Paleocene resurrection of a crocodylomorph taxon: Biotic crises, climatic and sea level fluctuations

Abstract

Postcranial material of a crocodylomorph from the Danian of Oulad Abdoun Basin (Morocco) is described. Several characters, in particular the shape of its dorsal osteoderms, allows its attribution to Pholidosauridae. Up till now, the latest known pholidosaurid was Terminonaris, from the Early Turonian of North America, so, the Moroccan pholidosaurid extends the stratigraphic range of the group to more than 20 million years younger, and shows that the pholidosaurids survived the K-Pg crisis. The reevaluation and the phylogenetic analysis of Dakotasuchus kingi, Woodbinesuchus byersmauricei, and Sabinosuchus coahuilensis, previously considered as goniopholidids and dyrosaurid, respectively, revealed rather that they are pholidosaurids. This analysis also suggests that at least two independent pholidosaurid lineages reached the Maastrichtian, among which one crossed the K-Pg boundary. This study proposes the first analysis of tethysuchian diversity from the Late Jurassic to the Early Paleogene. Two diversity peaks are observed during the Oxfordian and Cenomanian, two stages of high paleotemperatures evaluated with the δ18O. The tethysuchian diversity strongly decreases after the Cenomanian, a decline that may be correlated with the “Ocean Anoxic Event” (OAE 2), which caused the strong marine faunal turnover during the Cenomanian-Turonian time interval. The large Turonian-Coniacian oceanic regression could also be a factor in the tethysuchian decline. After that, tethysuchian diversity remains low until the Maastrichtian-lower Paleocene marine tethysuchian dyrosaurid diversification, correlated with the Late Cretaceous-Paleocene transgression. At least one pholidosaurid lineage crossed the K-Pg boundary, confirming the weak impact of this crisis on the crocodylomorphs. Pholidosaurids seem to go extinct at the beginning of the Paleocene, possibly due to the strong radiation of dyrosaurids in marine environments and crocodylians in fresh-water during this time period.