Osteology ofKlamelisaurus gobiensis(Dinosauria, Eusauropoda) and the evolutionary history of Middle-Late Jurassic Chinese sauropods

Fossil-rich deposits from the Middle and Late Jurassic of China have yielded a diverse array of sauropod dinosaurs, including numerous species referred toMamenchisaurusandOmeisaurus. Despite an abundance of fossils and a proliferation of taxa, the anatomy of Middle-Late Jurassic Chinese sauropods remains poorly documented. Here, we comprehensively redescribe and illustrateKlamelisaurus gobiensisfrom the Middle-Late Jurassic Shishugou Formation of northwest China. Phylogenetic analyses conducted under parsimony and time-calibrated Bayesian optimality criteria consistently recoverKlamelisaurusas a member of a predominantly Chinese radiation of exceptionally long-necked eusauropods that includesMamenchisaurusspp.,Chuanjiesaurus,QijianglongandWamweracaudia. In most analyses, this lineage also includesEuhelopus, reviving a 'traditional' Euhelopodidae and calling into question the macronarian affinities ofEuhelopus.Klamelisaurusshares several features withEuhelopusthat are unique to a subset of East Asian taxa or rare among sauropods, including a convex ventral margin of the prezygodiapophyseal lamina in middle-posterior cervical vertebrae, a ventrally bifurcated postzygodiapophyseal lamina in posterior cervical vertebrae, and development of a rugose projection extending anteriorly from the epipophysis into the spinodiapophyseal fossa in most cervical vertebrae. Anatomical comparisons of the cervical vertebrae ofKlamelisaurusto several other sauropodomorphs and insights from myological studies of extant archosaurs strongly suggest that this latter structure, often considered part of an epipophyseal-prezygapophyseal lamina, is an epaxial muscle scar that is distinct from pneumatic structures of the lateral surface of the neural spine. The phylogenetic and comparative anatomical data presented here provide a foundation for future revision of the taxonomy and systematics of sauropods from the Junggar and Sichuan basins.