Deciphering causes and behaviors: A recurrent pattern of tail injuries in hadrosaurid dinosaurs.

Elevated frequencies of repeated injuries are identified in the proximo-middle caudal region of hadrosaurid dinosaur tails. The affected vertebrae show healing injuries in the distal region of the vertebral neural spines, but the causes are yet indeterminate. A finite element analysis was performed on a modeled caudal vertebral series to test if such injuries were caused by loading weight. Our results indicate that the deforming stress resulted from the same dorsal force pressing upon a large area of the tail. We scrutinized all possible biological scenarios that could cause the pathological deformation of the bones. The affected area corresponds to the putative position of the cloacal opening, indicating the possibility that the dorsal force might correspond to the action of a mounting male. As such, these potential mating injuries may represent the first indirect evidence of sexual behavior in non-avian dinosaurs, and a novel approach to recognize female individuals.