0); pendant (1), trapezoidal (2).

45. Tibial posteromedial flange, lateral extension: does not reach fibula (0); extends posterior to medial margin of fibula (1); extends posterior to entire distal end of fibula and calcaneum (2).

46. Astragalar lateral facet for fubula: present (0); absent (1).

47. Pedal digit V phalanges: present (0); absent (1).

48. Metatarsal V length: 40 to 50% (0), or less than 25% (1), of metatarsal III length.

49. Distal tarsal 4 heel: present (0); absent (1).

50. Ossified epaxial tendons: absent (0); present (1).

51. Gastralia: present (0); absent (1).

Genasauria 52. Maxillary buccal emargination: absent (0); present (1).

53. Dentary coronoid process, depth: approximately 35% or less (0), or 50% or more (1), of the depth of the dentary at midlength.

54. Pubic peduncle, shape of distal end (lateral view): expanded (0); tapering (1).

Neornithischia 55. Premaxilla-maxilla diastema: absent (0); present (1).

56. Enamel on crowns of maxillary and dentary teeth, distribution: symmetrical (0); asymmetrical (1).

57. Predentary size: less (0), or equal to (1), the length of the premaxillary alveolar margin.

58. Anterior trochanter form: blade-shaped (0); finger-shaped (1).

59. Iliac acetabular flange: present (0); absent (1).

60. Iliac supraacetabular rim: present (0); absent (1).

61. Ischial peduncle of ilium, form: ventrally (0), or ventrally and laterally (1), projecting process.

Saurischia 62. Subnarial foramen: absent (0); present (1).

63. Jugal-lacrimal articular relation: lacrimal overlaps jugal (0); jugal overlaps lacrimal (1).

64. Jugal posterior process, shape: tapered (0); forked (1).

65. Epipophyses on mid- and posterior cervical vertebrae: absent (0); present (1).

66. Hyposphene-hypantrum articulation in dorsal vertebrae: absent (0); present (1).

67. Mid-cervical rib form: short, posteroventrally inclined (0); long, parallel to cervical column (1).

68. Distal carpal 5: present (0); absent (1).

69. Manual length (measured along digit II or III, whichever is longest): 20-30% (0), approximately 40% (1), or 50-70% (2) length of humerus + radius.

70. Manual digit I, phalanx 1 length: shorter (0), or equal to or longer (1), than metacarpal I. 71. Astragalar ascending process, shape: quadrangular (0); wedge-shaped (1); plate-shaped (2).

72. Metatarsals II-IV, form of basal articulation: nonoverlapping (0); overlapping II on III on IV (1).

Sauropodomorpha 73. External naris size: small (0); large (1).

74. Maxilla borders external nares: present (0); absent (1).

75. Narial fossa, ventral width: narrow, above subnarial foramen when present (0); deep, including subnarial foramen when present (1).

76. Premaxillary posterolateral process, articulation: lateral aspect of snout (0); dorsal aspect of maxillary anteromedial process (1).

77. Anterior maxillary foramen: absent (0); present (1).

78. Antorbital fossa, posterior portion of medial wall: present (0); absent (1).

79. Supra-jugular foramen: absent (0); present (1).

80. Proximal carpals (and distal carpal 4): present (0); very reduced or absent (1).

81. Ilium, pubic peduncle length: less (0), or more (1), than twice the distal width of the peduncle.

82. Ilium, axis of the pubic peduncle: straight (0); arched (1).

83. Ilium, ventral acetabular flange: present (0); absent (1).

84. Astragalus, fibular facet orientation: dorsolateral (0); lateral (1).

85. Pedal digit I, ungual length: shorter (0), or longer (1), than other pedal phalanges.

86. Metatarsal V, proximal shaft width: narrow (0); expanded transversely (1).

Theropoda 87. Ectopterygoid fossa: absent (0); present (1).

88. Intramandibular joint: absent (0); present (1).

89. Cervical epipophyses, shape: crest or rugosity (0); prong-shaped process (1).

90. Internal cavitation of centra and long bones: moderate (0); extreme (1).

91. Metacarpals I-III, intermetacarpal articular facets: absent (0); present (1).

92. Metacarpals I-III, asymmetrical extensor depressions: absent (0); present (1).

93. Iliac brevis fossa form: shallow (0); arched (1).

94. Ischial obturator process: absent (0); present (1).

95. Pubic blade, distal width: subequal to (0), or 65% or less than (1), proximal width of blade.

Herrerasauridae + Neotheropoda 96. Axial intercentrum width: less (0), or more (1), than maximum width of axial centrum.

97. Distal caudal prezygapophyses: short (0); elongate (1).

98. Scapular blade, length versus distal width: less (0), or more (1), than 3 times distal width.

99. Manual digits I-III, penultimate phalanx (digits II, III) length and ungual (digits I-III) form: shorter or subequal to preceding phalanx, short moderately recurved unguals (0); longer than preceding phalanx, long strongly recurved unguals (1).

100. Metacarpals IV and V, diameter: short (0); vestigial, less than 50% diameter of metacarpal III (or metacarpal II) (1).

101. Pubic foot: absent (0); present (1). (loss of broad blade-shaped distal end) 102. Femoral distal end, anterior attachment depression: absent (0); present (1).

Herrerasuridae 103. Intramandibular joint polarity: (0) splenial convex (0); splenial concave (1) 104. Femur, proximal shaft, anterolateral margin: rounded (0); crested (1).

Staurikosaurus + Chindesaurus 105. Iliac blade, inclination of dorsal margin: horizontal (0); posteroventrally inclined (1).

106. Iliac preacetabular process, form of ventral margin: rounded (0); everted (1).

Neotheropoda 107. Palatal teeth: present (0); absent (1).

108. Premaxilla-nasal suture: V-shaped (0); W-shaped (1).

109. Medial premaxillary foramen: absent (0); present (1).

110. Nasal posterolateral process: absent (0); present (1).

111. Antorbital fossa, size: anteroposterior diameter greater than the anteroposterior diameter of other skull openings (0), or greater than any diameter of other skull openings (1).

112. Promaxillary fenestra and antrum: absent (0); present (1).

113. Lacrimal crest with pneumatic excavation: absent (0); present (1).

114. Lacrimal ventral process with flange: absent (0); present (1).

115. Squamosal anterior process, orientation (lateral view): anterior (0); anterodorsal (1).

116. Palatine anterior process, shape: tapered distally (1); expanded distally (1).

117. Exoccipital-opisthotic, participation in basal tubera: absent (0); present (1).

118. Laterosphenoid, head articulation: frontal and postorbital (0); postorbital only (1).

119. Basisphenoid fontanelle: absent (0); present (1).

120. Prearticular-angular foramen: absent (0); present (1).

121. Cervical vertebrae (postatlantal), pleurocoels (anterior): absent (0); present (1).

122. Axis, neural canal diameter: more (0), or less (1), than 25% centrum diameter.

123. Axis, prezygapophyses, shape: low process (0); tab-shaped process (1).

124. Axis, transverse process, strength: low prominence (0); cylindrical process (1).

125. Cervical (postatlantal) centra, articular surfaces: amphicoelous (0); marked opisthocoely (1).

126. Axis, intercentrum length: 25% (0), or 50% (1), axial centrum length.

127. Caudosacrals 1 and 2: absent (0); present (1).

128. Caudosacral ribs, attachment position: along ventral margin (0), or rises to a posterodorsal corner (1), of postacetabular process.

129. Anterior caudal neural spines, anterior flange for interspinous articulation: absent (0); present (1).

130. Distal carpal 1, distal articulation: metacarpal I (0); metacarpals I and II (1).

131. Manual digits and metacarpals, longest: digit III, metacarpal III (0); digit II, metacarpal II (1).

132. Manual digit V: present (0); absent (1).

133. Metacarpal I length: longer (0), or shorter (1), than phalanx 1 or ungual of digit I. 134. Ischial distal end, anteroposterior dimension: less (0), or more (1), than greatest width of either ischial peduncle (i.e., "foot" present).

135. Pubic foot, shape of symphyseal area: distal margin only (0); broad median contact (1).

136. Tibia, proximal end, fibular crest: absent (0); present (1).

137. Cnemial crest form: low (0); prominent (1).

138. Tibial shaft proportions, transverse versus anteroposterior: subequal (0); transverse width 140-150% anteroposterior width (1).

139. Fibular mid-shaft, anteroposterior width: 40% (0), or 10-25% (1), of the anteroposterior width of the proximal end.

140. Astragalar crest (ascending process to posterolateral corner): absent (0); present (1).

141. Astragalar posteromedial crest: absent (0); present (1).

142. Metatarsal I length: more (0), or less (1), than 50% metatarsal II length.

143. Metatarsal I, location of articulation on metatarsal II: medial side of proximal end (0); posteromedial side halfway down shaft (1).

144. Metatarsal IV distal end and proximal phalanx base, proportions: broader than tall (0); taller than broad (1).

145. Metatarsal V shaft axis: straight (0); curved or sigmoid (1).

146. Metatarsal V shaft width: robust (0); slender (1).

Data Matrix Outgroups Dinosauromorph ancestor 000000?0000000000000000?0?0000002000000000?0X0000000X0?0?X000000000000X00?00000000000000?000?000?00000X00000000000000000000000000?0?00X0X0000?0000 Marasuchus ?????0?0?000000000?000?????0????000000000000000000?0?000?X000???00????X0??????00000000??X0??X000000??0?000?????0??????0?000?00000????0X0X000000?00 Ingroups Pisanosaurus ????????????11X1?1???111??????????00?00?0???10?????10??0??????????????00????????0??1??????????????????????????????????????????????????X0000?000???

Lesothosaurus 111111?1?11111??01111111111111111121111111112101111000000000000000??00200000000?000?0000X00000X0000000X00010000000000000000000100?0000X0000??0000?

THYREOPHORA 11111111111111111141111111111111112111111111211111111100000000X000000020000000000000000000000000000000X0001000000000000000000000000000X00000000000 ORNITHOPODA

111111111111111111211111111111111121111111112111111111111111100000000020000000000000000000000000000000X0001000000000000000000000000000X00000000000 MARGINOCEPHALIA 11?11111?11111111111111111111111112111111111211111111111111110X000000020000000000000000000000000000000X0001000000000000000000000000000X00000000000 PROSAUROPODA 1111111111111111111210000000000020000000000000100000X000X?00011111111111111111111111110000000000000000X0001000000000000000000000001000X00000000000 SAUROPODA 11011111101111X1X00210010000000041000000000X0010X000X000X?11011111110010111111111111110000000000000000X00010000000000000000010000X0000X00000000000 Eoraptor 1111?101111111?1110010000000000020???0??000000???0?0X000X?0001111?11111?000000?000??00111111111??0000000000001000000??0000??0?000?0001X0000?000000 Herrerasaurus 111111?111111111110010000010000000100000000000100000X000X?00011111112211000000?0000000?11111X111111111110010?0000000000000000000000000000000000000 Staurikosaurus ?????????11111????????00??????000000000?00000????00?X0?0X?000?????1???1?????????000????1?1??0?1?111???1111????????????????????000????000000???????

Chindesaurus ?????????111111??????????????????0????????0?00???????0????000?????????1?????????0000?????1??1???????????11??????????????????0?00???????0?0?00?????

CERATOSAURIA 1111111111111111110010000000000031000000001010000000X000X?1001111111221111010000001000111111111111111100001111111111111111111111111111111111111111 TETANURAE 1111111111111111110010000000000031000000001010000000X000X?1001111111220111010000001000111111111111111100001111111111111111111111111111111111111111

2--Thyreophora This dataset includes 118 characters in 17 thyreophoran taxa. Successively more remote outgroups include Neornithischia and Lesothosaurus.

Characters and Character-States Thyreophora 1. Jugal orbital ramus, depth versus transverse breadth: deeper (0); broader (1).

2. Parasagittal row of keeled scutes to each side of the midline on the dorsal aspect of the trunk: absent (0); present (1).

3. Lateral rows of scutes on the dorsal aspect of the trunk: absent (0); present (1).

Emausaurus + Scelidosaurus + Eurypoda 4. Dentary tooth row (and anterior edentulous margin), form (lateral view): straight (0); sinuous (1).

5. Palpebral shape: rod-shaped (0); plate-shaped (1).

6. Metacarpals I and V length: substantially shorter than (0), or subequal to (1), metacarpal III. 7. Manual and pedal unguals: claw-shaped (0); hoof-shaped (1).

Scelidosaurus + Eurypoda 8. Antorbital fossa size: large (0); small (1); absent (2).

9. Palpebral articulation, form: mobile contact with prefrontal (0); interdigitating contact with prefrontal, frontal and postorbital (1).

10. Quadrate condyle, shape: symmetrical (0); medial side larger (1).

11. Pterygovomerine keel, maximum depth: less (0), or more (1), than 50% of snout depth.

12. Basisphenoid length: longer (0), or subequal to or shorter (1), than the basioccipital.

Eurypoda 13. Anterior and posterior supraorbitals: absent (0); present (1).

14. Quadrate condyle, inclination of articular surface (posterior view): horizontal (0); ventromedially inclined at approximately 45 degrees (1).

15. Quadrate lateral ramus: present (0); absent (1).

16. Pterygovomerine keel, length: less (0), or more (1), than 50% of palate length.

17. Dentary symphysial ramus, width: more (0), or less (1), than half of the maximum depth of the mandibular ramus.

18. Premaxillary tooth count: 6 (0); 5 (1); 7 (2).

19. Atlantal neural arch and intercentrum, articulation: open (0); coossified (with maturity) (1).

20. Scapular blade shape: distally expanded (0); parallel-sided (1).

21. Iliac preacetabular process length: less (0), or more (1), than 50% of the length of the iliac blade.

22. Iliac preacetabular process, lateral deflection: 10-20 degrees (0); 45 degrees (1).

23. Ischial blade shape: distally expanded (0); distally tapering (1).

24. Femoral fourth trocanter, form: pendant (0); crest-shaped (1).

25. Femoral anterior trochanter: separated by narrow cleft (0); coossified with greater trochanter in the adult (1).

26. Pedal digit IV phalangeal number: 5 (0); 4 or less (loss of at least one nonterminal phalanx) (1).

27. Metatarsal arrangement: compact (0); spreading (1).

28. Metapodial length: more (0), or less (1), than 30% of propodial length.

Stegosauria 29. Oval fossa on pterygoid ramus of quadrate: absent (0); present (1).

