First mandible and deciduous dentition of juvenile individuals of Sinomastodon (Proboscidea, Mammalia) from the Early Pleistocene Renzidong Cave of eastern China

Sinomastodon (Proboscidea, Mammalia) is a unique brevirostrine trilophodont gomphotheriid from Eurasia, which mainly occurs in China during the Plio-Pleistocene. Although much is known about adult individuals, the morphology of juveniles of this taxon is still poorly understood due to the scarcity of pertinent fossils. The present contribution represents the first detailed systematic study of the mandible and deciduous dentition of juvenile individuals of Sinomastodon jiangnanensis from the early Early Pleistocene (2.14–2.15 Ma) Renzidong Cave of eastern China. Based on morphological comparisons, the Renzidong juvenile mandible bears, on one hand, the transitional characteristics between the typical long-jawed trilophodont and elephantoid proboscideans, and, on the other hand, more primitive features than adult mandibles of Sinomastodon. This study of juvenile individuals of S. jiangnanensis provides new information to enhance the diagnosis of S. jiangnanensis, and confirms the validity of the species. It also provides evidence to show that the morphological transition of genus Sinomastodon from Neogene to Quaternary is mirrored in adult and juvenile individuals.