brachychampsa montana gilmore - BioOne

Journal of Vertebrate Paleontology 23(4):832–841, December 2003 q 2003 by the Society of Vertebrate Paleontology

BRACHYCHAMPSA MONTANA GILMORE (CROCODYLIA, ALLIGATOROIDEA) FROM THE KIRTLAND FORMATION (UPPER CAMPANIAN), SAN JUAN BASIN, NEW MEXICO ROBERT M. SULLIVAN1 and SPENCER G. LUCAS2 1

Section of Paleontology and Geology, The State Museum of Pennsylvania, 300 North Street, Harrisburg, Pennsylvania 17120-0024; 2 New Mexico Museum of Natural History and Science, 1801 Mountain Rd. N.W., Albuquerque, New Mexico 87104

ABSTRACT—Three new specimens of the rare alligatoroid Brachychampsa montana from the upper Campanian Kirtland Formation (De-na-zin Member), San Juan Basin, New Mexico, are the first bona fide examples of this taxon from this stratigraphic interval. The most complete specimen (SMP VP-1312) consists of much of the skull table and snout and a nearly complete mandible. SMP VP-1264 consists solely of an incomplete partial skull table (parietal, right squamosal), partial basicranium (basioccipital, otoccipital), and incomplete right quadrate, whereas NMMNH P-7988 is an isolated frontal. Together, these new specimens supplement and allow for further comparison to other globidontans and to previously documented specimens of Brachychampsa. ?Brachychampsa sealeyi, from the Menefee Formation of the San Juan Basin, New Mexico, is based on a juvenile specimen that cannot be distinguished from B. montana, so it is a subjective junior synonym. The crocodylian assemblage of the Kirtland Formation consists of Brachychampsa montana, Leidyosuchus sp. and Denazinosuchus kirtlandicus. It is doubtful that tooth morphology alone can be correlated with ‘‘cheloniphagous’’ diet within the globidontans.

INTRODUCTION In 1911, Charles W. Gilmore named and described an alligatoroid, Brachychampsa montana, based on an incomplete skull from the ‘‘Hell Creek beds’’ in Dawson County, Montana. The holotype (AMNH 5032), which consists largely of the anterior part of the skull, was considered generically distinct from Leidy’s (1865) ‘‘Bottosaurus harlani,’’ from the Upper Cretaceous Green Sands of New Jersey, based in part on the ‘‘disparity in the proportional extent of the dental series.’’ Gilmore (1911) thus established the taxon Brachychampsa and included, without direct comparison, Cope’s species ‘‘Bottosaurus perrugosus’’ from the Upper Cretaceous ‘‘Arapahoe beds’’ of Colorado (Cope, 1873). The holotype of B. perrugosus (AMNH 1110) was lost at the time of Gilmore’s paper and was later rediscovered and designated a nomen dubium by Norell et al. (1994) because of its similarity to many named fossil and extant alligatorid species. Gilmore (1916) referred several isolated teeth from the Kirtland Formation of New Mexico to Brachychampsa montana, but no generically diagnostic alligatoroid material had then been discovered from this unit. However, numerous crocodylian scutes, teeth and postcranial material have been recovered in recent years and reside in the collections of the University of Kansas Museum of Natural History, Lawrence, New Mexico Museum of Natural History, Albuquerque, and The State Museum of Pennsylvania, Harrisburg. Erickson (1972) described a nearly complete skull from the Dinosaur Park Formation of Alberta as Albertochampsa langstoni (SMM P67.15.3). Later, Carpenter and Lindsey (1980) described a left dentary (DMNS 471) from the Hell Creek Formation of South Dakota and referred it to Brachychampsa montana. Norell et al. (1994) described a well-preserved skull and lower jaws (UCMP 133901) of B. montana from the Hell Creek Formation of North Dakota, which is the most complete specimen known of this taxon. More recently, Wu et al. (1996) described yet another Upper Cretaceous alligatoroid, Stangerochampsa mccabei (TMP 86.61.1) from the Horseshoe Canyon Formation of Alberta. These taxa, together with Allognathosu-

chus, which is known primarily from the Paleocene (Lucas and Estep, 2000), are in part characterized by enlarged, bulbous posterior teeth in the dentary and maxilla. The teeth were not considered (coded) in a recently phylogenetic analysis published by Brochu (1999), based on the fact that the shape of the posterior teeth varies in extinct and extant crocodylians, such as modern Alligator prenasalis and A. mississippiensis. Moreover, Brochu (1999) argued that Allognathosuchus is not monophyletic and that the species ‘‘Allognathosuchus mooki’’ should be considered ‘‘Navajosuchus mooki.’’ Lucas and Estep (2000) questioned Brochu’s (1999) conclusion that the taxon Allognathosuchus is not monophyletic based on character reassessment, and demonstrated that Allognathosuchus wartheni cannot be distinguished from A. mooki. Here, we describe three new specimens of Brachychampsa montana from the De-na-zin Member of the Kirtland Formation, San Juan Basin, New Mexico, with special attention to SMP VP-1312, an incomplete skull and left mandible briefly mentioned by Sullivan and Lucas (2001). Also, we briefly describe a right premaxilla referable to B. montana that was recently discovered in the collections of the Yale Peabody Museum collected from the Lance Formation of Wyoming. In addition, we reassess the validity of ?Brachychampsa sealeyi (Williamson, 1996), review the crocodylians from the Kirtland Formation, and reconsider the role and significance of the bulbous teeth in assessing the dietary preferences of these globidontans. Institutional Abbreviations AMNH, American Museum of Natural History, New York; DMNS (formerly DMNH), Denver Museum of Nature and Science, Denver; NMMNH, New Mexico Museum of Natural History and Science, Albuquerque; SMM, Science Museum of Minnesota, St. Paul; SMP, The State Museum of Pennsylvania, Harrisburg; TMP, Royal Tyrrell Museum of Palaeontology, Drumheller; UCMP, University of California, Museum of Paleontology, Berkeley; YPM, Peabody Museum of Natural History, Yale University, New Haven, Connecticut.

