Norman, 1996 by Felipe Elias

Zoological Journal of the Linnean Society (1996), 116: 303–315. With 9 figures

On Mongolian ornithopods (Dinosauria: Ornithischia). 1. Iguanodon orientalis Rozhdestvensky 1952 DAVID B. NORMAN F.L.S. Sedgwick Museum of Geology, Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ

Received September 1994, accepted for publication June 1995

The type material of the Cretaceous ornithopod Iguanodon orientalis Rozhdestvensky, 1952 is redescribed. The characters which were originally used to establish a new species are shown to be either incorrect or indistinguishable from Iguanodon bernissartensis Boulenger, 1881. Additional material, previously unrecognized, further confirms the similarity of I. orientalis to I. bernissartensis. It is proposed that I. orientalis should be relegated in synonymy as a junior subjective synonym of I. bernissartensis Boulenger, 1881. The identification of the Barremian species I. bernissartensis in Asia indicates an unusually wide geographic spread for this species, and provides a potential biostratigraphic indicator for beds in Mongolia which had been previously dated variously between the Cenomanian and Maastrichtian stages. ©1996 The Linnean Society of London

CONTENTS Introduction . . Systematics . . Material . . . Description . . Discussion . . . Conclusions . . Acknowledgements References . . .

. . . . . . . .

303 305 305 305 311 313 314 314

INTRODUCTION

In 1952 A.K. Rozhdestvensky described the fragmentary remains of a dinosaur which had been collected at a locality named Khamarin Khural (Fig. 1). which is approximately 30 km south-east of Buyant-Ukhaa, East Gobi Province, Mongolia. In the original article the right maxilla was illustrated and described, as was the left scapula. The structure of the teeth in the maxilla and the shape of the scapula, when compared with described specimens of Iguanodon bernissartensis (Dollo, 1882, 1883a, 1883b, 1884, 1923) and I. atherfieldensis (Hooley, 1925) were thought to indicate generic affinity with the genus Iguanodon; however the high maxillary tooth count (27 — the maximum thought to be present in the commensurate species I. bernissartensis 0024–4082/96/030303 + 13 $18.00/0

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Figure 1. Outline map of Mongolia showing the approximate location of Khamarin Khural at which the holotype of Iguanodon orientalis was collected.

was 23), shape of the crowns and curvature of the tooth row were suggested as sufficient reason for assigning the material to a new species: Iguanodon orientalis. In 1966, Rozhdestvensky reported on new material of ornithopod dinosaurs collected from Mongolia and, in the comparative discussion, commented (in a footnote) on the maxillary tooth count of I. orientalis which he considered to have been less than 27 as originally stated, but not less than 25. Norman (1980) redescribed the type and referred material of I. bernissartensis and noted that the maximum tooth count of the maxilla in known specimens was 29. Subsequently Norman (1986) observed that I. orientalis, as currently defined, appeared to be indistinguishable from I. bernissartensis. On a number of occasions during the past decade references have been made to additional material collected by Joint SovietMongolian collecting trips to Mongolia during the early 1970s. Most notable and relevant among these has been reference to a nearly complete skull of ‘Iguanodon orientalis’ (see Norman, 1985:115); this latter material has now been studied (Norman & Kurzanov, in preparation) and clearly is not referable to the taxon named Iguanodon orientalis. The material assigned to I. orientalis is of taxonomic, stratigraphic and biogeographic importance, bearing as it does on the distribution and evolutionary history of the ornithopod dinosaurs of the Cretaceous (Milner & Norman, 1984). Ignoring evidence based either on isolated teeth (Hasegawa et al. 1995 — which are of limited taxonomic value below the level of Iguanodontia) and footprints (Heintz, 1963 — which cannot be used to identify the print maker below the familial level with any real confidence), the genus Iguanodon has been reported on the basis of reasonable skeletal evidence from North American (Weishampel & Bjork, 1990), widely across Europe (Belgium (Norman, 1986), England (Hooley, 1925), France (Martin & Buffetaut, 1992), Germany (Norman, 1987), and Spain (Sanz, Casanovas & Santafe, 1984). So the description of Iguanodon from Asia would provide a northern hemisphere circum-global distribution. Since some of the earliest known hadrosaurian ornithopods (which temporally and geographically seem to replace iguanodontians during the early Late Cretaceous) come from the earliest Late Cretaceous of Asia (Brett-Surman, 1979; Weishampel & Horner, 1986), the spatial and phylogenetic relationship between the late iguanodontians and early hadrosaurs

