New Middle Triassic tetrapods from the upper Fremouw Formation of Antarctica and their depositional setting

ABSTRACT

Renewed field work in the Beardmore Glacier region of Antarctica has led to a new collection of tetrapod fossils from the upper member of the Fremouw Formation near Fremouw Peak. This locality records a sedimentary environment remarkably similar to that preserved at Gordon Valley, the only other locality known to preserve Cynognathus Assemblage Zone–equivalent taxa from Antarctica. Fossil bones are generally disarticulated and mixed with logs and reworked mudrock clasts, forming an intraformational channel-lag conglomerate. To date, very few bones of small-bodied taxa have been recovered from the upper Fremouw conglomerates, suggesting that they did not survive the reworking process. We use an apomorphy-based approach to record three previously unrecognized taxa from the upper Fremouw Formation: the dicynodont Angonisaurus, an indeterminate therocephalian therapsid, and an indeterminate crown-group archosaur. Combined with previous data, our work demonstrates that 10 distinct taxa can be recognized from the upper Fremouw, including two endemic temnospondyl species. Our recognition of Angonisaurus in the upper Fremouw Formation provides a new piece of evidence in favor of a correlation with the Cynognathus C subzone (uppermost Burgersdorp Formation) of South Africa and the Lifua Member of the Manda beds of Tanzania.

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