A new specimen of Uruguaysuchus aznarezi (Crocodyliformes: Notosuchia) from the middle Cretaceous of Uruguay and its phylogenetic relationships

Abstract

Uruguaysuchus is a small mesoeucrocodylian known from several partial skeletons and skulls from the Guichón Formation (middle Cretaceous, Uruguay). Several authors have pointed out derived similarities of this taxon with different basal notosuchian genera, highlighting its importance for mesoeucrocodylian phylogeny and biogeography. However, the holotype is only partially prepared and has not been available for study for many years. Thus, phylogenetic studies have included this form based on the original description, thereby resulting in a large amount of missing data in the character scorings of this taxon. Here, we describe a new specimen from the type locality consisting of a partial skull, lower jaw and cervical vertebrae which can be referred to U. aznarezi. The new specimen allows for the recognition and scoring of several characters previously unknown for this taxon, thus providing a more extensive diagnosis, as well as new information for understanding its phylogenetic relationships. These characters are congruent with the morphology present in basal notosuchians. The relationships of Uruguaysuchus are tested through a cladistic analysis using a recently published data set including the new information. The phylogenetic results differ from previous analyses, recovering this taxon as the sister group of the Araripesuchus clade. U. terrai is considered a juvenile individual of U. aznarezi.