Osteology and histology of a Plateosaurus trossingensis (Dinosauria: Sauropodomorpha) from the Upper Triassic of Switzerland with an advanced chronic pathology

Abstract The sauropodomorph Plateosaurus is one of the best-known dinosaurs from Europe due to the large numbers of articulated skeletons discovered from bonebed horizons in Switzerland and Germany. Plateosaurus exhibits high degrees of developmental plasticity, which makes investigations of specimen life-histories from gross morphology alone difficult. Furthermore, comparatively few specimens have been rigorously examined for possessing any evidence of pathology, i.e., injury or disease, that could provide insight into how these dinosaurs lived. Here, we provide an osteological description of a nearly complete Plateosaurus trossingensis (excavation ID SMF 18.1, collection NMZ 1000001) from the Late Triassic Klettgau Formation from Frick, Switzerland, with an unusual pathology in its right scapula and proximal portion of the right humerus. We also perform histological analyses on two dorsal ribs to investigate the relative ontogenetic stage and life history of the specimen and investigate the morphology and aetiology of its scapula-humerus pathology using Micro-Computed Tomography and comparisons with a previously undescribed Plateosaurus from Frick (SMF 11.4; comprising left and right radii and ulnae) that exhibits pathological tissues. We infer that NMZ 1000001 was an adult of around 23–25 years of age when it died. We estimate a total body length of around 7.7 m, making NMZ 1000001 one of the largest known specimens from Frick and an above average-sized adult for the species overall. The scapula-humerus pathology is characterised by highly rugose surface textures, possible element fusion and extensive remodelling of internal bone structures. We infer the pathology to be a chronic case of osteomyelitis (bone tissue infection). Based on the size and extent of the infected area it is likely one of most advanced cases known from the fossil record. We further document the process of producing an exhibit with a museum-grade life reconstruction based on the pathological fossil.