Unaysaurus is a genus of unaysaurid sauropodomorph herbivore dinosaur. Discovered in southern Brazil, in the geopark 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 to plateosaurid dinosaurs 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.
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 (including complete skull) ever recovered in Brazil.
|Skeletal diagram showing known remains|
Leal et al., 2004
Leal et al., 2004
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.
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.
Like most early dinosaurs, Unaysaurus was relatively small, and walked on two 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)).
Upon its description, Unaysaurus was assigned to the Plateosauridae. Under this assignment, the closest relative of Unaysaurus was, counter intuitively, not from South America, but rather Plateosaurus, which lived about 210 million years ago in Germany. However, in 2018, Unaysaurus was found to belong to the newly erected clade Unaysauridae, alongside Macrocollum and Jaklapallisaurus, the former of which was from Brazil.
Unaysaurus lived between about 225 to 200 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. 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 the Santa Maria and Ischigualasto Formations, from where the earliest dinosaurs are known.
The Caturrita Formation has uncovered a wide variety of fauna, although the formation is also referred to as the upper portion of the Santa Maria 2 Sequence. Multiple dinosauriforms are represented in the rock of the formation, including Sacisaurus agudoensis, the sauropodomorph Unaysaurus tolentoi, and the saurischian Guaibasaurus candelariensis, all of which are not found anywhere else. The basal archosaurs Jachaleria candelariensis (a dicynodont), an unclassified phytosaur, and isolated teeth of archosaur origin can also be unearthed in the formation. A single stereospondyl amphibian is known from the formation, but has not yet been identified specifically.
An extremely rich amount of small tetrapods have been recovered from the Caturrita Formation, which is quite surprising. They measure less than 15 cm (5.9 in) long. Species preserved are the procolophonid Soturnia caliodon, the lepidosaur Cargninia enigmatica, the sphenodontid Clevosaurus brasiliensis, and some small mammals coexisting with Faxinalipterus minima, a pterosaur. The mammals include Riograndia guaibensis, Brasilodon quadrangularis, Brasilitherium riograndensis, Irajatherium hernandezi and Minicynodon maieri.
The Anchisauria were a clade of sauropodomorph dinosaurs that lived during the Late Triassic and Early Jurassic. The name Anchisauria was first used by Galton and Upchurch in the second edition of The Dinosauria. Galton and Upchurch assigned two families of dinosaurs to the Anchisauria: the Anchisauridae and the Melanorosauridae. The more common prosauropods Plateosaurus and Massospondylus were placed in the sister clade Plateosauria.
However, recent research indicates that Anchisaurus is closer to sauropods than traditional prosauropods; thus, Anchisauria would also include Sauropoda.The following cladogram simplified after an analysis presented by Blair McPhee and colleagues in 2014.Averostra
Averostra, or "bird snouts", is a clade that includes most theropod dinosaurs that have a promaxillary fenestra (fenestra promaxillaris), an extra opening in the front outer side of the maxilla, the bone that makes up the upper jaw. Two groups of averostrans, the Ceratosauria and the Orionides, survived into the Cretaceous period. When the Cretaceous–Paleogene extinction event occurred, ceratosaurians and two groups of orionideans within the clade Coelurosauria, the Tyrannosauroidea and Maniraptoriformes, were still extant. Only one subgroup of maniraptoriformes, Aves, survived the extinction event and persisted to the present day.Avetheropoda
Avetheropoda, or "bird theropods", is a clade that includes carnosaurians and coelurosaurs to the exclusion of other dinosaurs.Cerapoda
Cerapoda ("ceratopsians and ornithopods") is a clade of the dinosaur order Ornithischia.Dinosauriformes
Dinosauriformes is a clade of archosaurian reptiles that include the dinosaurs and their most immediate relatives. All dinosauriformes are distinguished by several features, such as shortened forelimbs and a partially to fully perforated acetabulum, the hole in the hip socket traditionally used to define dinosaurs. The oldest known member is Asilisaurus, dating to about 245 million years ago in the Anisian age of the middle Triassic period.Jaklapallisaurus
