Crocodyliform remains from the Upper Cretaceous of Central Asia – evidence for one of the oldest Crocodylia?

Abstract

The Late Cretaceous is a key time interval for the understanding of origins and diversification of the crown-group Crocodylia and its extant lineages – Alligatoroidea, Crocodyloidea, and Gavialoidea. Yet, the fossil record of crocodylians in the beginning of the Late Cretaceous is scarce, obscuring the early evolutionary history of the clade. Here I review all known material of long-snouted crocodyliforms from the Upper Cretaceous (Cenomanian–Santonian) of Central Asia. Based on the extensive sampling in the Dzharakuduk locality (Bissekty Formation) and the distinctive anatomy of individual elements, they are referred to the enigmatic taxon Zholsuchus procerus Nessov et Cherepanov, 1989. Comparable specimens from other localities are tentatively attributed to Zholsuchus sp. or cf. Zholsuchus sp. Zholsuchus is herein confirmed as a valid taxon for the first time since its establishment. Based on extensive morphological comparison, I hypothesize that it is potentially a crown-group crocodylian that may be related to Gavialoidea. However, additional material is required to test taxonomic and phylogenetic hypotheses proposed in this study. Zholsuchus is allegedly a medium-sized crocodylian, attaining minimal total body lengths of 2 m and perhaps ranging up to 2.5–3 m. Remains associated with this taxon are rare but consistently recovered in the lower Cenomanian–Santonian deposits of Uzbekistan and Kazakhstan. Zholsuchus, along with Portugalosuchus from Cenomanian of Portugal, may be the oldest presently known crocodylians, which expands the fossil record of the crown-group back into the beginning of the Late Cretaceous and suggests the much earlier origins of the clade than it has been usually acknowledged.