A new choristodere (Reptilia: Choristodera) from an Aptian-Albian coal deposit in China

摘要

Choristoderes are a small clade of freshwater aquatic reptiles known from deposits of Jurassic-Miocene age. They show their greatest diversity in the Early Cretaceous of Asia, with seven recorded genera including longirostrine and brevirostine taxa, long- and short-necked taxa, and representatives of both neochoristoderes and non-neochoristoderes. The latter, informal grouping, comprising Monjurosuchus, Philydrosaurus, Hyphalosaurus, Khurendukhosaurus and, probably, Shokawa, is distinguished by the closure of the lower temporal fenestra. This differentiates them from typically diapsid stem choristoderes like the Jurassic Euramerican Cteniogenys and from all neochoristoderes like Champsosaurus and Simoeodosaurus. The recent description of Coeruleodraco jurassicus from the Callovian/Oxfordian of China provided the first example of an Asian non-neochoristodere with an open lower temporal fenestra. Here, we describe a second, geologically younger, genus and species from the Shahai Formation of Badaohao locality in western Liaoning, considered to be Aptian-Albian in age. This adds an eighth choristodere genus to the Early Cretaceous Asian record. The new species shares the diapsid skull morphology of C. jurassicus, demonstrating that a lineage of small, brevirostrine choristoderes with fully diapsid skulls persisted in Asia until the latter part of the Early Cretaceous.