The pectoral girdle and forelimb anatomy of the stem-sauropodomorph Saturnalia tupiniquim (Upper Triassic, Brazil)

Description of the pectoral girdle (scapulocoracoid) and forelimb (humerus, radius and ulna) elements of two specimens of Saturnalia tupiniquini, a stem-sauropodomorph from the Upper Triassic Santa Maria Formation, southern Brazil, reveals a distinctive set of plesiomorphic, derived and unique traits, which shed light on the function and phylogenetic significance of these skeletal elements within early dinosaurs. Autapomorphic features of S. tupiniquim include, among others, an unusually long olecranon process of the ulna. Its function is still unclear, but it might have helped to sustain a quadrupedal gait, as inferred from the structure of the entire forearm. Although less clear than previously suggested, some traits of S. tupiniquim, such as a long deltopectoral crest and a broad distal humeral end, are indicative of its sauropodomorph affinity. The taxon also bears several features previously regarded as autapomorphic of Herrerasaurus ischigualastensis, alluding to their broader distribution among basal dinosaurs. Variations within S. tupiniquini are mainly robustness-related and do not necessarily imply taxonomic distinctions.