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

Since its definition, Rinconsauria has been considered a titanosaurian clade more deeply nested than Lognkosauria and closely related to Aeolosaurini. However, some recent analyses include Lognkosauria within Rinconsauria, with other studies suggest that its specifiers, Rinconsaurus caudamirus and Muyelensaurus pecheni, are not particularly closely related, thereby affecting its taxonomic composition. This discrepancy may be a consequence of several different factors, from insufficient description of their anatomy, missing data, or even the presence of multiple species amongst the materials referred to Muyelensaurus. Recently, Rinconsaurus caudamirus was reviewed, but Muyelensaurus pecheni still requires a thorough re-evaluation. 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. The presence of repeated remains with varied morphologies indicates that there is more than one taxon amongst the materials of Muyelensaurus indicating that the specie is a chimeric assemblage. Consequently, we restrict Muyelensaurus pecheni to the holotype specimen only. Our osteological study modified an autapomorphic character of its diagnosis: a braincase with the basal tuber with a divergence angle of 90°. 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 all analyses, the instability of Muyelensaurus affected the taxonomic content of Rinconsauria. Therefore, we redefined Rinconsauria as the most inclusive clade containing Rinconsaurus caudamirus but not Mendozasaurus neguyelap or Gondwanatitan faustoi.