NEW MATERIAL OF LUPEROSUCHUS FRACTUS, THE EARLIEST KNOWN RAUISUCHIAN (DIAPSIDA: ARCHOSAURIA) FROM THE MIDDLE TRIASSIC OF ARGENTINA

DESOJO, J. B.; ARCCUCI, A.

Neuquen

Congreso; III Congreso Latinomaericano de Paleontologia de Vertebrados; 2008

Universidada Nacional del Comahue

Despite its abundance and worldwide distribution, Rauisuchia is a poorly understood group of Triassic archosaurs. Luperosuchus fractus Reig, discovered from Los Chañares Formation, Middle Triassic (Anisian), Ischigualasto-Villa Union Basin, Argentina, is one of their South American representatives. It is the largest member of the Chañares tetrapod assemblage and the earliest rauisuchian known from South America. New cranial material (PULR 057) from Los Chañares Formation found in the collection of the Museo de Ciencias Naturales de la Universidad Nacional de La Rioja is described. This material consist on the left maxilla, both premaxillae, and nasals preserved in articulation; other elements such as the left frontal with associated postorbital, left lacrimal, vomers, and both ectopterygoids were found disarticulated .The size, preservation, and close association suggest that all of the elements belong to the same individual. The new material is compared with the holotype and only specimen of L. fractus, and the definitions of some putative cranial characters of this group are reinterpreted. Luperosuchus fractus is characterized by presence of an elongated extra opening associated with a movable joint between the nasal and the maxilla, a ‘roman nose,’ and a deep excavation formed by the posterior margin of the premaxilla and anterior projection of the maxilla. Comparisons with other rauisuchians suggest that Luperosuchus is a basal taxon displaying many plesiomorphic features.