Unaysaurus tolentinoi is one of the oldest dinosaurs each known. It was discovered in southern Brazil in 1998, and announced in a press meeting on Thursday, December 3, 2004. A member of a collection of plant-eating dinosaurs known as "prosauropods", it is closely connected to a dinosaur found in Germany, which indicates that it was relatively easy for species to spread across the giant landmass of the time, the super continent of Pangaea.

Like most early dinosaurs, Unaysaurus was comparatively small, and walked on two legs. It was only 2.5 meters (8.2 feet) long, 70 to 80 centimeters tall, and weighed about 70 kilograms (155 pounds).

The fossils of Unaysaurus are well potted. They consist of an almost complete skull, complete with a inferior jaw, and partial skeleton with many of the bones still linked to each other in their natural positions. It is one of the most total dinosaur skeletons, and the most complete skull, ever recovered in Brazil.

One big world

Unaysaurus lived about 200 to 225 million years past, in the Carnian to Norian ages of the late Triassic period. It was establish in the south of Brazil, which at the time was connected to northwest Africa. The entire world was united into the great super continent of Pangaea, which was just preliminary to divide into Laurasia in the north and Gondwana in the south.

Unaysaurus was establishing in the southern Brazilian state of Rio Grande do Sul, near the city of Santa Maria. It was improved from the red beds of the Santa Maria Formation (also known as the Caturrita Formation), which is the geologic configuration where similarly old dinosaurs like Saturnalia have been establish. The oldest dinosaurs in the world are from here and close by in Argentina (like the Eoraptor), which suggests that the first dinosaurs may have originated in the area.

Unaysaurus is the first prosauropod exposed in Brazil. Prosauropods are semi-bipedal, herbivorous dinosaurs that are connected to the later and more advanced sauropods, which include some of the biggest creatures ever to walk the Earth, like the Brachiosaurus. Staurikosaurus, a prosauropodomorph (the ancestors of both the prosauropods and sauropods), has been exposed nearby; and it is possible that Teyuwasu barbarenai, another Brazilian dinosaur described in 1999, is also a prosauropod.

Counter to prospect, however, the closest relative of the Unaysaurus is not from South America. It is mostly intimately related to the Plateosaurus, which lived about 210 million years in Germany. This indicates that species were able to travel relatively easily across Pangaea.

Discovery and name

The new species and genus were formally described by Luciano A. Leal, Sergio A. K. Azevodo, Alexander W. A. Kellner, and Átila A. S. da Rosa in the October 18, 2004 issue of the technical journal Zootaxa. The name Unaysaurus comes from the word unay (u-na-hee), meaning "black water" in the local Tupy language, which in turn refers to Agua Negra (also "black water"), the Portuguese name for the area where the fossils were found. The species epithet tolentinoi is named after Tolentino Marafiga, who exposed the fossils by the side of a road in 1998.