Nhandumirim (meaning "small rhea" in the Tupi language) is a genus of basal sauropodomorph dinosaur from the Carnian age of Late Triassic Brazil. It is currently considered a saturnaliid sauropodomorph. The type and only species, Nhandumirim waldsangae, is known from a single immature specimen including vertebrae, a chevron, pelvic material, and a hindlimb found in the Santa Maria Formation in Rio Grande do Sul.
Nhandumirim is differentiated from other Santa Maria dinosaurs such as Staurikosaurus and Saturnalia on the basis of its more gracile, long-legged proportions and several more specific skeletal features. However, it is noteworthy that the holotype of Nhandumirim is an immature individual.
Several features of the tibia led the describers of the genus and species to consider Nhandumirim waldsangae possibly the earliest theropod, but some analyses in their study offer alternative positions within Saurischia.[1] All subsequent studies considered Nhandumirim an early sauropodomorph, closely-associated with Saturnalia and Chromogisaurus.[2][3][4][5][6]
Nhandumirim is known from a single partial skeleton, LPRP/USP 0651, which includes several vertebrae, a right ilium, and most of a right hindlimb. This skeleton was found at the site of Cerro da Alemoa (also known as Waldsanga or Sanga do Mato)[7] in Santa Maria, Rio Grande do Sul. Waldsanga is a historically important Triassic site which also preserved the type specimens of Saturnalia, Rauisuchus, Gomphodontosuchus, and Alemoatherium.[1][7] The site preserves Carnian-age sediments of the Santa Maria Formation, and LPRP/USP 0651 specifically comes from the top of the Alemoa member on that site. The generic name Nhandumirim roughly translates to "small rhea" in the Tupi-Guarani language. The specific name refers to Waldsanga.[1]
The dorsal vertebrae have spool-shaped centra which are about 1.4 times longer than high, making them more elongated than those of herrerasaurids. Several areas on the dorsals are incised, such as the sides of the centrum (which each have a shallow depression) and the rear of the neural arch (which has postzygapophyseal centrodiapophyseal and centrodiapophyseal fossae). There were likely three sacral vertebrae, with at least the first one articulating with the hip akin to the "primordial" first sacral of other reptiles. This contrasts with Saturnalia in which the first sacral vertebra is an incorporated dorsal vertebra without the hallmarks of a primordial sacral. The sacral vertebrae were thick and wide, but not fused to each other or their respective sacral ribs. The most complete sacral rib was fan shaped when seen from above and has a cross section which gradually curves upwards towards the front, also unlike Saturnalia which has a more L-shaped cross section. The caudal vertebrae increase in length and gradually reduce the size of their transverse processes from the base of the tail to the tip. Caudals at the base of the tail have pronounced midline keels along their entire lower edge. This characteristic is seemingly unique to Nhandumirim, as the only other dinosauromorphs with ventral keels in proximal caudals are Dracoraptor (which had paired, not midline, keels) and Efraasia (in which they were restricted to the front third of the centrum). The zygapophyses of the caudals are short, unlike the longer joints of herrerasaurids and neotheropods.[1]