Forster et al, 1998 by Felipe Elias

To verify that the Au is actually alloyed into the first layer of the Ni catalyst, we examined the structure and composition of the active catalyst by extended x-ray absorption fine structure spectroscopy (EXAFS). The EXAFS spectrum of the bimetallic catalyst was recorded in situ under synthesis conditions to make sure it is the active catalyst that is studied (Fig. 4). Only if we allow for the possibility that Au atoms have Ni neighbors at Ni interatomic distances can we account for the spectrum. Because Au is immiscible in bulk Ni, this demonstrates that Au is alloyed into the Ni surface layer as on the single crystal model systems. The steam-reforming activity was measured for the Ni catalyst and for the Au/ Ni catalyst for which the EXAFS data are recorded (Fig. 5). The only difference between the two samples is in the Au modification. Both samples were first reduced in pure H and subsequently exposed to a diluted n-butane gas at 550°C. We used nbutane to test the activity because it gives rise to the most severe graphite formation problems. The n-butane conversion as a function of time on stream starts out at about 99.99%. It is seen that the pure Ni catalyst deactivates rapidly, whereas the conversion for the Au/ Ni sample is almost constant. The deactivation is typical of a Ni catalyst under these extreme conditions, and it can be associated with the formation of graphite as seen in, for example, electron microscopy. The Au-containing sample, in contrast, does not produce graphite. This has been checked by independent thermogravimetric measurements. In conclusion, we are approaching a point where fundamental insight into surface structure and reactivity can be applied directly to the design of new catalysts. By combining several experimental surface science techniques with theory and insight into synthesis and in situ characterization of high surface area catalysts, it has been possible to go beyond our fundamental understanding of the atomic processes involved in catalysis to the design of an improved catalyst for the steam-reforming reaction. REFERENCES AND NOTES ___________________________ 1. G. Ertl, in Catalytic Ammonia Synthesis, J. R. Jennings, Ed. (Plenum, New York, 1991), p. 109; D. R. Strongin and G. A. Somorjai, in ibid., p. 1; D. W. Goodman, R. D. Kelly, T. E. Madey, J. T. Yates Jr., J. Catal. 63, 226 (1980); J. Yoshihara and C. T. Campbell, ibid. 161, 776 (1996); G. A. Papapolymerou and L. D. Schmidt, Langmuir 1, 488 (1985); V. P. Zhdanov and B. Kasemo, Surf. Sci. Rep. 20, 111 (1996); S. H. Oh, G. B. Fisher, J. E. Carpenter, D. W. Goodman, J. Catal. 100, 360 (1986). 2. D. A. King, Stud. Surf. Sci. Catal. 109, 79 (1997 ); J. M. Bradley, A. Hopkinson, D. A. King, J. Phys. Chem. 99, 17032 (1995). 3. J. Rostrup-Nielsen, in Catalysis, Science and Technology, J. R. Anderson and M. Boudart, Eds. (Springer, Berlin, 1984), vol. 5, p. 1.

7. 8. 9. 10.

11.

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iiii

, J. Catal. 85, 31 (1984); N. T. Andersen, F. Topsøe, I. Alstrup, J. Rostrup-Nielsen, ibid. 104, 454 (1987 ). J. H. Sinfelt, Bimetallic Catalysts: Discoveries, Concepts, and Applications ( Wiley, New York, 1983); V. Ponec, Adv. Catal. 32, 149 (1983). G. A. Attard and D. A. King, Surf. Sci. 188, 589 (1987 ); F. Besenbacher, L. Pleth Nielsen, P. T. Sprunger, in The Chemical Physics of Solid Surfaces and Heterogeneous Catalysis, D. A. King and D. P. Woodruff, Eds. (Elsevier, Amsterdam, 1997 ), vol. 8, chap. 10. L. Pleth Nielsen et al., Phys. Rev. Lett. 71, 754 (1993). M. B. Lee, Q. Y. Yang, S. T. Ceyer, J. Chem. Phys. 87, 2724 (1987 ). P. Kratzer, B. Hammer, J. K. Nørskov, ibid. 105, 5595 (1996). O. Swang, J. K. Faegri, O. Gropen, U. Wahlgren, P. E. M. Siegbahn, Chem. Phys. 156, 379 (1991); H. Yang and J. L. Whitten, J. Chem. Phys. 96, 5529 (1992); H. Burghgraef, A. P. J. Jansen, R. A. van Santen, ibid. 101, 11012 (1994). T. P. Beebe Jr., D. W. Goodman, B. D. Kay, J. T. Yates, J. Chem. Phys. 87, 2305 (1987 ); P. M. Holmblad, J. Wambach, I. Chorkendorff, ibid. 102, 8255 (1995).

12. B. Hammer and J. K. Nørskov, Nature 376, 238 (1995). 13. P. M. Holmblad, J. Hvolbœk Larsen, I. Chorkendorff, J. Chem. Phys. 104, 7289 (1996). 14. P. M. Holmblad et al., Catal. Lett. 40, 131 (1996). 15. The calculation is done selfconsistently with ultrasoft pseudopotentials, a slab of three metal layers, and plane waves with kinetic energies up to 25 rydberg at 54 k-points in the first Brillouin zone. Relaxation of the C and the metal atoms in the outermost surface layer is included. Exchange and correlation effects are described within the generalized gradient approximation of J. P. Perdew et al. [Phys. Rev. B. 46, 6671 (1992)]. 16. We gratefully acknowledge the important preparative work by J. Hyldtoft as well as help and suggestions from I. Alstrup and J. Rostrup-Nielsen. The present work was financed in part by the Danish Research Councils through the Center for Surface Reactivity, DANSYNC, and grant 9501775. We also thank Hasylab for offering beamtime at the ROEMO II E X AFS spectrometer. The Center for Atomic-scale Materials Physics (CAMP) is sponsored by the Danish National Research Foundation. A patent application describing the use of Au/Ni as a steam-reforming catalyst has been submitted [DK patent application 0683/97 (1997 )]. 26 November 1997; accepted 19 January 1998

The Theropod Ancestry of Birds: New Evidence from the Late Cretaceous of Madagascar Catherine A. Forster,* Scott D. Sampson, Luis M. Chiappe, David W. Krause A partial skeleton of a primitive bird, Rahona ostromi, gen. et sp. nov., has been discovered from the Late Cretaceous of Madagascar. This specimen, although exhibiting avian features such as a reversed hallux and ulnar papillae, retains characteristics that indicate a theropod ancestry, including a pubic foot and hyposphene-hypantra vertebral articulations. Rahona has a robust, hyperextendible second digit on the hind foot that terminates in a sicklelike claw, a unique characteristic of the theropod groups Troodontidae and Dromaeosauridae. A phylogenetic analysis places Rahona with Archaeopteryx, making Rahona one of the most primitive birds yet discovered.

