A new basal tomistomine (Crocodylia, Crocodyloidea) from Issel (Middle Eocene; France): Palaeobiogeography of basal tomistomines and palaeogeographic consequences

Abstract

A skull and mandible of a crocodylian from the late Lutetian of Issel, previously described as 'Atacisaurus glareae' is reconsidered. The holotype of 'A.glareae', a partial mandible, is lost, and the skull cannot be designated as a lectotype for the species. 'Atacisaurus glareae' is thus a nomen dubium. The skull bears a combination of characters, allowing us to assign it to the genus Kentisuchus. It differs from the, until now, only known species Kentisuchus spenceri from the Ypresian of England, in having a more robust snout, with the constriction of the snout at the level of the seventh-eighth teeth being 80% of the largest maxillary width, and not bearing anteroposterior shallow fossae along the lacrimomaxillary sutures. A new species is thus erected, Kentisuchus astreisp.nov. Phylogenetic analysis confirms that the genus Kentisuchus is one of the most primitive tomistomine. The phylogenetic and palaeogeographic distribution suggests that Kentisuchus was isolated in the Atlantic Ocean, and Ebro (Spain) and Aquitaine (France) basins, during the Ypresian, and that the south Pyrenean marine corridor between the Atlantic Ocean and the Tethys could have closed during the early Ypresian, earlier than previously supposed. This could be correlated with the first mammal migrations from the Iberian Peninsula to Southern France. The palaeogeographic distribution of early and middle Eocene tomistomines also suggests the possible presence of a marine corridor between the North Sea and the Central Tethys through the Polish Lowlands Basin during the early Lutetian. This marine corridor could be informative for studies on mammal migration, as the presence of a north-south marine corridor necessarily means there is an absence or less efficient east-west terrestrial passage. This could have consequences on the history of Asian-European mammal migrations.