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SULLIVAN AND LUCAS—BRACHYCHAMPSA MONTANA FROM NEW MEXICO

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FIGURE 1. Brachychampsa montana (SMP VP-1312); premaxillae, maxillae and nasals. A, dorsal view; B, ventral view. Abbreviations: mx, maxilla; n, nasal, pmx, premaxilla; t, tooth. Bar scale 5 1 cm.

SYSTEMATIC PALEONTOLOGY EUSUCHIA Huxley, 1875 CROCODYLIA Gmelin, 1788 ALLIGATOROIDEA Gray, 1844 BRACHYCHAMPSA Gilmore, 1911 Type Species Brachychampsa montana Gilmore, 1911 (5?B. sealeyi Williamson, 1996). Remarks Brachychampsa is a monotypic taxon known only from a few diagnostic specimens from North America, that range in age from early Campanian to late Maastrichtian.

Brachychampsa montana Gilmore, 1911 (Figures 1–5) Brachychampsa montana Gilmore, 1911, p. 298. ?Brachychampsa sealeyi Williamson, 1996, p. 422. Holotype AMNH 5032, anterior (rostral) part of skull. New Referred Material SMP VP-1312, incomplete skull and left mandible (the other specimens are discussed below). Locality SMP loc. 376a Willow Wash (north-central), San Juan Basin, New Mexico. Formation Kirtland (De-na-zin Member). Description The first of three new specimens (SMP VP-

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1312) from the Kirtland Formation is the most complete and hence is the primary focus of this paper. It consists of an incomplete skull and left mandible (Figs. 1–4). The skull is partly distorted and crushed in two regions–the right premaxilla and the right side of the supratemporal region. Skull Premaxillae Both premaxillae are preserved (Fig. 1); each bears five teeth, or parts of their respective bases. The right premaxilla is crushed inward (posteriorly) and is attached to the anteriormost part of the right maxilla. The left premaxilla has a broad, blunt anterior edge, with a broad posterior edge that contacts the anterior extension of the left maxilla. It is broken along its interior ventral margin that defines the edge of the incisive foramen. Ventrally, a large shallow pit for the reception of the fourth dentary tooth lies at the premaxilla-maxilla contact. The internal border of the naris is broad, indicating a large naris and, by extrapolation, the incisive foramen is also large. Dorsally, the contact between the premaxilla and the anterior portion of the right maxilla is readily visible, however, its trace is lost ventrally, obscured by fractures that run through the pit for the reception of the fourth dentary tooth on the right side. Premaxillary Teeth Both premaxillae bear five teeth (Fig. 1B). The teeth of the left premaxilla are broken off at their bases save for the posteriormost one, which appears to have been in the process of replacement. This same situation is mirrored by the right premaxilla. Four teeth are present on the right premaxilla, only one of which, the second from the midline, is complete. All of the teeth of the premaxilla are similar in size and are conical, with fine striations and prominent carinae that divide the crowns into a very convex external surface and a moderately convex internal surface. Maxillae Parts of both maxillae are preserved (Fig. 1), and they are broken along the posterior margins where they join with the jugals and lacrimals. The right maxilla is the more complete. Medially, it joins with the right nasal; contact with the anterior-most extension of the right prefrontal is not evident in dorsal view. The palatal surface of the right maxilla is smooth, nearly complete posteriorly and appears to be broken along the sutural contact with the right palatine. The right maxillary tooth row is largely intact, although it is badly damaged posteriorly. The tooth row is laterally flanked by a well-developed shelf, which is broken and incomplete posteriorly. This distinctive lateral shelf is preserved in its entirety on the left maxilla. It is broad and slopes dorsolaterally from the tooth row. Large foramina, in a sublinear row, flank the lateral margins immediately below the lateral dorsal edge. Another row of nutrient foramina lies medial to the maxillary tooth row. The spacing between foramina decreases posteriorly, and the number of foramina increases accordingly. The posteriormost foramina are characterized by distinct grooves that rise from the foramina and are directed medially, nearly parallel to each other. Maxillary Teeth The teeth of the maxilla (Fig. 1B) are arranged as a slightly sinuous row mirroring that of the dentary. There are 15 teeth, complete or partial, preserved in the left maxilla. The left maxilla is broken at the position of the first maxillary tooth, indicating that there were a total of 16 teeth. The teeth are heterodont in size and shape. The anterior teeth are conical. The teeth increase in size posteriorly to the fifth maxillary tooth, which is the largest, and in turn is followed by the sixth tooth, which is much reduced in size. The seventh, eighth and ninth maxillary teeth are also small, based on crosssections of their respective bases. The tenth is twice as large as the ninth and is subrectangular in occlusal shape. The 11th tooth is nearly twice the size of its predecessor, and retains a slightly conical appearance, despite its distinctive, bulbous shape. The 12th and 13th teeth are massive, blunt crushing teeth that are