The origin of birds has been debated for more than 100 years, with theropod dinosaurs (1–6) and basal archosauriforms (7, 8) most frequently hypothesized as their ancestors. Several workers have argued explicitly against the “birds as dinosaurs” theory (8– 12). We report here a new raven-sized primitive bird that adds new morphological data to the question of bird ancestry. The holotype specimen of this new bird, Rahona ostromi, gen. et sp. nov. (13), was recovered from a small quarry (site MAD93-18) in Upper Cretaceous rocks in northwestern C. A. Forster and D. W. Krause, Department of Anatomical Sciences, State University of New York at Stony Brook, Stony Brook, NY 11794, USA. S. D. Sampson, Department of Anatomy, New York College of Osteopathic Medicine, Old Westbury, NY 11568, USA. L. M. Chiappe, Department of Ornithology, American Museum of Natural History, 79th Street at Central Park West, New York, NY 10024, USA. * To whom correspondence should be addressed. E-mail: cforster@mail.som.sunysb.edu

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Madagascar. This quarry has produced a diverse, well-preserved vertebrate fauna, including the primitive bird Vorona berivotrensis (14). The skeleton of Rahona exhibits a striking mosaic of theropod and derived avian features (Fig. 1). The specimen appears to be adult, based on the complete fusion of neural arches to vertebral centra (Fig. 2). The single camellate cervicodorsal vertebra bears a large hypopophysis and bilateral pneumatic foramina, as in maniraptorans and birds, as well as a large vertebral canal (88% of the centrum height; Fig. 2B). Pneumatic foramina also occur on the dorsal vertebrae, lying within well-developed pneumatic fossae, as in some enantiornithines (Fig. 2A). The vertebral canals are large (42 to 62% of the centrum height), as in birds. The dorsal vertebrae have accessory hyposphene-hypantra articulations, a unique character of theropod and sauropod dinosaurs, retained only in Patagonykus (15)

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among birds. There are six sacral vertebrae, one more than in most theropods and Archaeopteryx. They are completely co-ossified into an avianlike synsacrum (Fig. 2C). Like Archaeopteryx, Rahona retains a long bony tail. Thirteen caudal vertebrae (Cd) are preserved, but the complete number is unknown (Fig. 2D). The transition point is

proximally placed at Cd9. The antebrachium of Rahona is avian; it is elongate (the ulna is 150% of the length of the femur), and the radius is reduced to 50% of the diameter of the ulna (Fig. 3, B and C and measurements in Table 1). The caudal (anconal) margin of the bowed ulna bears six low, slightly elongate papillae that

become less distinct distally (Fig. 3D). We interpret these to be quill knobs for the attachment of secondary flight feathers. These six quill knobs, which are regularly spaced (1.6 cm apart), cover only a portion of the ulnar shaft. We estimate that there is space for four additional feathers, for a total of approximately 10 secondary remiges,

A B

N 5 cm

Fig. 1. Rahona ostromi, a new primitive bird from the Late Cretaceous of Madagascar. (A) Reconstruction in left lateral view, with missing elements indicated by shading. (B) Skeleton of Rahona as found in situ. The specimen is lying on its right side with its axial column in dorsiflexion. Almost all elements of the skeleton were discovered within an area of 500 cm2; most are pristinely preserved. Most preserved parts of the axial column (the last 6 dorsal, the synsacral, and the first 12 caudal vertebrae and chevrons) were found in virtually direct articulation. A 13th caudal vertebra and two chevrons were found closely behind the 12th caudal vertebra. A cervicodorsal vertebra

was found 5 cm in front of the dorsal series and, although isolated, was oriented and spaced as if in articulation with them. The pelvic elements were found either articulated with the synsacrum (right ilium) or in close proximity. The right hind limb, with the femur slightly displaced from the acetabulum, is closely articulated, but digits are missing from the pes. The lower left hind limb is loosely articulated (the femur was displaced approximately 1 m to the north) but has an articulated and nearly complete pes. The left scapula and right ulna were found touching or close to the rest of the bones; the right radius was displaced approximately 15 cm to the west. Scale bar 5 5 cm.

Fig. 2 (left). Axial skeleton of Rahona ostromi. D (A) Last six dorsal vertebrae in right lateral view. A B C (B) Cervicodorsal vertebra in right lateral view. A (C) Synsacrum in left lateral view. (D) Caudal vertebrae and articulated chevrons in left lateral view. Cd1 through Cd9 are on the top row and Cd 10 through Cd13 are on the bottom row. Abbreviation: h, hyposphene-hypantra articulaB C tion. Scale bars 5 1 cm. Fig. 3 (right). Wing elements of Rahona ostromi. (A) Left scapula in lateral view, caudal end up. (B) Right radius in cranial view, proximal end up. (C) Right ulna in medial view, proximal D end up. The box indicates the limits of the scanning electron microscope photo shown in (D). (D) Scanning electron microscope photo of papillae on right ulna (left), with magnified views of two of the papillae (right). We interpret these as quill knobs. Abbreviations: ap, acromion process; gf, glenoid fossa. Scale bar for (A), (B), and (C) 5 1 cm. 1916

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REPORTS which is fewer than the 12 to 14 secondaries suggested for Archaeopteryx (16) but within the range known for extant birds. The main axis of the glenoid fossa is centered on the ventral edge of the scapular blade, as in Archaeopteryx and theropods, rather than lateral to the ventral edge as in Neornithes (Fig. 3A). Otherwise, the scapula is quite derived. It has a facet for the coracoid, indicating a mobile joint as in derived birds, rather than the plesiomorphic sutural contact of theropods and Archaeopteryx. A well-developed acromion process projects well cranial to the coracoid facet, as in Unenlagia, Archaeopteryx, and birds. On the basis of these forelimb characters (enlarged acromion process, coracoid facet, elongate ulna, and ulnar papillae), the scapula of Rahona was probably positioned dorsally on the ribcage rather than more ventrally as in theropods, resulting in a more laterally directed glenoid fossa. This orientation allows for the more extensive vertical excursion of the humerus needed to produce a flight stroke (17) and contributes to the wing-folding mechanism (18). The pelvic elements of Rahona closely resemble those of Archaeopteryx and Unenlagia (18). The ilium has a long preacetabular process (55% of the ilium length) and a short postacetabular process that is drawn back into a narrow, pointed posterior end. The pubis (90% of the ilium length) is oriented vertically (as in some maniraptorans, Archaeopteryx, and Unenlagia). Distally, the pubis sweeps caudally and expands into a foot; a well-developed hypopubic cup is present (Fig. 4A). A pubic foot is absent in nearly all avians, but is present in theropods, Archaeopteryx, Patagonykus, and enantiornithines (for example, Sinornis and Cathayornis). Like that of Archaeopteryx, the ischium of Rahona is short (45% of the length of the pubis), platelike, and has a pointed process at the anterodistal end (Fig. 4A). We interpret the latter as the obturator process, based on its shape and position. Behind the iliac articulation is a small dorsally projecting process [the “proximodorsal process” of Novas and Puerta (18)], a character shared exclusively with Unenlagia and the primitive birds Archaeopteryx, enantiornithines, Iberomesornis, and Confuciusornis. A second, smaller process is midway down the caudal ischial margin, as in Archaeopteryx and Confuciusornis. There is no evidence of an ischial symphysis. All pelvic elements are unfused, a plesiomorphic character state shared with nonavian theropods, Archaeopteryx, Unenlagia, and Iberomesornis. The femoral head is identical to that of Archaeopteryx, lacking both a neck and a fossa for the capital ligament. It also bears an avianlike undivided trochanteric crest (Fig. 4B). The tibia is long and straight

