Preliminary re-description of the fossil lizard Callopistes bicuspidatus Chani, 1976 (Squamata: Teiidae)

BRIZUELA, S.; ALBINO, A. M.

Neuquén, Argentina

Congreso; III Congreso Latinoamericano de Paleontología de Vertebrados; 2008

The assignment of lizard remains from the Monte Hermoso Formation in Farola Monte Hermoso, Buenos Aires province (Argentina) to Callopistes is problematic since the characters given by Chani (1976) are not totally diagnostic for the genus, and the present-day distribution of this genus is restricted western to the Andes. Based on Nydam et al. (2007) and personal observations, preliminary results of an ongoing redescription of these remains confirm that they fall within the Teiioidea-Borioteiioidea clade based on the deep subcircular dental replacement pits and hypertrophied splenial. The narial buttres resembles that of the teiids, not that of borioteioids nor gymnophthalmids. The parietal fossa, opened and posterioly located, further excludes the borioteioids. The anteromedial border of the supratemporal fenestra seems to be constituted by a lateral projection of the parietal as in the Tupinambinae. Moreover, the parietal morphology reinforces the fossil as a tupinambine (more closely resembling Tupinambis and Callopistes). Within the tupinambines, the separate postfrontal and postorbital excludes Dracaena (not the exctinct Paradracena). The orbital projection of the postfrontal resembles Callopistes, not Crocodilurus nor Tupinambis. An extended bicuspid tooth field in the dental series is present, within tupinambinae, only in Callopistes and supposedly in Crocodilurus. The only difference noted between both extant species of Callopistes (C. flavipunctatus and C. maculatus) and C. bicuspidatus seems to be the presence of posterior tricuspid teeth in the former and their absence in the latter. Further comparisons could allow us to give a better taxonomic evaluation of this fossil.