30. Quadrate head, shape: rounded (0); subrectangular (1).

31. Dorsal neural arch pedicel, height: less (0), or 150% or more (1), than centrum height.

32. Mid-dorsal transverse processes, orientation: less (0), or more (1), than 50Ć’ above the horizontal.

33. Anterior dorsal neural canal, size: less (0), or more (1), than 50% of the dorsoventral diameter of the centrum.

34. Anterior caudal neural spine end, shape: transversely (0), or anteroposteriorly (1), flattened.

35. Distal caudal centra, proportions: length greater than (0), or equal to (1), height.

36. Ossified epaxial tendons: present (0); absent (1).

37. Scapular acromion, shape: subtriangular (0); subquadrate with anterodorsal corner (1).

38. Triceps tubercle on humerus: subtle or absent (0); prominent with descending ridge (1).

39. Proximal carpals, form: ovoid (0); block-shaped (1).

40. Intermedium-ulnare articulation: free (0); fused (1).

41. Distal carpals: present (0); absent (1).

42. Pubic acetabular surface, orientation: dorsolateral (0); lateral (1).

43. Postpubic process length: less than 100% (0), 200% (1), or more than 200% (2) of acetabular diameter.

44. Pedal digit I: present (0); absent (1).

45. Pedal digit III, phalangeal number: 4 (0); 3 or fewer (1).

46. Parasagittal osteoderms near midline, prominence: low (0); hypertrophied as plates or spines (1).

47. Parascapular spine: absent (0); present (1).

Stegosauridae (Dacentrurus + Stegosaurinae) 48. Sacral intercostal fenestrae: present (0); closed by costal fusion (1).

49. Femoral length: less than 100% (0), or 150% or more (1), of humeral length.

Stegosaurinae 50. Humeral distal end, width: 30% (0), or 50% (1), of humeral length.

51. Ischial shaft, profile of dorsal margin: straight (0); angle near mid-shaft (1).

Ankylosauria 52. Occiput, maximum width: less (0), or more (1), than maximum height.

53. Antorbital fenestra: present, open (0); absent, closed by maxilla, lacrimal, and jugal (1).

54. Supratemporal fenestra: present, open (0); absent, closed by postorbital, squamosal and parietal (1).

55. Jugal-postorbital bar, width: narrower (0), or broader (1), than laterotemporl fenestra.

56. Quadratojugal, orientation of external surface: lateral (0); posterior (1).

57. Nasal septum dividing narial passage: absent (0); present (1).

58. Quadrate shaft, orientation: approximately vertical (0); inclined approximately 45Ć’ anteroventrally (1).

59. Pterygovomerine keel, ventral margin: above (0), or level with (1), maxillary alveolar margin.

60. Pterygoquadrate ramus, depth: deep (0); narrow (1).

61. Space between palate and braincase: open (0); very constricted or closed (1).

62. Accessory ossification separating antorbital and orbital spaces: absent (0); present (1).

63. Fusion and dermal sculpturing of skull roof (except ventral margin of premaxilla and maxilla and posterior portion of the quadratojugal): absent (0); present (1).

64. Jaw articulation, position: posterior (0), or medial (1), to adductor fossa.

65. Elongate, keeled mandibular osteoderm: absent (0); present (1).

66. Predentary ventral process, length: prong-shaped (0); rudimentary eminence (1).

67. Maxillary/dentary crowns, band-shaped cingulum: absent (0); present (1).

68. Atlantal neural arches, median contact above neural canal: absent (0); present (1).

69. Three sacrodorsals with long ribs attaching to the ventral aspect of the iliac preacetabular process: absent (0); present (1).

70. Anterior caudal vertebrae, length of transverse processes: subequal to (0), or approximately twice (1), the height of the neural spine.

71. Distal chevron shape, mutual contact: tongue-shaped, isolated (0); inverted T-shape, ends in contact (1).

72. Sternum with shaft-shaped posterolateral process: absent (0); present (1).

73. Scapular acromion, orientation: coplanar with blade (0); everted (1).

74. Acetabular fenestra: open (0); closed (1).

75. Postpubic process, length: more (0), or less (1), than 50% of ischial length.

76. Pospubic process, shape: rod-shaped (0); strap-shaped (1).

77. Two U-shaped cervical collars composed of contiguous keeled scutes: absent (0); present (1).

78. Mosaic of small osteoderms between larger osteoderms and on the ventral surfces of the neck, trunk, and proximal portions of the limbs: absent (0); present (1).

Nodosauridae 79. Snout low: maximum preorbital depth less (0), or more (1), than twice maximum preorbital length.

80. Premaxillary palate, shape: subtriangular (0); oval (1); subquadrate (2).

81. Occipital condyle, form: crescentic (0); hemispherical (ventrally deflected) (1).

82. Occipital condyle, composition: basioccipital and exoccipitals (0); basioccipital only (1).

83. Posterior margin of pterygoid, position: anterior to (0), or in transverse alignment with (1), the ventral margin of the pterygoid ramus of the quadrate.

84. Scute pattern on dorsal skull roof: large median interorbital and internarial scutes (0); paired interorbital and internarial scutes (1).

85. Dentary ventral margin: straight (0); sinuous (1).

86. Scapular blade, anteroposterior width of base: subequal to (0), or at least 25% less than (1), proximal width at glenoid.

87. Scapular glenoid, orientation: facing posteroventrally and laterally (0); facing posteroventrally (1).

88. Coracoid shape: subquadrate (0); subrectangular (1).

89. Coracoid glenoid, size: subequal to (0), or approximately half of (1), scapular glenoid.

90. U-shaped pectoral collar composed of contiguous keeled scutes: absent (0); present (1).

Ankylosauridae 91. Interpremaxillary notch: absent (0); present (1).

92. Accesssory dermal ossifications forming lateral margin of external nares: absent (0); present (1).

93. Accessory dermal ossifications on posterodorsal and posteroventral corners of the skull roof: absent (0); present (1).

Minmi + Shamosaurus + Ankylosaurinae 94. Skull width: less than (0), equal to (1), or greater than (2), maximum skull length.

95. Snout with lateral sinus: absent (0); present (1).

96. Premaxillary teeth: present (0); absent (1).

97. Hypaxial ossified tendons on distal caudals: absent (0); present (1).

98. Tail club composed of 2 pairs of large ossifications (anterior pair largest): absent (0); present (1).

Ankylosaurinae 99. Snout profile: level with (0), or arching above (1), the posterior skull table.

100. Premaxillary posteroventral rim: poorly developed (0); obscures anteriormost maxillary teeth (lateral view) (1).

101. Premaxillary rim, position of posterior end: in line with (0), or shifted lateral to (1), the maxillary tooth row.

102. Maxillary tooth rows, anterior separation: narrow (0); broad (1).

103. Respiratory passage, shape: straight (0); S-shaped (1).

104. Postocular (jugl-postorbital) wall: absent (0); present (1).

105. Posteroventral dermal plate, position: posterior (0), or posteroventral (1), to orbit.

Other ankylosaurines 106. Cranial acessory dermal plates, size: moderate (0); hypertrophied (1).

107. Dentary ramus, location of maximum depth: posterior end (0); mid length (1).

108. Coronoid height: moderate (0); low (1).

109. Posteriormost caudal pre- and postzygapophyses, length: extend over less (0), or more (1), than half of the adjacent centrum.

110. Distal caudal postzygapophyses, form: short, wedge-shaped (0); long, tongue-shaped (1).

111. Distal hemal arches, mutual contact: absent (0); present (1).

112. Sternal plates, median contact: open (0); coossified (1).

113. Humeral deltopectoral crest, orientation: anteriorly curved (0); transverse (1).

114. Iliac postacetabular process, length: longer (0), or shorter (1), than acetabular diameter.

115. Ischial acetabular margin, form: concave (0); convex (1).

116. Ischial shaft orientation: posteroventral (0); subvertical (1).

117. Pubis size, participation in acetabulum: small, participates (0); rudimentary, nearly excluded (1).

118. Tibia, maximum distal width: less (0), or greater (1), than maximum width of proximal end.

Data Matrix Outgroups Lesothosaurus 00000000000000000000000000000000000000000000000000000000000000000000000000000000000X000000000000000000000X000000000000 NEORNITHISCHIA 00000000000000000100000000000000000000000000000000000000000000000000000000000000000X00000000000000000000XX000000000000 Ingroups Scutellosaurus 1110000000?0000?0000000000000000000000???000000?00000000??????00?00000?000000000000X00000000000000000000XX00000?000000 Emausaurus 1111111000?0000?01??????????00000????????????00????00000000000000000000??????000000X0????0000000??000000XX0???????????

Scelidosaurus 111111111111000000?0000000000000000000000000000000000000000000000000000000000000000X00000000000000000000XX0?000?000000 Huayangosaurus 1110?111111111111211111111111111111111111111111000000000000000000000000000000000000X00000000000000000000XX00000?000000 Dacentrurus ?1?????????????????111111111??1111?1?111111111?1100?????????????????000??00000???????00000??????????????X??0????0?0000 Toujiangosaurus ???0???????1?11?1??111?11?????111?1111???????11111100000??????0???1?00???0000000000X000000?0000?00??????XX00????000000 Lexovisaurus ????????????????????11111111??111111111111111111111?????????????????0000000000???????00000??????00??????X?00000?000000 Other stegosaurines 11001111111111111X11111111111111111111111111111111100000000000000010000000000000000X00000000000000000000XX000000000000 Hylaeosaurus ???1??????????????????????????0000000000000??00??????????????????????11?0????????????11111??????00?????????0000???????

Pawpawsaurus ????1??11111111111??????????00?????????????????????1111111111111111???????????1111101?????000000??000000000???????????

Other nodosaurines 1111111211111111101111111111000000000000000000000001111111111111111111111111111111101111110000000000000000000000000000 Gargoyleosaurus ???????11111111112??????????00?????????????????????1111111111111111???????????00000???????111100??00000?100???????????

Shamosaurus ???????2111111111X??????????00?????????????????????111111111111111????????????00000??????01?????????????00????????????

Minmi 11111112111111111X111111111100000000000000000000000111111111111111111111111111000001000000111111110000??00?0000?000000 Gastonia 1??????2111111111X??????????00?????????????????????11111?1?1?1????????????????000001??????111111??11111?10???????????0 Pinacosaurus 1111111211111111111111111111000000000000000000000001111111111111111111111111110000000000001112111111111111111111111111 Other ankylosaurines 11111112111111111X1111111111000000000000000000000001111111111111111111111111111111?11111111112111111111111111111111111

3--Ornithopoda This dataset includes 149 characters in 12 ornithopod taxa. Successively more remote outgroups include Marginocephalia and Thyreophora.

Characters and Character-States Ornithopoda 1. Premaxilla-lacrimal contact: absent (0); present (1).

2. Paroccipital process, shape: subrectangular (0); crescentic (1).

3. Jaw articulation, position: approximately level with (0), or offset ventral to (1), the maxillary tooth row.

4. Premaxillary tooth row (or bill margin), position: level with (0), or ventral to (1), the maxillary tooth row.

Euornithopoda 5. Antorbital fenestra, maximum length: 75% or more of orbital diameter (0); approximately 50% of orbital diameter (1); very small or absent (2).

6. Quadrate foramen, location: posterolateral aspect of quadrate shaft (0); lateral aspect of quadrate or quadratojugal (1).

7. Quadrate foramen, size: foramen (0); fenestra (1).

8. External mandibular fenestra, length: more than 50% maximum depth of the lower jaw (0); small or absent (1).

9. Deltopectoral crest, form: projecting from shaft (0), or low or rounded (1) in lateral or medial view of the humerus.

10. Prepubic process, length: 15% or less (0), approximately 50% (1), or more than 100% (2) the length of the preacetabular process.

11. Ischial obturator process: absent (0); present (1).

Iguanodontia 12. Premaxilla, orientation of lower rim: ventrolateral (0); lateral (1).

13. Maxillary anteroventral process: absent (0); present (1).

14. Narial fossa, maximum length: shorter than (0), subequal to (1), or twice as long as (2) maximum anteroposterior diameter of the orbit.

15. Predentary bill margin, form: smooth (0); scalloped (1).

16. Dentary ramus, shape (lateral view): tapering anteriorly (0); rectangular (1); tapering posteriorly (to 70 % of maximum depth) (2).

17. Premaxillary teeth: present (0); absent (1).

18. Denticle shape: subconical (0); leaf-shaped (1).

19. Dentary crown, medial primary ridge: absent (0); present (1).

20. Manual digit III, phalangeal number: 4 (0); 3 (1).

21. Femoral anterior intercondylar groove: absent (0); V-shaped, broad (1); U-shaped, narrow (2).

22. Femoral posterior intercondylar groove: shallow (0); deep(1).

23. Tibial lateral malleolus, width: 60-70% (0), or 80-90% (1), of medial malleolus.

Dryomorpha 24. Quadrate, free portion of shaft: 10% or less (0), or 30% or more (1), of quadrate height.

25. Maxillary crowns, anteroposterior width: equal (0), or narrower (1), than dentary crowns.

26. Maxillary crowns, shape: subtriangular (0); diamond-shaped (1); lanceolate (2).

27. Maxillary primary ridge strength: less (0), or more (1), prominent than dentary primary ridge.

28. Ischial shaft, shape: dorsoventrally compressed (0); subcylindrical (1).

29. Ischial obturator process, position: just proximal to mid-shaft (0); between mid-shaft and pubic peduncle (1); near pubic peduncle (2).

30. Ischial foot: absent (0); present (1).

Ankylopollexia 31. Paroccipital process, width of base: equal to (0), or narrower than (1), broadest width of process.

32. Paroccipital process, shape of ventral tip: subtriangular (0); rod-shaped (1).

33. Inter-crown spaces: present (0); absent (1).

34. Denticules: absent (0); present (1).

35. Enamel, medial side of maxillary and lateral side of dentary crowns: present (partial or complete) (0), or absent (1), on medial side of maxillary crowns and lateral side of dentary crowns.

36. Postaxial cervicals, neural spine height: prominent (0); rudimentary (1).

37. Postaxial cervicals, form of postzygapophyses: weakly (0), or strongly (1), arched.

38. Cervicals 4-9, form of central surfaces: slightly amphicoelous (0); slightly opisthocoelous (1); strongly opisthocoelous (2).

39. Carpals and metacarpal I, articulation: free (0); coossified as two blocks (1).

40. Distal carpal 5-ulna, articulation: absent (0); present (1).

41. Manual digit I, orientation: 15-25Ć’ (0), 45Ć’ (1), or 60Ć’ or more (2), from the axis of digit III. 42. Metacarpal I, length: more (0), or less (1), than 50% of metacarpal II length.

