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

LECUONA, A.; DESOJO, J.B.; POL, D.

ZOOLOGICAL JOURNAL OF THE LINNEAN SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2017

0024-4082

Gracilisuchus stipanicicorumRomer, 1972a, the only species in its genus, is a small basal suchian,recovered from the Middle?Late Triassic Chañares Formation (La Rioja,Argentina). This species has been interpreted as related to various taxa withinArchosauria, including Ornithosuchidae, Rauisuchidae, and Crocodylomorpha. Recentphylogenetic analyses are concordant in recovering it in a basal positionwithin Suchia, and the most recent analysis recovered it within the clade Gracilisuchidae.Six specimens of G. stipanicicorum areknown and all of them were studied and included in a phylogenetic analysis ofArchosauriformes. Re-examination of the specimens allowed us to improve thediagnosis, identify new diagnostic characters (e.g. first sacral rib with aslight distal expansion relative to the proximal portion), and redescribeespecially the postcranial skeleton. The phylogenetic data matrix is an updatedversion of a previous study with the inclusion of additional characters andtaxa. The strict consensus supports the most recent phylogenetic results, recoveringGracilisuchus as a basal suchian withinGracilisuchidae. The results of this analysis resolve some important polytomiesand yield higher support values than recent analyses. All previous alternative hypotheseson the affinities of Gracilisuchus werefound to be highly suboptimal for the new data matrix.