A new crocodyliform form the Cerro Barcino Formation (Aptian-Albian) and its significance within basal mesoeucrocodylians

LEARDI, JUAN MARTÍN; POL, DIEGO

Ciudad de Neuquén, Neuquén, Argentina

Congreso; III Congreso Latinoamericano de Paleontología de Vertebrados; 2008

Universidad Nacional del Comahue

 The South American crocodyliforms are represented mainly by two groups of basal mesoeucrocodylians, the Notosuchia and the Peirosauridae. Other representatives of this fauna is a conflictive group of basal mesoeucrocodylians,  the genus Araripesuchus, which shows derived features present both in notosuchians and peirosaurids, and it has been recovered as a sister group of Notosuchia (Sereno et al., 2003; Pol and Apesteguia, 2005) or Neosuchia (Ortega et al., 2000; Turner, 2006).            A new crocodyliform specimen is presented here found in the Cerro Castaño Member of the Cerro Barcino Formation (Chubut Group). The material consists of cranial and postcranial remains representing a single individual and is deposited at the Museo Paleontológico Egidio Feruglio (MPEF-PV 3095). This specimen represents a new taxon diagnosed by the presence of spool shaped vertebrae; hypapophyses of the two first postaxial cervical vertebrae forming a steep; knob-shaped anterior dorsal vertebrae hypapophyses; well developed epipophyses; quadratojugal does not participate on the cranio-mandibular joint, but reaches the quadrate condyles; frontal takes part of the supratemporal fenestrae; mandibular teeth not compressed; medially displaced deltoid crest. Several characters suggest affinities with Araripesuchus or with Peirosauridae. The phylogenetic relationships of this new taxon are tested through a cladistic analysis based on the dataset of Gasparini et al. (2006). The new taxon is depicted nested within the South American clade of the genus Araripesuchus, which was found to be the basalmost member of Notosuchia. The inclusion of MPEF-PV 3095 within Araripesuchus is supported by the presence of dorsal surface of the mandibular symphysis strongly concave and narrow, tough shaped; maxilary and posterior dentary teeth not compresed laterally and lateral surface of the dentaries below alveolar margin vertically oriented, continous with rest of the surface of the dentaries. The new taxon would represent the southern-most record of the genus Araripesuchus and strengthens the biogeographical relationships between Africa and South America during the Lower Cretaceous. Alternative topologies depicting the new taxon closer to peirosaurids imply two additional steps, suggesting that the affinities with Araripesuchus are not robustly supported.