THE OSTEOLOGY AND RELATIONSHIPS OF LUPEROSUCHUS FRACTUS ROMER 1971 (PSEUDOSUCHIA: LORICATA) FROM THE EARLY LATE TRIASSIC CHAÑARES FORMATION OF ARGENTIN

DESOJO, J.B.; NESBITT, S.

CABA

Jornada; XXX Jornadas Argentinas de Paleontologia de Vertebrados; 2016

Mus.Arg.Cs.Nat. "Bernardino Rivadavia"

Archosaurs reached large sizes (greater than 3 meters) during their radiation through the Triassic Period, but large terrestrial archosaurs remain poorly represented in faunal assemblages prior to the mid Carnian, Late Triassic. We redescribe and reinterpreted the osteology of the single specimen (PULR 04) of Luperosuchus fractus , the largest reptile recovered from near the base of the early Late Triassic Chañares Formation, Northwest of Argentina. The incomplete articulated skull includes most of the left side, but lacks the anteroventral portion of the skull, and nearly all bones posterior to the postorbital. Additionally, we report fragments (parts of the braincase, jugal, maxilla, quadrate, and the intercentrum of the atlas) originally found with the holotype but separated soon after belong to the same individual. Luperosuchus is unique among Triassic archosaurs by the presence of an extremely elongated posterodorsal (=maxillary) process of the premaxilla, a narrow postorbital bar, and an anteriorly directed finger-like process of the prefrontal. Based on the unpublished skull bones, we scored Luperosuchus into a previous phylogenetic analysis of Nesbitt in 2011 with other recent modifications, and we found Luperosuchus to represent an early diverging in a polytomy with Prestosuchus and Saurosuchus. Like other loricatans, we find that Luperosuchus, Prestosuchus, and Saurosuchus share a deep maxillae with palpebral elements coossified with the skull roof. The long slit-like gap between the premaxilla and the maxilla in Luperosuchus is considered an artifact of preservation and this loose connection between the elements likely represents a plesiomorphic state among loricatans (e.g., Prestosuchus and Saurosuchus).