New material of Mongolemys elegans Khosatzky and Mlynarski, 1971 (Testudines: Lindholmemydidae), from the Late Cretaceous of Mongolia with comments on bone histology and phylogeny

Mongolemys elegans Khosatzky and Mlynarski, 1971, is a freshwater lindholmemydid turtle that is very abundant in Late Cretaceous (Maastrichtian) pond deposits from the Gobi Desert of Mongolia. Here, we present new data on the morphology, bone histology, and phylogenetic position of M. elegans based on hatchlings, juveniles, and adults collected by American Museum of Natural History and the Mongolian Academy of Sciences joint field expeditions at the Bugin Tsav locality. Phylogenetic analysis using a morphological dataset supports the placement of M. elegans as a stem testudinoid. Bone histology of M. elegans shows similar patterns of thickness and bone tissue type for the internal and external cortexes as in other freshwater turtles. Microstructural samples of fossil bone from M. elegans show exceptional preservation of osteocyte lacuno-canicular networks, and higher values of osteocyte density at the external cortex in contrast to cancellous bone and the internal cortex.