43. Manual digit I-phalanx 1, shape: longer than broad (0); broader than long (1); disc-shaped or absent (2).

44. Manual digit I-ungual, shape: claw-shaped (0); subconical (1).

45. Manual digit I-ungual, length: shorter (0); or longer (1), than manual digit II-ungual.

46. Pedal digit I, length: 50% or more (1), or 20% or less (2), of the length of pedal digit II. Styracosterna 47. Postorbital bar, minimum width: approximately 25% (0), or 10% (1), of maximum orbital diameter.

48. Dentary coronoid process, shape: subtriangular (0); subrectangular (1); lobe-shaped distal expansion (50 % greater than minimum width at base) (2).

49. Postdentary bones, location: anterior (0), or posterior (1), to midline of coronoid process.

50. Maxillary and dentary teeth, number in tooth row: less (0), or more (1), than 20.

51. Axial spine, anterior extension of anterior process: anterior tip extending as far as (0), or considerably beyond (1), the prezygapophyses.

52. Axial spine shape (side view): subtriangular, bifurcation to postzygapophyses near posterior end of centrum (0); crecsentic, birfurcation to postzygapohpyses near mid centrum (1).

53. Sternal ventorolateral process: absent (0); present (1).

54. Metacarpals II-IV, configuration: spreading (0); appressed, ligament-bound (1).

55. Metacarpal IV, length: 60-70% of (0), or subequal to (1), metacarpal III. 56. Prepubic process, depth of distal end: subequal to (0), 25% greater than (1), or 50% greater than (2) the minimum depth of the process.

57. Iliac peduncle of pubis: absent (0); present (1).

58. Postpubic process, length: 100% (0), 50% (1), or less than 50% (2), of ischium.

59. Metatarsal II, minimum shaft width: subequal to (0), or 50-60% of (1), the minimum shaft width of metatarsal IV. 60. Pedal digits II-IV, ungual shape: claw-shaped (0); hoof-shaped (1).

Hadrosauriformes 61. Maxilla, articular flange for jugal: absent (0); present (1).

62. Quadratojugal, extent of jugal overlap: anterior edge (0); majority of lateral surface (1).

63. Squamosals, separation in midline: 100 % (0), 50% (1), or 0% (2) of the minimum width of the parietals between the supratemporal fossae (dorsal view).

64. Postpalatine foramen: present (0); absent (1).

65. Foramen magnum and occipital condyle, position: positioned posterior (0), or anterior (1) to the posterior margin of the skull roof.

66. Posttemporal foramen (on paroccipital process): present (0); absent (1).

67. Predentary posterolateral process, form: single (0); bifurcate (1).

68. Dentary tooth 1, position relative to the predentary: adjacent (0); separated by a short diastema (1); separated by a long diastema (2).

69. Dentary tooth row, posteriormost tooth: anterior (0), ventral (1), or posterior (2) to the coronoid process.

70. Surangular, contribution to quadrate cotylus: less (0), or more (1), than articular.

71. Cervical number: 9 (0); 11 (1); 12 (2); 13-15 (3).

72. Sacral number: 6 (0); 7 (1); 8 (2).

73. Metacarpal II length: subequal to (0), or 70-80% of (1), metacarpal III length.

74. Manual digits II-IV, phalanx 2 length: less (0), or more (1), than twice the length of phalanx 1.

75. Manual digit II-ungual, shape: broader (0), or narrower (1), than manual digit III-ungual.

76. Manual digit V, phalangeal number: 2 (0); 3 (1).

77. Manual digit V-phalanx 1, length: less than 50% (0), or subequal to (1), the length of metacarpal V. 78. Manual digits II and III, ungual shape: claw-shaped (0); hoof-shaped (1).

79. Iliac blade, dorsal margin: horizontal midsection (0); convex with apex of over pubic peduncle (1).

80. Iliac preacetabular process, length: subequal to (0), or longer than (1), the postacetabular process.

81. Iliac preacetabular process, depth of distal end: subequal to (0), or greater than (1), the proximal end of the process.

82. Pedal digit V: present (0); absent (1).

83. Ossified epaxial tendons, arrangement: intertwined (0); 2-layered lattice (1).

Hadrosauroidea 84. Premaxillary rim, shape of lateral margin: arcuate (0) lateral corner (1).

85. Premaxillary internarial bar, transverse width at midlength (dorsal view): approximately 50% of maximum width across the premaxillaries (0); approximately 20% of maximum width across the premaxillaries (1); thin septum of negligible width (2).

86. Jugal anterior end, shape: tapered (0); expanded dorsoventrally (1).

87. Postorbital skull roof, shape in dorsal view: parallel-sided (0); tapering in width posteriorly (1).

88. Paroccipital process, orientation: ventrally (0), or anteroventrally (1), directed.

89. Supraoccipital shape (posterior view): taller than broad (0); broader than tall (1).

90. Quadrate condyle, anteroposterior width of medial side: slightly narrower than (0), or approximately 50% of (1), the width of the lateral condyle.

91. Caudal neural spines, height: shorter (0), or longer (1), than respective chevrons.

92. Scapular blade, form of dorsal margin: straight (0); convex (1).

93.Iliac pubic peduncle, shape (lateral view): tapers to stout, subrectangular process (0); subtriangular (1).

94. Iliac dorsal antitrochanter: absent (0); present (1).

95. Iliac preacetabular process, length: less (0), or more (1), than 50% of ilium length.

96. Distal tarsals 3 and 4: present (0); absent (1).

97. Pedal digit I: present (0); absent (1).

Protohadros + Hadrosauridae 98. Antorbital fenestra/fossa: present (0); absent (1).

99. Maxilla, posterior pterygoid process: absent (0); present (1).

100. Jugal-quadrate contact, exclusion of quadratojugal from margin of laterotemporal fenestra: absent (0); present (1).

101. Predentary, posteromedian ridge on transverse ramus: absent (0); present (1).

102. Dentary teeth in vertical series: 2 (0); 3-6 (2).

Hadrosauridae 103. Skull shape (posterior view): subrectangular (0); trapezoidal (1).

104. Maxilla-lacrimal contact (anterior extension of jugal): present (0); very limited or absent (intervening jugal process extending anterior to orbit) (1).

105. Nasal anteriomedial process, length: extends to the midpoint (0), or the anterior end (1), of the internarial bar.

106. Jugal, anterior prong: absent (0); present (1).

107. Jugal-lacrimal articulation, form: overlapping (0); butt joint and groove (1).

108. Palpebrals: present (0); absent (completely fused or lost) (1).

109. Occipital condyle, shape of basioccipital portion: hemispherical (0); low, convex (1).

110. Jugal-ectopterygoid contact: present (0); absent (1).

111. Pterygoid, lamina between mandibular flange and quadrate process: absent (0); present (1).

112. Pterygoid quadrate flange, articulation of ventral portion: overlapping pterygoid wing of quadrate (0); butt joint against internal aspect of quadrate shaft (1).

113. Predentary transverse ramus and ventral process, orientation (lateral view): approximately 45ƒ (0), or 20ƒ (0), to the axis of the lateral processes.

114. Predentary triturating surface, orientation: dorsally (0), or dorsolaterally (1), facing.

115. Dentary coronoid process, lateral displacement from tooth row: near (0), or offset far lateral to (1), dentary tooth row.

116. Splenial shape: subtriangular (0); strap-shaped (1).

117. Splenial, position: middle (0), or posterior third (1), of lower jaw.

118. Angular, relative position on lower jaw: ventromedial (0); medial (1).

119. Surangular coronoid process, shape: subtriangular (broad adductor fossa) (0); prong-shaped (rim of adductor fossa only) (1).

120. Surangular foramen: present (0); absent (1).

121. Internal mandibular fenestra: present (0); absent (1).

122. Coronoid: present (0); absent (1).

123. Prearticular: present (0); absent (1).

124. Teeth, number of positions (maxilla/dentary): 25-28/25 (0), or 30-40/30-40 (1).

125. Dentary teeth, shape: diamond-shaped (0); lanceolate (1).

126. Maxillary and dentary teeth, secondary ridges: present (0); very reduced or absent (1).

127. Atlantal postzygapophyses, length: long, extend posterior to intercentrum (0); rudimentary (1).

128. Axial centrum, proportions (lateral view): longer than deep (0); subquadrate (1).

129. Cervicodorsal column, curvature (lateral view): broad (0); deep (1) sinuous curve.

130. Caudal vertebrae, number: approximately 45 (0); approximately 60 (1).

131. Ossified tendons, distribution: anterior dorsals through caudals (0); mid dorsals through caudals (1).

132. Scapula, maximum width of proximal end: greater (0), or subequal to or less (1), than maximum blade width.

133. Acromion, orientation: dorsolateral (0); lateral (1).

134. Coracoid, notch in anterior margin: absent (0); present (1).

135. Coracoid posterior process, location of distal tip: near (0), or far posterior (1), to the glenoid.

136. Humeral deltopectoral crest, length: 40-45% (0), or 55-60% (1), of humeral length.

137. Humeral distal condyles, width: approximately 200% (0), or 120-130% (1), of minimum shaft width.

138. Carpal form: block-shaped with intercarpal contact (0); small ovoids, suspended (1).

139. Metacarpus, maximum length: 20-30% (0), or 50% (1), of radial length.

140. Manual digit I: present (0); absent (1).

141. Metacarpals II-IV, distal condyles: present (0); absent (1).

142. Metacarpal V length: 40-50% (0), or 30-40% (1), of metacarpal II length.

143. Manual digits II, III, shape of penultimate phalanges: subrectangular (0); subtriangular (1).

144. Iliac dorsal antitrochanter, form: rounded eminence (0); prominent flange (1).

145. Iliac margin above antitrochanter, form: straight (0); notched (1).

146. Postpubic symphysis: present (0); absent (1).

147. Femoral fourth trochanter, form: pendant (0); subtriangular (1).

148. Astragalus, orientation of medial margin: 20ƒ or less (0), or 45ƒ or more (1), from a transverse axis (anterior margin).

149. Dentary anterior end, ventral deflection: moderate (0); strong (as far ventrally as depth of dentary ramus at midsection) (1).

Data Matrix Outgroups THYREOPHORA 00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000X00000 MARGINOCEPHALIA 00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000X00000 Ingroups HETERODONTOSAURIDAE 11110000000000000000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000000X00000 HYPSILOPHODONTOSAURIDAE 11111111111000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000X00000 Muttaburrasaurus 111111111111?1???1??111000X???000000000???????0000??????0??0000?00???0????????1000??000010?0000??0?0?000??000?????0??000???000?????00?00000?1??X0?00?

Tenontosaurus 11111111011111111111111000000000000001000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000000000000X00000 DRYOSAURIDAE 11111111111111111111111111111100000001000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000X00000 CAMPTOSAURIDAE 11111111111111111111111111111111111112111111110000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000X00000 Probactrosaurus 11111111111111111111111111111111111112????????1111111??1???1??0???0?0?????????000??00?00??00000?????000?0???????000????????000??000000000?0?0??X0?000 IGUANODONTIDAE 11111111111112111111111111111111111112112121111111111111111111111111111111111111111000000000000000000000?0000000?0?0000000?00000000000000000000000000 Ouranosaurus 111111111111121211111111111121111111121111211X111111111211111111111101111111111111111111111111111000000?00000000?1?0000000?00000000000000000000000000 Protohadros 11111111???11212111????1121???11111???????????1111??????????0????????1?????????????111???1???????11111??000??0??000???00???000??????????????????????1 HADROSAURINAE 111111111111121111111111121121111111121XXX2XXX1211111112111101211111212211111111111121111111111111111111111111111111111111111111111111111111111111110 LAMBEOSAURINAE 111111111111121111111111121121111111121XXX2XXX1211111112111101211111213211111111111121111111111111111111111111111111111111111111111111111111111111111

4--Marginocephalia This dataset, described in more detail elsewhere (4), includes 155 characters in 17 marginocephalian taxa. Successively more remote outgroups include Ornithopoda and Thyreophora.

Characters and Character-States Marginocephalia 1. Parietosquamosal shelf: absent (0); present (1).

2. Premaxillary border of internal nares: present (0); absent (excluded by maxillae) (1).

3. Postpubic process length, distal symphysis: long, symphysis present (0); very short, symphysis absent (1).

Pachycephalosauria 4. Sacral rib length: subrectangular (0); strap-shaped (1).

5. Scapular blade, distal width: broad (0); narrow (1).

6. Preacetabular process, shape of distal end: tapered (0); expanded (1).

Goyocephale + more derived pachycephalosaurs 7. Frontal and parietal thickness: thin (0); thick (1).

8. Arched premaxilla-maxilla diastema, dentary canine: absent (0); present (1).

9. Postorbital and supratemporal bars, form: bar-shaped with smooth sutures (0); robust with interdigitating sutures (1).

10. Squamosal exposure on occiput: restricted (0); broad (1).

11. Anterior and posterior supraorbital bones: absent (0); present (1).

12. Postorbital-squamosal tubercle row: absent (0); present (1).

13. Postorbital-parietal contact: absent (0); present (1).

14. Squamosal, posterior tubercle row (5 to 7): absent (0); present (1).

15. Angular tubercle row: absent (0); present (1).

16. Basal tubera, shape: subcylindrical (0); plate-shaped (1).

17. Zygapophyseal articulations, form: flat (0); grooved (1).

18. Ossified interwoven tendons: absent (0); present (1).

19. Sternal shape: plate-shaped (0); shafted (1).

20. Humeral length: more (0), or less than (1), 50% of femoral length.

21. Humeral shaft form: straight (0); bowed (1).

22. Deltopectoral crest development: strong (0); rudimentary (1).

23. Iliac blade, lateral deflection of preacetabular process: weak (0); marked (1).

24. Iliac blade, medial tab: absent (0); present (1).

25. Fibular mid-shaft diameter: 1/4 or more (0), or 1/5 or less (1), mid-shaft diameter of tibia.

6. Preacetabular process, shape of distal end: tapered (0); expanded (1).

Homalocephale + Pachycephalosauridae 26. Parietal table, form: narrow and smooth (0); broad and rugose (1).

27. Quadratojugal free ventral margin, length: moderate (0); very short (1).

28. Pterygoquadrate rami, posterior projection of ventral margin: weak (0); pronounced (1).

29. Prootic-basisphenoid plate: absent (0); present (1).

30. Iliac blade, medial flange on postacetabular process: absent (0); present (1).

31. Ischial pubic peduncle, shape: transversely (0), or dorsoventrally (1), flattened.

32. Pubic body: substantial (0); reduced (1).

Pachycephalosauridae 33. Interfrontal and frontoparietal sutures: open (0); closed (1).

34. Frontoparietal doming: absent (0); partial (1); complete (posteriorly and laterally) (2).

35. Parietal-squamosal position relative to occiput: dorsal (0); posterodorsal (1).

36. Supratemporal opening: open (0); closed (1).

Pachycephalosaurinae 37. Jugal-quadrate contact: absent (0); present (1).

