Russian dinosaur. A pathological ulna of a specimen of Amurosaurus riabinini, preserved with a hypertrophied and swollen distal region and with the distal articular surface engulfed within a large overgrowth of newly formed bone, was described from the Maastrichtian Udurchukan Formation (Amur Region, Russia) by Bertozzo et al. (2022), who interpreted the bone as still healing prior to the animal's death, with the misalignment of the fracture and the resulting malunion of the two fragments of the bone probably causing the animal to limp and walk on three limbs. Description Amurosaurus is characterized by many autapomorphies, or unique features, of the skull, as well as the sigmoidal shape of the ulna (a lower arm bone) when viewed from the front or side. Most other known lambeosaurines have hollow crests on the top of their skulls, and although the bones that would make up such a crest are unknown in this dinosaur, the bones of the roof of the skull are modified to support one, so it can be assumed that Amurosaurus was crested as well. Classification The following cladogram on the left shows the results of a phylogenetic analysis of lambeosaur relationships from a 2013 study by Albert Prieto-Márquez and colleagues, showing Amurosaurus as a derived member of the tribe Lambeosaurini. The cladogram on the right depicts the results from a 2014 study by Yuri Bolotsky and colleagues; this study incorporated novel skull material of Amurosaurus which they found to indicate a more primitive spot among lambeosaurs. The 2020 osteological description of the material previously constituting the distinct genus Sahaliyania found the latter genus to be a synonym of Amurosaurus, allowing its newly restudied material to contribute to more robust tests of the classification of Amurosaurus. With this new data, Amurosaurus was found to be a derived member of Lambeosaurinae closely related to Lambeosaurus, something that had been recovered in some previous studies. The cladogram from this study is reproduced below: See also Timeline of hadrosaur research References Late Cretaceous dinosaurs of Asia Lambeosaurines Fossil taxa described in 1991 Taxa named by Sergei Kurzanov Maastrichtian genus first appearances Maastrichtian genus extinctions Ornithischian genera