中国中三叠世富源巨胫龙(主龙型小纲,长颈龙科)的骨骼学再描述

Over the past decades, an increasing number of reptiles have been described from the Middle Triassic of southern parts of China. Marine reptiles such as thalattosaurs, ichthyosaursand sauropterygians dominated these paleofaunas and are known to have had a Tethys-wide distribution. Indeed, several species have been described from both the eastern and western margins of that ancient ocean. The last addition to this list was a less common terrestrial reptile, Macrocnemus fuyuanensis, first discovered in Yunnan Province. The species was also tentatively inferred to be represented by a single disarticulated specimen in the paleofauna from the World Heritage Site of Monte San Giorgio in southern Switzerland (as Macrocnemus aff. fuyuanensis). The initial referral was mainly based on limb proportions and ratios rather than on discrete osteological characters, partially due to a limited anatomical description of the holotype specimen of M. fuyuanensis. Here we provide a re-description of the anatomy of the complete skeleton of the holotype and compare it with the available referred specimens. Our re-analysis shows that the pectoral girdle of the holotype specimen is more complete than previously reported, revealing the shape of the interclavicle, which is only partially exposed in the only referred specimen from China but well-preserved in the specimen from Europe. The interclavicle of M. fuyuanensis can be distinguished from M. bassanii by its short and fusiform posterior process and anterior facing rod-like processes that extend from a common base enclosing a narrow V-shaped median notch, among other features, and is here inferred to be the most important bone for discriminating species of Macrocnemus, apart from the limb ratios. We further document in detail the cranial anatomy of the holotype, which is virtually identical to that of the crania of M. bassanii, and due to its exquisite preservation and preparation, it adds important information on the palate, which was previously poorly known for Macrocnemus.