(137% of the femoral length) and lacks a medial cnemial crest as occurs in more derived ornithurine birds. The greatly reduced, splintlike fibula is birdlike in proportion (15% of the tibial diameter), and the tubercle for the m. iliofibularis faces posteriorly, as in Ornithurae (Fig. 4C). The right fibula is preserved in articulation with the tibia, and its distal portion shifts onto the cranial surface of the tibia. If this is its natural position (as in Patagopteryx), it could not have articulated with the calcaneum. Loss of contact between the fibula and calcaneum characterizes birds. The much reduced calcaneum is tucked into the lateral margin of the broad short astragalus (14% of tibial length), as in maniraptorans and Archaeopteryx. The astragalus and calcaneum are partially fused to one another but are not fused to the tibia (Fig. 4C). A free distal tarsal caps the right metatarsal IV. Plesiomorphic free tarsals are also retained in the primitive bird Iberomesornis and in some specimens of Archaeopteryx. The foot of Rahona is primitive in many respects; notably the metatarsals are not fused to one another (Fig. 4D). In some specimens of Archaeopteryx, the metatarsals also lack any fusion (for example, the Eichsta¨tt specimen), although other specimens exhibit partial fusion of the proximal metatarsals (for example, the London specimen). The digits of the left foot of Rahona were found in articulation and show that digit I is reversed relative to the other digits (Fig. 1B), a configuration known only in birds (10). The most striking feature in the nearly complete left foot, however, is the structure of digit II. It is extremely robust relative to the other digits (the first phalanx of digit II is 140% of the width of that of digit III at midshaft) and distinctive in morphology. The phalanges have large, ventrolaterally placed flexor keels, expansive distal exten-

Table 1. Lengths (in millimeters) of pelvic and limb elements of Rahona ostromi. Dash indicates that measurement is not possible because of an absent or incomplete element. Element

Left

Synsacrum Scapula Radius Ulna Ilium Pubis Ischium Femur Tibia Fibula Metatarsal I Metatarsal II Metatarsal III Metatarsal IV

82.2 – – 66.7 – 27.3 88.0 119.8 – 8.9 44.7 48.0 45.3

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Right 41.9 – 126.9 132.3 67.7 60.8 – 87.1 120.2 – – 44.1 48.1 47.7

sor surfaces, and deep, dorsally placed, collateral ligament pits. The digit ends in an enlarged sickle-shaped claw. Although unguals are missing from digits III and IV, their preserved distal phalanges indicate that they bore substantially smaller claws. On the left foot, digit II was found in hyperextension, whereas digits III and IV were flexed (Fig. 1B). This distinctive morphology of an enlarged hyperextendible digit II is found only in dromaeosaurid and troodontid maniraptorans (for example, Deinonychus, Velociraptor, and Troodon), resulting in the predatory “slashing” foot (19). The general skeletal morphology of Rahona is birdlike. Rahona is only slightly larger than the London Archaeopteryx specimen (though smaller than its avian contemporary Vorona) and extremely lightly built (the long bones are hollowed

E Fig. 4. Pelvis and hind limb of Rahona ostromi. (A) Left pelvis in lateral view. The ilium is complete; the pubis is missing its distal end; and the ischium is missing its obturator process, ischial articulation, and part of a small process in the middle of its caudal margin. These missing portions are present on the right pubis and ischium, and their outlines are indicated here by dotted lines. (B) Right femur in anterior view. (C) Right tibia, fibula, and proximal tarsals in anterior view. The proximal ends of the crural elements are slightly eroded but are complete on the left tibia and fibula. (D) Left pes in exploded medial view. (E) Articulated left pes in dorsal view. The ungual of digit III and the distal phalanx and ungual of digit IV are missing. Abbreviations: a, astragalus; c, calcaneum; f, fibula; op, obturator process; pf, pubic foot; pp, preacetabular process; t, tibia. Roman numerals refer to digit numbers. Scale bars 5 1 cm.

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to the same degree seen in other birds). These factors, combined with the elongate feathered ulna and raptorial slashing foot, suggest that this bird was lightweight, active, predatory, and capable of powered flight. The combination of derived wing morphologies with a vertically oriented pubis in Rahona counters the recent suggestion that the development of an avianstyle lung ventilation system suitable for the high metabolic demands of flight was coupled with a fully retroverted pubis (11). The vertical pubis of Rahona also bears a well-developed hypopubic cup, a morphology associated with suprapubic musculature and avian-style lung ventilation (11). Rahona thus shows that a hypopubic cup and opisthopuby did not develop in concert. It has been hypothesized that birds belong to a derived clade of theropods called Maniraptora (2–5). However, the arrangement of taxa within Maniraptora, including exactly where birds fit, is debated. Both Dromaeosauridae (4, 5) and Troodontidae (20) have been hypothesized to be the closest relatives of birds. We ran a phylogenetic analysis (21)

with two separate data sets, one including and one excluding forelimb elements for Rahona (22). The most parsimonious tree for both data sets shows the same arrangement of taxa within Aves (which includes Rahona). That is, the exclusion from the phylogenetic analysis of the strongly avian forelimb assigned to Rahona does not alter its phylogenetic position within Aves. Rahona is supported as a member of Aves [Avialae of others; for example, (3, 5)] by seven unambiguous derived characters; bootstrapping of the data set (500 replications) shows a 90% confidence level for our Aves node (Fig. 5A; the analyses depicted include forelimb characters for Rahona). Our most parsimonious analysis places the purported maniraptoran theropod Unenlagia within Aves as the sister taxon to a Rahona-Archaeopteryx clade (Fig. 5A). This three-taxon clade is united by four unambiguous characters of the pelvis and femur (node 3 in Fig. 5A). Uniting these three taxa in a single subclade places them on a side branch of early bird evolution and supports the suggestion that Archaeopteryx was not a direct precursor of modern birds (12, 23). However, this clade collapses to a

