A Late Cretaceous salamander (Caudata, Hynobiidae) from Jilin Province, China, and the taxonomically informative atlas in modern amphibians

Our knowledge of the origin and early evolution of salamanders has benefited greatly from Asian Mesozoic taxa: stem salamanders are known from the Late Triassic to Early Cretaceous of Central and North Asia, and the earliest crown salamanders mainly from the Middle Jurassic to Early Cretaceous of East Asia. No salamanders of Late Cretaceous age have previously been reported from East Asia, hindering our understanding of this crucial time interval when modern salamander families originated. Here we report a new salamander, Changchunerpeton nonganensis gen. et sp. nov., based on computed tomography analyses of an atlantal centrum and four partial long bones from the Upper Cretaceous (Campanian) Nenjiang Formation in Nongan County, Jilin Province, China. The atlantal centrum bears a number of diagnostic features of the primitive salamander family Hynobiidae, including the presence of the spinal nerve foramen, interglenoid tubercle wide and dorsoventrally thin, continuous articular facet on the anterior and lateral faces of interglenoid tubercle, and the spinal cord support extending anterodorsally. This information fills a c . 110 myr gap in the hynobiid fossil record between the Early Cretaceous (Aptian) and Late Miocene (MN9). Evolutionary and developmental patterns of the commonly preserved atlas in fossil lissamphibians are summarized. The interglenoid tubercle has an absent, small to large evolutionary trend in early lissamphibians and its presence is possibly linked to the importance of the centrum in vertebral development. Spinal cord supports in the atlas are found in salamanders and caecilians, and their location and orientation are informative in lissamphibian taxonomy.