Jaklapallisaurus is a genus of unaysaurid sauropodomorph dinosaur. It lived during the Late Triassic period (late Norian to earliest Rhaetian) in what is now Andhra Pradesh, central India. It is known from the holotype ISI R274, postcranial material which was collected from the Upper Maleri Formation (late Norian–earliest Rhaetian) of the Pranhita–Godavari Basin and from the referred material ISI R279, partially complete right femur which was collected from the Lower Dharmaram Formation (latest Norian–Rhaetian). It was first named by Fernando E. Novas, Martin D. Ezcurra, Sankar Chatterjee and Tharavat S. Kutty in 2011 and the type species is Jaklapallisaurus asymmetrica. The generic name is derived from the Indian town of Jaklapalli which is close to the type locality. The specific name refers to the highly asymmetrical astragalus of this species in distal view. A cladistic analysis by Novas et al. found that all valid plateosaurid species form a large polytomy. Jaklapallisaurus was found along with the basal sauropodomorph Nambalia, a guaibasaurid, and two basal dinosauriforms.Jeholosauridae
Jeholosaurids were herbivorous neornithischian dinosaurs from the Cretaceous Period (Aptian - Santonian, with a possible Campanian record) of Asia. The family was first proposed by Han et al. in 2012. The jeholosaurids were defined as those ornithischians more closely related to Jeholosaurus shangyuanensis than to Hypsilophodon foxii, Iguanodon bernissartensis, Protoceratops andrewsi, Pachycephalosaurus wyomingensis, or Thescelosaurus neglectus. The Jeholosauridae includes the type genus Jeholosaurus and Yueosaurus.Jingshanosaurus
Jingshanosaurus (meaning "Jingshan lizard") is a genus of sauropodomorph dinosaurs from the early Jurassic period.Macrocollum
Macrocollum is a genus of unaysaurid sauropodomorph dinosaur that lived during the Late Triassic period (early Norian) in what is now Brazil. It is one of the oldest dinosaurs known.Melanorosauridae
The Melanorosauridae were a family of sauropodomorph dinosaurs which lived during the Late Triassic and Early Jurassic. The name Melanorosauridae was first coined by Friedrich von Huene in 1929. Huene assigned several families of dinosaurs to the infraorder "Prosauropoda": the Anchisauridae, the Plateosauridae, the Thecodontosauridae, and the Melanorosauridae. Since then, these families have undergone numerous revisions. Galton and Upchurch (2004) considered Camelotia, Lessemsaurus, and Melanorosaurus members of the family Melanorosauridae. A more recent study by Yates (2007) indicates that the melanorosaurids were instead early sauropods.Mussaurus
Mussaurus (meaning "mouse lizard") is a genus of herbivorous sauropodomorph dinosaur that lived in southern Argentina during the Late Triassic, about 215 million years ago. It receives its name from the small size of the skeletons of juvenile and infant individuals, which were once the only known specimens of the genus. However, since Mussaurus is now known from adult specimens, the name is something of a misnomer; adults possibly reached 6 metres (20 ft) in length and weighed more than 1,000 kilograms (2,200 lb). Mussaurus possesses anatomical features suggesting a close, possibly transitional evolutionary relationship with true sauropods.Neotheropoda
Neotheropoda (meaning "new theropods") is a clade that includes coelophysoids and more advanced theropod dinosaurs, and the only group of theropods who survived the Triassic–Jurassic extinction event. Yet all of the neotheropods became extinct during the early Jurassic period except for Averostra.Orionides
Orionides is a clade of tetanuran theropod dinosaurs from the Middle Jurassic to the Present. The clade includes most theropod dinosaurs, including birds.Orodrominae
Orodrominae is a subfamily of parksosaurid dinosaurs from the Cretaceous of North America and Asia.Paleontological Site of Agua Negra
Paleontological Site of Agua Negra is located in the Agua Negra in the city of São Martinho da Serra, Rio Grande do Sul, Brazil. The site is approximately 8 kilometers from the city of Santa Maria. Site belongs to the region paleorrota. Here was found Unaysaurus.Riojasauridae
Riojasauridae is a family of sauropod-like dinosaurs from the Upper Triassic. It is known primarily from the genera Riojasaurus and Eucnemesaurus. Sites containing Riojasauridae include the Lower Elliot Formation of Orange Free State, South Africa (where fossils of Eucnemesaurus have been found), and Ischigualasto, in La Rioja Province, Argentina ( where fossils of Riojasaurus have been recovered).Sarahsaurus
Sarahsaurus is a genus of basal sauropodomorph dinosaur which lived during the lower Jurassic period in what is now northeastern Arizona, United States.Unaysauridae
Unaysauridae is a family of basal sauropodomorphs from the Late Triassic of India and Brazil.Xixiposaurus
Xixiposaurus is a genus of prosauropod dinosaur which existed in what is now Lower Lufeng Formation, China during the lower Jurassic period. It was first named by Sekiya Toru in 2010 and the type species is Xixiposaurus suni.