slightly compressed mediolaterally. The tips or crowns of teeth 11–13 are slightly worn. The last two teeth (15 and 16) are unerupted; the tips of their crowns are visible within the alveoli of the maxilla. The right maxilla preserves parts of only a few teeth (numbers 3, 4, 5, 7, 8, 9, 10,11, and 13). Only three teeth on the right maxilla are preserved in their entirety and in situ; they are numbers 3, 11 and 13. The posteriormost teeth are missing, presumably there were 16 teeth, as in the left maxilla. The external surfaces of the bulbous teeth are finely striated as are those of the premaxillae. Nasals The right nasal is nearly complete, with only its posteriormost section missing (Fig. 1). The anterior tip of the right nasal is preserved and extends anteriorly to a point overhanging the posterior part of the external naris. The suture between the right maxilla and the lateral edge of the right nasal is distinct. The left nasal is less complete and is represented by two sections, an anterior part separated by a gap from the posterior part, which is broken along its lateral and posterior margins. Frontal The frontal (Fig. 2A) is damaged dorsally, especially along the right lateral margin and posterior region where it contacts the parietal. The frontoparietal suture is difficult to trace because of fracturing consistent with the suture’s presumed position, and it appears to enter the anterior medial portion of the left supratemporal fossa, its relationship to the right supratemporal fossa is problematic as there is distortion in the postorbital-supratemporal region. Ventrally, the frontal is partly exposed and articulates with the anterior ascending processes of the left and right laterosphenoids. Prefrontal The left prefrontal is preserved as an isolated element broken along its left lateral margin with a medial section missing on its right. It tapers to a point anterolaterally and articulates with the frontal posteromedially. The posterolateral portion flanks the anteromedial wall of the orbit. Parietal The parietal is present, although it is badly damaged dorsally, particularly in the region between the right supratemporal fossae and the posterior right margin where it articulates with the right squamosal (Fig. 2A). The lateral margin of the parietal is exposed on the left side within the left supratemporal fenestra. The sutures delineating the parietal from the frontal and squamosals are not distinct. The round supratemporal fenestrae are visible dorsally, but the left one is incomplete, missing the lateral margins of both the left postfrontal and left squamosal. The right supratemporal fenestra is deformed due to lateral crushing of the skull table. Postorbital The right postorbital (Fig. 2A) is preserved in articulation with the skull table. However, dorsally, its contact with the parietal, frontal and right squamosal is not clearly discernible. The anterolateral edge of the postorbital is rounded (Fig. 2B). Ventrally, the descending process of the postorbital is broken, and a small foramen lies immediately below the skull table posterior to the top of the descending process. An isolated fragment has been tentatively identified as the left postorbital. The posterior skull table is rounded anteriorly, along the anterior margin of the right postorbital. Based on the right side of the specimen, it articulates with the squamosal processes, posterolaterally. The left margin of the skull table is not preserved. Pterygoid Only the posterior portion of the pterygoids is preserved, in part, together with the posterior margin of the choana and the medial ascending parts that articulate dorsally with both the laterosphenoids (anteriorly) and the anteroventral extension of the quadrates (Figs. 2B, 3). The right pterygoid is more complete, preserving most of the posterior wing. It is broken laterally and anteriorly and slightly offset due to crushing. Only the basal medial part of the left pterygoid is preserved. Squamosals The right squamosal (Fig. 2A) is nearly complete, although it is damaged where it joins the parietal and


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FIGURE 2. Brachychampsa montana (SMP VP-1312): A, incomplete skull table (dorsal view); B, right lateral view of basicranium (see Fig. 1 for abbreviations). Additional abbreviations: bo basioccipital; ex, exoccipital (projecting posteriorly over foramen magnum); f, frontal; fo, foramen ovale; lbr, laterosphenoid bridge; ls, laterosphenoid; p, parietal; po, postorbital; pt, pterygoid; q, quadrate; sq, squamosal; stf, supertemporal fenestra. Bar scale 5 1 cm.

along the interior margin of the right supratemporal fossa. The suture that unites the squamosal with the postorbital anteriorly is not discernible in dorsal view. Although there is some fracturing along the lateral sides of the squamosal/quadrate contact, it appears that the ventro-posterior contact with the quadrate resides along the posterior wall of the external auditory meatus. Quadrate The right quadrate is nearly complete, whereas the left is badly damaged (Fig. 2A). The right quadrate is a relatively massive bone, with a strong, well-developed articular end. Its dorsal right margin is marked by the sutural attachment for the right quadratojugal, which is missing. Its relationship to the right pterygoid and laterosphenoid is unclear due to the inability to identify sutures with these two elements. The left quadrate is represented by the medial part, broken and eroded both along its lateral and medial edges. Basicranium Otoccipital The exoccipital is fused with the opisthotic (Norell et al., 1994), forming the single otoccipital (Fig. 3). The

paired wings of the otoccipitals flare out posterolaterally and fuse with their respective quadrates along the ventral surface. The posterior exit for the cranioquadrate passage is preserved. The foramen magnum lies ventrally, and its lateral borders and roof are formed by two descending processes, one on each side, of the otocciptal, and its floor is formed by the superior limit of the occipital condyle of the basioccipital. The otoccipital processes are rather long, extending two-thirds the height of the basioccipital. On the right side of the foramen mangnum is an opening presumably for cranial nerves IX through XI. The left side is obscure due to a slight separation of the otoccipital from the basioccipital. We are also unable to identify the foramina for cranial nerve XII. Basioccipital (including the occipital condyle) The basioccipital is sub-u-shaped in posterior (caudal) view (Fig. 3). A well-developed occipital condyle occupies the dorsomedial position. The lateralmost edges of the basioccipital are joined with the ‘‘exocciptal processes.’’ At the ventral edge, the basioccipital is shaped like a broad, inverted ‘‘v’’ behind which lies the

