Paleopathology of a putative colossosaurian caudal vertebra (Neosauropoda: Titanosauria) from the Presidente Prudente Formation, Brazil

Studies investigating paleopathologies in sauropods remain scarce despite their relative abundance in the fossil record. In this study we report new occurrence of paleopathological features, corresponding to a neoplasm found in a middle caudal vertebra (MCT.R.2120) of an advanced titanosaur from the Presidente Prudente Formation (Bauru Basin, Upper Cretaceous). At the posteriormost portion of the vertebral centrum, the specimen exhibits a rounded bone callus outgrowth with smooth edges and a heavily eroded periosteum, exposing bone trabeculae at the apex of this knob-like structure. The bone callus measures 30 mm transversely, and 18 mm anteroposteriorly in the ventral view. We conducted a computed tomography analysis of the specimen, which revealed a compact and homogeneous central portion in the callus, with higher density than the surrounding bone tissue. Paleohistopathological analysis further showed a core of fibrolamellar bone with longitudinal vascular canals and secondary osteons, surrounded by irregular globular vascularization and avascular fibrous tissue at the periphery. These microstructural features are consistent with a benign, actively remodeling neoplastic process. Thus, these combined features strongly indicate a neoplastic condition in the studied specimen. As neoplasms are commonly found in the appendicular remains of other titanosaurs, their presence in caudal elements may indicate distinct causes from previous occurrences, such as biomechanical stress as contributing factors. Biomechanical studies have suggested a pentapodal posture (at least occasionally) for these sauropods, which would use part of their tail as support during mating and feeding. Thus, the new occurrence of a neoplasm in titanosaurs not only underscores the importance of continued paleopathological studies but also suggests that biomechanical stress might have played a significant role in developing these conditions.