The first spinicaudatan (Crustacea: Diplostraca) from Permo-Triassic continental sequences of South America and its palaeoecological context

Abstract

Cornia martinsnetoi sp. nov., the first spinicaudatan from Permian–Triassic continental sequences of southern South America, is described. The new species has characters diagnostic of the typical late Palaeozoic–Early Triassic subfamily Vertexiinae from Gondwana. This new taxon was found in tuffaceous siltstones in the upper part of the Quebrada de los Fósiles Formation (Puesto Viejo Group), which may span the Permo-Triassic boundary in Argentina. The lower and coarser-grained interval of the Quebrada de los Fósiles Formation was deposited in distal alluvial fans and low- to high-sinuosity rivers. The upper fine-grained interval of this formation, which hosts the spinicaudatans and associated fossils (ostracods, megaspores, fish scales), was deposited in shallow floodplain lakes. Intense volcanic activity influenced the sedimentary evolution of this succession and was accompanied by aridification and some climatic seasonality that likely generated stressful conditions for the biota. Previous biostratigraphic studies support an Early Triassic age for the beds containing Cornia martinsnetoi sp. nov.