Peltosaurus piger Gilmore, 1928

Sahni, Ashok, 1972, The vertebrate Fauna of the Judith River formation, Montana, Bulletin of the American Museum of Natural History 147 (6), pp. 319-416 : 354

Peltosaurus piger Gilmore, 1928

Figure 8G, H

A right dentary, AMNH 8494 from Clambank Hollow, is not specifically distinguishable from that of Peltosaurus piger (fig. 8H).

Although its teeth are missing in the dentary, a number of other characteristics confirm the identification. Anteriorly the Meckelian fossa is ventral in position but posterior to the notch representing the internal mental foramina it becomes lingual. As in the Maestrichtian specimens of P. piger there are 10 or 11 teeth anterior to the notch. The intramandibular septum is broken posteriorly in the specimen but originates slightly anteroventral to the notch of the internal mental foramina. The distance from the foramina to the anterior of the dentary is 0.64 mm. in AMNH 8494, and is 0.9 mm. in UCMP 49772, from the Lance Formation. Externally the dentary is smooth and the mental foramina relatively large.

A maxilla fragment, AMNH 8495 from Clambank Hollow, can be referred to Peltosaurus piger (fig. 8G). The teeth are pleurodont, linguolabially expanded, and the transverse width is only slightly smaller than the height. The crown is expanded relative to the shaft and consists of a distinct anteroposteriorly directed crest rather than separate cuspules.

DIscUSSION: Peltosaurus is a common lizard in the faunas of the early Tertiary. Its range has now been extended down to the Campanian from the upper part of the White River Formation (late Oligocene). Geographically, it has been found in most of the Great Plains states and as far west as the late Eocene Sespe Formation, Ventura County, California ( Brattstrom, 1955). The presence of anguid lizards in the Campanian of North America is not surprising considering their presence in the Middle Cretaceous sediments of Mongolia. The Cretaceous P. piger has been differentiated from Tertiary species on the basis of "relatively shorter-crowned teeth, and shorter lower jaw" ( Estes, 1964, p. 120). The Judith River material consists of three jaw fragments apparently similar in all respects to later Maestrichtian forms.

Peltosaurus piger was described originally from the Lance Formation by Gilmore (1928, p. 136) and placed in the Anguidae . McDowell and Bogert (1954, p. 116) were doubtful of such affinities and stated: " Gilmore (1928, p. 136) has assigned some jaw fragments from the Lance to Peltosaurus as P. piger . This material is probably not anguinid [anguid], and is too fragmentary to make certain the generic assignment." Recently Estes (1964, p. 121) has shown that P. piger should be placed in the Anguidae .

Gilmore (1943, p. 381) described the species Isodontosaurus gracilis from the Djadochta beds of Mongolia. This lizard, which is known by 18 well-preserved specimens, comes from the localities famous for their mammal skulls. Isodontosaurus was referred to the Anguidae on the basis of its resemblance to Peltosaurus . Gilmore (1943) and McDowell and Bogert (1954, p. 113) believed that a relationship to this family is unlikely and considered the genus to have scincinoid affinities. This is based on scincinoid-like morphology of the splenial, the internal mental foramina, and the anteriorly extended angular. Judged from Gilmore's (1943) illustrations, Isodontosaurus does not appear to have much in common with Peltosaurus and consequently the Campanian occurrence of the latter genus would seem to be the oldest record of the Anguidae .

Figures

FIG. 8. A. Chamops segnis. AMNH 8486, labial view of left dentary. B. Lingual view. Both x 5. C. AMNH 8488, lingual view of left maxilla. D. Labial view. Both x 5. E. cf. Xenosauridae, AMNH 8498, labial view of left maxilla. F. Lingual view. Both x 5. G. Peltosaurus piger, AMNH 8495, lingual view of left maxilla, x 5. H. AMNH 8494, lingual view of right dentary, x 5. I. Paraderma bogerti, AMNH 8504, lingual view of right maxilla. x 5. J. Parasaniwa wyomingensis, AMNH 8499, lingual view of left dentary, x 5. K. Leptochamops denticulatus, AMNH 8491, lingual view of right maxilla, x 5. L. Exostinus lancensis, AMNH 8497, lingual view of right maxilla, x 5. M. Deinodon horridus, AMNH 8513, posterior view of isolated tooth. N. Lateral view. Both x 13. 0. AMNH 8515, lateral view of anterior dentary tooth. P. Posterior view. Both x 13. Q. AMNH 8514, posterior view of?premaxillary tooth. R. Lateral view. Both x 12. S. Paronychodon lacustris, AMNH 8522, lingual view of isolated tooth. T. Labial view. Both x 12. U. Kritosaurus cf. K. breviceps, AMNH 8525, lateral view of isolated tooth. V. Posterior view. Both x 1 2. W. Procheneosaurus altidens, AMNH 8527, labial view of isolated tooth. X. Anterior or posterior view. Both x 12. Y, Z.?Sebecosuchia, AMNH 8549, views of an solated tooth. Both x 10.