Taxonomic position of Oxemys gutta Nessov, 1977, a problematic turtle from the Upper Cretaceous of Uzbekistan, and basisphenoid morphology in some groups of Late Mesozoic turtles of Asia

The holotype (basisphenoid) of Oxemys gutta Nessov, 1977, a problematic skull-based turtle taxon from the Khodzhakul Formation (Lower Cenomanian, Upper Cretaceous, Uzbekistan) is redescribed and its systematic position is reviewed. The literature and original morphological data on the basisphenoid complex of some Late Mesozoic turtles of Asia are discussed. A list of 14 characters of the basisphenoid complex, many of which have never been used in phylogenetic reconstructions, is provided. A comparison of O. gutta with other Late Mesozoic turtle taxa of Asia based on these characters shows that it is most similar to members of Macrobaenidae/Sinemydidae and Lindholmemydidae. The analysis of possible associations of O. gutta with shell-based turtle taxa known from the Khodzhakul Formation suggests that it most likely belongs to Macrobaenidae/Sinemydidae.