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

ABSTRACTA 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 <i>Australerpeton cosgriffi</i>, and the weak ossification of the temnospondyl postcranium renders their preservation generally uncommon. A detailed comparative description of the material allowed its assignment to <i>Australerpeton cosgriffi</i>, 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 <i>Australerpeton cosgriffi</i>, with information drawn from the new specimen, confirms a basal stereospondyl position, between <i>Peltobatrachus pustulatus</i> 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, <i>Australerpeton cosgriffi</i> 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.