Craniomandibular osteology of Macrocollum itaquii (Dinosauria: Sauropodomorpha) from the Late Triassic of southern Brazil

Several new sauropodomorphs have been described in recent years, including the unaysaurid sauropodomorph Macrocollum itaquii (Late Triassic, Brazil). This study presents a detailed description of the craniomandibular anatomy of M. itaquii based on the holotype, a paratype and a newly referred specimen. A phylogenetic analysis using an updated dataset is performed to test a previous hypothesis regarding the affinities of this taxon and its potential influence in the phylogeny of Triassic and Early Jurassic sauropodomorphs. The taxon is supported as a member of Unaysauridae. This clade is recovered as the basal-most group within Massopoda rather than the sister group to Plateosauria. However, the position of M. itaquii (and unaysaurids) is likely to be highly labile due to specific, transitional aspects of its anatomy. The most recently discovered M. itaquii specimen, in conjunction with other newly discovered specimens, serve to elucidate the transition from slender basal sauropodomorphs to more robust derived members within this group.