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FIGURE 3. Brachychampsa montana (SMP VP-1312); posterior (caudal) view of basicranium (see Figs. 1 and 2 for abbreviations). Additional abbreviations: bs, basisphenoid; fm, foramen magnum; oc, occipital condyle. Bar scale 5 1 cm.

opening for the middle eustachian tube. The paired lateral eustachian tubes are not visible. Basisphenoid The basisphenoid is visible in posterior (occipital) view (Fig. 3) where it emerges anterior to and below the basioccipital, and posterior to and above the pterygoids, where it forms a broad ‘‘v’’ shape. It is here, between the basioccipital and the basisphenoid that the middle eustachian tube exits ventrally. Laterosphenoid Both laterosphenoids are preserved and exposed anteroventrally (Fig. 2B). They are distorted and offset medially. They are indistinguishably fused to the prootic posteriorly, and its posterior ventralmost margin forms the anterior wall of the exit for cranial nerve V (trigeminal foramen) on both the right and left sides. The laterosphenoid bridge is preserved along the anterior margin of this opening. Prootic The prootic, which lies posterior to the opening of the trigeminal nerve V and the respective laterosphenoids and anteroventrally to the respective supraoccipitals, is exposed on both the right and left sides. However, the sutures of the prootic are not readily discernible, so it is not possible to comment on their actual shape, size and extent.

Supraoccipital The supraoccipital is present, and viewed posteriorly its ventral margins form a broad v-shape articulating with the left and right exoccipital (Fig. 3). The sutures between the supraoccipital and exoccipitals are faint. It appears that the posterior medial portion of the supraoccipital is visible in dorsal aspect, but the region is damaged, so the extent of the posterior part of the parietal, with respect to the supraoccipital, is not clear. Mandible Only the left mandible (Fig. 4) is preserved, and only the posterior part of the mandible is broken. Some isolated fragments may belong to this region, but we cannot identify them with certainty. Dentary The dentary is complete and relatively robust. Its lateral and ventral surfaces are ornamented with randomly spaced pits and shallow grooves. In lateral view (Fig. 4A), the dentary is only slightly curved, not strongly bowed. The superior distal lateral extension of the dentary reaches midway above the mandibular fenestra, and its complement, the inferior →

FIGURE 4. Brachychampsa montana (SMP VP-1312); incomplete left mandible. A, lateral view; B, medial view; C, close-up of mandibular symphysis (showing relationship of the splenial, dentary, and Meckelian groove); D, occlusal view; E, close-up of posterior teeth (occlusal view). Bar scale 5 1 cm. Additional abbreviations: d, dentary; Mg, Meckelian groove; sp, splenial; sym, mandibular symphysis.


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distal lateral extension of the dentary, reaches to midway below the mandibular fenestra. In occlusal view (Fig. 4C), the anterior portion of the dentary expands medially towards the mandibular symphysis, forming a distinct and broad shelf. The posterior extent of the shelf reaches back to the 15th tooth, where it wedges out between the tooth row of the dentary and the splenial medially. Dentary Teeth There are 20 teeth in the dentary, which are aligned in a slightly sinuous row that compliments that of the maxilla. All of the teeth, or their bases, are preserved except for the ninth. The first three dentary teeth are small, and the fourth is much larger. Behind the fourth tooth, the teeth are relatively small, smaller than the first three. The 14th tooth is a very large conical tooth, which is followed by three smaller, sub-bulbous teeth (15th–17th), each increasing slightly in size posteriorly. The last three teeth are large, blunt, bulbous teeth that are slightly compressed mediolaterally, giving them a rectangular outline in occlusal view (Fig. 4D). The occlusal (apical) surface of the 18th tooth has a distinctive wear pattern. A wear surface is also present on the apex of the 14th tooth, but it is not as prominent due to the size of the tooth. The 19th tooth shows some wear, and the 20th is greatly worn, so its crown is lower than the preceding tooth. The crowns of all the teeth are finely striated. Splenial The splenial (Fig. 4C) is nearly complete, being broken along its posterior margins where it joins with the angular at the foramen intermandibularis caudalis. Two large vertical fractures, separated by approximately 40 mm, cut the mandible anteriorly. The medial surface of the splenial is very smooth. It is pierced by the foramen intermandibularis medius posteriorly, where the anteromedial extension of the coronoid laps onto the splenial, approximately 10 mm below the parapet of the splenial. This foramen is located behind the posteriormost extent of the tooth row and lies in advance of the anteriormost margin of the foramen intermandibularis caudalis. Below, and approximately 20 mm anterior to the anterior margin of the foramen intermandibularis caudalis, is an irregular depression that lies along a crack, coincident with the ventral splenial/dentary contact. This depression may be an artifact of crushing as it has no known corollary, unless it represents the posteriormost foramen intermandibularis oralis. No other foramina are visible on the medial surface of the splenial. The rostral tip of the splenial abruptly ends just short of the mandibular symphysis where is meets with the Meckelian groove (Fig. 4C). The dorsal surface of the splenial that lies adjacent to the last six bulbous teeth is distinctly broad; it is expanded medially, forming a prominent shelf that overhangs its ventral surface. Coronoid Only the sub-rounded anterior edge of the coronoid is preserved, broken along its posterior border and inferior margin where it contacts the angular. The foramen intermandibularis medius is situated at the coronoid/splenial contact just below the posteriormost dorsal surface of the splenial. Surangular The dorsal and ventral anterior processes of the surangular are bifid and subequal in their anterolateral extent (Fig. 4E). The dorsal process almost reaches to the midpart of the 19th (penultimate) tooth, whereas the ventral process reaches only to the anterior margin of the last tooth. The surangular forms the dorsal edge of the posterior half of the intramandibular fenestra. Posteriorly, it is broken where it articulates with the angular and the articular. Angular The angular is incomplete and broken posteriorly, as well as in the anteroventral region of the foramen intramandibularis caudalis on the medial surface. The anteriormost extent of the angular reaches just behind the last tooth projected down along the ventrolateral surface of the mandible. Miscellaneous Elements There are several broken fragments of SMP VP-1312, some of which are sculptured, and

