New early opisthodontian sphenodontid (Lepidosauria: Rhynchocephalia) from the Quebrada del Barro Formation, Marayes-El carrizal Basin, NW Argentina

MARTÍNEZ, RICARDO N.; APALDETTI, CECILIA; PRADERIO, ANGEL; FERNANDEZ, ELIANA; COLOMBI, CARINA; ALCOBER, OSCAR A.; SANTI MALNIS, PAULA; CORREA, GUSTAVO; ABELÍN, DIEGO

La Rioja

Jornada; Jornadas Argentinas de Paleovertebrados; 2013

Sphenodontids were a successful group of rhynchocephalian reptiles that dominate the fossil record of Lepidosauria during the Triassic and Jurassic of Pangea. Nevertheless, Sphenodon Gray from New Zealand is the only extant genus of the group. Opisthodontia—the herbivore branch of Sphenodontia—is known from the Upper Jurassic (e.g., Opisthias Guillmore, Eilenodon Rasmussen and Callison) to Upper Cretaceous (e.g., Kaikaifilusaurus Simon and Kellner). Here we report a new sphenodontid (PVSJ 886) from the Upper Triassic Quebrada del Barro Formation from Marayes-El Carrizal Basin of Northwestern Argentina. PVSJ886 belongs to a new vertebrate association (including tritheledontids, sphenosuchids and sauropodomorphs) found in the upper levels of Quebrada del Barro Formation, which confirms the Norian age of the unit. The new specimen is characterized by its relatively large size (skull length greater than 10 cm), derived herbivore traits (e.g., robust dentary, lateromedially expanded dentary teeth, propalinal jaw movement) and autapomorphic characters such as the palatine bearing a small cluster of conical teeth, four prominent rows of dozens of small teeth on the anterior palatal shelf of the pterygoids, and very wide additional teeth with transversal width:anteroposterior length ratio equals 5. Phylogenetic analysis depicted PVSJ886 as the basal-most member of Opisthodontia, extending the known record of opisthodontians by 50 million years.