A successful European vertebrate lineage: The “double-canine” crocodile

The Cenozoic period witnessed numerous turnovers in European fauna and flora composition, by all of which entire clades went extinct on the continent. Among these groups, crocodylians maintained a continuous presence in Europe until the late Neogene. The genus Diplocynodon, particularly, survived for more than 40 Myr and left a very rich fossil record. This genus therefore has the potential to offer rare insights into speciation mechanisms in response to long-term changes in climatic and tectonic contexts. The complex ingroup taxonomy of Diplocynodon, arising from an often perplexingly extensive fossil record, discouraged researchers to work comprehensively on this genus albeit a complete systematic and taxonomic revision is long due. Among Diplocynodon species, Diplocynodon darwini (Ludwig, 1877) is represented by the largest record, made of tens of specimens, but yet critically lacks a detailed and complete osteological description. The species represents an exceptional opportunity to perform an in-depth study of intraspecific variation for an extinct crocodylian taxon. The abundance of excellently preserved specimens from emblematic European Lagerstätten enables the study of ontogenetic variation in temporally restricted populations. Moreover, the rich fossil record provides critical comparative data for a much-needed revision of the species-level taxonomy. The combination of these morphological, temporal and paleogeographical data may allow distinguishing between speciation mechanisms throughout the Cenozoic, as either: allopatry, due to geographical isolation in separate European basins; sympatry, within constrained biogeographical areas; or even anagenesis, if revised topologies reveal a continuous origination/extinction pattern of species.