New data on the late triassic aetosaur Neoaetosauroides Bonaparte, 1969 from the Los Colorados Formation, west-central Argentina.

DESOJO, J.B.

Norman, Oklahoma, Estados Unidos

Congreso; Sixty-two Annual Meeting of Society of Vertebrate Paleontology (SVP); 2002

University of Oklahoma and Society of Vertebrate Paleontology

The middle-sized aetosaur Neoateosauroides engaeus was originally described by Bonaparte based on fragmentary skull remains, incomplete postcranial material, and dorsal, ventral and caudal armors. These specimens were collected in the uppermost section of the Triassic sequence, from levels that yielded abundant prosauropod remains. This taxon is presently diagnosed by the presence of a postglenoid process on the coracoid, reduction of the fifth metatarsal, and faint ornamentation of the dorsal paramedial scutes consisting of radiating ridges and pits. Except for most of the lower jaw and partial maxilla, the skull was unknown as were the cervical vertebrae and associated scutes, and distal forelimbs.  Preparation of undescribed specimens collected several years ago in the same section revealed features that suggest that this material is referable to Neoateosauroides engaeus. These additional specimens consist mainly of articulated skull remains, cervical vertebrae, and dermal plates with the same ornamentation pattern as the holotype. This new material provides meaningful information on many characters, such as the extent of the maxillary tooth row with respect to the posterior margin of the external nares, position of the maxilla relative to the external nares, anterior extent of the premaxillary tooth row, shape of the infratemporal fenestra, and presence of ventral keel on cervical centra.  As a result of recent phylogenetic analyses, Neoaetosauroides is considered the sister taxon of a clade that includes Typothorax, Desmatosuchus, Longosuchus and Paratypothorax, although this placement is weakly supported. The new evidence on Neoaetosauroides permits to score, as well as change, the state of several characters for this taxon used in those studies and hence helps to ascertain the phylogenetic relationships of Neoaetosauroides within Aetosauria. These relationships are currently being reevaluated.