Analysis of fused mid-caudal vertebrae of the titanosaur Uberabatitan ribeiroi (Dinosauria) from the Late Cretaceous of Brazil

AGUSTIN MARTINELLI; PEDRO MORAIS FONSECA; CAMILA LOURENCINI CAVELLANI; LUIZ CARLOS RIBEIRO; MARA FERRAZ; VICENTE TEIXEIRA

Ituiutaba

Simposio; 1st Brazilian Dinosaur Symposium; 2013

Two fused mid-caudal vertebrae referred to the titanosaur Uberabatitan ribeiroi Salgado & Carvalho (CPPLIP-1020, specimen B) were analyzed in detail. This specimen was found at Serra da Galga Site, located about 25km north of Uberaba city (Minas Gerais State, Brazil) on a road cut of the Federal Highway BR-050, coming from rocks of the Marília Formation (Bauru Group, Late Cretaceous). CPPLIP-1020 consists of two fused procoelous mid-caudal vertebrae with ossified longitudinal ligaments (tendons) and overgrown bone on both lateral sides. CT scan exhibits a total fusion of the vertebral bodies, without empties cavities, suggesting ossification of the annulus fibrosus and intervertebral disc. In addition, the zygapophyseal processes of CPPLIP-1020 were affected. The right prezygapophysis is extremely large in comparison to the left one, having a healing fracture callus. The antero-medial surface is fused to the neural arch of the anterior vertebra, without articulation and antero-laterally to the postzygapophysis. Studies on fused amphicoelous caudals in Jurassic sauropods (e.g., Camarasaurus, Diplodocus) have shown that this condition is a physiologic (diffuse idiopathic skeletal hyperostosis ?DISH) rather than a pathological (e.g., traumatic osteoarthritis). In the mentioned dinosaurs, there is only ossification of longitudinal ligaments without affecting the annulus fibrosus, the intervertebral disc, and the zygapophyseal processes. In contrast, the condition observed in CPPLIP-1020 likely illustrates that these features involve ossification of longitudinal ligaments plus the annulus fibrosus and the intervertebral disc, affecting also the zygapophyses. This association of traits in CPPLIP-1020 indicates a pathology in specimen B of Uberabatitan produced by a traumatism at this portion of the tail rather than a physiological result