Pathological ulna of Amurosaurus riabinini from the Upper Cretaceous of Far Eastern Russia

Bone fractures are the most common type of injuries preserved in the dinosaur fossil record. Poor healing of deep lesions could lead to infection and misalignment of the fracture parts, causing the animals to limp and jeopardising their survival. A wide variety of fossilised fractures have been identified in dinosaur remains, and the type of bone response can provide information about their resilience and ability to survive even major traumatic events. Here we describe a pathological ulna of the lambeosaurine dinosaur Amurosaurus riabinini, from the Udurchukan Formation (Maastrichtian, Upper Cretaceous) of Blagoveshchensk (Amur Region, Russia). Its distal region is hypertrophied and swollen, and the distal articular surface is engulfed within a large overgrowth of newly formed bone. CT-scanning identifies an oblique fracture resulting from an impact, implying that the swollen portion corresponds to callus formation. The bone was still healing prior to the moment of death, although the misalignment of the fracture parts appears to have resulted in a malunion of the two fragments. During locomotion, the wrist would have suffered from a continuous weight-bearing pressure that placed stress upon the fracture site and probably caused the animal to limp and perhaps walk on three limbs.