The first adocid turtle in South Korea (Lower Cretaceous) and the early evolution of the Adocidae

Abstract

An adocid turtle was collected from the Lower Cretaceous Hasandong Formation, representing the first occurrence of the Adocidae in South Korea. The specimens consist of moderately preserved hard shells (carapace and plastron) with a limb bone (humerus). They turned out to be a new taxon named Proadocus hadongensis, gen. et sp. nov., characterized by combining synapomorphic characters of adocids and primitive characters ancestrally retained from basal pantrionychians. The pattern of marginal scales extension and pygal shape are shared with Sinaspideretes wimani and Basilochelys macrobios, the basal pantrionychian taxa of the Late Jurassic–Early Cretaceous in Southeast Asia. A cladistic analysis places it as the most basal taxon in Adocidae. Such phylogenetic position of Proadocus involves important implications about the origin and early evolution of the Adocidae. First, Proadocus supports the Southeast Asian origin of this family. Secondly, a new paleobiogeographic analysis, including Proadocus in Korea, requests a new interpretation of the adocid diversification and dispersion in East Asia during the Early Cretaceous.