Fig. 5. (A) Phylogenetic Ornithurae Ornithurae A B hypothesis of relationPatagopteryx Patagopteryx ships of Rahona to thero4 Enantiornithes Enantiornithes • pods and birds (this is a 3 • AVES 2 Iberomesornis Iberomesornis strict consensus tree of • AVES 2 1• • our two most parsimoniAlvarezsauridae Alvarezsauridae 1• ous trees). Unambiguous Unenlagia Rahona synapomorphies distrib3 Archaeopteryx • Archaeopteryx uted at each labeled node are as follows. Rahona Unenlagia Node 1 ( Troodontidae 1 Troodontidae Troodontidae Aves): contact lost beDromaeosauridae Dromaeosauridae tween distal ischia. Node 2 (Aves): teeth only slightOviraptoridae Oviraptoridae ly laterally compressed Ornithomimidae Ornithomimidae and nearly conical, loss of Compsognathus Compsognathus separate coronoid bone, number of caudal verteTyrannosauridae Tyrannosauridae brae reduced to 20 to 25, Allosaurus Allosaurus loss of pneumatic foramen on sacral vertebrae, ulnar distal condyle subtriangular in distal view and twisted more than 54° with respect to the proximal end, midshaft diameter of fibula reduced to one-fifth or less that of the tibia, and loss of deep fossa on the medial side of the proximal fibula. Node 3 (Unenlagia 1 Archaeopteryx 1 Rahona): preacetabular process of ilium twice as long as postacetabular process, postacetabular process shallow (less than 50% of the depth at the acetabulum) and drawn back into a pointed process, pubic foot projects caudally only, and loss of femoral neck. Node 4 (Metornithes): loss of jugular postorbital process, medial otic process of quadrate articulates with the prootic, ventral tubercle of humerus projects caudally and is separated from the humeral head by distinct capital incision, carpometacarpus present, prominent antitrochanter on ilium, loss of pubic foot, obturator process on ischium rudimentary or absent, and pubic apron transversely narrowed with pubic symphysis restricted to distal one-third of shaft. (B) Alternative phylogenetic hypothesis of one more step than that shown in (A). An Archaeopteryx-Unenlagia-Rahona arrangement is equally parsimonious but is not depicted here. Unambiguous synapomorphies distributed at each labeled node are as follows. Node 1: pubic foot projects caudally only. Node 2: teeth only slightly laterally compressed and nearly conical, loss of separate coronoid bone, number of caudal vertebrae reduced to 20 to 25, loss of pneumatic foramina on sacral vertebrae, ulnar distal condyle subtriangular in distal view and twisted more than 54° with respect to the proximal end, and midshaft diameter of fibula reduced to one-fifth or less that of the tibia. Node 3: ratio of height of neural canal in dorsal vertebrae to height of cranial articular face more than 0.40, undivided trochanteric crest, deep fossa on medial side of fibula absent, and fibula does not reach tarsus. 1918

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paraphyletic configuration of (in order) Unenlagia–Archaeopteryx–Rahona– other birds, or Archaeopteryx–Unenlagia–Rahona– other birds, with only one additional step (see Fig. 5B for one of these trees). This suggests that the characters uniting these taxa may represent primitive features for birds rather than synapomorphies of a separate primitive bird lineage. These alternative hypotheses may prove more tenable, as Rahona shares a number of characters with more derived birds exclusive of Archaeopteryx (for example, six fused sacral vertebrae, a mobile scapulocoracoid joint, and an undivided trochanteric crest). Rahona remains firmly nested within Aves in all trees. In addition to its numerous bird features (for example, a reversed hallux, a splintlike fibula, and ulnar papillae), Rahona retains specific theropod synapomorphies. The accessory hyposphene-hypantra articulations on its dorsal vertebrae are a synapomorphy of Saurischia (Sauropodomorpha 1 Theropoda) and are unknown in any other amniote clade (24). The singular pedal morphology is known only in derived maniraptoran theropods, which are the purported precursors of birds (25). Thus, the combination of morphological characters found in Rahona strongly supports its membership in Aves, as well as its theropod ancestry, and thus the dinosaurian origin of birds. REFERENCES AND NOTES ___________________________ 1. E. D. Cope, Proc. Acad. Nat. Sci. Phila. 1867, 234 (1867); T. H. Huxley, Geol. Mag. 5, 357 (1868); S. W. Williston, Kans. City Rev. Sci. 3, 457 (1879); L. Witmer, in Origin of the Higher Groups of Tetrapods, H.-P. Schultze and L. Trueb, Eds. (Comstock, Ithaca, NY, 1991), pp. 427– 466; P. C. Sereno and C. Rao, Science 255, 845 (1992); L. M. Chiappe, Nature 378, 349 (1995). To increase readability and conserve space, we use the shorthand terms “theropod” and “maniraptoran” in place of “nonavian theropod” and “nonavian maniraptoran,” respectively. 2. J. H. Ostrom, Biol. J. Linn. Soc. 8, 91 (1976). 3. J. A. Gauthier, Mem. Calif. Acad. Sci. 8, 1 (1986). 4. T. R. Holtz Jr., J. Paleontol. 68, 1100 (1994). 5. F. E. Novas, Mem. Queensl. Mus. 39, 675 (1996). 6. L. M. Chiappe, ibid., p. 533. 7. G. Heilman, The Origin of Birds (Appleton, New York, 1927); A. S. Romer, Vertebrate Paleontology (Univ. of Chicago Press, Chicago, IL, 1966); P. Brodkorb, in Avian Biology, D. S. Farner, J. R. King, K. C. Parkes, Eds. (Academic Press, New York, 1971), pp. 19 –55. 8. S. Tarsitano, in Origin of the Higher Groups of Tetrapods, H.-P. Schultze and L. Trueb, Eds. (Comstock, Ithaca, NY, 1991), pp. 541–576. 9. A. Feduccia and R. Wild, Naturwissenshaften 80, 564 (1993); A. C. Burke and A. Feduccia, Science 278, 666 (1997). 10. A. Feduccia and L. Martin, Mus. North Ariz. Bull. 60, 185 (1996). 11. J. A. Ruben et al. Science 278, 1267 (1997). 12. L. D. Martin, in Origin of the Higher Groups of Tetrapods, H.-P. Schultze and L. Trueb, Eds. (Comstock, Ithaca, NY, 1991), pp. 485 –540. 13. The holotype specimen of Rahona ostromi is cataloged as Universite´ d’Antananarivo (UA) 8656. Locality: MAD93–18, Upper Cretaceous (?Campanian) Maevarano Formation, Mahajanga Basin, northwestern Madagascar; collected by a joint expedition of the State University of New York at Stony Brook

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14. 15.

16.

17.

18. 19. 20.

21.