probably pertain to the lacrimals, right prefrontal and jugals. Others may belong to the posterior part of the left mandible (articular and angular). Fragments with smooth surfaces are probably from the palatines, pterygoids and the maxilla. A second specimen, SMP VP-1264 (Fig. 5), collected in 1999 by the senior author from the same locality as SMP VP1312, is a juvenile of B. montana, consisting largely of the posterior region of the skull. This specimen is also slightly distorted due to postmortem crushing. Bones of this specimen include the parietal, right squamosal, right quadrate, otoccipital, (including the right exoccipital), basioccipital, and basisphenoid. Unlike SMP VP-1312, sutures that delineate the contacts are clearly visible. Briefly, the parietal of SMP VP-1264 is complete (Fig. 5A). A fracture crosses the posteromedial part and extends into the supratemporal fenestra midway on the left side. Laterally, the junction of the parietal-laterosphenoid-quadrate is preserved within the medial margin of the left supratemporal fenestra. The latter two bones consist of fragments of the posterodorsal portion and the medial prong of the anterodorsal extension, respectively. The right squamosal is largely complete, damaged only along its anterolateral margin. In dorsal view, the squamosal tapers posterolaterally, with its medial margin convexly curved. In posterior view, its ventral suture separating the supraoccipital medially, and the exoccipital process of the otoccipital is distinct. In lateral view, the squamosal-quadrate suture is slightly irregular for its entire length, extending midway above the external auditory meatus where it reaches an apex and returns posteroventrally, where it meets the external auditory meatus. Posterolaterally, the cranioquadrate passage exits posteriorly from between the right quadrate/otoccipital contact. The right quadrate is broken along both its articular surface and its lateral edge. Ventrally, the quadrate extends down along the side of the basicranium, lateral to the basioccipital and basisphenoid, where it is damaged. The basioccipital (Fig. 5B) is deep, as in SMP VP-1312, and bears a prominent medial keel. Its ventral margin is fused to the basisphenoid and pierced only by the median eustachian opening. Its lateral margins are flanked by the ventral extensions of the exoccipital (of the otoccipital), with the extension on the right being slightly damaged. The occipital condyle is complete and is well developed. The basisphenoid is nearly complete, being broken only along the dorsal and anterior margins. However, the ventral part of the basicranium is preserved, and bears the choanal septum and marks the roof of the choanal aperture. The posteroventral surface of the septum is slightly damaged in the middle, but its anterior-most and posterior-most ends are intact. The septum appears to have been incipient and thus was recessed within the choanal aperture. A third specimen, a complete frontal (NMMNH P-7988), is indistinguishable in morphology and size from the frontal of SMP VP-1312 and is here referred to B. montana. It is also from the De-na-zin Member of the Kirtland Formation at Willow Wash. Finally, a fourth specimen, recently discovered in the collections of the Peabody Museum of Natural History (YPM 56582), consists of the major portion of the right premaxilla. It is slightly larger than the corresponding right premaxilla of SVP VP1312, but conforms to the premaxillary morphology of Brachychampsa montana. The specimen is damaged at its anteromedial end. Laterally, and distally, the right premaxilla is complete. Ventrally, the teeth are missing but two complete alveoli (5 and 4), and two incomplete alveoli (3 and 2), are preserved. Alveolus 1 is missing due to breakage. The ‘‘pit’’ for the reception of the 4th dentary (mandibular) tooth is prominent and is located posterior to alveoli 5 and 4, approximately half-way


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FIGURE 5. Brachychampsa montana (SMP VP-1264); incomplete skull table. A, dorsal view; B, posterior (caudal) view (see Figs. 1 and 2 for abbreviations). Bar scale 5 1 cm.

between the posterior borders of the alveoli and the posterior extension of the premaxilla/maxilla contact. The specimen was collected by J. B. Hatcher in 1890 from the Lance Formation of Wyoming. THE TAXONOMIC STATUS OF ?B. SEALEYI SMP VP-1312 is identified as Brachychampsa montana on the basis of possessing the following combination of features that are derived characters of B. montana (Norell et al., 1994; Brochu, 1999): broad rostrum with large naris and, by extrapolation, large incisive foramen; large fifth maxillary tooth, exclusion of the splenial from the symphysis of the mandible, lack of foramen intermandibularis oralis on the splenial, and rounded/tapered anterolateral edge of postorbital. SMP VP-1264 is morphologically consistent with SMP VP-1312, except for size, so it, too, is identified as B. montana. As noted previously, both specimens are from the same locality and horizon. ?Brachychampsa sealeyi (holotype NMMNH P-25050) was diagnosed by Williamson (1996) as a distinct species of Brachychampsa based on possession of: (1) 15 maxillary teeth; (2) fifth maxillary tooth the largest; (3) tapered rostrum; (4) an incisive foramen small relative to the width of the posterior rostrum at the level of the first maxillary tooth; and (5) posterior maxillary teeth bulbous and nearly circular in occlusal view and much larger than the largest anterior maxillary tooth. Nevertheless, these features and/or their interpretation do not support differentiation from B. montana. The holotype of Brachychampsa montana bears 14 maxillary

