Several abnormal caudal vertebrae are described in an indeterminate sauropod specimen from ?Middle—Late Jurassic strata of Niger. The anterior and posterior articular surfaces of caudal vertebrae 7–11 exhibit erosive perforations (‘holes’) of the subchondral compact bone into the trabecular bone of the vertebral centrum. Additionally, the vertebral centra of caudal vertebrae 17 and 18 are fused and show a bulging mass of abnormal bone growth, most probably caused by infection. The erosive lesions of the anterior tail vertebrae closely resemble the morphological and radiological characteristics of Schmorl's nodes in humans and other mammals, in which the gel-like nucleus pulposus of the intervertebral discs penetrates through the endplate into the cancellous bone of the vertebral body and creates an erosive cavity of mushroom-like shape. The diagnosis of Schmorl's nodes in this sauropod, however, would be incompatible with the extant phylogenetic bracket and osteological correlates that suggest that dinosaurs had no intervertebral discs. Rather, they possessed synovial joints with a joint space filled with synovial fluid between adjacent vertebral centra. Therefore, the lesions can best be interpreted as subchondral cysts and as an analog of Schmorl's nodes in synovial joints. Similar to Schmorl's nodes, the regular pattern and location of the lesions suggest that the cysts were caused by axial stress. One may hypothesize that the fusion of caudals 17 and 18 led to altered mechanical loading that may have facilitated rupture of the articular cartilage and subchondral bone and forced synovial fluid into the spongiosa of the vertebral centra.
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