22.

and the Universite´ d’Antananarivo in 1995. Etymology: Rahona (RAH-hoo-nah; Malagasy): meaning menace/threat or cloud; intended interpretation: “menace from the clouds”; ostromi: in honor of Dr. John H. Ostrom. Diagnosis: Rahona ostromi is distinguished from all other avians by retention of a robust, hyperextendible, pedal digit II; from all other avians except Patagonykus by hyposphenehypantra articulations on dorsal vertebrae; from Archaeopteryx by six fused sacral vertebrae and a greatly reduced fibula lacking contact with the calcaneum; from nonavian theropods, Archaeopteryx, and alvarezsaurids by its relatively elongate ulna with ulnar papillae and mobile scapulocoracoid articulation; from all other avians except Archaeopteryx and alvarezsaurids by retention of a long tail lacking a pygostyle; and from nonavian theropods by neural canals at least 40% of the height of the dorsal vertebral centra, proximal tibia of equal width and length, lack of a medial fossa on the fibula, and a reversed pedal digit I. C. A. Forster et al., Nature 382, 532 (1996). The placement of Patagonykus and other alvarezsaurids (Mononykus and Alvarezsaurus) within Aves, although supported by cladistic analyses [for example, see (5, 6) and this analysis], is questioned by other researchers (10). Elimination of Alvarezsauridae from the phylogenetic analyses presented in this report does not alter the placement of Rahona within Aves. B. Stephan, Urvo¨gel Archaeopterygiformes ( Ziemsen, Wittenberg, Germany, 1974); S. Rietschel, in The Beginnings of Birds, M. K. Hecht, J. H. Ostrom, G. Viohl, P. Wellnhofer, Eds. (Bro¨nner and Daentler, Eichsta¨tt, Germany, 1984), pp. 251–260. F. A. Jenkins, Am. J. Sci. 293-A, 253 (1993); S. A. Poore, A. Sa´nchez-Haiman, G. E. Goslow Jr., Nature 387, 799 (1997). F. E. Novas and P. F. Puerta, Nature 387, 390 (1997). J. H. Ostrom, Peabody Mus. Bull. 30, 1 (1969). P. J. Currie, J. Vertebr. Paleontol. 7, 72 (1987); P. J. Currie and X. Zhao, Can. J. Earth Sci. 30, 2231 (1993). Morphological information from Rahona was combined with that of six bird and eight maniraptoran taxa into a 113-character matrix and analyzed with the PAUP and MacClade programs. Characters were unordered and unweighted, and trees were optimized with the use of delayed transformations. Tree statistics are as follows: The most parsimonious tree shown in Fig. 5A is 228 steps; consistency index (CI) 5 0.579, homoplasy index (HI) 5 0.421, retention index (RI) 5 0.712. The tree shown in Fig. 5B is 229 steps; CI 5 0.576, HI 5 0.424, RI 5 0.709. The character matrix and character list for this phylogenetic analysis are available at www.sciencemag.org/ feature/data/972697.shl. The three forelimb elements of Rahona were found either next to or touching the hind portion of the skeleton (Fig. 1B). Because they were not in direct articulation with the rear of the animal, we recognize the possibility, albeit remote in our opinion, that they do not belong to the same individual or taxon. Although material of more derived avians was found elsewhere in the quarry, with the exception of one articulated partial tibiotarsus-tarsometatarsus (14) all avian material occurred as widely scattered, isolated elements. The only articulated skeleton found anywhere in the quarry is that of Rahona. Because of the taphonomic distribution of bone in the quarry and the juxtaposition of these forelimb elements with the rear portion of the skeleton, we believe they belong to the same specimen and are confident in assigning them to Rahona. Nevertheless, to test the effect of an erroneous association, the phylogenetic analysis was run with two data sets, one including and one excluding forelimb elements for Rahona. Each data set resulted in two most parsimonious trees; the ambiguity in these trees was due to the switching of the positions of the theropod taxa Oviraptoridae and Ornithomimidae. The topology of taxa within Aves was consistent across all four most parsimonious trees, with Rahona firmly nested within this clade.

23. J. H. Ostrom, The Beginnings of Birds, M. K. Hecht, J. H. Ostrom, G. Viohl, P. Wellnhofer, Eds. (Bro¨nner and Daentler, Eichsta¨tt, Germany, 1984), pp. 161– 176; L. Hou, L. D. Martin, Z. Zhou, A. Feduccia, Science 274, 1164 (1996); N. Bonde, in The Continental Jurassic, M. Morales, Ed. (Museum of Northern Arizona, Flagstaff, A Z, 1996), pp. 193–199. 24. It cannot be ascertained whether Archaeopteryx possesses hyposphene-hypantra articulations. Among more derived birds, only the alvarezsaurid Patagonykus retains this character. 25. The foot of Unenlagia is not known. However, it has been suggested that Archaeopteryx retains vestiges of an enlarged, hyperextendible, second pedal digit and claw. This observation was first advanced by J. Gauthier (3) and more recently revived by G. Paul [Programs and Abstracts, Society of Avian Paleontology and Evolution (Washington, DC, 1996), p. 15].

26. We thank B. Rakotosamimanana, P. Wright, B. Andriamihaja, the staff of the Institute for the Conservation of Tropical Environments, the people of Berivotra, and all expedition members for their help; and L. Witmer, J. Clark, and an anonymous reviewer for discussions and critiques. D. Varricchio, J. Clark, M. Norell, H. Osmo´lska, and P. Wellnhofer provided valuable information on theropods and Archaeopteryx. Rahona was prepared by V. Heisey and photographed by M. Stewart and F. E. Grine (with a scanning electron microscope), and figures were drawn by L. Betti-Nash and C.A.F. This work was supported by grants from NSF and The Dinosaur Society (to C.A.F., S.D.S., and D.W.K.) and the J. S. Guggenheim Foundation and F. Chapman Memorial Fund (to L.M.C.). 9 January 1998; accepted 5 February 1998

Age and Origin of Carlsbad Cavern and Related Caves from 40Ar/39Ar of Alunite Victor J. Polyak,* William C. McIntosh,* Necip Gu¨ven, Paula Provencio 40 Ar/39Ar dating of fine-grained alunite that formed during cave genesis provides ages of formation for the Big Room level of Carlsbad Cavern [4.0 to 3.9 million years ago (Ma)], the upper level of Lechuguilla Cave (6.0 to 5.7 Ma), and three other hypogene caves (11.3 to 6.0 Ma) in the Guadalupe Mountains of New Mexico. Alunite ages increase and are strongly correlative with cave elevations, which indicates an 1100-meter decline in the water table, apparently related to tectonic uplift and tilting, from 11.3 Ma to the present. 40 Ar/39Ar dating studies of the hypogene caves have the potential to help resolve late Cenozoic climatic, speleologic, and tectonic questions.