teeth and/or alveoli (Gilmore, 1911). But, it has been pointed out (Iordansky, 1973; Norell et al., 1994) that the number of maxillary teeth (14 vs. 15) is variable within extant species of alligatoroids and thus is not taxonomically significant. Given that the new specimen described here bears 15 maxillary teeth, and that it readily conforms with the holotype in all other features, we interpret differences in the number of maxillary teeth in specimens of Brachychampsa as intraspecific variation. Moreover, the diminutive 15th maxillary tooth in SMP VP-1312 lies within its alveolus and has not fully erupted. Note also that Erickson (1972) reported 15 maxillary teeth for Albertochampsa langstoni. Second, the fifth maxillary tooth is the largest in all other specimens of Brachychampsa, so this feature is not unique to ?B. sealeyi. The fourth maxillary tooth is the largest in Albertochampsa, Stangerochampsa, Allognathosuchus mooki and Alligator (Erickson, 1972; Wu et al., 1996; Brochu, 1999; Lucas and Estep, 2000). Third, Williamson (1996) interpreted ?B. sealeyi as having both a tapered rostrum and a relatively small incisive foramen (compared to the width of the posterior rostrum at the level of the first maxillary tooth). However, the skull is broken along the midline, casting doubt on the shape and extent of these features. A slight repositioning of the left and right premaxillae of the holotype of ?B. sealeyi demonstrates that the snout was broad and blunt and that the incisive foramen is relatively just as large as in B. montana. Moreover, Williamson (1996) explicitly stated that the skull was damaged along its midline, so

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any definitive statements made regarding features coincident with this region must be considered tentative. Our examination of the holotype skull of ?B. sealeyi demonstrates that there is no evidence to support Williamson’s interpretations of a narrow rostrum and small incisive foramen. Lastly, bulbous teeth vary in size and shape among living and fossil alligatoroids (e.g., Brochu, 1999). Moreover, they are often quite indistinguishable from one another across taxa (e.g., the paratype tooth of Bottosaurus harlani [ANSP 9174] is identical to bulbous teeth of Brachychampsa montana [SMP VP1312] based on a side-by-side comparison). While the 13th and 14th bulbous teeth in SMP VP-1312 are more mediolaterally compressed than circular in outline (viewed occlusally), the 12th, 14th and 15th are more circular in appearance. Williamson (1996) used the more circular appearance of the posterior teeth in the holotype of B. sealeyi as one of the defining features of this taxon. However, we note that one tooth illustrated by Williamson (1996: fig. 8E) clearly is a mediolaterally compressed posterior tooth in the dentary of the holotype of B. sealeyi, which is identical in morphology to those found in adult B. montana. This fact supports the interpretation that the posterior dentary, and presumably maxillary teeth, become mediolaterally compressed with maturity. We believe the holotype of B. sealeyi is a subadult (juvenile) individual based on the fact that Williamson (1996) misinterpreted not only the shape of the rostrum, but also the interorbital width being greater than the distance between the supratemporal fenestra. Both these features are not certain owing to the fragmentary nature of the holotype. Furthermore, we view the variation in tooth outline as being ontogenetic, so it is not taxonomically significant. In summary, we conclude that none of the characters used by Williamson (1996) to diagnose B. sealeyi are valid or taxonomically significant. Therefore, B. sealeyi is a subjective junior synonym of B. montana. It has been pointed out by Brochu (pers. comm., 2002) that the orientation of the tooth row (‘‘premaxillary tooth row forms a more concave arc and the maxillary tooth row diverges slightly more caudally,’’ compared to B. montana) and narrow narial region of B. sealeyi supports its distinct identity. However, we argue that these features are not sufficient for species recognition; indeed, they are probably artifacts of ontogenetic and/or individual variation. CROCODYLIANS/CROCODYLIFORMS FROM THE KIRTLAND FORMATION Three crocodylian/crocodyliform taxa have been reported from the Kirtland Formation of New Mexico: Brachychampsa montana, Leidyosuchus canadensis and Denazinosuchus kirtlandicus. Gilmore (1916) cited two localities within the Kirtland Formation that yielded teeth belonging to Brachychampsa sp. Until now, no skull material pertaining to Brachychampsa has ever been recovered from the Kirtland Formation. Wiman (1932) named the species Goniopholis kirtlandicus based on an incomplete skull from the Kirtland Formation (probably from the De-na-zin Member). As noted by Mateer (1981), this specimen lacks the depressed area anterior to the orbit that, in part, has been used to diagnose ‘‘goniopholidids.’’ Moreover, the large supratemporal fenestrae of the New Mexico specimen departs from not only Goniopholis of the Late Jurassic of Europe, but also from the Late Jurassic taxon Eutretauranosuchus. Therefore, reference to either of these genera cannot be made based on the presence of this feature. Although, Wiman (1932) made comparisons to the various species then assigned to Goniopholis, he failed to establish that ‘‘Goniopholis’’ kirtlandicus is indeed referable to the Late Jurassic Goniopholis. Moreover, he did not convincingly demonstrate that the specimen is ‘‘mesosuchian’’ (i.e., basal mesoeucrocodylia of Benton

