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Sphenodontians were a successful group of rhynchocephalian reptiles that dominated the fossil record of Lepidosauria during the Triassic and Jurassic. Although evidence of extinction is seen at the end of the Laurasian Early Cretaceous, they appeared to remain numerically abundant in South America until the end of the period. Most of the known Late Cretaceous record in South America is composed of opisthodontians, the herbivorous branch of Sphenodontia, whose oldest members were until recently reported to be from the Kimmeridgian-Tithonian (Late Jurassic). Here, we report a new sphenodontian, Sphenotitan leyesi gen. et sp. nov., collected from the Upper Triassic Quebrada del Barro Formation of northwestern Argentina. Phylogenetic analysis identifies Sphenotitan as a basal member of Opisthodontia, extending the known record of opisthodontians and the origin of herbivory in this group by 50 Myr.

A new continental fauna from the Late Triassic of Argentina: Cynodonts, turtles, pseudosuchians, and dinosauromorphs.Remains from the Late Jurassic of Chile indicates high sauropod diversity in South America.Jurassic confierous wood from western Argentina and the role of basidiomycetes in wood decay during the Mesozoic in Gondwana.

-The record of non-mammaliaformes eucynodonts from the Carnian-Norian Ischigualasto Formation is diverse and abundant, including a medium to large size herbivore and small carnivores. Here is described a new small eucynodont from the Ischigualasto Formation, on the basis of a partial skull. The new taxon is characterized by palatal process of the premaxilla extending posterior to the level of the fi rst postcanine; deep and large maxillary laterodorsal fossa that opens at the level of the root of the upper canine; and postorbital bar diverging posterolaterally at very low angle (35.6°) from the anteroposterior axis of the skull. Results from a phylogenetic analysis supports the new genus placement as a probainognathian eucynodont, more derived than Probainognathus Romer, and more closely related to Ecteninion Martinez, May & Forster and Trucidocynodon Oliveira, Soares & Schultz than to any other eucynodont. Ecteniniidae is proposed as a new clade including the new genus, Ecteninion and Trucidocynodon, and in the phylogenetic hypothesis represents the sister-group of Prozostrodontia (Prozostrodon Bonaparte & Barberena, Tritylodontidae and Mammaliaformes). Additionally, the new taxon from the Ischigualasto Formation shows that the Scaphonyx-ExaeretodonHerrerasaurus biozone has similar cynodont diversity than the supposedly contemporaneous Hyperodapedon Assemblage Zone of Santa Maria 2 Sequence, in Southern Brazil.Key words: Triassic, Argentina, Ischigualasto Formation, Cynodontia, Eucynodontia, Ecteniniidae. RESUMO -O registro dos eucinodontes não-mamaliformes do Carniano-Noriano da FormaçãoIschigualasto é diversifi cado e abundante, incluindo herbívoros de médio a grande porte e pequenos carnívoros. Descreve-se aqui um pequeno novo eucinodonte da Formação Ischigualasto, com base em um crânio parcial. O novo táxon é caracterizado pelo processo palatal da pré-maxila estendendo-se posteriormente até o nível do primeiro dente pós-canino; uma fossa profunda e ampla abrindo-se látero-dorsalmente na maxila ao nível da raiz do canino superior; e uma barra pós-orbital divergindo póstero-lateralmente em ângulo muito baixo (35,6°) em relação ao eixo ântero-posterior do crânio. Resultado da análise fi logenética sugere que o novo gênero é um eucinodonte Probainognathia, mais derivado que Probainognathus Romer e estreitamente relacionado a Ecteninion Martinez, May & Forster e Trucidocynodon Oliveira, Soares & Schultz do que qualquer outro eucinodonte. O clado novo gênero + Ecteninion + Trucidocynodon é aqui reivindicado como uma nova família chamada Ectininiidae, que é considerada como o clado-irmão de Prozostrodontia (Prozostrodon Bonaparte & Barberena, Tritylodontidae e Mammaliaformes). Além disso, a nova espécie da Formação Ischigualasto mostra que a biozona Scaphonyx-Exaeretodon-Herrerasaurus tem uma diversidade de cinodontes semelhante à da supostamente contemporânea Zona de Associação de Hyperodapedon, da Sequência 2 da Supersequência Santa Maria no sul do Brasil. Palavras-chave: