PEIROSAURID AFFINITIES OF A CROCODYLIFORM FROM THE BAJO DE LA CARPA FORMATION, UPPER CRETACEOUS, NEUQUÉN

LUCAS FIORELLI; DIEGO POL; JUAN PORFIRI; JORGE CALVO; RUBÉN JUÁREZ VALIERI

Corrientes, Argentina

Jornada; Reunión Anual de Comunicaciones de la Asociación Paleontológica Argentina; 2007

Facultad de Ciencias Exactas y Naturales y Agrimensura, Universidad Nacional del Nordeste

In 1991 Bonaparte briefly described the remains of a crocodyliform (MUCPv-27) along with other fossil vertebrates from the Bajo de la Carpa Formation (Santonian) of the Neuquén Group, found at the university campus of Neuquén city. The specimen consists of fragmentary cranial remains, 9 dorsal vertebrae, appendicular elements, numerous presacral osteoderms, and an almost complete caudal region (completely enclosed by osteoderms). Although MUCPv-27 was originally considered as related to Araripesuchus, a phylogenetic analysis of Crocodyliformes indicates this crocodyliform is closely related to peirosaurids (e.g., Lomasuchus, Peirosaurus). This relationship is supported by the simultaneous presence of the following characters: narrow and elongated nasals with parallel lateral borders, deep longitudinal groove in the ventral surface of anterior caudal centra, well developed spinopostzygapophyseal and spinoprezygapophyseal laminae in caudal vertebrae, and neural spines in the first caudals dorsoventrally high, with the apex posterodorsally directed. One of the most remarkable features of this specimen is the morphology and preservation of the dermal armor. The caudal region is completely enclosed by osteoderms, which are subquadrangular in the proximal region and anteroposteriorly elongated toward the caudal end. The surface of these elements is heavily ornamented with subcircular pits and bears a slightly developed ridge. The presacral dorsal osteoderms have been preserved in natural articulation, indicating the presence of a single row of parasagittal osteoderms flanked by accessory (rounded) osteoderms. This morphology contrasts with that of other peirosaurids (e.g., Mahajangasuchus, Uberabasuchus), suggesting a high degree of diversity in osteoderm morphology and arrangement in the members of this poorly studied clade.