New paracrocodylomorph (Archosauria, Pseudosuchia) remains from the Chañares Formation (Middle Triassic) from La Rioja, Argentina

LEARDI, JUAN MARTÍN

Buenos Aires

Jornada; XXVI Jornadas Argentinas de Paleontología de Vertebrados; 2012

Fundación de Historia Natura Felix de Azara, Universidad de Maimónides

The Chañares Formation bears one of the most diverse arcosauriform assemblages registered during the Middle-Upper Triassic. In this contribution new paracrocodylomorph remains from this Formation are reported. The specimen was recovered from the Talampaya National Park, at La Rioja province. It is badly preserved, being the left pubis the only bone complete enough to bear valuable data. The pubis is a gracile bone, bearing a well developed pubic apron and has a distal end slightly expanded with a broad distal section, characters that up to now have been only observed in paracrocodylomorphs. Although this specimen gives few phylogenetic data, it gives valuable information regarding how the Chañares archosauriform community was formed. This community is widely dominated by animals of small to middle size (8-20 kg of estimated mass), where the large forms (more than 300 kg) are only represented by the paracrocodiliform Luperosuchus fractus which is only represented by a small (probably juvenile) individual and a large fragmentary skull. When compared to other paracrocodylomorphs, this specimen size is estimated to have a body mass around 350-550 kg, representing the putuative largest carnivore arcosauriform recorded in the Chañares Formation.