Pneumatic Structures in Murusraptor Barrosaensis (Theropoda: Megaraptora), a Large-Bodied Predator Theropod From the Upper Cretaceous of Patagonia

Megaraptora is a clade of tetanuran theropod dinosaurs of uncertain phylogenetic affinity. Members of the constituent family Megaraptoridae are notable for their extreme skeletal pneumaticity. This is exemplified in Murusraptor barrosaensis from the Sierra Barrosa Formation of Patagonia, Argentina. We describe the postcranial pneumaticity of Murusraptor providing naked eye observations and CT scans of internal structures, comparing them with other megaraptorids and other theropod taxa, including birds. Murusraptor, as with other megaraptorids, exhibits pneumaticity patterns that are repeated along the vertebral sequence (e.g., centrum with a central camara surrounded by camellate tissue). However, Murusraptor is unique, given the presence of exposed camellate tissue in the neural spines and two pneumatic foramina in the pubis connected to the iliac peduncle in the ilium. Compared with other related taxa, Murusraptor possesses a pneumaticity pattern intermediate between tyrannosauroids (camellate tissue) and allosauroids (camerae). The exposed camellate tissue in the neural spine may correspond to a "multiple foramina" pattern present only in avian theropods; however, in birds, this feature is found in the neural canal. Further studies of this kind are needed to unravel the paleobiology of this enigmatic group of theropods.