first poposaurid record (Archosauria: Rauisuchia) from the Los Colorados Formation (latest Triassic), La Rioja Province, NW Argentina

EZCURRA, M.; DESOJO, J. B.; NOVAS, F.

San Luis

Jornada; XXV Jornadas Argentinas de Paleontología de Vertebrados; 2010

UNSL

The tetrapod assemblage of the Los Colorados Formation (late Norian-Rhaetian, La Rioja Province) has provided a diverse and abundant record of an archosaur-dominated fauna. In particular, the currently available record shows tha the most taxonically diverse group is that of the Crurotarsi, with five described species, including the aetosaur Neoaetosauroides Bonaparte, the rauisuchid Fasolasuchus Bonaparte, and the crocodylomorphs Hemiprotosuchus Bonaparte and Pseudhesperosuchus. In this contribution we provide the reappraisal of an ilium (PULR 076) found in direct association with the holotype of the basal neotheropod Zupaysaurus Arcucci and Coria, found in the Quebrada de Los Jachaleros locality, upper levels of the formation. This bone was previously reconized as a probable basal saurischian, but clearly not belongging to the holotype of Zupaysaurus. Nevertheless, we reinterpret this elements as belongging to that of a poposaurid rauisuchian. The bone can not be referred to Dinosauria because of the lacking of a brevis shelf, brevis fossa, and a high and thin iliac blade. By contrast, PULR 076 presents the following synapomorphies of Poposauridae: first sacral rib articulating extensively with the anteriorly pointing crest of the ilium, supraacetabular crest with an anteriorly extending crest, and a posterodorsally orieted postacetabular process. In addition, this specimens exhibits a suite of autapomorphies which allow distinguishing it from other archosaurs, such as a thick and laterally convex iliac blade and strongly dorsoventrally low and slightly medially deflected postacetabular process. Accordingly, this specimen seems a new poposaurid species which increases the alreadly highly diversity of one of the youngest known crurotarsan-dominated assemblage.