Cretaceous trionychids of asia: An expanded review of their record and biogeography

This chapter presents an expanded review of all described and/or figured specimens and taxa of trionychids from the Cretaceous (Barremian to Maastrichtian) of Asia. Cretaceous occurrences in Asia are limited to indeterminate trionychids and to the subfamily Trionychinae; cyclanorbines are unknown and previous reports of plastomenids are based on misidentified trionychine material. For the Trionychinae, we recognize 13 taxa of uncertain placement within the subfamily (“Aspideretes” maortuensis, four species of Khunnuchelys, “Paleotrionyx” riabinini, “Trionyx” kansaiensis and “T.” kyrgyzensis, and Trionychinae indet. 1–5), seven taxa within the tribe Trionychini (“Amyda” menneri and “Am”. orlovi, “Aspideretes” alashanensis, Aspideretoides riabinini and Aspideretoides sp., and Trionychini indet. 1 and 2), and three taxa within the subtribe Apalonina (Apalonina indet. 1–3). We also recognize Sinamyda and four indeterminate taxa as Trionychidae incertae sedis. Although two other tribes (Ulutrionychini and Rafetini) have been proposed to include some Asian Cretaceous trionychines, monophyly of those tribes has yet to be satisfactorily demonstrated. During the Cretaceous, earlier and more basal trionychids (i.e., trionychines with eight neurals) were more broadly distributed across Asia, whereas later and more derived taxa had more restricted ranges. The recognition of Aspideretoides spp. and three indeterminate Apalonina in the Cretaceous of Asia provides evidence for a shared history with North American trionychids.