A snake dentary from the Upper Cretaceous of Patagonia

GÓMEZ, R.O.

Neuquén

Congreso; III Congreso Latinoamericano de Paleontología de Vertebrados; 2008

Universidad Nacional del Comahue

Cranial material of Cretaceous snakes is particularly scarce and in South America it is restricted to only two taxa from the Upper Cretaceous of Patagonia, Dinilysia patagonica Woodward, 1901, and Najash rionegrina Apesteguía and Zaher, 2006. Dinilysia is represented by cranial and postcranial remains and, although its morphology has been extensively studied (e.g. Estes et al., 1970; Caldwell and Calvo, 2008), its phylogenetic position is far from having been clarified (Rieppel et al., 2002; Lee and Scanlon, 2002). Najash, known by material ascribed to a single individual, is the only known terrestrial limbed snake; this taxon is possibly basal to all other snakes (Apesteguía and Zaher, 2006). Herein I describe the first snake cranial remains from the Campanian-Maastrichtian of South America. The material comes from the Allen Formation (Late Campanian-Early Maastrichtian) at Bajo Trapalcó, Río Negro province, Argentina; it was found in association with several isolated vertebrae, most of which belong to ?madtsoiid? snakes. The specimen consists of the anterior portion of a left dentary. Regardless of the fragmentary condition, some meaningful comparisons can be made. As in the dentary of the small Australian ?madtsoiid? Patagoniophis australiensis Scanlon, 2005, and apparently also in that of Najash, the Meckelian groove is not ventrally limited by the medioventral crest. The alveoli are transversely oriented, a condition observed in non-macrostomatan snakes. A distinctly high pleura is present, as in scolecophidians (Zaher and Rieppel, 1999) and to a lesser degree in Najash and in Australian small ?madtsoiids?. The size and position of the mental foramen in the fossil dentary suggest that there might be additional, more posteriorly located foramina; extant snakes have a single, relatively large mental foramen, which is more dorsal than that on the dentary from the Allen Formation. The latter bone resembles the dentary of the basal limbed snake Najash, as well as that of Australian small ?madtsoiids? from the Eocene-Miocene interval, in the possession of these and other presumably plesiomorphic features.