Re-assessment of the Late Jurassic eusauropod dinosaur <i>Hudiesaurus sinojapanorum</i> Dong, 1997, from the Turpan Basin, China, and the evolution of hyper-robust antebrachia in sauropods

<i>Hudiesaurus sinojapanorum</i> is a Late Jurassic sauropod from northwestern China that was erected on the basis of a cervicodorsal vertebra, four teeth, and a nearly complete forelimb. However, re-evaluation of this material, and comparisons with other taxa, indicate that there are few grounds for regarding these specimens as congeneric. Consequently, although we retain the vertebra as the holotype specimen of <i>Hudiesaurus</i>, the forelimb is assigned to a new taxon—<i>Rhomaleopakhus turpanensis</i>, gen. et sp. nov. The teeth previously referred to <i>Hudiesaurus</i> are poorly preserved but resemble those of several other ‘core <i>Mamenchisaurus</i>-like taxa’ (CMTs) from East Asia, such as <i>Mamenchisaurus sinocanadorum</i>. Phylogenetic analyses confirm that <i>Hudiesaurus</i> is a CMT and the sister taxon of <i>Xinjiangtitan</i>. Despite some uniquely shared features, their large size, and close geographic provenance, <i>Hudiesaurus</i> and <i>Xinjiangtitan</i> are retained as distinct genera based on their stratigraphic separation and numerous anatomical differences. <i>Rhomaleopakhus</i> is also shown to be a CMT in all analyses, being most closely related to <i>Chuanjiesaurus</i> and <i>Analong</i>. We link the convergent evolution of robust antebrachia and an enlarged olecranon in CMTs, titanosaurs, and some ornithischians (e.g., ceratopsids) to a more flexed orientation of the forearm, an enhanced role for the forelimb in locomotion, and an anterior shift in the whole-body center of mass. CMTs and titanosaurs potentially converged on a feeding strategy in which the ability to increase browse height via bipedal rearing was sacrificed in return for more efficient locomotion that improved travel between patchily distributed food sources.