Tylocephale + Prenocephale 38. Quadratojugal fossa: absent (0); present (1).

Stygimoloch + Pachycephalosaurus 39. Preorbital skull length: much less than (0), or subequal to (1), length from anterior orbital margin to posterior aspect of quadrate head.

40. Squamosal node cluster: absent (0); present (1).

41. Anterior snout nodes: absent (0); present (1).

Ceratopsia 42. Rostral bone: absent (0); present (1).

43. Narial fossa, position: adjacent to (0), or separated by a flat margin from (1), the ventral margin of the premaxilla.

44. Jugal, lateral projection: chord from frontal orbital margin to extremity of jugal is less (0), or more (1), than minimum interorbital width.

45. Jugal (or jugal-epijugal) crest: absent (0); present (1).

46. Jugal infraorbital ramus, relative dorsoventral width: less (0), or subequal to or greater (1), than the width of the infratemporal ramus.

47. Premaxillary palate, form: flat (0); vaulted (1).

48. Predentary ventral process, width of base: less (0), or equal to or more (1), than half the maximum transverse width of the predentary.

Neoceratopsia 49. Premaxillary tooth number: 3 or more (0); 2 (1); 0 (2).

50. Premaxillary teeth, crown shape: recurved, transversely flattened (0); straight, subcylindrical (1).

51. Skull length (rostral-quadrate): 15% or less (0), or 20 to 30% (1), of length of postcranial skeleton.

52. Rostral lateral processes: rudimentary (0); well developed (1).

53. Snout anterior margin: rounded (0); keeled with point (1).

54. Predentary anterior margin: rounded (0); keeled with point (1).

55. Predentary posteroventral process, shape: broader distally (0); narrower distally (1).

56. Retroarticular process length: long (0); very short or absent (1).

Archaeoceratops + Leptoceratops + Coronosauria 57. Edentulous maxillary/dentary margin, length: 2 (0), or 4 or 5 (1), tooth spaces.

58. Maxillary teeth, primary ridge strength: low (0); prominent (1).

59. Maxillary/dentary primary ridge, position: near midline (0); offset posteriorly/anteriorly, respectively (1).

60. Maxillary/dentary teeth, packing: space between roots in adjacent teeth (0); no space between roots in adjacent tooth columns (1); no space between crowns within a tooth column (2).

61. Dentary tooth row, position of last tooth: anterior to (0), coincident with (1), or posterior to (2), the apex of the coronoid process.

62. Antorbital fossa shape: subtriangular (0); oval (1).

63. Postorbital and supratemporal bars, maximum width: narrow, bar-shaped (0); broad, strap-shaped (1); very broad, plate-shaped (2).

64. Infratemporal bar length: long, subequal to supratemporal bar (0); short, less than one-half supratemporal bar (1).

65. Jugal/epijugal crest: low (0); pronounced (1).

66. Quadrate shaft, anteroposterior width: broad (0); or narrow (1).

67. Predentary dorsal margin, form: sharp edge (0); bevelled cropping surface (1).

68. Dentary coronoid process, width and depth: narrow dentary process, low coronoid process (0); broad dentary process, moderately deep coronoid process (1); broad dentary process with distal expansion, very deep coronoid process (2).

Leptoceratops + Coronosauria 69. Maxillary/dentary crown, height: subequal to (0), or 1.5 times (1), maximum crown width.

70. Lateral maxillary/medial dentary crown base, form: convex (0), or inset (1), from root.

71. Jugal-squamosal contact above laterotemporal fenestra: absent (0); present (1).

72. Epijugal: absent (0); present (1).

73. Supratemporal fossae, relation: separated (0); joined in midline (1).

74. Posterior shelf composition: squamosal and parietal equal (0); squamosal dominant (1); parietal dominant (2).

75. Parietal shelf, inclination: horizontal (0); inclined posterodorsally (1).

76. Exoccipital-exoccipital contact below foramen magnum: absent (0); present (1).

77. Predentary surface between dentaries: absent (0); present (1).

78. Coronoid shape: strap-shaped (0); lobe-shaped (1).

79. Surangular eminence: absent (0); present (1).

80. Splenial symphysis: absent (0); present (1).

81. Axial neural spine, cross-section: V-shaped or subtriangular (0); blade-shaped (1).

82. Cervicals 1-3, vertebral articulations: free (0); fused (1).

83. Cervicals 3-4, neural spine height: much shorter than (0), or subequal to (1), the axial neural spine.

84. Posteriormost caudals, neural spines and chevrons: absent (0); present (1).

85. Mid and posterior caudals, neural spine cross-section: subrectangular (0); oval (1).

86. Tail shape: tapering (0); leaf-shaped (1).

Coronosauria 87. Enamel distribution, maxillary/dentary teeth: both sides of crown (0); restricted to lateral/medial sides in maxillary/dentary teeth (1).

88. Nasal horn: absent (0); present (1).

89. Supratemporal fenestra, shape: oval (0); subtriangular (1).

90. Supratemporal fenestra, orientation of long axis: parasagittal (0); posterolaterally divergent (1).

91. Parietal width: subequal to (0), or much wider than (1), the dorsal skull roof.

92. Parietal posterior extension: as far posteriorly as (0), just posterior to (1), or far posterior to (2), the quadrate head.

93. Paired parietal fenestrae: absent (0); present (1).

94. Hypocentrum: absent (0); present (1).

95. Sacral number: 5 or 6 (0); 8 (1 dorsal, 1 caudal added) (1).

96. Sacral neural spines, mutual contact: absent (0); present (1).

Ceratopsoidea 97. Dentary teeth, primary ridge strength: low (0); prominent (1).

98. Nasal horn position: posterior (0), or dorsal (1), to posterior margin of external nares.

99. Dentary ramus, position of maximum dorsoventral width: posterior (0); anterior (1).

100. Hypocentrum shape: wedge-shaped (0); U-shaped (1); ring-shaped (hemispherical occipital condyle) (2).

101. Mid cervical (C5-C7) neural spines, height: low (0); as high as dorsal neural spines (1).

Turanoceratops + Ceratopsidae 102. Maxillary/dentary teeth, root form: single (0); double (1).

103. Maxillary/dentary crowns, apical plane orientation: less (0), or more (1), than 45 degrees from the primary axis of the root.

104. Lateral maxillary/medial dentary crowns, secondary ridges: present (0); rudimentary or absent (1).

105. Postorbital horn: absent (0); present (1).

Ceratopsidae 106. Narial fossa, size: narrow margin (0), or broad area (1), anterior and ventral to external nares on the premaxilla.

107. Narial fossa, position of medial wall: parasagittal (0); median (1).

108. External naris, size: smaller than (0), or twice the size of (1), the orbit.

109. Antorbital fossa, size: 30% of maxilla (0); limited to a narrow margin (1).

110. Maxillary margin anterior to tooth row, orientation: anterodorsally inclined (0); horizontal (1).

111. Maxillary posterior alveolar process, length: less than 25% (0), or more than 30% (1), of maxillary tooth row length.

112. Jugal shape: subtriangular, extends under orbit (0); T-shaped, extends anterior to orbit (1).

113. Epijugal shape: crescentic (0); pyramidal (1).

114. Jugal-ectopterygoid contact: present (0); absent (1).

115. Squamosal-jugal contact below infratemporal fenestra: absent (0); present (1).

116. Squamosal frill process, orientation of lateral portion: vertical (0); oblique (1).

117. Frontal-parietal fontanelle: absent (0); present (1).

118. Pineal opening (in frontal-parietal fontanelle): absent (0); present (1).

119. Squamosal-paroccipital contact, orientation: dorsal (0); lateral (1).

120. Squamosal and parietal frill margin, form: smooth (0); scalloped (1).

121. Parietal medial rim over supratemporal fossa: absent (0); present (1).

122. Supraorbital, form of articulation with orbit: ligmentous (0); sutural (1); coossified (2).

123. Quadrate head, shape: rounded (0); plate-shaped (1).

124. Quadrate lateral process: present (0); absent (1).

125. Epoccipitals: absent (0); present (1).

126. Secondary palate, transversely broadest region: maxillary (0); premaxillary (1).

127. Posterior palate, ectopterygoid exposure: present (0); covered by palatine and pterygoid.

128. Pterygoid maxillary and quadrate rami, depth of separation: deep (0); shallow (1).

129. Supraoccipital border of the foramen magnum and participation in braincase wall: present (0); absent (1).

130. Paroccipital processes, parasagittal oval depressions: absent (0); present (1).

131. Supraocciptal lateral processes: present (0); absent (1).

132. Occipital condyle, basioccipital contribution: 50% (0); 30% (1).

133. Opening for CN I: single (0); divided (1).

134. Dorsal border of CN I: frontal (0); laterosphenoid (1).

135. Number of foramina for CN X-XII: 3 (0); 2 (1).

136. Quadrate head and jaw articulation, position: head posterior to orbit, jaw articulation level with tooth rows (0); head ventral to orbit, jaw articulation displaced below tooth rows (1).

137. Maxillary/dentary teeth, teeth in vertical series: two (0); four or five (1).

138. Maxillary/dentary teeth, number of tooth columns: 10-20 (0); 25 or more (1).

139. Body size: less (0), or more (1), than 1 ton.

140. Atlantal intercentrum length: shorter than (0), or subequal to (1), axial centrum.

141. C2 and C3 neural spines, orientation: erect (0); strongly posterodorsally inclined (1).

142. Cervical neural spines, shape: narrow (0); broad (1).

143. Sacrum shape (dorsal view): rectangular (0); oval (S4-6 ribs long, S1-3 and S7-9 shorter) (1).

144. Sacrum, median groove on the ventral surface: absent (0); present (1).

145. Glenoid composition: one-half (0), or two-thirds (1), of glenoid formed by scapula.

146. Scapular spine: absent (0); present (1). (from glenoid lip to middle of scapular blade) 147. Ossified clavicles: present (0); absent (1).

148. Iliac blade, orientation: vertical (0); horizontal (1).

149. Iliac pre- and postacetabular processes, maximum width: preacetabular process narrower (0), or broader (1), than postacetabular process.

150. Iliac antitrochanter: absent (0); present (1).

151. Prepubic process, length: shorter than (0), or subequal to (1), iliac preacetabular process.

152. Prepubic process, shape of distal end: tapered (0); flared (1).

153. Pubic acetabular process: absent (0); present (1).

154. Femoral fourth trochanter, shape: pendant (0); crescentic (1).

155. Tibia-astragalus contact, form: free (0); coossified (1).<9> Data Matrix Outgroups THYREOPHORA 0000000000000000000000000000000000000000?0000000000X00?000000000X000000000X0000000000000000000000X0X000000000000X00X000X00000X00000000000000000000100000000 ORNITHOPODA 000000000000000000000000000000000000000000000000000X000000000000X000000000X0000000000000000000000X0X000000000000X00X000X00000X00000000000000000000100000000 Ingroups Stenopelix ??1111???????????0?00?000????000???????????????????????????????????????????????????000????????0???????????????????????????????????????????0???0????00000000 Goyocephale 11???1111111111111111111?0??11??0000??00?0000000000X0??0000?0X0?X??000000100?000?0?00000000?0?0?0X0??00000000000X?0X000X010000??00?0???00000??00???000????0 Homalocephale 1?11?11?111111??111???1111111111000000000??000????0??????00??X00X0??00000100???????0000?000?0?00?????0000???0?00X00X000X01000?000000??00000???0????00000000 Stegoceras 11??11111111111111111111111111111111000000000000000X0??0000??X00X0?000000100?000????0?00000?0?0?0X0??00000000100X00X000X0100000000000000000????000?000???10 Tylocephale 1?????1?1111111??????????11?????121111000??000??????????0???0?00X1??00000100????????????XX0?0????????0000?????00X?0X000X01000??????0???0000????????????????

Prenocephale 11?1?111111111?1?1????11?1X11111121111000000000?000X0???000??X00X0??00000100??????????00XX0?0?0??X???00000000000X00X000X010000000000??00000???0????000???0?

Stygimoloch 1?????1?111?11???????????1??????1211??111???????????????????????????????010?????????????XX0?0???????????0?????????????????????????0?00????1????????????????

Pachycephalosaurus 1?????1?111111???????????1X11???121110111??000???????????000?X00X0??00000100??????????00XX0?0????X???0000000??00X?0X000X010?0?0?0000???0001????????????????

Psittacosaurus 1110000000000000000000000000000000000000011111112X00000000000X00000000000000000000000000000000000X0X00000000X000X00X000X00000000000000000000000000000000000 Chaoyangsaurus ????0?????????0??????0????0?????????000??11111?11111111100000??00??000?00??0??00000???0????0????0?0?0000?0000000X??????????????????0???0000?00??00?????????

Archaeoceratops 1?10?0000000000?00????00??00?0?000000000011111??11111111111111111111??0????????0???000?00001??000X0??00000000?000?0X000000?00??????0???0000??000???000000?0 Leptoceratops 1110000000000000000000000000000000000000011111112X11111111111111111111111211111111111100000100000000000000000000000X00000000000000000?000000000000000000000 PROTOCERATOPSIDAE 1110000000000000000000000000000000000000011111111110111111111111111111111211111111111111111211110000000000000000000000000000000000000?000000000000000000000 Montanoceratops 1?1000000000?00000000000000?0000000000000??11??1??1???1??11?11210??111?1?211?11111111111??021111111110000???00?00?000??000000????0?0??000000000000000000000 Turanoceratops ?????????????0??????????0??????????????????????1?????11?111???????1?11?1????1???????????????????1????1111????0??????????????????????????000????????????????

CENTROSAURINAE 1110000000000000000000000000000000000010010101112X11111111122X210112111112111110111100111112111111121111111111111111111112111111111111111111111111111111111 CERATOPSINAE 1110000000000000000000000000000000000010010101112X11111111122X210112111112111110111100111112111111121111111111111111111112111111111111111111111111111111111

5--Prosauropoda This dataset includes 32 characters in 9 prosauropod genera. Successively more remote outgroups include Sauropoda and Theropoda.

Characters and Character-States Prosauropoda 1. Premaxillary beak: absent (0); present (1).

