Vertebral pneumaticity of the North American therizinosaurNothronychus

Nothronychuswas a large, derived therizinosaur from the Upper Cretaceous of Utah and New Mexico. The genus is known from elements that have been referred to single individuals. Therizinosaurs were unusual maniraptoran theropods close to the origin of birds. The axial skeleton is extensively pneumatized, but CT scans reveal an apneumatic synsacrum. Inferred air sacs invade the basicranium, the presacral vertebrae, and the proximal caudal vertebrae, but bypassed the sacrum resulting in a caudosacral hiatus similar to some sauropods and reflecting the development of multiple diverticula from the abdominal air sac. The vertebral pneumatic chambers are described here and compared with those observed in the theropodAllosaurusand the recent avianDinornis. The vertebrae ofNothronychusare intermediate between those two theropods. It is inferred to have possessed avian-like abdominal air sacs. This theropod would have had unidirectional lungs, as in birds, but this character cannot be related to endothermy.

Automated summary

Nothronychus is a large, derived therizinosaur from the Upper Cretaceous of Utah and New Mexico, with extensively pneumatized axial skeleton. It is inferred to have possessed avian-like abdominal air sacs.