A new sebecid mesoeucrocodylian from the Paleocene of northwestern Argentina

Abstract

A new crocodyliform, Sebecus ayrampu, sp. nov., is described based on the rostral region of the skull, mandibular rami, and a distal portion of the femur collected in Paleocene rocks of northwestern Argentina. The new taxon is diagnosed (among other characters) by the presence of a sharp sagittal torus on the palatal surface of the premaxilla and maxilla, the surface of the alveolar region of the premaxilla descending vertically with respect to the palatal surface of the maxilla and the rest of the premaxilla, deep premaxillary fossa for the hypertrophied mandibular tooth with a ridge along its anterior margin, a differential pattern of ornamentation of the rostrum external surface, and a V-shaped anterior margin of the choana (with the vertex pointing anteriorly). This specimen is recovered as a new member of Sebecidae in a phylogenetic analysis, increasing the taxonomic diversity of the group in the Paleogene of northwestern Argentina. A sensitivity parsimony analysis using equal and implied weights (with different K values) retrieves two distinct lineages within Sebecidae: the Ayllusuchus + Bretesuchus clade and the Sebecus clade (in which the new taxon is included). Sebecidae is also recovered as a sister group to Baurusuchidae, forming together the monophyletic Sebecosuchia within Notosuchia.