2. Premaxilla-maxilla external suture: oblique (0); L-shaped (1).

3. Secondary antorbital fossa wall: absent (0); present (1).

4. Maxillary vascular foramina, form: irregular (0); 1 directed posterior, 5-6 anterior (1).

5. Squamosal ventral process, shape: tab-shaped (0); strap-shaped (1).

6. Dentary tooth 1, position: terminal (0); inset (1).

7. Axial postzygapophyses, length: overhang (0), or flush with (1), the posterior centrum face.

8. Deltopectoral crest, length: less (0), or equal to or more (1), than 50% of the length of the humerus (1).

9. Deltopectoral crest, deflection: 45ƒ-60ƒ (0), or 90ƒ (1), to the transverse axis of the distal condyles.

10. Distal carpal 1, size: small (0); large (1).

11. Metacarpal I, basal articulation: flush with other metacarpals (0); inset into the carpus (1).

12. Metacarpal I, basal width: less than 50% (0), or more than 65% (1), maximum length.

13. Manual digit I, phalanx 1, proximal heel: absent (0); present (1).

14. Manual digit I-phalanx 1, rotation of axis through distal condyles: rotated slightly ventromedially (0); rotated 45ƒ ventrolaterally (1); rotated 60ƒ ventrolaterally (2).

15. Iliac preacetabular process, shape: blade-shaped (0); subtriangular (1).

16. Iliac preacetabular process, scar: absent (0); present (1).

17. Ischial distal shaft cross-section: ovate (0); subtriangular (1).

18. Metatarsal II proximal articular surface: subtriangular or subquadrate (0); hourglass-shaped (1).

19. Metatarsal IV proximal end, transverse width: subequal (0), 3 times broader than (1), dorsoventral depth.

Plateosauria 20. Premaxillary posterodorsal process, shape of distal end: tapered (0); transversely expanded (1).

21. Nasal anteroventral process, basal width: subequal to (0), or 50% broader than (1), anterior process.

22. Median nasal depression: absent (0); present (1).

23. Prefrontal posterior process, size: small (0); large (1).

24. Cervicals 2-8 centra, length: less than (0); more three times diameter (1).

Plateosauridae 25. Frontal exposure between nasal and prefrontal: absent (0); present (1).

26. Jaw articulation, position: just below (0), or approximately 25% of the length of the tooth row below (1), the tooth row.

Coloradisaurus + Sellosaurus + Plateosaurus 27. Dentary anterior end, orientation: straight (0); ventrally curved (1).

28. Basal tubera/basiptrygoid processes, position: near (0), or offset below (1), the level of the occipital condyle.

29. Deep transverse septum between basipterygoid processes: absent (0); present (1).

Sellosaurus + Plateosaurus 30. Nasal participation in secondary antorbital fossa wall: absent (0); present (1).

31. Premaxillary tooth number: 4 (0); 5 (1); 0 (2).

Massospondylidae 32. Snout, maximum width: subequal (0), or 30% greater (1), than maximum snout height.

Data Matrix Outgroups THEROPODA 00000000000000000000000000000000 SAUROPODA 00000000000000000000000000000000 Ingroups Riojasaurus 1111111111111111111???0000000000 "Griposaurus" sinensis ??????1111111111111????0????????

Ammosaurus (= Anchisaurus) ?111111111111210111????100000000 Yunnanosaurus ?11111111?1112111111??11?00??001 Massospondylus 111111?11111121111111111?0000001 Lufengosaurus ?1111111111112111111111111000000 Coloradisaurus ?11111?????????????11??1?1111000 Sellosaurus ?11111111111121111111??111111110 Plateosaurus 11111111111112111111111111111110

6--Sauropoda 116 characters are considered in 11 sauropod taxa, with Prosauropoda and Theropoda serving as successively more remote outgroups. This dataset differs only slightly from that in a recent analysis of basal sauropod phylogeny (5). Two major subclades (Dicraeosauridae, Diplodocidae) of one terminal taxon (Diplodocoidea) are scored separately and seven characters (86-92) have been added supporting diplodocoid monophyly (5).

Characters and Character-States Sauropoda 1. Posture: bipedal (0); columnar, obligatory quadrupedal posture (1).

2. Sacral vertebrae, number: 3 or fewer (0); 4 (1); 5 (2); 6 (3). (2) 3. Humerus, deltopectoral attachment, development: prominent (0); reduced to a low crest or ridge (1).

4. Ulna, olecranon process: prominent, projecting above proximal articulation (0); rudimentary, level with proximal articulation (1).

5. Ulna, proximal condyle, shape: subtriangular (0); triradiate, with deep radial fossa (1).

6. Radius, distal condyle, shape: round (0); subrectangular, flattened posteriorly and articulating in front of ulna (1).

7. Ilium, ischial peduncle, size: large, prominent (0); low, rounded (1).

8. Ischial blade, length: much shorter than (0); equal to or longer than pubic blade (1).

9. Ischial distal shaft, shape: triangular, depth of ischial shaft increases medially (0); bladelike, medial and lateral depths subequal (1).

10. Femur, cross-section, shape: round (0); elliptical, with long axis oriented mediolaterally (1).

11. Femur, fourth trochanter, development: prominent (0); reduced to crest or ridge (1).

12. Astragalus, foramina at base of ascending process: present (0); absent (1).

13. Distal tarsals 3 and 4: present (0); unossified (1).

14. Metatarsal I and V proximal condyle, size: smaller than (0); subequal to metatarsal II and IV (1).

15. Metatarsal V, length: shorter than (0); at least 70% length of metatarsal IV (1).

16. Pedal digit I ungual, length relative to pedal digit II ungual: subequal (0); 25% larger than that of digit II (1).

17. Pedal ungual I, shape: broader transversely than dorsoventrally (0); sickle-shaped, much deeper dorsoventrally than broad transversely (1).

Eusauropoda 18. External nares, position: terminal (0); retracted to a level with orbit (1); retracted above orbit (2).

19. Premaxilla, anterior margin, shape: without step (0); with marked step, anterior portion of skull sharply demarcated (1).

20. Antorbital fossa: present (0); absent (1).

21. Maxillary border of external naris, length: short (0); long (1).

22. Prefrontal, anterior process: present (0); absent (1).

23. Squamosal-quadratojugal contact: present (0); absent (1).

24. Quadratojugal, anterior process, length: short, anterior process shorter than dorsal process (0); long, anterior process approximately twice as long as the dorsal process (1).

25. Orbit, ventral margin, anteroposterior width: broad, subcircular orbital margin, laterotemporal fenestra posterior to orbit (0); reduced, acute orbital margin, laterotemporal fenestra extends under orbit (1).

26. Supratemporal region, anteroposterior width: temporal bar longer anteroposteriorly than transversely (0); temporal bar shorter anteroposteriorly than transversely (1).

27. Supratemporal fossa, lateral exposure: not visible laterally, obscured by temporal bar (0); visible laterally, temporal bar shifted ventrally (1).

28. Quadrate, posterior fossa: absent (0); present (1).

29. Palatine, lateral ramus, shape: plate-shaped (long maxillary contact) (0); rod-shaped (narrow maxillary contact) (1).

30. Dentary, anterior end of ramus, depth: slightly less than that of dentary at midlength (0); 150% minimum depth (1).

31. Tooth rows, shape of anterior portions: narrowly arched, anterior portion of tooth rows V-shaped (0); broadly arched, anterior portion of tooth rows U-shaped (1).

32. Tooth crowns, cross-sectional shape at mid-crown: elliptical (0); D-shaped (1); cylindrical (2).

33. Enamel surface texture: smooth (0); wrinkled (1).

34. Tooth crowns, orientation: aligned along jaw axis, crowns do not overlap (0); aligned slightly anterolingually, tooth crowns overlapping (1).

35. Crown-to-crown occlusion: absent (0); present (1).

36. Occlusal pattern: V-shaped facets (interlocking) (0); high-angled planar facets (1); low-angled planar facets (2).

37. Cervical vertebrae, number: 9 or fewer (0); 10 (1); 12 (2); 13 (3); 15 or greater (4).

38. Cervical centra, articular face shape: amphicoelous (0); opisthocoelous (1). (38) 39. Mid-cervical neural spines, height: less than that of posterior centrum face (0); greater than height of posterior centrum face (1).

40. Dorsal neural spines, breadth: narrower transversely than anteroposteriorly (0); much broader transversely than anteroposteriorly (1).

41. Chevrons, shape: Y-shaped (0); "forked" with anterior and posterior projections (1).

42. Carpal bones, shape: round (0); block-shaped, with flattened proximal and distal surfaces (1).

43. Manual digits II and III, phalangeal number: 2-3-4-3-2 or more (0); reduced, 2-2-2-2-2 or less (1).

44. Manual phalanges (other than unguals), shape: longer proximodistally than broad transversely (0); broader transversely than long proximodistally (1).

45. Iliac blade, dorsal margin, shape: flat (0); semicircular (1).

46. Pubic apron, shape: flat (0); canted anteromedially, with gentle S-shaped medial margin (1).

47. Tibia, cnemial crest, orientation: projecting anteriorly (0); laterally (1).

48. Tibia, distal posteroventral process, size: broad transversely, covering posterior fossa of astragalus (0); reduced, posterior fossa of astragalus visible posteriorly (1).

49. Fibula, lateral trochanter: absent (0); present (1).

50. Metatarsal III length: 30% or more (0), or 25% or less (1), that of tibia.

51. Metatarsal I, minimum shaft width: less than (0) or greater than (1) that of metatarsals II-IV. 52. Metatarsus, posture: bound (0); spreading (1).

53. Pedal phalanges (other than unguals), shape: longer proximodistally than broad transversely (0); broader transversely than long proximodistally (1).

54. Pedal digit I ungual, length relative to metatarsal I: shorter than metatarsal I (0); longer than metatarsal I (1).

55. Pedal digits II-IV, penultimate phalanges, development: subequal in size to more proximal phalanges (0); rudimentary or absent (1).

56. Pedal ungual II-III, shape: broader transversely than dorsoventrally (0); sickle-shaped, much deeper dorsoventrally than broad transversely (1).

57. Pedal digit IV ungual, development: subequal in size to unguals of pedal digits II and III (0); rudimentary or absent (1).

Barapasaurus + Omeisaurus + Neosauropoda 58. Posterior cervical and anterior dorsal neural arches, intraprezygapophyseal lamina: absent (0), present (1).

59. Anterior dorsal centra, articular face shape: amphicoelous (0); opisthocoelous (1).

60. Middle and posterior dorsal neural spines, lateral lamina formed by the union of spinodiapophyseal and suprapostzygapophyseal laminae: absent (0); present (1).

61. Sacrum, sacricostal yoke: absent (0); present (1).

62. Fibula, proximal tibial scar, shape: not well-marked (0); well-marked and deepening anteriorly (1).

63. Astragalus, posterior fossa, shape: undivided (0); divided by vertical crest (1).

64. Pedal unguals, orientation: aligned with (0), or deflected lateral to (1), digit axis.

Omeisaurus + Neosauropoda 65. Frontal contribution to supratemporal fossa: present (0); absent (1).

66. Supratemporal fenestra, long axis orientation: anteroposterior (0); transverse (1).

67. Dentary teeth, number: greater than 20 (0); 17 or fewer (1).

68. Presacral pleurocoels, shape: shallow lateral depressions (0); deep lateral excavations bordered by a sharp lip (1).

69. Cervical pleurocoels, shape: simple, undivided (0); complex, divided by bony septa (1).

70. Dorsal vertebrae, number: 15 (0); 14 (1); 13 (2); 12 or fewer (3).

71. Cervical rib, tuberculum-capitulum angle: greater than 90ƒ (0); less than 90ƒ, rib ventrolateral to centrum (1).

72. Scapula, acromion process, size: narrow (0); width more than 150% minimum width of blade.

73. Metatarsals III and IV, minimum transverse shaft diameters: subequal to (0) or less than 65% (1) that of metatarsals I or II (1).

Neosauropoda 74. Preantorbital fenestra: absent (0); present (1).

75. Postorbital, ventral process, shape: transversely narrow (0); broader transversely than anteroposteriorly (1).

76. Jugal-ectopterygoid contact: present (0); absent (1).

77. External mandibular fenestra: present (0); absent (1).

78. Marginal tooth denticles: present (0); absent (1).

79. Carpal bones, number: 3 or more (0); 2 or fewer (1).

80. Metacarpus, shape: spreading (0); bound, with subparallel shafts, and articular surfaces extending half their length (1).

81. Metacarpals, shape of proximal surface: gently curving, forming a 90ƒ arc (0); U-shaped, subtending a 270ƒ arc (1).

82. Pelvis, anterior width: narrow, ilia longer anteroposteriorly than distance separating preacetabular processes (0); broad, distance between preacetabular processes exceeds anteroposterior length of ilia (1).

83. Tibia, proximal condyle, shape: narrow, long axis anteroposterior (0); expanded transversely, condyle subcircular (1).

84. Astragalus, ascending process, length: limited to anterior two-thirds of astragalus (0); extending to posterior margin of astragalus (1).

85. Astragalus, shape: rectangular (0); with reduced anteromedial corner (1).

Diplodocoidea 86. Dentary, form of anteroventral corner: rounded right angle (0); ventrally projecting "chin" (1).

87. Basipterygoid processes, length: stout, twice diameter (0); subcylindrical, at least 4 times diameter (1).

88. Cervical ribs, length: longer (0), or shorter (1), than respective centra.

89. Dorsal and anterior caudal vertebrae, neural arch height: less (0), or more (1), than 2.5 times height of anterior centrum.

90. Posterior caudal vertebrae, form: gradual decrease in size, centrum length 2-3 times height (0); 20 or more subcylindrical, biconvex centra.

91. Calcaneum: present (0); absent (or unossified) (1).

92. Metatarsal I lateral distal condyle, form: symmetrical (0); flared laterally (1).

Macronaria 93. Middle and posterior dorsal neural spines, shape: tapering or not flaring distally (0); flared distally, with triangular lateral processes (1).

94. Chevrons, proximal "crus" bridging superior margin of haemal canal: present (0); absent (1).

95. Ischial distal shafts, cross-sectional shape: V-shaped, forming an angle of nearly 50ƒ with each other (0); flat, nearly coplanar (1).

Camarasaurus + Titanosauriformes 96. External naris, maximum diameter: shorter (0), or longer (1) than orbital maximum diameter.

97. Quadrate, posterior fossa, depth: shallow (0); deep (1).

98. Surangular, depth: less than twice (0); or more than two and one-half times (1) maximum depth of the angular.

99. Posterior dorsal centra, articular face shape: amphicoelous (0); opisthocoelous (1).

100. Highest metacarpal-to-radius ratio: close to 0.3 (0); 0.45 or more (1).

101. Metacarpal I, length: shorter than metacarpal IV (0); longer than metacarpal IV (1).

102. Puboischial contact, length: approximately one-third (0); or one-half (1) total length of pubis.

Titanosauriformes 103. Pterygoid, dorsomedially oriented basipterygoid hook: present (0); absent (1).

