Unaysaurus

Unaysaurus is a genus of sauropodomorph dinosaur, and is one of the oldest dinosaurs known. It was discovered in southern Brazil, in the geopark of paleorrota, in 1998, and announced in a press conference on Thursday, December 3, 2004. A member of a group of plant-eating dinosaurs known as "prosauropods", it is closely related 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 supercontinent of Pangaea.

Like most early dinosaurs, Unaysaurus was relatively small, and walked on two legs. It was only 2.5 meters long (8.2 ft), 70 to 80 centimeters tall (2 to 3 ft), and weighed about 70 kilograms (155 lb).

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

Biogeography
Unaysaurus lived between about 200 to 225 million years ago, in the Carnian or Norian age of the late Triassic period. It was found in the south of Brazil, which at the time was connected to northwest Africa. The whole world was united into the great supercontinent of Pangaea, which was just starting to divide into Laurasia in the north, and Gondwana in the south.

Unaysaurus was found in the southern Brazilian state of Rio Grande do Sul, near the city of Santa Maria. It was recovered from the red beds of the Caturrita Formation, which is the geologic formation where similarly old dinosaurs like Saturnalia have been found. The oldest dinosaurs in the world are from here and nearby in Argentina (like the Eoraptor), which suggests that the first dinosaurs may have originated in the area.

Unaysaurus is the first prosauropod discovered in Brazil. Prosauropods were semi-bipedal, herbivorous dinosaurs that are related to the later and more advanced sauropods, which include some of the largest creatures ever to walk the Earth, like the Brachiosaurus. Staurikosaurus, another early dinosaur, has been discovered nearby, and it is possible that Teyuwasu, another Brazilian dinosaur described in 1999, is also a prosauropod.

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

Discovery and name
The new species and genus were officially 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 scientific journal Zootaxa. The name Unaysaurus comes from the word unay (u-na-hee), meaning "black water" in the local Tupi language, which in turn refers to Agua Negra (also "black water"), the Portuguese name for the region where the fossils were found. The species epithet tolentinoi is named after Tolentino Marafiga, who discovered the fossils by the side of a road in 1998.