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would appear to have become focused on Asia generally, even though the dinosaurs themselves are (to date) rather poorly known. The purpose of this short series of papers is to review the anatomy, taxonomy and systematic position of the ornithopod fauna which has been collected from a number of localities in Mongolia; all of these taxa have a direct bearing on our current understanding of the range of problems outlined above. Repository abbreviations: PIN: Palaeontology Institute Nauk (Moscow); BMNH: Natural History Museum (London); IRSNB: Royal Institute of Natural Sciences (Brussels).

SYSTEMATICS

Indented classification hierarchy Ornithischia (Seeley, 1887) Cerapoda (Sereno, 1986) Ornithopoda (Marsh, 1881) Iguanodontia (Dollo, 1888) Binomial: Iguanodon bernissartensis Boulenger, 1881 Junior subjective synonym. Iguanodon orientalis Rozhdestvensky, 1952.

MATERIAL

Holotype. PIN 559-1/1, 559-1/2, 559-1/3, 559-1/7. Right maxilla, left scapula, several large rib fragments, vertebral neural arch fragments, portion of right posterior premaxillary ramus, distal metatarsal fragment, partial right nasal. Locality. Khamarin Khural (30 kilometres due South of Buyant-Ukhaa, in Dornogov' (East Gobi Province), Mongolia — S.M. Kurzanov personal communication). Described by Rozhdestvensky as “50 km south-east of Sajn-Shandy”. Horizon. Probably Barremian/Aptian on the basis of comparative anatomy. Previously dated: ?Cenomanian (Rozhdestvensky, 1952, 1966). ?Cenomanian/ ?Maastrichtian (Norman & Weishampel, 1990).

DESCRIPTION

Maxilla. PIN 559-1/1. The maxilla is from the right side of the skull, is 400 mm long as preserved, and is mostly complete (Figs 2, 3). There are 27 tooth positions identifiable and, despite some areas being broken or cracked, the general shape and proportions of the maxilla are well shown and can be compared quite readily to the maxillae of other, known species: specifically I. bernissartensis (Norman, 1980) with which it is commensurate, and the somewhat smaller I. atherfieldensis (Norman, 1986). The maxilla is long and wedge-shaped at the caudal end, forked at the rostral end and along the ventral edge is a notched arcade of tooth sockets; in lateral view (Fig. 2) this latter margin is interrupted somewhat by breakages in this specimen. The medial surface of the maxilla is vertical and smooth; above the alveolar margin there

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Figure 2. PIN 559-1/1. Holotype I. orientalis. Right maxilla, lateral view. Even tone = plaster of Paris; cross-hatching = broken surface. Abbreviations: ap, median anterior process of the maxilla; ect, ectopterygoid suture; jug. p, jugal process (broken away); la, contact area for lacrimal; lap, lateral anterior process; rug, rugosities for attachment of premaxilla; tr, trough to receive the posterior lateral process of the premaxilla.

