Osteological reassessment of Muyelensaurus pecheni (Dinosauria: Sauropoda): Systematics and its phylogenetic implications for the clade Rinconsauria

Abstract

Since its definition, Rinconsauria has been considered a clade more derived than Lognkosauria and closely related to Aeolosaurini, although some recent analyses include Lognkosauria within it. Additionally, some studies suggest that its specifiers, Rinconsaurus caudamirus and Muyelensaurus pecheni, are more distantly related, altering its taxonomic composition. This discrepancy may be due to the insufficient description of their anatomy. Recently, Rinconsaurus caudamirus was reviewed, but Muyelensaurus pecheni still required a thorough reevaluation. This titanosaur from the Late Cretaceous (Plottier Formation) was discovered at the Loma del Lindero site in the northeast of the Neuquén Province. Here, we present a detailed description of its holotype, paratypes, and originally referenced remains. Our osteological study modified an autapomorphic character of its diagnosis: the basal tuber with a divergence angle of 90°. Additionally, the presence of repeated remains with varied morphologies confirms that the paratype is a chimeric assemblage. In the present analysis, only the holotype of Muyelensaurus pecheni was included in six phylogenetic analyses using three independent datasets, under both equal weights and extended implied weights approaches. In five analyses, the instability of Muyelensaurus affected the stability of Rinconsauria, though in four analyses, taxa grouped around Rinconsaurus. Therefore, we redefined Rinconsauria as the most inclusive clade containing Rinconsaurus caudamirus but not Mendozasaurus neguyelap or Gondwanatitan faustoi.