Soft-shelled turtles (Trionychidae) from the Cenomanian of Uzbekistan

Localities from the Cenomanian of Uzbekistan are the oldest in Middle Asia and Kazakhstan to preserve two broadly sympatric species of trionychid turtle. Material described here comes from multiple Cenomanian formations from the Itemir locality, and from multiple localities in the Cenomanian Khodzhakul Formation. The first taxon from the locality, “Trionyx” cf. kyrgyzensis, has multiple morphological similarities with the older, Early Cretaceous “Trionyx” kyrgyzensis. In contrast, the second taxon, “Trionyx” dissolutus, has multiple similarities with “Trionyx” kansaiensis, one of two species of trionychid found in younger Late Cretaceous localities. “Trionyx” dissolutus bears some superficial resemblance to other trionychid taxa within the clade Plastomenidae because of its highly ossified plastron with a hyoplastral lappet and an epiplastral notch. However, Plastomenidae is diagnosed primarily through characters that are absent or cannot be observed in the available material of “T.” dissolutus, and other shared features are plesiomorphic. In addition, “T.” dissolutus shares other synapomorphies with Trionychinae. A heavily ossified plastron may be more homoplastric within Trionychidae than has been previously recognized. Finally, we provide an improved understanding of the subtle similarities and differences between several closely related Cretaceous turtle assemblages of Middle Asia and Kazakhstan.