104. Dorsal ribs, proximal pneumatocoels: absent (0); present (1).

105. Metacarpal I, distal condyle shape: divided and asymmetrical (0); undivided and flat with respect to axis of shaft (1).

106. Ilium, preacetabular process, shape: pointed, arching ventrally; semicircular, oriented anterodorsally (1).

107. Femoral shaft, lateral margin shape: straight (0); proximal one-third deflected medially (1).

Somphospondyli 108. Cervical vertebrae, neural arch lamination: well-developed, with well- defined laminae and coels (0); rudimentary; diapophyseal laminae only feebly developed if present (1).

109. Presacral vertebrae, bone texture: solid (0); spongy, with large, open internal cells (1).

110. Anterior and mid-cervical neural spines, orientation: nearly vertical with respect to the vertebral axis (0); posterodorsally inclined, approximately 45ƒ from vertical in lateral view (1).

111. Scapular glenoid, orientation: relatively flat (0); strongly beveled medially (1).

Particularly homoplastic characters 112. Posterolateral processes of premaxilla and lateral processes of maxilla, shape: without midline contact (0); with midline contact forming marked narial depression, subnarial foramen not visible laterally (1).

113. Posterior cervical and anterior dorsal neural spines, shape: single (0); bifid (1).

114. Cervical centra, anteroposterior length/height of posterior face: 2.5-3.0 (0); >4 (1).

115. Distalmost caudal centra, articular face shape: platycoelous (0); biconvex (1).

116. Scapula, distal blade, shape: acromial edge not expanded (0); with rounded expansion on acromial side (1).

Data Matrix Outgroups THEROPODA 00000000000000000000000000000000000X00000000000000000000000000000000X00X00000X000000000000000000X0001000000100000000 PROSAUROPODA 00000000000000000000000000000000000X10000000000000000000000000000000X100000000000000000000000000X0000000000100000000 Ingroups Vulcanodon 11111111111111111????????????????????????????00?000000000???0000????????0?????????000??????0?00????0?0????0????????0 Shunosaurus 11111111?1111111111111111111111111113111111111111111111110000??0000002000?00010000?000000000010000000000000100000000 Barapasaurus 1111111111111???1??????????????1?????1111???11111????????1111111???00????????0???00?????0???000???0??0???000000?0000 Omeisaurus 12111111?1111111111111111111?1111111410111111111?111111111111111111113111???00000000000000000000000000?0000000000100 DICRAEOSAURIDAE 121111111111111112011111111111121012211111111111111111111111111111111311111111111111111111110000000000?0000000001000 DIPLODOCIDAE 121111111111111112011111111111121012411111111111111111111111111111111311111111111111111111110000000000?0000000001010 Haplocanthosaurus 12????11111?????????????????????????3111????11???????????1111??????11210?????????1?????000??111???0??0?0?000000?00?0 Camarasaurus 12111111111111111111110111111111111121111111111111111111111111111111131111111111111110000000111111111100000000011001 BRACHIOSAURIDAE 1201111111111111111111111111101110113111?1111111111111111111111111111?11111111111111100000?01111111111111110000101?1 Euhelopus 131???1111111??111111?11???1111111114111????1111111111?1?111???1??111211101?11???11?100000101?1?011????1?111111010?0 TITANOSAURIA

13101110111111111111?11111111111101331110?1X1111111111111111111111111310111?1111111110000010111?11111111111111110011

7--Ceratosauria This dataset includes 60 characters in 11 ceratosurian taxa, with Tetanurae and Herrerasauridae serving as successively more remote outgroups.

Characters and Character-States Ceratosauria 1. Postaxial cervical and dorsal vertebrae, posterior pleurocoel: absent (0); present (1).

2. Pelvic girdle sutures: open (0); fused (1).

3. Supraacetabular crest, size: shelflike (0); pendant (1).

4. Brevis fossa, posterior end: narrow (0); broad (1).

5. Iliac postacetabular process, posterior margin: convex (0); concave (1).

6. Ischial antitrochanter, anterior margin: straight (0); notched (1).

7. Ischial antitrochanter, size: less (0), or subequal or greater (1), than adjacent articular surface for ilium.

8. Ischial foot: absent (0); present (1).

9. Pubic fenestra: absent (0); present (1).

10. Femoral anterior trochanter, dimorphism: absent (0); present (1).

11. Femoral trochanteric shelf, development: rugosity or low ridge (0); trough-shaped (1).

12. Femoral fibular condyle, separation: weak (0); marked (1).

13. Astragalus-calcaneum, suture and mutual processes: open, present (0); fused, absent (1).

Ceratosauroidea 14. Premaxilla shape: longer than deep (0), or deeper than long (1), under the external naris.

15. Sacral number: 3 (0); 5 (1); 6 (2).

16. Mid sacral centra, ventral margin: horizontal (0); dorsally arched (1).

17. Humeral shaft axis: sigmoid (0); straight (1).

Abelisauridae 18. Tooth row, transverse curvature: minor (0); marked (1).

19. Skull, external sculpturing: absent (0); present (1).

20. Antorbital fossa width: broad (0); narrow (1).

21. Nasal-nasal suture: open (0); fused (1).

22. Lacrimal-postorbital contact: absent (0); present (1).

23. Frontal-parietal suture: open (0); fused (1).

24. Parietal sagittal crest: absent (0); present (short) (1).

25. Nuchal wedge and parietal alae, size: small (0); hypertrophied, elevated well above rest of skull roof (1).

Carnotaurinae 26. Pre-orbital skull length: more (0), or less (1),than 50 % of skull length.

27. Maxilla-jugal contact, length: short (0); long, broad (1).

28. Postorbital ventral process, form near ventral end: rounded (0); inset (1) 29. External mandibular fenestra, size/position: anterior end posterior (0), or ventral (1), to last dentary tooth.

30. Dentary posteroventtral process, length: long (0); short, extending only as far posteriorly as the posterodorsal process.

31. Cervical epipophyses, anterior process: absent (0); present (1).

32. Mid sacral centra, transverse dimensions: similar to adjacent sacrals (0); strongly constricted (1).

Coelophysoidea 33. Skull length: less (0), or more (1), than 3 times posterior skull height.

34. Premaxilla-maxilla arched diastema: absent (0); present (1).

35. Alveolar premaxilla-maxilla suture: present (0); absent (1).

36. Premaxillary tooth row, position of posterior end: ventral (0), or anterior (1), to external naris.

37. Dentary anterior end, form: rounded (0); expanded dorsoventrally (1).

38. Dentary tooth 3, size: subequal (0), or enlarged (1), relative to tooth 2.

39. Axis, anterior pleurocoel: present (0); absent (1).

40. Distal caudal prezygapophyses, length: 40% (0), or 30% or less (1), overlap of preceding centrum.

41. Pubic foot, anteroposterior length: longer (0), or shorter (1), than ischial foot.

42. Distal tibial flange posterior to fibula, shape: lobe-shaped (0); tabular (1).

Liliensternus + Coelophysidae 43. Antorbital fossa, anterior end: posterior (0), or ventral (1), to posterior end of external naris.

44. Antorbital fossa ventral margin, rounded rim: absent (0); present (1).

45. Mid-cervical (C3-C6) centrum length: less than 3 (0), 3 (1), or more than 4 (2), times centrum height.

46. Ischium length: subequal to (0), or shorter than (1), pubis length.

47. Ischial mid-shaft, cross-sectional shape (paired): oval (0); heart-shaped (1); subrectangular (2).

Coelophysidae 48. Dorsal centrum length: subequal to (0), or more than 2.5 times (1), centrum height.

49. Distal tarsal 3 and metatarsals II and III, sutures: open (0); fused (1).

50. Pubic shaft, axis: straight (0); bowed anteriorly (1).

Procompsognathinae 51. Pubic shaft, rodlike lateral portion: robust (0); reduced (1).

52. Pubic foot: present (0); absent (1).

Coelophysinae 53. Promaxillary fenestra: present (0); absent (1).

54. Supratemporal fossa, postorbital participation: present (0); absent (1).

55. Basisphenoid fontanelle: present (0); absent (1).

56. Posterior cervical and dorsal vertebrae, transverse process shape: subrectangular (0); subtriangular (1).

57. Sacrum shape, dorsal view: subrectangular (0); subtriangular (1).

58. Sacral transverse processes: separate (0); joined (1).

59. Distal caudal centrum length: three-to-four (0), or seven (1), times centrum height.

60. Postacetabular process, lateral attachment scar: subtle (0); pronounced (1).

Data Matrix Outgroups HERRERASAURIDAE 000000000000000000000000000000000000000000000000000000000000 TETANURAE 000000000000001000000000000000000000000000000000000000000000 Ingroups Elaphrosaurus 111111111?111?211?????????????00???????000??1??0000????00000 Ceratosaurus 1111?1111111112110000000000000010000000000000000000000000000 Abelisaurus ?????????????1???111111110?0????0000??????00????????00??????

Majungatholus ??1??????????1???11111111111111?000000????0000??????0000????

Carnotaurus 111111111?11112111111111111111110000000000000000?000000000?0 Dilophosaurus 1?1111111111101000000000000000001111111111001000000000000000 Liliensternus 101111111?011?1000??0???????0000?1??11111111211000000??0?000 Procompsognathus 111???????1?1????????0????????0?????????X?????211111???0????

Segisaurus ?11????01?1?????1???????????????????????X????12??111????????

Syntarsus 111111111111101010000100000000001111111111112111110011111111 Coelophysis

8--Tetanurae This dataset includes 204 characters in 17 tetanuran taxa, with Ceratosauria and Herrerasauridae serving as successively more remote outgroups. Analysis (under maximum parsimony) results in six trees (CI, 0.67; RI, 0.81).

Characters and Character-States Tetanurae 1. Lacrimal, antorbital pneumatic recess: absent (0); present (1).

2. Lacrimal-jugal articulation, form: overlapping (0); slotted (1).

3. Maxillary tooth row, posteriormost tooth position: ventral (0), or anterior (1), to the orbit.

4. Axial neural spine width: tapers (0), or expands (1), distally.

5. Chevron base, paired anterior and posterior processes: absent (0); present (1).

6. Metacarpal III, mid-shaft transverse diameter, and III-ungual length: subequal to digit II (0); diameter 55% or less metacarpal II, ungual length less than 70% II-ungual (1).

7. Iliac-ischial articulation, anteroposterior width: subequal to (0), or much smaller than (1), iliac-pubic articulation (1).

8. Ischial obturator notch (or foramen): absent (0); present (1).

9. Femoral anterior trochanter, form: sigmoid (0); blade-shaped (1).

10. Tibial distal end, extension of posterolateral flange: partially (0), or completely (1), backs the distal end of fibula and calcaneum.

11. Fibular distal end, maximum width: more (0), or less (1), than twice minimum anteroposterior width of fibular shaft.

12. Astragalar ascending process, thickness: wedge-shaped (0); 3-4 times taller than thick anteroposteriorly at midpoint (1); plate-shaped, more than 5 times taller than thick at midpoint (2).

13. Astragalar articular surface for distal end of fibula, size: 75% or more (0), or approximately 30 % (1), of distal articular cup for fibula.

14. Astragalar distal articular surface, orientation: ventrally directed (0); ventrally and anteriorly directed (1).

15. Metatarsal III, shape and area of proximal articular surface: subrectangular, with minimum transverse width subequal to, or greater than, either metatarsals II or IV (0); hourglass-shaped, with minimum transverse width less than either metatarsals II or IV (1); subrectangular, with maximum transverse width less than either metatarsals II or IV (2); vestigal, with metatarsals II and IV contacting anteriorly (3).

16. Metatarsal III, mid-shaft shape: subrectangular (0); wedge-shaped (anterior overlap on metatarsals II and IV).

Neotetanurae 17. Maxillary fenestra: absent (0); present (1).

18. Promaxillary recess, degree of anterior invagination: medial to rim of antorbital fossa (0); extending into anterior ramus of maxilla (1).

19. Jugal, antorbital pneumatic excavation: absent (0); present (1).

20. Prefrontal-frontal articulation: planar or grooved (0); peg-in-socket (1).

21. Jugal, antorbital pneumatic excavations: absent (0); present (1).

22. Ectopterygoid pneumatic excavation, form: depression (0); invaginated on lateral side (1).

23. Splenial border of internal mandibular fenestra, shape: concave (0); notched (1).

24. Articular, orientation of retroarticular face: dorsal (0); posterior (1).

25. Anterior dorsal vertebrae, pendant hypapophyses: absent (0); present (1).

26. Posterior chevrons, blade shape (lateral view): gently curved (0); L-shaped (1).

27. Furcula (clavicular fusion): absent (0); present (1).

28. Coracoid posterior process and fossa, shape: subtriangular with subcircular fossa (0); crescentic with crescentic fossa (1).

29. Distal carpal(s), form of proximal articular surface: subplanar (0); transverse trochlea (1).

30. Manual digit IV: present (0); absent (1).

31. Iliac preacetabular process, form of anterior margin (lateral view): smoothly convex (0); notched (1).

32. Iliac preacetabular fossa: absent (0); present (1).

33. Iliac pubic peduncle, shape of distal articular surface: subquadrate (0); twice as long anteroposteriorly as broad transversely (1).

34. Pedal digit I, phalangeal length: digit I-ph 1+2 longer than (0), or subequal to (1), digit III-ph 1 Coelurosauria 35. Maxillary secondary palate: insignificant (0); substantial (1).

36. Frontal with deep cerebral fossa: absent (0); present (1).

37. Antorbital fossa, maximum width of anterior margin: 20-30% (0), or 40-50% (1), of maximum length of the antorbital fossa.

38. Ectopterygoid pneumatic excavation, shape: anteroposteriorly elongate (0); subcircular (1).

39. Sacral vertebrae, number: three (0); five (1); six or more (second sacrodorsal attached to preacetabular process) (2).

40. Elongate caudal prezygapophyses, distribution: CA25 (0), or CA15 (1), and more distal caudal vertebrae.

41. Iliac preacetabular fossa, development on pubic peduncle: along anterior margin (0); over most of the peduncle (1).

42. Ischium, maximum length: 80-100% (0), 60-70% (1), or 50% or less (2), pubis length.

43. Ischial obturator flange, shape: trapezoidal (0); triangular (1).

44. Pubic obturator opening, form: foramen (0); notch (1).

45. Femoral fourth trochanter, form: crescentic flange (0); low crest or rugosity (2).

46. Fibular fossa, size: occupying part (0), or all (1), of medial aspect of proximal end.

47. Feathers (or feather-like filaments): absent (0); present (1).

Maniraptoriformes 48. Pterygopalatine fenestra: absent (0); present (1).

