Redescription of Rayososaurus agrioensis Bonaparte (Sauropoda, Diplodocoidea), a rebbachisaurid from the early Late Cretaceous of Neuquén

Abstract

The material belonging to the holotype of Rayososaurus agrioensis Bonaparte is redescribed. The great development of the acromion process, directed in a markedly posterior direction, and the ventral margin of the scapula with a strong ventrodistal expansion, interpreted as autapomorphies of the taxon, justify the validity of the species. Although the material is rather fragmentary, the racquet-shaped scapula, the distal expansion positioned at the same height as the proximal expansion, and the well-developed acromion process allow the taxon to be included within Rebbachisauridae. At the same time, the angle of less than 90̊ between the coracoid articulation and the scapular blade, together with the great development of the acromion process of the scapula, justify its inclusion in a clade situated as a sister group of Cathartesaura. On the basis of the stratigraphic calibration of the phylogenetic analysis, an important diversification event of the rebbachisaurids is deduced during the Hauterivian-Barremian. In this context, the presence of two monophyletic groups, one of which comprises African-European taxa and the other South American taxa, would place the definitive separation of South America and Africa within this time interval.