A new bauriamorph therocephalian adds a novel component to the Lower Triassic tetrapod assemblage of the Fremouw Formation (Transantarctic Basin) of Antarctica

Abstract

ABSTRACT The Fremouw Formation (Transantarctic Basin) of Antarctica preserves an exceptional fossil record of tetrapods from the beginning of the Mesozoic at high paleolatitude. Many of these fossils can be identified to species that also occur in the much richer Lystrosaurus declivis Assemblage Zone of South Africa’s Karoo Basin, but endemic species also occur. A third category of Antarctic fossils includes those that can only be broadly classified or lack sufficient diagnostic features for a synapomorphy-based identification. Therocephalians are a prime example of the last category, with Akidognathidae indet., Baurioidea indet., and cf. Ericiolacerta parva, currently recognized from the lower Fremouw Formation. Here we describe the most complete skull for an Antarctic therocephalian discovered to date. Notictoides absens, gen. et sp. nov., preserves a unique dental formula, a large intranarial portion of the septomaxilla, two bony excrescences along the rostral margin of the lacrimal, and a complete secondary palate formed by the maxilla. These features, in combination with a sagittal crest with a slit-like parietal foramen, a long, low dentary, and reduced upper and lower antecanine tooth count, suggest a relatively derived position for N. absens within baurioids. Indeed, the results of an updated cladistic analysis unite N. absens with the clade including Nothogomphodon, Ordosiodon, and Bauriidae. More broadly, the discovery of a third endemic species in the Lower Triassic rocks of the Fremouw Formation suggests that diversification in the wake of the Permian–Triassic mass extinction was likely more geographically complex than currently appreciated.