Paleobiology of Rinconsaurus caudamirus and Muyelensaurus pecheni (Sauropoda, Titanosauria) from the Neuquén Group, Upper Cretaceous of Argentina: inferences from long bone histology

Abstract

Titanosauria is the most successful and diverse clade of sauropodomorph dinosaurs, with some of the largest and smallest sauropod species known to date. Rinconsaurus caudamirus and Muyelensaurus pecheni were two small-sized titanosaurs recollected from the Neuquén Group (Upper Cretaceous) of Argentina. The bone remains of both specimens include axial and appendicular elements corresponding to several individuals. These taxa have been anatomically and phylogenetically studied, but did not analyzed from paleohistological viewpoint yet. This contribution focuses on the description of the long bone histology of both species including several aspects of its paleobiology. For this, thin transverse sections were made at the diaphysis level and were analyzed under microscope. The histology of M. pecheni and R. caudamirus shows a uniform bone microstructure similar to other titanosaurs, with changes in bone tissue types being mostly related to the different life story. The major difference between the taxa is in the type of bone matrix. Whereas woven fibered bone predominates in the cortex of M. pecheni, R. caudamirus shows parallel-fibered bone. The presence of this last primary tissue is consistent with the reduced size of R. caudamirus. The long bone histology of M. pecheni resembles that of large basal neosauropods. Contrary to the reported for other noesauropods, the data obtained in this study does not reveal a correlation between the ontogenetic stage and the body size in R. caudamirus and M. pecheni. Finally, as was mentioned previously to others titanosaurs, both specimens show a high rate of secondary remodeling.