and Clark, 1988). Indeed, most of Wiman’s characters reviewed by Lucas (1992) are primitive (i.e., general shape of the skull; configuration of premaxillae; [wide] width between orbits; lacrimals separate prefrontals from maxillae; frontals border much of the supratemporal fenestrae; number, shape and sculpture of teeth, etc.) and have no phylogenetic value, as they are present in basal crocodyliforms such as Teleorhinus and other pholidosaurids. Of significance is the fact that the frontals of ‘‘G.’’ kirtlandicus are almost eliminated from the orbital border by the prefrontal and postorbital, giving validity to the species. We recently concluded that the holotype of ‘‘G.’’ kirtlandicus is a new ‘‘mesosuchian’’ genus (Denazinasuchus), unique to the San Juan Basin Cretaceous (Lucas and Sullivan, 2003). The taxon Leidyosuchus has been cited as occurring in the Upper Cretaceous strata of New Mexico. Isolated teeth, purportedly pertaining to this genus, have been published by Hutchinson and Kues (1985), Armstrong-Ziegler (1978), and Lehman (1985). However, again no skull material of Leidyosuchus from the Kirtland Formation or other Upper Cretaceous strata of New Mexico has been recovered. Indeed, many of the isolated conical teeth previously attributed to Leidyosuchus may in fact be from Brachychampsa montana. A spot-survey of isolated teeth in collections of the SMP (and NMMNH) reveals that they compare favorably to B. montana. In fact, only one isolated tooth in the SMP collections could not be referred to Brachychampsa. Therefore, the presence of Leidyosuchus in the Kirtland Formation must be considered tentative. DIET OF BRACHYCHAMPSA The heterodonty and the presence of bulbous teeth in Brachychampsa montana have been the focus of attention with regard to dietary considerations and phylogenetic systematics (Carpenter and Lindsay, 1980; Brochu, 1999). A similar type of heterodonty (consisting of tapered narrow conical teeth, with minor variations, followed by large bulbous, somewhat bulbous, or ‘‘button teeth’’ posteriorly), not only characterizes Brachychampsa (and Stangerochampsa) but is also seen, to a lesser extent, in Allognathosuchus and Procaimanoidea, although this morphology is much reduced in the latter two taxa. Bulbous posterior teeth have been reported among modern alligators, hence dismissing any diagnostic utility (Brochu, 1999). However, with respect to Diplocynodon, the bulbous teeth of Brachychampsa, Stangerochampsa, Albertochampsa, Allognathosuchus, Ceratosuchus, to a much lesser extent Procaimanoidea, is arguably a shared-derived character that is lost or subdued subsequently among later, more derived members of the Alligatoridae. Reappearance of bulbous dentition in modern species is nothing more than a character convergence. Carpenter and Lindsay (1980) attempted to provide a compelling case for a cheloniphagous (turtle-eating) diet for Brachychampsa based on the presence of posterior bulbous, crushing teeth, robust dentary, and blunt U-shaped snout. Other bulbous-tooth-bearing crocodylians, notably the Paleocene/Eocene Allognathosuchus and related taxa, have also been interpreted as having a ‘‘cheloniphagous’’ diet (Abel, 1928). Simpson (1930) argued that the heterodonty exhibited in Allognathosuchus indicated that these alligatoroids were more opportunistic with respect to their dietary demands rather than being restricted to any one principal food source, based on analogy with modern alligators. Bartels (1984) made a case for a more generalized diet (small invertebrates and vertebrates, including juvenile turtles) for the globular tooth-bearing genera Allognathosuchus and Ceratosuchus. However, both the snout and teeth in these two taxa are much reduced in size compared to that of Brachychampsa. Aoki (1989) presented evidence that the posterior teeth were used for crushing, a thesis not totally embraced by Bartels (1984). Indeed, there is no direct correlation in living

SULLIVAN AND LUCAS—BRACHYCHAMPSA MONTANA FROM NEW MEXICO alligators between the possession of blunt teeth and a ‘‘chelonivorous’’ diet. Modern alligators are known to eat turtles (as well as a variety of other prey), yet most do not have bulbous teeth, and the ability to take large prey items may be correlated with having relatively broad snouts and large, robust size (Pooley, 1989). Moreover, dietary preferences change during the life span of crocodylians. Clearly, turtles were a plentiful potential food source for these early alligatoroids during the Late Cretaceous based on their co-occurrence with these crocodylians. It is likely, however, that Brachychampsa, Stangerochampsa and other Late Cretaceous broad-snouted, blunt-toothed alligatoroids also preyed upon other animals, such as fish, birds and possibly small dinosaurs. Loss or reduction of blunt teeth coupled with the apparent reduction of broad snouts among the more derived alligatoroids, especially the Paleocene and Eocene taxa, may indicate a shift in dietary opportunities from a supposed predominantly ‘‘chelonivorous’’ to a more diverse diet that may have included more small mammals. It is worth noting that many of the Late Cretaceous adult turtles are large, arguably larger than adult Brachychampsa could ingest. Consequently, if chelonians were the mainstay of Brachychampsa, smaller and/ or immature turtles would have been the likely prey. ACKNOWLEDGMENTS We thank Ted Daeschler and Ned Gilmore (Academy of Natural Sciences of Philadelphia) for the loan of ANSP 35305 (Alligator mississippinensis) for comparative purposes. We also thank Ryan Ridgely and Geb Bennett, who helped collect SMP VP-1312, which was largely prepared by Fred Widmann and Geb Bennett. We are grateful for comments and criticisms presented by Chris Brochu (University of Iowa), but acknowledge here that we often disagree with him on interpretations with respect to analysis of characters and their taxonomic significance. We also thank Xiao-Chun Wu (Canadian Museum of Nature) for his useful comments, suggestions and insights. Arjan Boere (University of Amsterdam) also reviewed this paper and we thank him for his comments. We thank Mary Ann Turner (Peabody Museum of Natural History) for the loan of YPM 56582. Both specimens (SMP VP-1264 and 1312) were collected under Paleontological Resource Use Permit: SMP 8270RS/WA/WSA-98-C issued by the Bureau of Land Management, which is gratefully acknowledged. LITERATURE CITED Abel, O. 1928. Allognathosuchus, ein an die cheloniphage Nahrungsweise angepasster Krokodiltypus des nordamerkanischen Eoza¨ns. Palaeontologisches Zeitschrift 9:367–374. Aoki, R. 1989. The jaw mechanics in the heterodont crocodylians. Current Herpetology in East Asia 1:17–21. Armstrong-Ziegler, J. G. 1980. Amphibia and Reptilia from the Campanian of New Mexico. Fieldiana Geology (n.s.) no. 4:1–39. Bartels, W. 1984. Osteology and systematic affinities of the horned alligator Ceratosuchus (Reptilia, Crocodilia). Journal of Paleontology 58:1347–1353. Benton, M. J., and J. M. Clark. 1988. Archosaur phylogeny and the relationships of the Crocodylia; pp. 295–338 in M. J. Benton (ed.), The Phylogeny and Classification of the Tetrapods, Vol. 1. Clarendon Press, Oxford. Brochu, C. A. 1999. Phylogenetics, taxonomy, and historical biogeography of Alligatoroidea. Memoir 6, Journal of Vertebrate Paleontology, Supplement to No. 2:9–100.

