Peltosaurus piger

Figure 8 G, H

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