Osteohistology of Uberabatitan ribeiroi (Dinosauria, Sauropoda) provides insight into the life history of titanosaurs

Abstract

The Serra da Galga Formation is a geological unit that has provided a taxonomically diverse fossil record for the Late Cretaceous of Brazil. The formation highlights the richest evidence of titanosaurs in this country, with a handful of described species, (e.g. Uberabatitan ribeiroi). Over time, palaeobiological works based on the osteohistology of fossils are becoming more frequent. However, U. ribeiroi has never been the subject of a purely histological study. We performed osteohistological descriptions of specimens referred to this species. The results support that the hyper-elongated cervical ribs of U. ribeiroi are tendons that have developed through metaplasia, as occur in other neosauropods. Further, samples show rapid and uninterrupted growth, evidenced by a continuous deposit of fibrolamellar tissue. Subsequently, growth would have ceased with the appearance of periodic interruptions (at least in appendicular bones), in the most advanced stages of development. The variable presence of an external fundamental system reveals that not all the specimens studied here reached somatic maturity. Finally, the high degree of bone remodelling described in the samples, especially in the ribs, is higher than expected for other neosauropods in the same ontogenetic stages. This supports the previous idea that this feature would be typical of Titanosauria.