Caracterización histológica y osteológica de la neumaticidad en la región caudal del titanosaurio Rocasaurus muniozi (Sauropoda: Titanosauria).

Abstract

Saltasaurini is a derived clade of titanosaurian sauropods whose members are characterized by their small size, dermal ossicles, and a high development of postcranial pneumaticity. Such pneumaticity is generally recognized by osteological correlates, although recently it has been proposed that it can be identified at the histological level through the presence of pneumosteal tissue (or pneumosteon). In addition, postcranial pneumaticity can be measured at the morphological level through the calculation of the aerial space proportion (ASP), which indirectly infers the space of the osseous element occupied with air. The following bachelor’s degree final project focuses on the osteological and histological correlates of caudal vertebrae assigned to Rocasaurus muniozi, a saltasaurine from the Late Cretaceous of the Allen Formation, from the locality of Salitral Moreno, of the Rio Negro Province in the Argentinian Patagonia. The objectives of the work proposed here are to identify pneumosteal tissue within internal or external cavities, in order to increase its register; to analyze differences regarding its development among the internal structure types (i.e. camellate tissue and camerae); and to compare the ASP value between transversal and longitudinal sections, to evaluate if a preference for the type of orientation in the section exists. In order to achieve these objectives, histological sections were made and observed afterwards with a petrographic microscope. Additionally, tomographic sections were obtained and digitally processed using the software Adobe Photoshop, and the ASP calculation was developed by the software ImageJ. As a result of the histological analysis, for the first time in the caudal series of a titanosaurian sauropod a potential register of pneumosteon was recognized, located in endosteal trabecular bone associated to camellate tissue. Regarding the ASP analysis, the values vary between 0.64-0.68 for the MPCA-Pv-SM 47 element; between 0.51-0.56 in the MPCA-Pv-SM 46/9; and between 0.48-0.5 for the MPCA-Pv-SM 605 vertebrae. The ASP value difference between transversal and longitudinal sections is 0.02-0.04. In conclusion, it was also found that there is no preferred section orientation for developing the ASP analysis.