Abstract

Rocks of the Fremouw Formation (Beacon Basin) of Antarctica preserve an exceptional fossil record of tetrapods from the beginning of the Mesozoic at high paleolatitude. Many of the Antarctic fossils can be identified to species that also occur in the much richer Katberg Formation of South Africa’s Karoo Basin (e.g., Lystrosaurus murrayi, Lystrosaurus maccaigi, Micropholis stowi, Myosaurus gracilis, Procolophon trigoniceps, Prolacerta broomi, Thrinaxodon liorhinus), but endemic species also occur (e.g., Antarctanax shackletoni, Kombuisia antarctica). A third category of Antarctic fossils include 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 in the literature. 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 (I5/i3, C1/c1, PC13(?)/pc15, plus one upper pre-caniniform maxillary tooth), 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, the probable lack of a complete postorbital bar, 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 suggest a sister taxon relationship of 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 of Antarctica suggests that diversification in the wake of the Permian-Triassic mass extinction was likely more geographically complex than currently appreciated.