Review of a basal archosauriform from the Early Triassic of the Puesto Viejo Group, Mendoza, Argentina

EZCURRA, M. D.; LECUONA, A.; MARTINELLI, A.

San Rafael

Jornada; XXIV JORNADAS ARGENTINAS DE PALEONTOLOGÍA DE VERTEBRADOS; 2009

Museo de Historia Natural de San Rafael

The clade Archosauriformes encloses the Archosauria and several Late Permian and Triassic stem-groups. These non-archosaurarchosauriforms are well-known from the Early and Middle Triassic of North America, Europe, Asia, Oceania,and Africa, but its South American fossil record is mostly restricted to the endemic Middle and Late Triassic proterochampsids.Accordingly, the Early Triassic is an obscure period for the South American archosauriform history. At present,the only known South American Early Triassic archosauriform belongs to a putative proterosuchid briefly reportedby Bonaparte in the 80?s, from the Quebrada de los Fósiles Formation (Puesto Viejo Group, Mendoza Province). This specimen(MACN-PV 18119) is based on well-preserved natural external moulds of a partial postcranium: dorsal vertebrae,osteoderms, dorsal rib, chevron, humerus, radius?, left ilium, and pedal ungual. Due to its importance, a review of themorphology and phylogenetic affinities of this specimen was undertaken. A cladistic analysis depicted MACN-PV 18119as a basal archosauriform more derived than proterosuchids due the presence of dorsal centra with lateral fossa belowthe neurocentral suture, preacetabular process on the iliac blade, and osteoderms. Nevertheless, the Argentine specimenwas found as more basal than Euparkeria Broom, Erythrosuchus Broom, and more derived forms (e.g. Doswellia Weems,proterochampsids, archosaurs) by the absence of ribs with capitulum and tuberculum developed as distinct tubercles.Accordingly, MACN-PV 18119 represents a taxon which does not fit with the currently known lineages of non-archosaurarchosauriforms (e.g. Proterosuchidae, Erythrosuchidae, ?Euparkeriidae?, Proterochampsidae), increasing the diversityof the group during the biotic recovery after the Permo-Triassic mass extinction event.