Material previously assigned to the Late Triassic cynodont Therioherpeton cargnini Bonaparte & Barberena, 1975 from the upper Santa Maria Formation (late Carnian) is reevaluated. A phylogenetic analysis groups Therioherpeton Bonaparte & Barberena, 1975 and Riograndia Bonaparte, Ferigolo & Ribeiro, 2001 in a monophyletic group, although support for this hypothesis is weak. Therioherpetidae are distinguished from all other probainognathians by upper teeth with the imbrication angle increasing in the posterior postcanines. In addition, upper and lower postcanine teeth are labio-lingually narrow. The Therioherpetidae are the sister group of the Tritheledontidae by virtue of characters such as the presence of some enlarged incisors, lower incisor 1 enlarger and the others small, and by the presence of simple longitudinal facet in most of the crown length. In contrast to previous phylogenetic analyses, therioherpetids and tritheledontids compose with Brasilitherium Bonaparte, Martinelli, Schultz & Rubert, 2003 and Brasilodon Bonaparte, Martinelli, Schultz & Rubert, 2003 a monophyletic group, which in turn is the sister-group of an unresolved group including Prozostrodon Bonaparte & Barberena, 2001 and Mammaliaformes.
Probainognathia, Therioherpetidae, Cynodontia, Therioherpeton, Late Triassic, Carnian, skull, humerus, Brazil