Carlsbad Cavern and Lechuguilla Cave are world renowned for their size, geology, and mineral decorations. These and other related caves are located in the Permian Capitan Limestone, Goat Seep Dolomite, and associated backreef carbonate rocks in the Guadalupe Mountains of southeastern New Mexico and West Texas (1) (Fig. 1). Carlsbad, Lechuguilla, and other major caves of the Guadalupe Mountains formed partly, if not largely, by sulfuric acid dissolution (2– 4) rather than solely by carbonic acid dissolution as was initially thought (5). Caves formed by ascending hydrothermal or sulfuric acid–bearing waters are termed hypogene (6–8). Hypogene caves represent at least 10% of the 3001 (9) caves in the Guadalupe Mountains; these are generally the larger caves. Some hypogene caves in the Carlsbad area contain small amounts of alunite, a potassium-bearing aluminum sulfate, which is a by-product of cave genesis (10). Alunite has been used for K-Ar and V. J. Polyak and N. Gu¨ven, Department of Geosciences, Texas Tech University, Lubbock, TX 79409 –1053, USA. W. C. McIntosh, New Mexico Geochronology Research Laboratory, New Mexico Institute of Mining and Technology, Socorro, NM 87801– 4796, USA. P. Provencio, Sandia National Laboratories, Albuquerque, NM 87185, USA. * To whom correspondence should be addressed. E-mail: aqvjp@ttuvm1.ttu.edu and mcintosh@nmt.edu

www.sciencemag.org

40 Ar/39Ar dating of hypogene and supergene hydrothermal ore deposits (11) and supergene paleoweathering sequences (12). Here, we use alunite to determine the absolute age of formation of Carlsbad Cavern and other related hypogene caves. Previously, ages of these (13) or any other dissolution caves could be estimated only by dating detrital sediments and carbonate precipitates, which establish only the earliest ages of calcite or clastic deposition in the caves. Alunite is present in Carlsbad Cavern and related caves in floor deposits and wall residues and most commonly within pockets of altered bedrock or solution cavity fillings (10), which may represent paleokarst cavities. Alunite and hydrated halloysite are products of the reaction of acidic cave-forming waters with clays such as montmorillonite, illite, dickite, and kaolinite that occur as detrital components of cavity fillings or in scarce thin Permian clay beds. The Green Clay Room in Carlsbad Cavern presents the most convincing evidence of alteration by sulfuric acid of green montmorillonite–rich sediments that fill solution cavities; white reaction rims around these cavity fillings consist of alunite and hydrated halloysite (Fig. 2A). In Endless Cave, pods of white alunite and hydrated halloysite at the base of a 10-cm-thick Permian clay bed also provide

z SCIENCE z VOL. 279 z 20 MARCH 1998

1919

Supplemental Data

Character matrix for phylogenetic analysis of Rahona ostromi. 5 50 95

10 55 100

15 60 105

20 65 110

25 70 113

30 75

35 80

40 85

45 90

Allosaurus

00000 00000 00000

00000 00000 000

00000 00000

Compsognathus

0100? ?0000 ?????

00000 ???0? ?????

10??? ?0000 ?00??

?0?11 00??0 00000

01??0 0?00? 1?0

?00?0 000??

??00? 1?100

00??0 10?00

?0000 0??0?

Archaeopteryx

02111 11010 111??

00111 01110 0111?

10110 00010 ?0111

01?11 01112 00100

01000 10111 100

100?1 11001

00101 11111

1?101 12110

10010 11000

Rahona

????? ????0 21200

????? ????? 01112

????? ??01? 11010

????? ????2 0?101

????? ??11? 100

??111 11101

11?01 11111

10??1 12110

10011 11000

Oviraptoridae

1???1 10000 11000

10101 01100 00000

10110 00000 00000

00001 00001 00000

01001 00001 100

00101 00000

10000 00000

00000 11000

10000 00000

Dromaeosauridae 01001 10010 11100

10001 01010 00000

00110 00000 00010

11011 01111 00001

01000 00011 000

00101 00000

00001 10110

10001 11000

00000 01000

Ornithomimidae

02011 10000 11000

11010 00000 00000

10110 00000 00001

10111 00011 00010

01001 00000 000

00000 00000

00000 00010

00010 11000

00000 00000

Troodontidae

00011 10000 11200

01111 00?10 00001

001?0 00010 00110

?0111 01011 0?011

11001 10011 100

?0100 0000?

10001 ?0011

10011 11000

00000 01000

Tyrannosauridae 00001 00000 00000

11101 00000 00000

00000 00000 00000

00000 00020 00010

10010 00000 000

00001 00000

00000 00100

00000 10000

00000 00000

Alvarezsauridae ?1111 10000 21000

01?10 00211 00111

11??1 00001 11110

11011 0??20 00?10

1?001 11101 100

?0110 0??1?

11101 02201

10110 2??00

11000 00211

Enantiornithes

01111 21120 21?11

01?10 12211 1011?

111?? 11111 11211

1???1 11112 01100

????1 00111 100

?1110 00111

11211 0?201

?111? 2?101

10111 11100

Ornithurae

11111 21121 21011

11110 12211 10112

11021 11111 11211

1?011 11112 11100

11111 01111 111

11110 00211

11211 02201

?111? 2?001

10101 11211

Unenlagia

????? ????0 11000

????? ????0 01???

????? 0???? ?????

????? ????? ?????

????? ????? ???

???01 11001

11??? 11111

?0??? 11100

??01? 11000

Patagopteryx

????? 21121 210?1

?1?10 1?11? 10011

????1 ??011 11211

1???1 ??0?? 11000

??11? 0111? 111

?1110 00010

11??? 02201

?111? 20001

11111 10211

Iberomesornis

????? 21?20 ?1???

????? 12??? ??1??

????? 00?1? ????0

????? ????? 0?100

????? ???1? 1?0

?01?0 0????

0011? ??1??

???1? 2?10?

101?? 1????

