The palate and choanae structure of the Susisuchus anatoceps (Crocodyliformes, Eusuchia): phylogenetic implications

PeerJ. 2018 Aug 10:6:e5372. doi: 10.7717/peerj.5372. eCollection 2018.

Abstract

Crocodyliformes is a group with a broad fossil record, in which several morphological changes have been documented. Among known transformations the most iconic is perhaps the series of changes seen in the structural evolution of the choanae. The change in the position of the choanae was important during the evolutionary history of the Crocodyliformes. This structure is relevant in the phylogenetic position of many crocodyliforms. The new skull of Susisuchus anatoceps from the Crato Formation of the Santana Group (Lower Cretaceous) is described and the preservation in the ventral view allows character encoding not yet observed for the species. The new specimen shows a typical eusuchian palate for Susisuchus anatoceps, in which the choana is fully enclosed by the pterygoid. The Susisuchidae clade has been placed in different phylogenetic positions: as a sister group of Eusuchia, advanced Neosuchia and in Eusuchia. In Isisfordia there are reports that the choana of this taxon is or is not fully enclosed by the pterygoid. The encoding of the ventral characters of S. anatoceps places Susisuchidae in Eusuchia. However, this position must be further studied, since the matrices showed fragility in the reconstitution of the Neosuchia-Eusuchia transition.

Keywords: Araripe Basin; Crocodyliformes; Eusuchia; Lower Cretaceous.

Grants and funding

This work was financially supported by CAPES (doctorate scholarship) and CNPq of Brazil (no 462381/2014-5 and no 310168 / 2016-3). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.