is an arcade of small foramina (Fig. 3, f) each one corresponding to a vertical tooth family; these are by convention interpreted (Edmund, 1957) as foramina for the entry of nutritive blood vessels and sensory nerves to the dental lamina. All the foramina are linked together by a shallow groove which presumably marks the path taken by the main blood vessel and nerve trunk supplying these foramina. The area between these nutritive foramina and the alveolar margin forms a thin alveolar wall or parapet (Fig. 3, al.p), which supports the roots of functional teeth and the crowns of successional teeth. The height of the alveolar parapet is greatest just caudal of the mid-point along the upper jaw and it is here that the largest teeth emerge; the surface of this parapet, which has a fine irregular ornament, is totally unlike that of the rest of the maxilla. This bone structure presumably relates to the metabolic needs of this region; the rapid replacement of teeth, which occurred in these animals, implies a rapid turnover of minerals in the alveolar bone for the continuous remodelling which must have occurred as the teeth grew. Rostral to the tooth row there is an incomplete, tapering process which extends ventrally, curving beneath the area originally occupied by the lateral margin of the premaxilla (Fig. 2, lap) Along the mediodorsal edge of this process the bone is markedly rugose, marking an area for attachment of ligaments binding the premaxilla to the maxilla. Laterally, this surface slopes away to form a smoothly rounded lateral surface. Above the first few tooth positions, the dorsal edge of this process is compressed and forms a relatively thin vertical wall which has a thicker and rugose dorsal edge. The anterior part of this dorsal edge projects forwards as a distinct finger-like process, which bears distinct facets laterally and medially (Figs 2,3, rug). The rugose facets on the medial edge of this rostral process are probably for articulation against the median, posterior premaxillary process (evidence for which can be seen in I. atherfieldensis - Norman, 1986). Caudally, this dorsal edge runs roughly horizontally and merges with the main body of the maxilla â&#x20AC;&#x201D; though this area is broken and crushed. Between the vertical septum which supports the dorsal edge, and the lateral surface of the maxilla, there is an obliquely inclined, elongate trough (Fig. 2, tr), somewhat crushed and distorted in this specimen, into which would have fitted the lateral portion of the posterior premaxillary process. Caudally the groove in the upper surface of the maxilla is interrupted by breakage in the dorsal

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Figure 3. PIN 559-1/1. Holotype I. orientalis. Right maxilla, medial view. Even tone = plaster filling, cross-hatching = broken surface. Abbreviations: al, alveoli exposed by destruction of alveolar parapet and removal of teeth; al.p, alveolar parapet; ap, anterior median process of the maxilla; f, furrow and arcade of foramina; pal, palatine suture; rug, rugose facets for attachment of the premaxilla.

lateral wall before continuing to an apex which represents a lamina of bone which would have overlapped the lacrimal (Norman, 1986: fig. 9A); the lacrimal process which would have been located immediately caudal to this apex of bone has been broken away. Posterior to the area for attachment of the lacrimal, the maxilla is rather damaged. The dorsal profile of the maxilla curves quite sharply downward to its caudal end. Laterally, the area associated with the finger-like process for the attachment of the basal portion of the jugal is broken away (Fig. 2, jug. p), and the area between this process and the lacrimal process (which would be the area occupied by the antorbital opening) is mutilated. The mediodorsal edge of the maxilla is rugose for attachment of the palatine (Fig. 3, pal) and pterygoid bones, while the external surface faces posteriorly and somewhat laterally with a shallow facet for the attachment of the ectopterygoid (Fig. 2, ect). The external surface of the maxilla, though somewhat distorted is characterised by a broad horizontal swelling across the middle/upper portion. The ventral part of the external surface of the maxilla has a conspicuous longitudinal recess (Fig. 2), so that the main body of the maxilla overhangs the tooth row. Nasal. PIN 559-1/7. The nasal (Fig. 4) was not previously identified and has been reconstructed by the author from several isolated fragments. Though imperfect the specimen is quite distinctive, comprising the central portion of the bone, and is in most respects very similar to the isolated nasal of I. atherfieldensis (Norman, 1986: fig. 11). The nasal is thin and somewhat arched transversely and would originally have formed a considerable portion of the roofing to the snout. The dorsomedial edge (Fig. 4B) of the nasal shows the nasal-nasal suture as a diagonal butt-joint (Fig. 4B, nn.s); rostrally this suture was overlain by the median dorsal premaxillary process (Fig. 4B, pmx.s). Posteriorly and ventrally, its anterior border descends as a smooth though slightly irregular curve, forming the posteriorly upper margin of the bony nasal opening. Ventrally the extreme rostral part of the nasal-premaxillary suture is preserved (Fig. 4B, pm.s), and shows that the margin of the nasal is recessed so that it clasps the upper border of the premaxilla. Caudal to this small portion of the nasal the lower edge is notched by what appears to be the edge of a small channel (Fig. 4A,