Character List for phylogenetic analysis of Rahona ostromi dental 1. 2. 3. 4.

teeth in premaxilla: present (0); absent (1). denticles on teeth: present on anterior and posterior carinae (0); present on posterior carina, but absent or severely restricted on anterior carina (1); absent (2). (adapted from Martin et al., 1980) shape of teeth: laterally compressed and recurved (0); slightly compressed, nearly conical (1). (Ostrom, 1976) constriction between crown to root: absent (0); present (1). (Martin et al., 1980)

skull 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24.

jugal contribution to antorbital fenestra: absent, eliminated by lacrimal-maxilla contact (0), present (1). (Holtz, 1994) maxilla contribution to naris: absent, excluded by a nasal-premaxilla contact (0); present (1). (Martin et al., 1980; Currie, 1995) shape of frontals: anteriorly broad (0); triangular, narrow rostrally (1). (Currie, 1987b; Russell and Dong, 1993) extreme reduction or loss of prefrontal: absent (0); present (1). (Gauthier, 1986) frontal length relative to parietal: smaller or subequal (0); nearly two times as long (1). narrow sagittal crest on parietals: absent (0); present (1). (Currie and Zhao, 1993) jugal bar shape: robust (0); thin and straight (1). (Ostrom, 1976) jugular postorbital process: present (0); absent (1). (Chiappe) subsidiary foramen between palatine and pterygoid: absent (0); present (1). (Gauthier, 1986) palatine-ectopterygoid contact: no contact, ectopterygoid present (0); contact present, ectopterygoid present (1); no contact, ectopterygoid absent (2). (adapted from Currie, 1995) medial otic process of quadrate that articulates with prootic: absent (0); present (1). (Chiappe, 1995) distal quadrate articulation set well anterior to proximal quadrate cotyle: absent (0); present (1). (Ostrom, 1976) shape of paroccipital process: straight and vertically oriented (0); distal end with distinct twist as to face caudodorsally (1). (Colbert and Russell, 1969; Currie, 1995) bulbous parasphenoid capsule (cultriform process): absent (0); present (1). (Osmolska et al., 1972) accessory lacrimal fenestration: present (0); absent (1). supraoccipital crest: absent or weak (0); well pronounced (1). fusion between parietals and laterosphenoid in adults: present (0); absent (1). accesory fenestra between premaxilla and maxilla: present (0); absent (1). quadratojugal cotyla in the lateral face of the mandibular process of the quadrate: absent (0); present (1). pneumatic quadrate: absent (0); present (1).

lower jaw 25. 26.

unfused interdental plates: present (0); absent (1). (Currie, 1987; Holtz, 1994) separate coronoid bone: present (0); absent (1). (Elzanowski and Wellnhofer, 1996)

vertebral column 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42.

heterocoelus cervical vertebrae: absent (0); present (1). (Sanz et al., 1995) ventral processes (hypapophyses) on cervicodorsal vertebrae: absent or very weakly developed (0), present, well developed (1). (Gauthier, 1986) ratio of height of neural canal in dorsal vertebrae to height of cranial articular face: less than .40 (0); more than .40 (1). (Sanz et al., 1995) pneumatic foramina on dorsal vertebrae: absent (0); present (1). (Ostrom, 1976) number of sacral vertebrae: 5 or less (0), 6 or more (1). (adapted from Ostrom, 1976) fusion of all sacral vertebrae in adult: absent or partially fused (0); present, all completely fused (1). number of caudal vertebrae: 30 or more (0), 20-25 (1), or less than 15 (2). pygostyle: absent (0); present (1) (Sanz and Buscalioni, 1992) transition point on caudal vertebrae: distal, behind caudal 10 (0); proximal, no further back than caudal 10 (1) (Gauthier, 1986; Gatesy, 1996) middle and distal chevron shape: laterally compresses, expanded dorsoventrally (0); dorsoventrally flattened into a thin horizontal plate behind transition point (1). (adapted from Ostrom, 1976; Gauthier, 1986) hyposphene-hypantrum articulations on dorsal vertebrae: present (0); absent (1). pneumatic foramen on sacral vertebrae: present(0); absent (1). cervical neural spines: dorsoventrally tall, axially short (0); dorsoventrally short, axially elongate (1). length of middle and posterior caudal vertebrae: subequal to length of proximal caudals (0); elongate, at least 130% the length of the anterior caudals (1). prezygopophyses on middle and posterior caudal vertebrae: elongate, extend at least half the way across preceeding vertebral centrum (0); reduced or absent, extend over 25% or less the length of preceeding vertebral centrum (1). well-developed procoely in anterior caudal vertebrae: absent (0); present (1).

shoulder girdle 43. 44. 45. 46.

scapula with tapered distal end: absent (0); present (1). (Ostrom, 1976) anterior projection of acromion process: absent (0); present, extends well anterior to glenoid fossa (1). scapulocoracoid articulation: immobile, sutural (0); mobile, cartilagenous (1) (adapted from Sanz et al., 1995) acroracoid of coracoid: absent, biceps tubercle small (0); absent, biceps tubercle large (1); present, extends above scapulocoracoid articulation, biceps tubercle large (1). (Perle et al., 1993; Walker, 1972; Ostrom, 1976)

47. 48. 49. 50. 51. 52. 53.

body of coracoid forming sharp angle with the body of the scapula: absent (0); present (1) (Ostrom, 1976; Tarsitano and Hecht, 1980) long axis of coracoid portion of glenoid relative to long axis of scapular portion of glenoid: alligned (0); form a 90 degree angle (1). (Chiappe) coracoid shape: short, rounded sternal border (0); elongate, subrectangular profile, rounded sternal border (1); elongate, strutlike (2). (adapted from Ostrom, 1976; Gauthier, 1986) dorsoventrally curved scapular shaft: absent (0); present (1). supracoracoid nerve foramen (incision) located in the medial margin of coracoid: absent (0); present (1). (Sanz et al., 1995) shape of fused clavicles: absent (0); present, interclavicular angle greater than 90 degrees (1); present, interclavicular angle less than 90 degrees (2). (Ostrom, 1976; Chiappe, 1991) ossified sternum: paired (0); fused or partially fused into a single structure (1); fused with a midline keel (2).

forelimb 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68.

69. 70.

distal condyles of humerus located mainly on the distal (0), or cranial (1), aspect. (Perle et al., 1993) ventral tubercle of humerus projects distinctly caudally, separated from the humeral head by a deep capital incision: absent (0); present (1) (Sanz et al., 1995) well-developed transverse ligamental groove on the humerus: absent (0); present (1) (Sanz et al., 1995) humerus length relative to ulna: longer (0); subequal to or shorter (1). (Perle et al., 1993) dorsal condyle of ulna developed as a semilunar ridge: absent (0); present (1) (Sanz et al., 1995) ratio of diameter of shaft of radius to ulna: more than .70 (0); thinner than ulna, less than .70 (1). (adapted from Tarsitano and Hecht, 1980; Perle et al, 1993; Chiappe and Calvo, 1994) carpometacarpus: absent (0); present (1). (Sanz et al., 1995) extensor process on metacarpus: absent (0); present (1). (Sanz et al., 1995) metacarpal I greater than (0), or less than (1) one-third the length of MC II. (Tarsitano and Hecht, 1980; Gauthier, 1986) metacarpal III: straight (0); bowed laterally (1). (adapted from Tarsitano and Hecht, 1980; Gauthier, 1986) combined lengths III-1 and III-2 relative to III-3 on manus: longer (0); subequal (1); absent (2). (Gauthier, 1986) forelimb elongatation relative to presacral length: less than one half presacral length (0); 60-90% presacral length (1); more than 100% presacral length (2). (adapted from Ostrom, 1976; Gauthier, 1986) manus length relative to ulna length: manus shorter than or subequal to ulna (0); manus longer than ulna by at least 20% (1). proximal and distal ends of humerus: twisted, do not lie in the same plane (0); expanded into the same plane (1). ulnar distal condyle: transversely compressed and craniocaudally extended proximally in the same plane as the humero-ulnar flexion-extension movement (0); subtriangular in shape in distal view, with a dorsomedial condyle, and twisted more than 54 degrees with respect to the proximal end (1). shape of ulnar posterior margin: sigmoid (0); uniformly convex (1). distal radial carpal: proximodistally flattened (0); semilunate (1).