49. Pterygoid mandibular ramus: broad flange (0); short process (1).

50. Postaxial cervical centra, form of anterior face: strongly convex (0); weakly convex or flat (1).

51. Mid cervical (C4-8) rib length: longer than (0), or subequal to (1), centrum length.

52. Posterior chevron blades, shape: dorsoventrally (0), or anteroposteriorly (1), elongate.

53. Sternal lateral trabecula: absent (0); present (1).

54. Sternal ribs (three pairs): absent (0); present (1).

55. Coracoid posteroventral process, length: length from glenoid lip to tip of posteroventral process equal to (0), or more than twice (1), the diameter of the coracoid glenoid fossa.

56. Semilunate carpal, composition: two carpals (0); single carpal (1).

57. Ischial obturator notch, shape: circular or U-shaped with parallel sides (0); U-shaped with divergent sides (1).

58. Pubic ischial peduncle, ventral flange: present (0); absent (1).

59. Astragalar condyles, position of transverse axis: ventral to articular cup for tibia (0); ventral to ascending process (1).

60. Astragalar condyle, transverse groove below anterior rim: present (0); absent (0).

61. Astragalar ascending process, position of dorsomedial edge: low-angle crossing (0); high-angle crossng (1); parallels medial margin of tibia (2).

Tyrannoraptora 62. Lacrimal-frontal contact: absent (0); present (1).

63. Quadrate height: 70-90% (0), or 40-50% (1), of the height of the skull at mid-orbit.

64. Coracoid dorsoventral length: 2-3 times (0), or 5 times or more (1), coracoid glenoid diameter.

65. Radial distal end: subcylindrical (0); flattened anteroposteriorly (1).

66. Iliac pubic peduncle, orientation of distal end: sloping posteroventrally (0); horizontal (1).

67. Iliac supraacetabular crest, transverse width: semicircular (0), or straight (1), lateral margin in dorsal view of the ilium.

68. Ischial foot: present (0); absent (1).

69. Femoral anterior trochanter, height: shorter (0), or as tall as (1), greater trochanter.

70. Anterior and greater trochanters, position of junction: near base (0), or distal end (1), of anterior trochanter.

71. Calcaneum, distal articular width: 20-25% (0), or 10% (1), of maximum transverse width of astragalus.

Maniraptora 72. Lacrimal ventral process, orientation: laterally (0), or anteriorly (1), directed.

73. Jugal anterior process, shape: expanded anteriorly (0); tapered anteriorly (1).

74. Laterosphenoid head, size: large (0); small, synovial joint small or absent (1).

75. Uncinate ossifications on several dorsal ribs: absent (0); present (1).

76. Sternal anterior margin: rounded (0); slotted for coracoid (1).

77. Acromion height (distance from axis of blade): 50% or more (0), or 40% or less (1), of the distance from the central axis of the blade to the acromion.

78. Humeral deltoid depression, shape: narrow (0); broad triangular (1).

79. Olecranon process: present (0); absent (1).

80. Ulna, articular surface for humerus, shape: anteroposteriorly elongate (0), or equilateral (1), triangle.

81. Ulna, articular surface for humerus, form: undivided (0); low intercondylar crest (1).

82. Ulna, shaft curvature: straight (0); bowed transversely away from radius (1).

83. Ulna, shape of distal end: transverse width approximately 1.5 (0), or 3.0 (1), times maximum anteroposterior depth.

84. Metacarpal I, medial extent of anterior rim of carpal trochlea: terminates on proximomedial corner (0); extends distally down medial margin (1).

85. Metacarpal I, position of medial condyle: level with (0), or positioned dorsal to (1), lateral condyle.

86. Iliac postacetabular process, shape: trapezoidal (0); half-crescentic (1).

87. Ischial obturator notch, size: less (0), or greater (1), than anteroposterior diameter of acetabulum.

88. Femoral fourth trochanter, shape: crescentic flange (0); low crest or rugosity (1).

89. Femoral distal end, anterior muscle scar: present (0); absent (1).

90. Tibial malleoli: present (0); absent (1).

91. Astragalus, surface for medial half of distal end of tibia, form: cupped (0); flat (1).

92. Astragalus, anterior vascular fossa: present (0); absent (1).

93. Vaned feathers (rachis, barbs, barbules): absent (0); present (1).

Paraves 94. Lacrimal ventral ramus, orbital and antorbital separation: rugose margin (0); smoothly confluent surface (1).

95. Lacrimal posterior process: absent (0); present (1).

96. Prefrontal: present (0); rudimentary or absent (1).

97. Postorbital medial process, orientation: anteriorly directed (0); anterodorsally directed (1).

98. Pterygopalatine fenestra, size: slit-shaped (0); broad fenestra (1).

99. Pterygoid palatal ramus, width: one-fifth (0), or one-tenth (1), length.

100. Laterotemporal fenestra, dorsoventral diameter: subequal to (0), or less than 75% of (1), dorsoventral diameter of the orbit.

101. Dentary posterior process dorsal to external mandibular fenestra: present (0); absent (1).

102. Trunk length: 150% or more (0), or 125% or less (1), of femur length.

103. Caudal vertebrae, position with posteriormost neural spine: CA20-30 (0); CA11-12 (1).

104. Coracosternal articulation, extent: medial portion (0), or all (1), of the anterior margin of the sternum.

105. Coracoid anteroventral margin, shape: arcuate (0); straight (1).

106. Acromion position: dorsal (0), or anterior (1), to the glenoid fossa (with the central axis of the scapular blade held horizontal).

107. Scapular blade, distal expansion: 160% or more (0), 130% or less (1), of minimum width of blade (proximal neck).

108. Metacarpal II, distal condyle proportions: subequal (0); medial condyle broader transversely, deeper dorsoventrally, longer distally than lateral condyle (1).

109. Metacarpal III, proximal heel on base: absent (0); present (1).

110. Metacarpal III shaft axis: straight (0); bowed laterally (1).

111. Manual phalanges III-1+2, length: longer (0), or shorter (1), than phalanx III-3.

112. Iliac peduncles, ventral projection: subequal (0); pubic peduncle extends ventral to ischial peduncle (1).

113. Ischium, form of shaft mid section: rod-shaped or oval (0); subplanar (1).

114. Ischial symphysis, area: entire distal end (0); only ventral edge of distal end (1).

115. Femoral posterior trochanter: absent (0); present (1).

116. Metatarsals III, IV, size of distal condyles: unexpanded (0); bulbous (1).

117. Metatarsal III, separation of distal condyles: undivided (0); divided (1).

118. Pedal digit II, hyperextendable claw: absent (0); present (1).

Spinosauroidea 119. Maxillary anterior ramus, length: 70% (0), or 100% or more (1), of maximum depth.

120. Lacrimal anterior ramus, length: more (0), or less (1), than 65% of the ventral ramus.

121. Humeral deltopectoral crest, length: less (0), or more (1), than 45% humeral length.

122. Radial (forearm) length: more (0), or less (1), than 50% of humeral length.

123. Manual digit I-ungual, length: approximately 250% (0), or 300% (1), the depth of the proximal end.

Allosauroidea 124. Nasal, participation in antorbital fossa: absent (0); present (1).

125. Palatine, flange-shaped articular process for lacrimal: absent (0); present (1).

126. Quadrate, articular flange for quadratojugal: rudimentary or absent (0); present (1).

127. Pneumatic fossa around opening for the internal carotid artery: absent (0); present (1).

128. Basioccipital, participation in basal tubera: present (0); absent (1).

129. Articular, pendant medial process: absent (0), present (1).

Ornithomimosauria 130. Subnarial foramen: present (0); absent (1).

131. Maxilla, preantorbital ramus length: less (0), or equal to or more (1), than 50% of the length of antorbital fossa.

132. Antorbital fossa, form of ventral margin: rounded crest (0); invaginated (1).

133. Nasal anteroventral process: present (0); absent (1).

134. Internal mandibular fenestra: present (0); reduced to a narrow slit or absent 135. Surangular ridge dorsal to posterior surangular foramen: present (0); absent (1).

136. Metacarpal I, length: less than 40% (0), approximately 50% (1), or 60% or more, of metacarpal II length.

137. Metacarpal-phalangeal joint, maximum extension: approximately 45Ć&#x2019;(0), or 15Ć&#x2019; or less (metacarpal distal extensor pits absent) (1), above the horizontal.

Ornithomimoidea 138. Premaxilla, shape of internarial process: transversely (0), or dorsoventrally (1), flattened.

139. Prefrontal exposure on dorsal skull roof: less (0), or more (1), than the lacrimal.

140. Prefrontal orbital flange: absent (0); present (1).

141. Dentary length: 60-70% (0), or 80% (1), of lower jaw length.

142. Implantation, maxillary and dentary tooth rows, i: separate alveoli (0); groove in maxilla and dentary (1).

143. Maxillary tooth row, posteriormost tooth: directly above or posterior to (0), or significantly anterior to (1), posteriormost maxillary tooth.

144. Tooth size along maxillary and dentary tooth rows: increasing to a maximum near the anterior end (0); uniform (1).

145. Crown size, upper and lower tooth rows: dentary crowns subequal in size (0), or smaller than (1), maxillary crowns.

146. Chevron length: approximately twice (0), or 4-5 times (1), corresponding neural spine height.

147. Metacarpals I-III, extent of shaft-to-shaft contact: metacarpal bases only (0); 60-70% of shafts (1).

148. Manual proximal phalanges, marked flexor depression proximal to distal condyles: absent (0); present (1).

149. Manual proximal phalanges, paired flexor processes: absent (0); present (1).

150. Manual I-1 phalanx, dorsomedial tubercle: absent (0); present (1).

151. Manual unguals, form of ventral surface: transversely rounded and narrow (0); flattened and broad (1).

152. Manual unguals, position of flexor tubercles: proximal (0); displaced distally (2).

153. Iliac blades, separation in midline: erect and separated (0); deflected toward midline with partial contact along dorsal margin (1).

Oviraptorosauria 154. External naris, elevation of ventral margin: at the level of (0), or dorsal to (1), the maxilla.

155. Premaxilla participation in antorbital fossa: absent (0); present (1).

156. Mid-snout length: nasal longer (0), or shorter (1), than frontal.

157. Maxilla, form of ramus along ventral margin of antorbital fossa: flat (0); inset medially for dentary and surangular of lower jaw.

158. Jugal orbital ramus, form of mid-section: transversely compressed (0); rod-shaped (1).

159. Primary palate, position: mostly between (0), or ventral to (1), maxilla and jugal.

160. Dentary dorsal margin, form: straight or gently concave (0); convex (1).

161. External mandibular fnestra, length: 15-20% (0), or 40% (1), length of lower jaw.

162. Caudal vertebrae, proportions of articular faces: witdth and height subequal (0); width twice height (1).

163. Anterior caudal (CA1-8) transverse processes, length: subequal to (0), or approximately twice (1), corresonding neural spines.

164. Acromion, form: dorsal tabular flange (0); everted edge (1); anterior or anterodorsal prong (2).

165. Subacromial notch: absent (0); present (1).

Oviraptoroidea 166. Dentary symphysis, state of articulation: free (0); coossified (1).

167. Dentary anterior end, form: undifferrentiated (1); upturned (1).

168. Dentary rami dorsal and ventral to external mandibular fenestra, depth at mid-length: ventral (0), or dorsal (1), ramus is deeper.

169. Dentary dorsal process for surangular, position: lateral (0), or medial (1), side of lower jaw.

170. Surangular, orientation of coronoid margin: vertical (0); deflected medially (1).

171. Jaw joint, position: far (0), or close (1), to the midline.

172. Articular (and quadrate condylar) width: less (0), or more (1), than twice thickness of surangular.

173. Adductor fossa, anterior margin: present (0); absent (1).

174. Splenial posterior ramus, position on lower jaw: ventral or ventromedial (0): medial (1).

175. Dentary teeth: present (0); absent (1).

176. Pleurocoels, anterior caudal vertebrae: absent (0); present (1).

Deinonychosauria 177. Postorbital ventral process, length: longer than (0), or subequal to (1), posterior process.

178. Parietal-squamosal occipital margin: low (0); plate-shaped (1).

179. Splenial-angular sliding articulation, postion on lower jaw: medial (0); ventral (1).

180. Splenial border of internal mandibular fenestra, shape: arcuate (0); V-shaped (1).

181. Posterior surangular foramen, size: small (0); at least twice primitive diameter (1).

182. Articular posteromedial process: absent (0); present (1).

183. Articular smooth ("vascular") surface, location: medial aspect of articular (0); extends across articular between glenoid and retroarticular faces (1).

184. Articular contact with surangular medial process: non-synovial (0); synovial (1).

185. Mid and posterior chevrons with bifurcate anterior and posterior processes: absent (0); present (1).

Particularly homoplastic characters and homoplasious autapomorphies 186. Premaxillary posterolateral process, length: long, extending onto the side of the snout (0); short, terminating within the narial fossa (1).

187. Upper alveolar margin, anterior end: V-shaped (0); broadly U-shaped (1).

188. Posterior tympanic recess, location: lateral (0), or within (1), the columellar recess.

189. Parasphenoid pneumatic bulla: absent (0); present (1).

190. Lower jaws, form of symphyseal region: V-shaped (0); spout-shaped (1).

191. Coronoid: present (0); absent (1).

192. Crown recurvature: present (0); very reduced or absent (1).

193. Crown size and number: more than 50% depth of dentary ramus, 10-18 teeth (0); less than 25% depth of dentary ramus, 20 or more teeth (1).

194. Crown base: continuous with root (0); wasted (1).

195. Premaxillary teeth: present (0); absent (1).

196. Mid-cervical vertebrae (C3-C7), postzygapophyseal form: short, distal epipophyses (0); long (overhanging) and arched with inset epipophyses (1).

197. Mid- and posterior caudal vertebrae, prezygapophyseal length: elongate, overlapping 30-50% of preceding centrum (0); short (1).

198. Coracoid glenoid: concave (0); flat (1); hemisellar (concave anteroposteriorly) (2); convex (3).

199. Forelimb/hindlimb length: forelimb length 45-60% (0), or 70% or more (1), of hind limb length.

200. Humeral ectepicondyle, size: low crest (0); flared laterally as a process as broad as the distal condyles (1) 201. Supraacetabular crest, posterior end: tapers along acetabulum (0); ends abruptly on lateral aspect of ischial peduncle (1).

202. Femoral anterior trochanter, size: wing-shaped (0); narrow (1); splint-shaped (2) 203. Femoral greater trochanter, anteroposterior width: subequal to (0), or twice or more as broad as (1), femoral head.

