A paleopathological caudal vertebra of a Lithostrotian Titanosaur (Neosauropoda: Titanosauria) from the Presidente Prudente Formation, Brazil

Abstract

Paleopathological records in vertebrate fossils are quite uncommon. However, they provide key paleobiological insights into lifestyle and behavior. Despite their visibility, studies investigating paleopathologies in dinosaurs, particularly titanosaurs, remain scarce. In Brazil, three paleopathologies have been reported in titanosaurs from the Bauru Basin, and one from the Açu Formation (Potiguar Basin, Early Cretaceous). Here, we report a neoplasm found in a middle caudal vertebra (MCT.LE.4580, Museu de Ciências da Terra-SGB) of a late-diverging titanosaur from the Presidente Prudente Formation (Bauru Basin, Upper Cretaceous). The specimen includes the vertebral centrum and the neural arch but lacks the neural spine and zygapophyses. When compared to taxa with more complete caudal sequences, such as Baurutitan britoi, MCT.LE.4580 can be tentatively identified as a 9th or 10th caudal vertebra due to the limited development of the transverse processes and the anterior displacement of the neural arch. At the anteriormost portion of the vertebral centrum, MCT.LE.4580 exhibits a rounded bone outgrowth with smooth edges and a heavily eroded bone surface, exposing bone trabeculae at the convex end of this button-shaped structure. The bone outgrowth measures 3 cm in diameter. A CT-scan analysis of MCT.LE.4580 provided detailed images revealing an abnormally high density in this bone outgrowth. This abnormality suggests potential irregularities in the ossification process, warranting further investigation through paleohistology to determine the cause and its implications. The combined features presented by MCT.LE.4580 indicate a neoplastic condition in this specimen. Recently, another caudal vertebra from the Presidente Prudente Formation displayed a combination of two neoplasms, an osteoma and a hemangioma, differing from MCT.LE.4580, which has a single neoplasm. As neoplasms are commonly found in the appendicular remains of other titanosaurs, their presence in caudal elements may be associated with biomechanical stress. Biomechanical studies have suggested a pentapodal posture (at least occasionally) for these sauropods, as seen in titanosaurs like Arrudatitan maximus and Trigonosaurus pricei. These studies inferred that both species used part of their tail as support, probably during mating and feeding. Thus, the identification of this neoplasm underscores the importance of continued paleopathological studies and suggests that biomechanical stress might have been associated with the development of these paleopathological conditions. [CNPq 308071/2022-0, FAPERJ E-26/210.536/2019, PROCIÊNCIA - FAPERJ-UERJ, KLNB - FAPERJ E-26/205.002/2022, 2ASB-CNPq 68270/2023-4, CNPq 407158/2022-7, FAPERJ E-26/210.294/2021]