The postcranial anatomy of Yacarerani boliviensis and the phylogenetic significance of the notosuchian postcranial skeleton

Abstract

In this contribution, we describe new specimens of Yacarerani boliviensis from the Cajones Formation (Upper Cretaceous) of Bolivia. We focus on the postcranial anatomy of Y. boliviensis, because this anatomical region is completely unknown in other sphagesaurid notosuchians up to the present. At least eight individuals representing almost the entire postcranial skeleton are described. Although the postcranial anatomy of Yacarerani resembles that of other notosuchians in many features, five autapomorphic characters were identified: pedicles of the atlas bearing a lateral bulge; absence of rounded depressions on the dorsal surface of the anterior to middle dorsal vertebrae; coracoid bearing an oblique crest on its lateral surface; lateromedially compressed anterior ungual phalanges; and femur with a shallow depression for the M. puboischiofemoralis internus 1 and M. caudifemoralis longus. Observed variation in the postcranial anatomy of basal mesoeucrocodylians was incorporated as new characters in a phylogenetic analysis, expanding the postcranial information used in current phylogenetic data sets. The phylogenetic analysis depicts Yacarerani forming a clade with Adamantinasuchus, which is positioned at the base of Sphagesauridae. This family is well nested among a clade of ’advanced notosuchians,’ and Mariliasuchus is recovered as its sister group. The cladistic analysis recovered new postcranial synapomorphies for Notosuchia and less inclusive clades, although the fact that many taxa lack postcranial remains limits the number of unambiguous postcranial synapomorphies within Notosuchia.