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Figure 4. PIN 559-1/7. Holotype I. orientalis. Nasal, right. A, lateral view. B, medial view. Abbreviations: ch, channel; for, foramen; nn.s, nasal-nasal suture; pr.s, prefrontal suture; pm.s, premaxillary suture; pmx.s, recess for dorsal median process of premaxilla.

ch), which is identical to the form of the preserved right nasal of a referred specimen of I. atherfieldensis (BMNH R.11521). The external surface (Fig. 4A) of the nasal of I. orientalis is smoothly curved with a slightly puckered surface and marked by a curious small â&#x20AC;&#x2DC;bossâ&#x20AC;&#x2122; near its rostro-dorsal margin; near the narial margin there is a prominent vascular opening (Fig. 4A, for) which again is positioned very similarly to that seen in specimens of I. atherfieldensis. The caudomedial surface of the nasal appears to show signs of a sutural contact which might represent the anterior extent of the prefrontal (Fig. 4B, prf.s). Premaxilla. PIN 559-1/7. Another isolated bone previously unidentified, is tentatively suggested as a central portion of the right, lateral, posterior premaxillary process of the premaxilla (Fig. 5). The bone is broken at both ends and rather crushed transversely, but has a characteristic axial twist, and sutural surfaces which would seem to help place this bone with a measure of confidence. It is also possible to

Figure 5. PIN 559-1/7. Holotype I. orientalis. Right nasal and premaxilla shown in lateral view and articulated. Cross-hatching = broken bone. Abbreviation: e.n, external naris.

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articulate crudely the newly identified nasal with this premaxillary fragment as shown in Figure 5. The lateral surface (Fig. 5) shows a post mortem depressed area which has distorted the general appearance of the caudal half of this bone. The dorsal edge is raised and rugose (for attachment to the nasal). Rostrally, from the nasal suture, the upper surface curves gradually downward and splays laterally forming the lower part of the narial opening above the premaxillary beak. The medial surface has a twisted appearance with the rostral area showing the possible sutural area for attachment to the inner wall of the maxilla. Teeth. A number of tooth crowns, in various stages of eruption, are preserved in the right maxilla and this allows their form to be described, and comparison of these teeth with those of other species. The crowns of maxillary teeth are narrow, tall and asymmetric in lateral (labial) view (Fig. 6). The asymmetry of the crown is emphasised by a prominent primary ridge which bisects, unequally, the labial surface vertically. The larger rostral (mesial) portion of the crown forms a smooth, tapered surface, which expands from the apex toward the junction between the root and crown. The apical portion of this surface is developed into a â&#x20AC;&#x2DC;shoulderâ&#x20AC;&#x2122; which serves to broaden the mesial half of the crown; the mesial edge of this surface is delimited by a coarse denticulate margin which forms a slightly raised and thickened edge to the crown; small tertiary ridges are visible originating from the bases of marginal denticles near the apex of the crown, but this is a variable trait in the crowns exposed here. The smaller caudal (distal) surface of the crown is similarly delimited by the primary ridge and marginal denticles. The medial (lingual) surface of the crown is smooth, slightly concave vertically, and strongly convex mesiodistally. The marginal denticles are well developed, being formed from curved, irregularly crenelated ledges which are wrapped around the leading and trailing edges of the crown (rather than being small pointed structures as is the case in the majority of

Figure 6. PIN 559-1/1. Holotype I. orientalis. Maxillary teeth of I. orientalis. Stereoscopic view in oblique lateral view to show the structure of the labial surfaces of the crowns.

