A new turtle from the Xiagou Formation (Early Cretaceous) of Changma Basin, Gansu Province, P. R. China

Changmachelys bohlini gen. et sp. nov., from the Lower Cretaceous Xiagou Formation, Changma Basin, north-western Gansu Province, adds to our understanding of the diversity and distribution of Early Cretaceous turtles in Asia. Changmachelys bohlini is similar to Early Cretaceous turtles from Asia included in “Macrobaenidae” in having a low domed carapace and a reduced, cruciform plastron with buttresses that do not extend onto the costals. With a carapace that exceeds 34 cm in length, it is one of the largest Early Cretaceous “macrobaenids”. Despite the addition of this new taxon and new characters to previous phylogenetic analyses, the relationships of “macrobaenid” turtles remain poorly resolved. In addition to adding to the diversity of “macrobaenid” turtles in the Early Cretaceous of Asia, Changmachelys bohlini is of interest because each of the four available specimens documents a distinct stage of ontogenetic development of the shell. In the carapace, the dermal portions of the costals are unossified in the most juvenile specimen but peripherals are present. In contrast with the late ossification of the dermal bone of the carapace, the plastron ossifies relatively early.