204. Metatarsal III with proximal extension on ventral aspect of the distal end: absent (0); present (1).

Data Matrix Outgroups HERRERASAURIDAE 00000000000000000X0000000000000000000X00000000000100X00X0000000000010000000X0000000000X00000?

0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000X00?0000000000X00 CERATOSAURIA 00000000000000000X0000000000000000000X10000000?00000000X000000000000000000000000000000X00000?

000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000010000000000000000 Ingroups TORVOSAURIDAE 11??1?111111111100010???00????000?000??000000????000??0?0000000000000?000???0000000000X00000?00000000000000000000000001111100000000000010000000000000000000000?0?

0000000??00000000000000000?00?0000000000000 SPINOSAURIDAE 11110111111111??00????0?10?0??000?100?1?000000???0????0?0000000000000000??0?0000000??0X00000?000000000000000000000000011111000000100000??

01000000000000001000000000000000000000000000000000X00?0000000000000 ALLOSAURIDAE 1111111111111111111111111111111111000010000100?00000X0000000101000000000000X0000000000X00000?

0000000000000000000000000000001111110000000000000000000000000000000000000000000000000000000000X0000000000000000 SINRAPTORIDAE 11101111111111111111111(01)11?1?1111100001000000??0000?00??00000000?000000000000????????0X00000?000000000000000000000000000???111111000000?

000000000000000000000000000000000000000000000000000X00?0000000000000 COMPSOGNATHIDAE 1?1??1111111?1??1?1?1??101?1111111??1?1011111?1??000X00?0????000000000?00?0X0?000000?00?????00000??0?01?000?0000000000000000?0????000??1????

000000000000000000000000000????00000000?????000?00?000001000000?

Ornitholestes 111?1?11111111111111111111????111??11111111111??00?0????00???00??00??0?000???0000000000?00???0000000001????????00000000000?000??0000001?0000000000?00?0000000001000??

0000000000000000000000?00?000000?00000? Deltadromeus ???????111111111????????01?1???????????1??1111????????0???001??0??0?000?????00000??????10000?????000?00000??????000000??0????????????????????????0??????0????????

0000??????????0????????0???????????00?00000 THERIZINOSAURIDAE 001??1011112?1110X00010001?11111?011112X11X11X11111???1011111000001000100???0?0000000000000000000000000?000000?

0000000000000000001111111100000000000000000000000000000000000000000000000000?1111011010110110 ALVAREZSAURIDAE 001?1X111112111110000?X0010111?111111?2X11?11X?110110011?1110000000100101?000000000000010000?

00010000000000000000000000000000000011111111111111111111111100001000000000000000000000000000101011111?110011110 ORNITHOMIMIDAE 0011111111121111100001X0010111111111111111111111111111111111100000000010110?

0X00000000010000000010000000000000100000000000000000011111111111111111111111100000000100000000000000000000000010(01)1?0110100000000 TYRANNOSAUROIDEA 1111111111121121111111111111111111111121111101?11001??111111111111111110000X0000000000000000?

000000000000000000000000000000000000000000000000000000000001000000000000000000000000000000000100000000000001001 Caudipteryx ??1?11111112X1111???????1111111111?11?1112111?1??101001111111?11111111111???1111111111111111100000000000000000?011000000000000000?01?00000??

000001000000011111111112100000?0??1000?00???000?01?0010113000110 CAENAGNATHIDAE ?????1?1?????????1?????01????1????1???2??211?????1??????11?????????1????????????????0111111?????????0?0?0????0?01100000???000??00101?00000??0XXXX??00000011111111?1??

11111111111??0X0000?00X011XX01?1????000 OVIRAPTORIDAE 10X111111112?111110X10X01111111111111X2X121111?011111111111111111111111111111111111111111111?

000000000000000000011000000000000000001000000000XXXX1000000011111111112111111111111000X0000000?011XX01113000110 TROODONTIDAE 0011111111121121110X11?111?111?111?11121121111?11111??11111111111111111111??1111111111111111?

1111111111111111110111111000000000000000000000000000000000000000000000000000000000011111111111X11?010010?000211 DROMAEOSAURIDAE 1111111111121111111111111111111111?111211211111111111111111111111111111111111111111111111111?

111111111111111111111111100000000000000000000000000000000000000000000010000000000001111111110000000000003100200 AVES 00111111X112?1111?0X01X00111111111?1111112111?1111011111111111111111111111(01) 11111111111111111111111111111111111111111110000000000000000000000000000000000000000000002000000000000000000000001001100000(12)100X00

9--Basal Aves This dataset includes 99 characters in 4 basal avian taxa, with Deinonychosauria and Oviraptorosauria serving as successively more remote outgroups.

Characters and Character-States Aves 1. Prenarial snout, length: shorter (0), or longer (1), than maximum snout height.

2. External nares, diameter: shorter (0), or longer (1), than horizontal diameter of the antorbital fenestra.

3. Crown ornamentation: serrations (0); vestigial serrations or absent (1).

4. Crown base form: unconstricted (0); constricted (1).

5. Caudal vertebrae, number: more than 23 (0); 23 or fewer (1).

6. Furcula, maximum shaft width: narrower (0), or broader (1), than minimum width of the neck of the scapular blade.

7. Glenoid midpoint, orientation: posteroventral and slightly lateral (0); lateral (1).

8. Scapular blade, orientation of axis: anteroventral to (0), or nearly parallel with (1), the axis through the anterior and mid-dorsal vertebral column.

9. Coracoid shape: medial (0), or lateral (1), margin longer.

10. Scapular acromial process, shape: flange-shaped (0); quadrangular or pyramidal process (1).

11. Corocoid ventral deflection: less (0), or equal to or more (1), than 90Ć&#x2019;.

12. Coracoid biceps tubercle, position: inset from (0), or along (1), the ventral margin of the coracoid.

13. Coracoid ventral fossa: present (0); absent (1).

14. Semilunate carpal, height: 30-35% (0), or 50% (1), of maximum transverse width.

15. Manual I-1 phalanx, shaft width: subequal to (0), or more slender than (1), metacarpal II. 16. Manual II-1 and -2 phalanges, shaft shape: subcylindrical (0); subtriangular (1).

17. Metacarpals II, III, and phalanges II-1, III-1, collateral ligament pits: present (0); absent (1).

18. Metacarpal III, proximal shaft shape: subcylindrical (0); strap-shaped (1).

19. Manual digits II and III, distal articulation: absent (0); present (1).

20. Manual digits II and III, relative position: parallel (0); digit III crosses under digit II (1).

21. Acetabular medial wall: absent (0); partial wall formed by flange from the pubic peduncle of the ilium (1).

22. Pedal I-ungual, direction of tip: posteromedial (0); anteromedial (reversed) (1).

23. Vaned feathers, distribution: primary, secondary, rectrix only (0); primary secondary, rectrix, covert, contour (1).

Ornithurae 24. Premaxillary posteromedial process, location of posterior tip: near posterior margin of external nares (no frontal contact) (0); posterior to external nares (frontal contact) (1).

25. Mid-cervical centra , form of articular faces: amphiplaytan (0); heterocoelic (1).

26. Sacral vertebrae, number: 6 (0); 8 or more (1).

27. Free caudal vertebrae: 23 or more (0), 6 (1).

28. Pygostyle: absent (0); present (1).

29. Cervical ribs, attachment: free (0); fused (1).

30. Cervical rib shaft, form: subcylindrical (0); flattened (1).

31. Cervicodorsal rib transition: gradual (0); abrupt (1).

32. Furcular proximal articular end, form: rounded (0); club-shaped (1).

33. Scapular acromial process, orientation of long axis: anterior (0); anterodorsal (1).

34. Coracoid shape, anterior view: subrectangular (0); subtriangular with constricted shaft proximally (1).

35. Coracoid foramen, location: centered on coracoid (0); medial margin of coracoid (1); embayment along medial margin or absent (2).

36. Ulnar shaft, maximum mid-shaft diameter: subequal (0), or 70% or more (1) that of the radius.

37. Humeral distal condyles, position: distal (0); anterior (1).

38. Ulna-radius and proximal carpals, configuration: carpals located distally (0), or shifted laterally (1), relative to the distal ends of the ulna and radius.

39. Radius, proximal articular surface for ulna: flattened facet on shaft (0); raised platform distinct from shaft (1).

40. Semilunate carpal-metacarpal I, II, articulation: open (0); coossified (1).

41. Semilunate carpal-metacarpal I articulation, extent of contact: entire proximal end of metacarpal I (0); one-half proximal end of metacarpal I (1); absent (2).

42. Manual II-1 phalanx, lateral shaft form: convex (0); excavated with lateral flange (1).

43. Ischial obturator process: present (0); absent (1).

44. Ilioischial fenestra: absent (0); present (1).

45. Tibia and proximal tarsals, articulation: free (0); completely coossified (1).

46. Distal tarsals and metatarsals, articulation: free (0); completely coossified (1).

47. Metatarsus, anterior tuber: absent (0); present (1).

Ornithothoraces (Enantiornithes + Euornithes) 48. Premaxillary posteromedial processes, articulation: free (0); coossified (1).

49. Ectopterygoid: present (0); absent (1).

50. Hypapophyses in posterior cervical and anterior dorsals: crest-shaped (0); pendant (1).

51. Dorsal vertebrae, number: about 15 (0); 11 or less (1).

52. Anterior dorsal vertebrae, form of transverse processes: rod-shaped (0); plate-shaped (1).

53. Caudal transverse processes, length: subequal to (0), or longer than (1), respective chevrons.

54. Caudal transverse processes, relative length: decrease posteriorly (0); increase posteriorly (1).

55. Dorsal ribs, size distribution: D3 though mid-dorsals subequal (0); D3 largest, decreasing posteriorly (1).

56. Gastralia: present (0); absent (1).

57. Sternal length: shorter (0), or subequal (1), to scapular length.

58. Sternal keel: absent (0); present (1).

59. Sternal trabecula, form: subquadrate (0); strap-shaped with distal flare (1).

60. Sternal trabecula, orientation: lateral and slightly posterior (0); posterior and slightly lateral (1).

61. Furcula and coracoid, length: 50% (0), or at least 80% (1), length of scapula.

62. Intrafurcular angle: greater (0), or less (1), than 70ƒ.

63. Hypocleideum: absent (0); present (1).

64. Hypocleideum, shape: anteroposteriorly (0), or transversely (1), compressed.

65. Scapula-coracoid articulation, form: flat (0); pit-tuber (1).

66. Coracoid shape (lateral view): inverted-L (0); straight (1).

67. Coracoid, acrocoracoid process (biceps tubercle), size: tubercle (0); robust process (1).

68. Triosseal canal (furcula-acrocoracoid articulation): absent (0); present (1).

69. Coracoid, acrocoracoid process (biceps tubercle), location: ventral (0), or dorsal (1), to glenoid.

70. Coracoid, glenoid form: concave, subcircular (0); convex, oval (1).

71. Coracoid, glenoid orientation: posterolateral (0); lateral (1).

72. Humeroulnar length ratio: greater (0), or less (1), than 1.0.

73. Ulnar biceps tubercle: absent (0); present (1).

74. Ulnar distal end, articular rim for ulnare: absent (0); present (1).

75. Radius, lateral groove on mid shaft: absent (0); present (1).

76. Ulna-radiale articulation: absent (0); present (1).

77. Ulnare size: small (0); large (subequal to distal ulna or radius) (1).

78. Ulnare, notch for manus: absent (0); present (1).

79. Radiale form: wedge-shaped (0); tabular (1).

80. Manual digit I, length: 50% (0), or 30% (1), of length of digit II. 81. Manual digit II, length: longer (0), or shorter (1), than forearm or humerus.

82. Manual digit II, diameter: subequal to (0), or nearly twice (1), diameter of corresponding elements of digit I. 83. Manual II-2 phalanx, shaft shape: cylindrical (0); subtriangular, excavated (1).

84. Manual II-2 phalanx, length: longer (0), or shorter (1), than II-1 phalanx.

85. Metacarpal III, length: slightly shorter (0), or slightly longer (1), than metacarpal II. 86. Metacarpal III, distal flexor process: absent (0); present (1).

87. Manual III-1 phalanx, shaft form: subcylindrical (0); excavated, expanding distally (1).

88. Manual III-2, -3, -ungual phalanges: present (0); absent (1).

89. Iliac antitrochanter on acetabular margin: weak or absent (0); prominent (1).

90. Ischial length: less than 50% (0), or 75% or more (1), of the length of the pubis.

91. Pubic symphysis, extent: along ventral half (0), or distal end (1), of pubic shaft.

92. Tibial fibular trochanter, shape: semilunate (0); subtriangular (1).

93. Fibula distal end, form: rod-shaped (0); splint-shaped, terminating before tarsus (1).

94. Metatarsal I distal condyles, position: proximal to (0), or opposite (1), those of metatarsals II-IV. 95. Pedal digit II, hyperextension and ungual size/shape: present, largest, more recurved (0); absent, smaller than digit III-ungual, similar recurvature (1).

96. Metatarsal V: present (0); absent (1).

97. Pedal unguals, flexor tubercle size: strong (0); weak (1).

98. Alular feathers: absent (0); present (1).

Particularly homoplastic character 99. External mandibular fenestra: present (0); absent (1).

Data Matrix Outgroups OVIRAPTOROSAURIA 00000000000000000000000000000000X0000000000000000000000000000010000000000000000000000000000000100X0 DEINONYCHOSAURIA 00000000000000000000000000000000X0000000000000000000000000000000000000000000000000000000000000000X0 Ingroups Archaeopteryx 1111111111111111111111100000000000000000000000000000000000XX000XX0000000000000000000000000000000001 Confuciusornis 11XX111111111111111111111111111111111111111111100000??000000000XX0000000000000000000000000000000000 ENANTIORNITHES 111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111110 EUORNITHES 111111111111111111111111111111110111111111111111111111111111111111111111111111111111111111111111111 References 1.

2.

3.

4.

5.

P. C. Sereno, N. Jb. Geol. Pal”ontol. Abh. (in review).

D. L. Swofford, PAUP (v. 3.1), IL Natural History Survey (1993).

P. C. Sereno, J. Vert. Paleontol. Suppl. (1991); P. C. Sereno and A. B. Arcucci, J. Vert. Paleontol. 13, 385 (1993); ibid. 14, 53 (1994).

P. C. Sereno, in M. Benton, E. Kurochkin, M. Shishkin, D. Unwin, Eds., The Age of Dinosaurs in Russia and Mongolia (Cambridge Univ. Press, Cambridge, in press).

J. A. Wilson and P. C. Sereno, J. Vert. Paleontol. Suppl. 15, 1 (1998).

Copyright © 2001 by The American Association for the Advancement of Science.