| Unaysaurus | |
|---|---|
 | |
| Skeletal diagram showing known remains | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Bagualosauria |
| Clade: | †Unaysauridae |
| Genus: | †Unaysaurus Lealet al., 2004 |
| Type species | |
| †Unaysaurus tolentinoi Lealet al., 2004 | |
Unaysaurus is agenus of herbivorousunaysauridsauropodomorphdinosaur. Discovered in southernBrazil, in thegeopark of Paleorrota, in 1998, and announced in a press conference on Thursday, December 3, 2004, it is one of the oldest dinosaurs known. It is closely related toplateosaurid dinosaurs found inGermany, which indicates that it was relatively easy forspecies to spread across the giant landmass of the time, thesupercontinent ofPangaea.[1] Thefossils ofUnaysaurus are well-preserved. They consist of an almost completeskull, including alower 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 (including complete skull) ever recovered in Brazil.
Unaysaurus was found in the southern Brazilian state ofRio Grande do Sul, near the city ofSanta Maria. It was recovered from the red beds of theCaturrita Formation, which is the geologic formation where similarly old dinosaurs likeSaturnalia have been found. The oldest dinosaurs in the world are from here and nearby inArgentina (like theEoraptor), which suggests that the first dinosaurs may have originated in the area.
In 2004, Luciano A. Leal, Sergio A. K. Azevodo, Alexander W. A. Kellner, and Átila A. S. da RosadescribedUnaysaurus tolentinoi as a new genus and species on the basis of theholotype specimen UFSM 11069. Thegeneric name, "Unaysaurus", comes from the wordunay (u-na-hee), meaning "black water" in the localTupi language, which in turn refers toAgua Negra (also "black water"), thePortuguese name for the region where the fossils were found. Thespecific name, "tolentinoi" honors Tolentino Marafiga, who discovered the fossils by the side of a road in 1998.[1]
Like most early dinosaurs,Unaysaurus was relatively small, and walked ontwo legs. It was only 2.5 meters (8.2 feet) long, 70 to 80 centimeters (2.3 to 2.6 ft) tall, and weighed about 70 kilograms (150 lb)).
In 2023, Müller and colleagues described the remains of a juvenile specimen ofUnaysaurus that was found associated with the holotype. The bones, including partial vertebrae and various foot material, are similarly proportioned to the bones of the holotype.[2]
Upon its description,Unaysaurus was assigned to thePlateosauridae. Under this assignment, the closest relative ofUnaysaurus was, counter intuitively, not fromSouth America, but ratherPlateosaurus, which lived about 210 million years ago inGermany.[1] However, in 2018,Unaysaurus was found to belong to the newly erected cladeUnaysauridae, alongsideMacrocollum andJaklapallisaurus, the former of which was fromBrazil.[3]
Unaysaurus lived between about 225 to 200 million years ago, in theCarnian or Norianage of the lateTriassicperiod. It was found in the south of Brazil, which at the time was connected to northwestAfrica. The whole world was united into the great supercontinent of Pangaea, which was just starting to divide intoLaurasia in the north, andGondwana in the south.[1] A U-Pb (Uranium decay) dating found that the Caturrita Formation dated around 225.42 million years ago, putting it less than 10 million years younger than theSanta Maria andIschigualasto Formations, from where the earliest dinosaurs are known.[4]
TheCaturrita Formation has uncovered a wide variety of fauna, although the formation is also referred to as the upper portion of theSanta Maria 2 Sequence. Multipledinosauriforms are represented in the rock of the formation, including thesilesaurSacisaurus agudoensis, and the coevalsauropodomorphGuaibasaurus candelariensis,[5] all of which are not found anywhere else.[1] ThedicynodontJachaleria candelariensis, an unclassifiedphytosaur, and isolated teeth of archosaur origin can also be unearthed in the formation. A singlestereospondyl amphibian is known from the formation, but has not yet been identified specifically.[5]
An extremely rich amount of smalltetrapods have been recovered from the Caturrita Formation, which is quite surprising. They measure less than 15 cm (5.9 in) long. Species preserved are theprocolophonidSoturnia caliodon, thelepidosaurCargninia enigmatica, thesphenodontidClevosaurus brasiliensis, and some smalltherapsids coexisting withFaxinalipterus minima, a putative pterosaur. The therapsids includeRiograndia guaibensis,Brasilodon quadrangularis, andIrajatherium hernandezi .[5]
