A new capitosauroid temnospondyl from the Middle Triassic upper Fremouw Formation of Antarctica

ABSTRACT

We describe a new capitosauroid temnospondyl, Antarctosuchus polyodon, gen. et sp. nov., on the basis of a large and relatively complete skull from the upper Fremouw Formation of Antarctica. The new species is characterized by its possession of numerous, extremely small maxillary, palatine, and ectopterygoid teeth, a dental pattern that suggests specialization on small prey items, possibly invertebrates. The taxon is also characterized by a parachoanal tooth row that extends far posterior to the choana and occipital condyles set close to the midline. A combination of features, including a flat skull and low occiput together with well-developed sensory canals, suggests an aquatic lifestyle. We address the phylogenetic relationships of Antarctosuchus by adding it to a recent cladistic analysis of Capitosauria. The revised data set includes 27 taxa and 53 characters. The results of this analysis place Antarctosuchus within a clade of derived Triassic stereospondyls as the sister taxon to Paracyclotosaurus crookshanki from the Triassic Denwai Formation of India. To date, the upper Fremouw Formation has yielded two endemic temnospondyl species (viz., Kryostega collinsoni and Antarctosuchus polyodon), although indeterminate remains referred to benthosuchids and a cranial fragment assigned to Parotosuchus sp. have also been noted. In contrast to the broadly distributed therapsid taxa recognized from the Middle Triassic of Antarctica (e.g., Cynognathus, Diademodon), the temnospondyl fauna suggests more limited interchange with other coeval southern Pangean basins (e.g., Karoo, Luangwa, Ruhuhu, Waterberg).

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ACKNOWLEDGMENTS

We thank B. Ryan, J. Tamplin, and S. DeFauw for excavating fossils from Gordon Valley, B. Ryan and B. Crowley for preparation, T. Keillor for molding and casting, and J. Swales for drawing Figures 3–6. Reviews provided by J. McHugh, J. Fortuny, and B. Rubidge improved the final manuscript. Antarctic research has been supported by NSF-ANT 0229698 (to W.R.H.) and NSF-ANT 0838762 and ANT 1146399 (to C.A.S.). Additional support was provided by the CNRS and Cossima Productions (to J.S.S.).

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