pelvic girdle 71. 72. 73. 74. 75. 76. 77. 78. 79. 80. 81. 82. 83. 84. 85. 86. 87. 88. 89. 90.

length of preacetabular process of ilium relative to length of postabetabular process: subequal (0); twice as long (1). (adapted from Tarsitano and Hecht, 1980; Currie and Russell, 1988) postacetabular process depth: relatively deep, more than 50% depth a acetabulum (0); shallow, less than 50% depth at acetabulum, drawn back into a low, pointed process (1). (adapted from Ostrom, 1976; Novas, 1997) ratio of lengths of acetabulum to ilium: .15 or more (0); .11 to .13 (1); .10 or less (2). (adapted from Sanz et al., 1995) antitrochanter on ilium: absent or very small (0); present, prominent (1). (adapted from Ostrom, 1976; Perle et al., 1993) tubercle on dorsal margin of ilium above caudal acetabulum: absent (0); present (1). craniocaudal width of pubic peduncle on ilium relative to width of acetabulum: narrow, less than acetabular width (0); wide, exceeds acetabulum in width (1). pubic foot: projects cranially and caudally (0); projects caudally only (1); absent (2). (adapted from Ostrom, 1976; Gauthier, 1986; Sanz et al., 1995) angle of pubic shaft relative to the long axis of sacral vertebrae: projects cranially (0); subvertical (1); projects caudally (opisthopubic) (2). ratio of length of ischium to length of pubis: more than .66 (0), less than .66 (1). (adapted from Ostrom, 1976; Gauthier, 1986) contact between distal ischia: present (0); absent (1). (Tarsitano and Hecht, 1980; Sanz et al., 1995) obturator process on ischium: present, square (0); present, peaked and broadly triangular (1); rudimentary or absent (2). placement of obturator process: proximal (0); mid-shaft (1); distal (2). "postacetabular" process on proximal ischium behind iliac contact: absent (0); present, nearly contacts postacetabular process of ilium (1). (Ostrom, 1976) process on caudal border of midshaft of ischium: absent (0); present (1). (Ostrom, 1976) fusion of pelvic elements: absent (0); present (1). (Sanz et al., 1995) shape of ischial shaft: rod-like in part with a circular or subcircular cross section (0); mediolaterally compressed and plate-like along entire length (1). postacetabular blade on ilium: brevis shelf caudolaterally oriented, medial flange ventrally curved (0); postacetabular blade vertical, medial flange strongly reduced and perpendicular to iliac blade (1). (Novas, 1997) pubic apron: transversely broad, pubes fused for distal 2/3rds of their length (0); transversely narrowed, pubes fused only along the distal 1/3rd of their length (1). contact between distal pubes: present (0); absent (1). iliac fossa for m. cupedicus: present (0); absent (1).

hindlimb 91.

92. 93. 94. 95. 96. 97. 98. 99. 100. 101. 102. 103. 104. 105. 106. 107. 108. 109. 110. 111. 112. 113.

configuration of lesser trochanters: large and flange-like, separated from femoral shaft, head, and greater trochanter by a deep cleft (0); nearly confluent with the greater trochanter, and separated from the proximal head of femur by only a small cleft or groove (1); joined to greater trochanter to form an undivided trochanteric crest, proximal articular surface confluent with that of femoral head (2). (adapted from Ostrom, 1976; Tarsitano and Hecht, 1980; Gauthier, 1986; Currie and Russell, 1988; Perle et al., 1993) shape of fourth trochanter on femur: present, large (0); reduced to a low ridge or absent (1). (adapted from Tarsitano and Hecht, 1980; Gauthier, 1986; Chiappe, 1996) "posterior trochanter" on femur: absent (0); present, cranially placed (1); present, centered on the trochanteric crest (2). (adapted from Ostrom, 1986; Sanz et al., 1995) fossa for capital ligament: absent (0); present (1). popliteal fossa of femur bounded distally by transverse bridge: absent (0); present (1). (Perle et al., 1993) tibiofibular crest on the lateral condyle of distal femur: absent (0); present (1). (Sanz et al., 1995) femoral neck: present, constriction developed that separates trochanteric region from femoral head (0); absent (1) (adapted from Russell, 1969) proximal tibia: craniocaudal length twice that of mediolateral width (0); length and width of proximal tibia subequal (1). midshaft diameter of fibula relative to tibia: approximately one-fifth or more that of tibia (0); one-fifth or less that of tibia (1). orientation of iliofibularis tubercle on fibula: craniolateral (0); lateral (1); caudolateral or caudal (2). (Forster et al., 1996) deep fossa on medial side of proximal fibular head: present (0); absent (1). fibular articulation with the calcaneum: present (0); absent, fibula does not reach tarsus (1) fusion of proximal tarsals to crus: absent (0); present, partially fused (1); present, completely fused (2). (adapted from Ostrom, 1976; Forster et al., 1996) fusion of astragalus to calcaneum in adults: absent (0); present, partial to complete (1). (Currie and Peng, 1993) fusion of distal tarsals to metatarsus: absent (0); present (1). (Ostrom, 1976) fusion of metatarsus: absent or partially fused (0); completely fused (1). (Ostrom, 1976) metatarsal V: present (0); absent (1). (Ostrom, 1976) position of pes digit I: parallel to other digits (0); reversed to oppose other digits (1). (Ostrom, 1976) relative contributions of metatarsals II, III, and IV to ankle joint: all contribute approximately equally (0); partially or completely arctometatarsalian, MT III is nearly or completely eliminated from joint (1). (Currie and Peng, 1993) relative size of pes digit II: phalanges and ungual subequal in size and robustness to digits III and IV (0); developed into a robust, hyperextendable slashing digit with an enlarged sickle-like ungual (1). (Gauthier, 1986) ratio of length of tibia to length of femur: tibia no more than 15% longer than femur (0); tibia elongate, at least 25% longer than femur (1). extensor canal on tibiotarsus: absent (0); present (1). distal vascular forament on metatarsus (tarsometatarsus): absent (0); present (1).