Postcranial osteology of the giant oviraptorosaur Gigantoraptor erlianensis

Gigantoraptor erlianensis is an unexpectedly large-bodied oviraptorosaurian dinosaur from the Late Cretaceous of Inner Mongolia, China. Exhibiting a bizarre body plan, G. erlianensis is key to revealing the high morphological disparity and complex evolutionary history near the transition to birds. However, the briefness of the original article and poorly known caenagnathid materials back at the time of description hinder thorough evaluation on the evolutionary significance of its features. Subsequently, only the mandible of the holotype was further described and analyzed from a functional perspective, whereas our knowledge of the postcranial features remains limited. Here we provide a detailed osteological description of the postcranial skeleton of the G. erlianensis holotype, and compare it with other oviraptorosaurians—especially caenagnathids—under updated understanding of their anatomical features. Our study identified numerous features similar to the caenagnathids and oviraptorids. While the new information in general supports its phylogenetic placement as an early-diverging caenagnathid, it also demonstrates the complex evolutionary history in Caenagnathoidea (Caenagnathidae + Oviraptoridae). Aside from these, several features unique to G. erlianensis, including the medially deflected metatarsal II and proportionately long pedal digit IV, add to an increasing evidence of the morphological disparity among oviraptorosaurians as well as coelurosaurian dinosaurs.