Abstract
We reevaluate the taxonomic status of therocephalian fossils recovered from the lower Fremouw Formation (Lower Triassic) of the central Transantarctic Mountains, Antarctica. The material, which includes mostly fragmentary juvenile specimens, is reidentified using an apomorphy-based approach. We recognize the presence of three higher-level taxa: Eutherocephalia, Akidnognathidae, and Baurioidea. The only genus-level identification is for a partial lower jaw and pterygoid tentatively attributed to the baurioid, Ericiolacerta parva. An indeterminate theriodont partial skull is reassigned to the therocephalian family Akidnognathidae. The holotypes of Pedaeosaurus parvus and Rhigosaurus glacialis are represented by indeterminate juvenile baurioids and, in the absence of clear autapomorphies, are considered nomina dubia. The results of the taxonomic revision indicate that the therocephalian fauna of Antarctica lacks endemic genera and thus corresponds to that of the Triassic Lystrosaurus Assemblage Zone fauna of South Africa's Karoo Basin. More generally, we consider the southern Gondwanan basins of South Africa and Antarctica to sample a broadly distributed Lower Triassic tetrapod fauna, although the latter basin documents the first occurrence of several taxa (e.g., Kombuisia, Palacrodon). More precise (i.e., species-level) identifications are needed to better constrain the biogeographic signal for therocephalians, but the presence of juveniles strongly suggests that this group of therapsids, like dicynodonts, were year-round high-latitude inhabitants during Early Triassic times.
Highlights
Over 40 years of collecting in the Triassic Fremouw Formation of Antarctica has produced a diverse terrestrial vertebrate fauna (Colbert, 1982; Hammer, 1990)
Colbert and Kitching’s (1981) description of five noncynodont theriodont specimens from near Shackleton Glacier, including two specimens assigned to the therocephalian Ericiolacerta parva, was the first to extend the geographic range of Ericiolacerta and Gondwanan “scaloposaurids” outside South Africa
Reexamination of the holotypes of the Antarctic therocephalians Pedaeosaurus parvus (AMNH FARB 9548) and Rhigosaurus glacialis (AMNH FARB 9525) leads us to conclude that the species were established on nondiagnostic material referable only to Baurioidea
Summary
Over 40 years of collecting in the Triassic Fremouw Formation of Antarctica has produced a diverse terrestrial vertebrate fauna (Colbert, 1982; Hammer, 1990). (as in some akidnognathids); palatal process of maxilla bears well-developed crista choanalis, contacting or nearly contacting the vomer medially, and extending posteriorly onto the pala¬ tine; interpterygoid vacuity of adults large and somewhat heart shaped; dentary is long, slender, and relatively straight with smooth ventral edge; upper incisors numerous, greater than five (except in Bauria).
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