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Carpenter, K., and D. Lindsey. 1980. The dentary of Brachychampsa montana Gilmore (Alligatorinae; Crocodylidae), a Late Cretaceous turtle-eating alligator. Journal of Paleontology 54:1213–1217. Cope, E. D. 1873. On the extinct Vertebrata of the Eocene of Wyoming, observed by the expedition of 1872, with notes on the geology. Annual Report of the U. S. Geological and Geographic Survey the Territories 6:545–649. Erickson, B. R. 1972. Albertochampsa langstoni, gen. et sp. nov., a new alligator from the Cretaceous of Alberta. Scientific Publications of the Science Museum of Minnesota 2:1–13. Gilmore, C. W. 1911. A new fossil alligator from the Hell Creek beds of Montana. Proceedings of the United States National Museum 41:297–301. ——— 1916. Vertebrate faunas of the Ojo Alamo, Kirtland, and Fruitland Formations. United States Geological Survey Professional Paper 98:279–302. Hutchinson, P. J., and B. S. Kues. 1985. Depositional environments and paleontology of Lewis Shale to lower Kirtland Shale sequence (Upper Cretaceous), Bisti area, northwestern New Mexico. New Mexico Bureau of Mines and Mineral Resources Circular 195:25–54. Iordansky, N. N. 1973. The skull of the Crocodylia; pp. 201–262 in C. Gans (ed.), Biology of the Reptilia. Academic Press, New York. Leidy, J. 1865. Cretaceous reptiles of the United States. Smithsonian Contributions to Knowledge 192:1–135. Lehman, T. M. 1985. Depositional environments of the Naashoibito Member of the Kirtland Shale, Upper Cretaceous, San Juan Basin, New Mexico. New Mexico Bureau of Mines and Mineral Resources Circular 195:55–79. Lucas, S. G. 1992. Cretaceous-Eocene crocodylians from the San Juan Basin, New Mexico; pp. 257–264 in S. G. Lucas, B. S. Kues, T. E. Williamson, and A. P. Hunt (eds.), San Juan Basin IV. New Mexico Geological Society. ——— and J. W. Estep. 2000. Osteology of Allognathosuchus mooki Simpson, a Paleocene crocodilian from the San Juan Basin, New Mexico, and the monophyly of Allognathosuchus; pp. 155–168 in S. G. Lucas (ed.), New Mexico’s Fossil Record 2, New Mexico Museum of Natural History and Science Bulletin 16. ———, and R. M. Sullivan. 2003. A new crocodylian from the Upper Cretaceous of the San Juan Basin, New Mexico. Neues Jarbuch fu¨r Geologie und Pala¨ontologie, Monatshefte 2002:109–119. Mateer, N. J. 1981. The reptilian megafauna from the Kirtland Shale (Late Cretaceous) of the San Juan Basin, New Mexico; pp 49–75 in S. G. Lucas, J. K. Rigby, Jr., and B. S. Kues (eds.), Advances in San Juan Basin Paleontology. University of New Mexico Press, Albuquerque. Norell, M. A., J. M. Clark, and J. H. Hutchison. 1994. The Late Cretaceous alligatoroid Brachychampsa montana (Crocodylia): new material and putative relationships. American Museum Novitates, No. 3116:1–26. Pooley, A. C. 1989. Food and feeding habits; pp. 76–91 in C. A. Ross (ed.), Crocodiles and alligators. Facts on File, New York. Simpson, G. G. 1930. Allognathosuchus mooki, a new crocodile from the Puerco Formation. American Museum Novitates 445:1–16. Sullivan, R. M., and S. G. Lucas. 2001. A new specimen of the rare alligatoroid Brachychampsa from the Kirtland Formation (Upper Campanian), San Juan Basin, New Mexico. Journal of Paleontology, Abstracts of Papers, 106A. Williamson, T. E. 1996. ?Brachychampsa sealeyi, sp. nov., (Crocodylia, Alligatoroidea) from the Upper Cretaceous (Lower Campanian) Menefee Formation, northwestern New Mexico. Journal of Vertebrate Paleontology 16:421–431. Wiman, C. 1932. Goniopholis kirtlandicus n. sp. aus der obereb Kreide in New Mexico. Bulletin of the Geological Institution of the University of Uppsala 23:181–189. Wu, X.-C., D. B. Brinkman, and A. P. Russell. 1996. A new alligator from the Upper Cretaceous of Canada and its relationships of early eusuchians. Palaeontology 39:351–375. Received 9 November 2001; accepted 23 October 2002.