First occurrence of polymicrobial ulcer in dinosaurs

Abstract Evidence of palaeopathological bone lesions in large-sized ornithopod dinosaurs is nowadays increasing significantly. However, most of these lesions are documented in derived ornithopods such as hadrosaurs, while pathologies associated with other styracosternans are scarcely documented. Here we document the occurrence of a palaeopathological lesion in a long bone of the iconic Iguanodon bernissartensis from the late Barremian Arcillas de Morella Formation (eastern Spain). The pathological long bone, a tibia, exhibits an anomalous overgrowth area at the midshaft covering part of its posteromedial side. Gross examination reveals a smooth and swollen surface with a well-defined lobulated morphology while computed tomography scan reveals a moderate cortical expansion (hyperdense subperiosteal bone area). Based on a differential diagnosis, including traumatic fracture callus, neoplastic growths and infections, the bone lesion is consistent with a pathological periosteal reaction and cortical thickening caused by a skin ulceration in an advanced stage affecting the osseous tissue. This is, to our knowledge, the first report of this type of pathological response to a bacterial infection in a dinosaur.