A New Ladinian Nothosauroid (Sauropterygia) From Fuyuan, Yunnan Province, China

Brevicaudosaurus jiyangshanensis, gen. et sp. nov., a new nothosauroid, is established on the basis of two nearly complete skeletons from the Middle Triassic (Ladinian) of China. Its skull is diagnostic in having a wide and constricted snout, a large supratemporal fossa slightly larger than the orbit, and a parietal table strongly constricted posteriorly. Postcranial specializations include a short trunk with 14 dorsal vertebrae, a short tail shorter than the skull-neck region in length, a stout anterolateral process on the clavicle, an extremely massive and broadened mid-diaphysis of the humerus, a strongly expanded proximal head of the ulna, seven ossified carpals, and a phalangeal reduction in the pes. In addition, the strongly pachyostotic postcranial skeleton may indicate a slow mode of swimming underwater and a benthic carnivorous feeding habit for B. jiyangshanensis. Phylogenetically, it is the sister taxon of the Nothosaurus-Lariosaurus clade within Nothosauroidea. The discovery of this new nothosauroid not only contributes to local faunal diversity and expands the known range of sauropterygian life styles during the late Middle Triassic, but also provides a chance to test the phylogenetic relationships of the Eosauropterygia hypothesized by previous studies.