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Figure 7. PIN 559-1/2. Holotype I. orientalis. Scapula in (A) lateral and (B) medial view. Abbreviations: bl, blade of scapula; but, buttress above the glenoid; cor. s, coracoid suture; gl, glenoid; ac. pr, acromion process.

smaller ornithischians). The mesial denticles are rather more strongly rolled on to the labial surface of the crown than the distal ones. The manner of replacement and interlocking of the functional and replacement teeth in the maxillary magazine is, as far as can be ascertained, identical with that seen in the two well-described species of Iguanodon (Norman, 1980, 1986). Worn teeth, of which there are three examples in the maxilla, show an abruptly truncated crown, the triturating surface approximates to a ‘D’ shape, with the straight edge of the ‘D’ marked by perpendicular spine formed by the sectioned primary ridge, flanked on either side by the raised denticulate margins. Scapula. PIN 559-1/2. The scapula (Fig. 7) is almost complete (parts of the distal margin are eroded) and very large. As can be seen from the comparative measurements tabulated below, the size and relative dimensions of this specimen are similar to those of I. bernissartensis (measurements based on the holotype IRSNB 1534; Norman, 1986). The main difference lies in the broader base of the scapula seen in I. bernissartensis.

I. orientalis I.bernissartensis

Length

Width(prox)

Width(dist)

Width(min)

940mm 970mm

290mm 370mm

210mm 210mm

130mm 150mm

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The scapula is typical of that of ornithopod dinosaurs: it is broad and flattened distally and curved both medially (to fit against the ribcage) and caudally. The proximal end is expanded to support the glenoid and to provide a sutural surface for the coracoid (Fig. 7A, cor.s). The coracoid suture is slightly curved and occupies much of the proximal end; rostrally the surface curves upwards into the main blade of the scapula and is supported by a thickened acromial ridge (Fig. 7A, ac.pr), which is prominent proximally but gradually merges indistinguishably with the blade (bl). The caudal corner of the proximal end has a semicircular embayment which forms the humeral socket (Fig. 7, gl); this is supported distally by a curved and laterally prominent buttress (Fig. 7, but). Distally the buttress contracts inwards against the blade. Between the acromial process and the glenoid buttress the lateral surface of the scapula forms a shallow embayment. Distal to the coracoid and humeral areas of the scapula the scapular blade has its minimum width, but is comparatively thick transversely, progressing distally the blade thins transversely and broadens rostrocaudally to form the typical blade of the scapula. The upper (distal) end of the blade is eroded both rostrally and caudally, though a small segment of its upper margin remains in the middle. The slight thickening and irregular surface of the distal end of the blade is suggestive of a suprascapular cartilage. Ribs. PIN 559-1/7. Portions of two quite well-preserved dorsal ribs are among numerous other fragments. These show no distinctive characters, being typical of those seen in many ornithopod ornithischians, and thus broadly similar to those already described in other species of Iguanodon. Metatarsal. PIN 559-1/7. A distal fragment, unremarkable, and typical in form of that of ornithopod ornithischians generally. Other. There are likewise a number of indeterminable fragments of bone, and some broken pieces of neural arch from the dorsal series of vertebrae.

DISCUSSION

In his original description (Rozhdestvensky, 1952) a number of features were mentioned which were held to justify the separate specific identity of this then new material. (1) ‘Number of tooth positions’. The count of 27 tooth positions (revised downwards to 25 [incorrectly] by Rozhdestvensky, 1966) does not serve to distinguish I. orientalis from I. bernissartensis — there can be as many as 29 tooth positions in the maxilla of the latter species (Norman, 1980). (2) ‘Replacement teeth’. The growth pattern of teeth in the maxilla was described by Rozhdestvensky (1952: 1244) as consisting of three teeth (an initial crown, a larger tooth, and above these a functional tooth). Examination of the maxilla did not allow this point to be verified and it is considered that the replacement pattern is as seen in other species of Iguanodon, with a single replacement crown growing beneath a freshly emergent or functional tooth. (3) ‘Tooth form’. Teeth of I. orientalis were distinguished from European species (I. atherfieldensis and I. bernissartensis) by having a single longitudinal ridge on the flattened (labial) surface of the crown. This feature is in fact one of the primary characters of iguanodontian dinosaurs.

