Rinconsaurus

Abstract: RECORD OF AN AEOLOSAURINI DINOSAUR (SAUROPODA, TITANOSAURIA) IN THE UPPER CRETACEOUS (PLOTTIER FORMATION) OF NORTHERN NEUQUEN PROVINCE, ARGENTINA, AND COMMENTS ON THE SOUTH AMERICAN AEOLOSAURINI. The clade Aeolosaurini is represented by several specimens found, so far, only in Argentina and Brazil. The material reported here corresponds to a sauropod titanosaur consisting of four incomplete anterior caudal vertebrae, from the Narambuena Paleontological Site, Rincon de los Sauces, Neuquen Province, Argentina. The specimen comes from the Plottier Formation (late Coniacian-lower Santonian, Upper Cretaceous), Neuquen Group. The specimen has a combination of features that includes it into the clade Aeolosaurini: anterior caudal centra with anterodorsal margin bent forward; prezygapophyses elongated in anterior caudal, in correlation with the extreme displacement of the neural arch forward; and anteroposteriorly elongated articular facets of prezygapophyses, at least in the anterior caudals. However, it differs from other Aeolosaurini by having postzygapophysis with anteroposteriorly short articular facets, not as elongated in the prezygapophyses. This specimen corresponds not only to the fi rst discovery of an Aeolosaurini in the north of the Neuquen Basin (because Rinconsaurus caudamirus Calvo & Gonzalez Riga has been included in another clade, Rinconsauria), but also the oldest record of the group.

Abstract: Abstract. Titanosaurs were the predominant herbivores during the Late Cretaceous, inhabiting all continents. This clade was especially diverse in South America with some of the largest and smallest sauropod species known to date. Despite its diversity, the evolution of this clade is far from being well-known, although some recent analyses have begun to find some consensus in their results. Rinconsauria (defined as the least inclusive clade containing Rinconsaurus and Muyelensaurus) includes small titanosaurs and is considered as closely related to the lineage of giant titanosaurs, Lognkosauria (defined as the least inclusive clade containing Futalognkosaurus and Mendozasaurus), both being part of the recently named clade Colossosauria. The titanosaur Rinconsaurus caudamirus, from the Bajo de la Carpa Formation (Santonian), Río Negro, Argentina, is represented by several axial and appendicular elements from at least four specimens. This taxon was only briefly described when it was named and most of its originally proposed autapomorphies are now recognized as having a more widespread distribution amongst titanosaurs. Herein we present a detailed osteological description of the axial skeleton and a revised diagnosis for this taxon that firmly establishes its validity. Based on comparisons with other titanosaurs, we found three new possible autapomorphies for the axial skeleton of Rinconsaurus, which added to its original combination of characters, endorsing this taxon as a valid genus. Besides, this revision of Rinconsaurus provides additional osteological data that will contribute to a better resolution of titanosaur phylogeny, contributing at the same time to our understanding of the clade Rinconsauria.

Abstract: The discovery of Muyelensaurus pecheni gen. et sp.nov., a new slender titanosaurid, is relevant from anatomical and systematic viewpoints. The specimens come from the Upper Cretaceous strata of the Portezuelo Formation (Turonian-Early Coniacian) at Loma del Lindero, Rincon de los Sauces area, Neuquen Province, Argentina. The remains include a braincase, cervical, dorsal, sacral and caudal vertebrae, and numerous appendicular bones. It is characterized by the following association of autapomorphies: basal tubera diverge 70 degrees from each other; thin and concave lamina that unit basal tubera ventrally, basioccipital condyle wider than the proximal portion of the basal tubera; posterior dorsal neural spines with large prespinal lamina reinforced by two small accessory laminae, distal end of pubic blade rectangular and medially thick. A cladistic phylogenetic analysis placed Muyelensaurus pecheni gen. et sp.nov. and Rinconsaurus caudamirus in a new eutitanosaur clade named herein Rinconsauria. This new clade include middle-sized sauropods different from Aeolosaurini, Opisthocoelicaudiinae or Saltasaurinae taxa.