Redescription and phylogenetic affinities of the caimanine Eocaiman cavernensis (Crocodylia, Alligatoroidea) from the Eocene of Argentina

Caimaninae is one of the few crocodylian lineages that still has living representatives. Today, most of its six extant species are restricted to South and Central America. However, recent discoveries revealed a more complex evolutionary history, with a fossil record richer than previously thought and a possible North American origin. Among the oldest caimanines is Eocaiman cavernensis, from the Eocene of Patagonia, Argentina. It was described by George G. Simpson in the 1930s, representing the first caimanine reported for the Paleogene. E. cavernensis has then been ubiquitous in phylogenetic studies on the group, but a more detailed morphological description and revision of the taxon was lacking. Here, we present a reassessment of E. cavernensis, based on first-hand examination and micro-computed tomography of the holotype, and reinterpret different aspects of its morphology. We explore the phylogenetic affinities of E. cavernensis and other caimanines using parsimony and Bayesian infer...