New information on the postcranial skeleton of Gracilisuchus stipanicicorum (Archosauria: Suchia) and reappraisal of its phylogenetic position

LECUONA, AGUSTINA; DESOJO, JULIA B.; POL, DIEGO

ZOOLOGICAL JOURNAL OF THE LINNEAN SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2017

0024-4082

Gracilisuchus stipanicicorum Romer, 1972a, the only species in its genus, is a small basal suchian, recovered from theMiddle?Late Triassic Chañares Formation (La Rioja, Argentina). This species has been interpreted as related to varioustaxa within Archosauria, including Ornithosuchidae, Rauisuchidae and Crocodylomorpha. Recent phylogeneticanalyses are concordant in recovering it in a basal position within Suchia, and the most recent analysis recoveredit within the clade Gracilisuchidae. Six specimens of G. stipanicicorum are known and all of them were studied andincluded in a phylogenetic analysis of Archosauriformes. Re-examination of the specimens allowed us to improvethe diagnosis, identify new diagnostic characters (e.g. first sacral rib with a slight distal expansion relative to theproximal portion) and, in particular, redescribe the postcranial skeleton. The phylogenetic data matrix is an updatedversion of a previous study with the inclusion of additional characters and taxa. The strict consensus supports themost recent phylogenetic results, recovering Gracilisuchus as a basal suchian within Gracilisuchidae. The results ofthis analysis resolve some important polytomies and yield higher support values than recent analyses. All previousalternative hypotheses on the affinities of Gracilisuchus were found to be highly suboptimal for the new data matrix.