Metaceratodus kaopen comb. nov. and M. wichmanni comb. nov., two Late Cretaceous South American species of an austral lungfish genus (Dipnoi)

Abstract

Metaceratodus wollastoni, an Australian species, was reported from Late Cretaceous beds of Patagonia in 1997. Later, three new species (Ceratodus wichmanni, Ptychoceratodus kaopen and Ptychoceratodus cionei), based on scarce material, were described. Finally, two of these species were referred to genus Ferganoceratodus. After examining much more abundant and better-preserved material, we suggest that neither the occurrence of the species Metaceratodus wollastoni nor that of genera Ptychoceratodus and Ferganoceratodus in the Cretaceous of South America is supported. In this paper, we consider that C. wichmanni and P. cionei are synonyms and we reassign the three putative species to genus Metaceratodus under two new combinations: M. kaopen comb. nov. and M. wichmanni comb. nov. Both differ from the other species of the genus because specimens have occlusal pits over most of the occlusal surface and a different tooth plate occlusal profile, and most have four ridges in the lower and upper tooth plates. M. wichmanni differs from M. kaopen in several features. M. kaopen is known from the late Santonian–early Campanian of Anacleto Formation at Río Negro province and M. wichmanni from late Campanian–early Maastrichtian units of Chubut, Río Negro, Neuquén and Mendoza provinces, Argentina. The occurrence of Metaceratodus in southern South America corroborates a close biogeographical relationship with Australia in the latest Cretaceous.