A new specimen of the temnospondyl Australerpeton cosgriffi from the late Permian of Brazil (Rio do Rasto Formation, Paraná Basin): comparative anatomy and phylogenetic relationships

ABSTRACT

A new temnospondyl specimen from the Rio do Rasto Formation (late Permian, Paraná Basin) of south Brazil is composed of a left mandible, right pelvis, femur, tibia, and fibula. Preserved lower jaws are rare for Australerpeton cosgriffi, and the weak ossification of the temnospondyl postcranium renders their preservation generally uncommon. A detailed comparative description of the material allowed its assignment to Australerpeton cosgriffi, and yielded new information about the morphology of mandible, pelvis, and hind limb of that taxon. This long-snouted temnospondyl has uncertain affinities and has been assigned either to stereospondyl Rhinesuchidae or to archegosaurid Platyoposaurinae. Reassessment of the phylogenetic placement of Australerpeton cosgriffi, with information drawn from the new specimen, confirms a basal stereospondyl position, between Peltobatrachus pustulatus and Rhinesuchidae. The synapomorphies shared with other stereospondyls include tabular and exoccipital contacting in the paroccipital process; parasphenoid articulates with corpus of the pterygoid forming a broad contact along the lateral margins of the parasphenoid plate; internal carotid passes through the dorsal surface of the parasphenoid plate; and parasphenoid denticles field enlarged to a transverse ‘belt’ extending between the pterygoid-parasphenoid articulations. Accordingly, Australerpeton cosgriffi represents one of the first stereospondyls, and the oldest long-snouted member of the group. The Paraná Basin can be included within the stereospondyl ancestral range, and dispersion and diversification of this clade appears to have happened before the Permo-Triassic boundary.

SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at http://www.tandfonline.com/UJVP.

ACKNOWLEDGMENTS

We are thankful to J. S. Bittencourt and F. C. Montefeltro for helping with the phylogenetic analysis and for suggestions with the language. For access to Australerpeton cosgriffi, we thank C. L. Schultz (UFRGS). M. Ruta and R. Schoch gave helpful comments. Useful comments by an anonymous reviewer and Anne Warren helped to improve the manuscript. The research was supported by Fundação de Amparo à Pesquisa no Estado de São Paulo (FAPESP; 09/546560-9).

Handling editor: Jason Anderson