A new Triassic temnospondyl from Antarctica and a review of Fremouw Formation biostratigraphy

A new temnospondyl, Krostega collinsoni, gen. et sp. nov., is described on the basis of a large snout fragment from the Triassic upper Fremouw Formation of Antarctica. K. collinsoni is characterized by greatly enlarged teeth of the transvomerine and parachoanal tooth rows, a reduced transvomerine tooth row, as well as a distinct process oil the palatal surface of the premaxilla. Although key palatal and tabular features are not preserved. the shape and position of the external naris, choana. and anterior palatal vacuity suggest that K. collinsoni may be allied to the Heylerosauridae or basal Mastodonsauridae. The discovery of K. collinsoni in the tipper Fremouw is surprising. given that Triassic vertebrates from Antarctica are typically considered a subset of coeval taxa from the Karoo Basin of South Africa. Based on its unique occurrence in Antarctica. K. collinsoni suggests that high latitude Triassic tetrapods had a more restricted geographic distribution than previously considered. Biostratigraphically, the fauna of the upper Fremouw Formation is best correlated with the Cynognathus Assemblage Zone of South Africa's Beaufort Group, although the lack of species-level identifications for many of the Antarctic fossils precludes a more refined correlation. A review of the Triassic fossil record identifies several tetrapods that make their first appearance in the Fremouw, with a later appearance in the Karoo Basin, suggesting that the high latitude regions of Gondwana might have served as an important area for speciation.