New osteological information from a ‘juvenile’ specimen of Yunguisaurus (Sauropterygia; Pistosauroidea)

Abstract

An articulated ‘juvenile’ skeleton of Yunguisaurus liae (Sauropterygia; Pistosauroidea) reveals new osteological features of the taxon, such as the supraoccipital, epipterygoid, the interclavicle, the ischium and a complete tail. Irregular variations of vertebral morphology are recognized in the tail within the single individual. Comparison with previously described conspecific specimens suggests additional diagnostic feature of the temporal bar, a constant difference of the positions of posterior end of the neck defined by different features, and intraspecific variability or ontogenetic plasticity in the proportion of clavicular arch and coracoids. The morphology of braincase elements indicates the reduction of epipterygoid, as well as the presence of an open occiput as is typical for plesiosaurs and differs from nothosauroids. Most of the tarsals and phalanges are ossified in the new specimen but ossification of carpals is delayed as in many other diapsids. Mesopodial ossification varies among similarly-sized individuals.