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(4) ‘Curvature of the tooth row’. Smaller curvature of the tooth row in I. orientalis compared with other known species. Rozhdestvensky’s use of the term ‘tooth row’ is ambiguous. Crushing of the maxilla has straightened the tooth row unnaturally so this character is not significant. Alternatively the curvature of the vertical series of teeth in each alveolus (if this was the intended feature) is again not significantly different from those of closely related species of Iguanodon. Rozhdestvensky (1952) claimed that these differences were correlated with specific adaptations to differences in the environments inhabited by known species of Iguanodon, and, in some slightly less obvious way, to ‘evolutionary trends’. The discussion in the 1952 paper makes it clear that Rozhdestvensky understood that this new species had an important bearing on the evolution of ornithopod dinosaurs, particularly in relation to the origin of the closely similar hadrosaurs, which were also known in Asia (Gilmore, 1933; Weishampel & Horner, 1986). Additional information The holotype material, now it has been re-examined, refutes all of Rozhdestvensky’s specifically distinct characters, thus throwing doubt upon the validity of the taxon. The only anatomical feature of possible significance is shown by the scapula which, although it is large, well-preserved and comparable to that of I. bernissartensis has a proximal width which is smaller than that seen in the latter species; in the opinion of the author this difference is unlikely to be taxonomically robust. Furthermore examination of the holotype has enabled identification of one other fragment which is of material importance to the identity of not only this taxon, but also to the identity of material which has been in the recent past referred to Iguanodon orientalis. The nasal bone (Fig. 4), though incomplete, conforms in all respects to that which is seen in the European species I. bernissartensis; this further strengthens similarities to this latter species. The skull bones identified in the holotype of I. orientalis are shown superimposed on the skull outline of I. bernissartensis (Fig. 8, shaded area). The form of the nasal seen in the holotype of I. orientalis and other species of the genus Iguanodon differ radically from that seen in an ornithopod collected during the Soviet-Mongolia Expeditions of the early 1970s by Dr S.M. Kurzanov from the

Figure 8. Skull of Iguanodon bernissartensis in right lateral view, with the skull bones of I. orientalis indicated in position as the shaded portions (from Norman, 1980).

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Figure 9. Nasal bones in lateral view. A. New species of iguanodontian from Khuren Dukh (PIN 3386/7). B. PIN 559-1/7. Holotype I. orientalis. Abbreviations: e.n, external naris; pm.s, premaxillary suture.

locality known as Khuren Dukh (Norman & Kurzanov, in preparation). This latter has been frequently referred to the species I. orientalis; this is incorrect. These two nasals are shown for simple visual comparison in Figure 9 and indicate the existence of a new species of iguanodontian ornithopod.

CONCLUSIONS

(1) The holotype, and referred material of Iguanodon orientalis Rozhdestvensky, 1952 have been examined and the holotype is redescribed. (2) Iguanodon orientalis differs in no significant anatomical respect from the European species of Iguanodon bernissartensis and on the basis of the holotype should be regarded as a junior subjective synonym of Iguanodon bernissartensis. (3) No other material should be referred to Iguanodon orientalis unless new discoveries are made at or near the original site of discovery at Khamarin Khural. (4) If correctly identified, these remains confirm that the species Iguanodon bernissartensis had an exceptionally broad Eurasian distribution, and that it might be expected that the species I. atherfieldensis might eventually be recognized in similarly aged beds in this region. (5) Identification of I. bernissartensis in Mongolia is suggestive of a Barremian (late Lower Cretaceous) age for the â&#x20AC;&#x2DC;greenish-grey clays bearing pebblesâ&#x20AC;&#x2122; from which this specimen was collected in the Dornogov' (East Gobi Province) of Mongolia at the locality known as Khamarin Khural. (6) Extensive new material, including skull and postcranial elements collected from Khuren Dukh and previously referred to I. orentalis are referable to a new taxon of ornithopod dinosaur.

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D. B. NORMAN ACKNOWLEDGEMENTS

This research would not have been possible without the support offered by the Royal Society of London and the Russian Academy of Science, I gratefully acknowledge their assistance. I thank Dr Sergei Kurzanov for considerable help in locating ornithopod material in the collections housed at the Palaeontological Institute of the Academy of Sciences, Moscow. I also thank Academician L.P. Tatarinov for allowing me free use of his research room and facilities during my research visit to the Palaeontology Institute Nauk, Moscow. I am very grateful to Prof. T. Koren' who kindly translated A.K. Rozhdestvensky’s 1952 paper on Iguanodon orientalis.

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