''Unaysaurus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

of unaysaurid sauropodomorph herbivore

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

. Discovered in southern

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

, in the

geopark A geopark is a protected area with internationally significant geology within which sustainable development is sought and which includes tourism, conservation, education and research concerning not just geology but other relevant sciences. In 200 ...

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 Plateosauridae is a family of plateosaurian sauropodomorphs from the Late Triassic of Europe, Greenland, Africa and Asia. Although several dinosaurs have been classified as plateosaurids over the years, the family Plateosauridae is now restricte ...

dinosaurs found in

Germany Germany, officially the Federal Republic of Germany (FRG),, is a country in Central Europe. It is the most populous member state of the European Union. Germany lies between the Baltic and North Sea to the north and the Alps to the sou ...

, which indicates that it was relatively easy for

species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...

to spread across the giant landmass of the time, the

supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", which lea ...

Pangaea Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 millio ...

. The

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s of ''Unaysaurus'' are well preserved. They consist of an almost complete

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, t ...

, 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.

Discovery and naming

''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 The Caturrita Formation is a rock formation found in Rio Grande do Sul, Brazil. Its sediments were deposited in the Paraná Basin. The formation is from the Upper Triassic and forms part of the Santa Maria Supersequence in the upper section of the ...

, which is the geologic formation where similarly old dinosaurs like ''

Saturnalia Saturnalia is an ancient Roman festival and holiday in honour of the god Saturn, held on 17 December of the Julian calendar and later expanded with festivities through to 23 December. The holiday was celebrated with a sacrifice at the Temple o ...

'' have been found. The oldest dinosaurs in the world are from here and nearby in

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, t ...

(like the ''

Eoraptor ''Eoraptor'' () is a genus of small, lightly built, basal sauropodomorph. One of the earliest-known dinosaurs, it lived approximately 231 to 228 million years ago, during the Late Triassic in Western Gondwana, in the region that is now northwest ...

''), 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 ' (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.

Description

Like most early dinosaurs, ''Unaysaurus'' was relatively small, and walked on

two legs In sports (particularly association football), a two-legged tie is a contest between two teams which comprises two matches or "legs", with each team as the home team in one leg. The winning team is usually determined by aggregate score, the sum ...

. It was only long, tall, and weighed about ).

Classification

Upon its description, ''Unaysaurus'' was assigned to the Plateosauridae. Under this assignment, the closest relative of ''Unaysaurus'' was, counter intuitively, not from

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the souther ...

, but rather '' Plateosaurus'', which lived about 210 million years ago in

. However, in 2018, ''Unaysaurus'' was found to belong to the newly erected clade Unaysauridae, alongside '' Macrocollum'' and '' Jaklapallisaurus'', the former of which was from

Paleoecology

''Unaysaurus'' lived between about 225 to 200

million years ago The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds. Usage Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago). ...

, in the

Carnian The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic Series (or earliest age of the Late Triassic Epoch). It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followe ...

or Norian age of the late

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

period. It was found in the south of Brazil, which at the time was connected to northwest

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

. The whole world was united into the great supercontinent of Pangaea, which was just starting to divide into

Laurasia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pan ...

in the north, and

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final st ...

in the south. A U-Pb (

Uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weakly ...

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

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 Dinosauromorpha is a clade of avemetatarsalian archosaurs (reptiles closer to birds than to crocodilians) that includes the Dinosauria (dinosaurs) and some of their close relatives. It was originally defined to include dinosauriforms and lage ...

are represented in the rock of the formation, including the silesaur ''

Sacisaurus agudoensis ''Sacisaurus'' ("Saci lizard") is a silesaurid dinosauriform from the Late Triassic (Norian) Caturrita Formation of southern Brazil. The scientific name, ''Sacisaurus agudoensis'', refers to the city where the species was found, Agudo in the R ...

'', and the coeval sauropodomorph '' Guaibasaurus candelariensis'', all of which are not found anywhere else. The

dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivorous animals with a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, typica ...

'' Jachaleria candelariensis'', an unclassified phytosaur, and isolated teeth of archosaur origin can also be unearthed in the formation. A single

stereospondyl The Stereospondyli are a group of extinct temnospondyl amphibians that existed primarily during the Mesozoic period. They are known from all seven continents and were common components of many Triassic ecosystems, likely filling a similar ecologi ...

amphibian is known from the formation, but has not yet been identified specifically. An extremely rich amount of small

tetrapod Tetrapods (; ) are four-limb (anatomy), limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant taxon, extant and extinct amphibians, sauropsids (reptiles, including dinosaurs and therefore birds) and synapsids (p ...

s have been recovered from the Caturrita Formation, which is quite surprising. They measure less than long. Species preserved are the

procolophonid Procolophonidae is an extinct family of small, lizard-like parareptiles known from the Late Permian to Late Triassic that were distributed across Pangaea, having been reported from Europe, North America, China, South Africa, South America, Antar ...

'' Soturnia caliodon'', the lepidosaur '' Cargninia enigmatica'', the

sphenodontid Rhynchocephalia (; ) is an order of lizard-like reptiles that includes only one living species, the tuatara (''Sphenodon punctatus'') of New Zealand. Despite its current lack of diversity, during the Mesozoic rhynchocephalians were a diverse gro ...

'' Clevosaurus brasiliensis'', and some small

therapsid Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented mor ...

s coexisting with ''

Faxinalipterus minima ''Faxinalipterus'' is a genus of ornithodiran archosaur, originally described as a pterosaur, from the Late Triassic Caturrita Formation of southern Brazil. A study from 2022 reinterpreted the fossil remains and instead suggests them to bel ...

'', a putative pterosaur. The therapsids include '' Riograndia guaibensis'', '' Brasilodon quadrangularis'', and '' Irajatherium hernandezi'' .

References

External links

* * *
Dinosaurs of Rio grande do Sul.
{{Taxonbar, from=Q133130 Sauropodomorphs Dinosaur genera Late Triassic dinosaurs of South America Fossils of Brazil Paleontology in Rio Grande do Sul Triassic Brazil Taxa named by Alexander Kellner Fossil taxa described in 2004