''Unaysaurus'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of unaysaurid

sauropodomorph Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lo ...

herbivore

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

. Discovered in southern

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

, in the

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

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 Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...

, which indicates that it was relatively easy for

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

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 continent, continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", ...

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 period approximately 335 mi ...

. 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 preserve ...

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

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

, complete with a

lower jaw In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

, 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 Rio Grande do Sul (, ; ; "Great River of the South") is a Federative units of Brazil, state in the South Region, Brazil, southern region of Brazil. It is the Federative units of Brazil#List, fifth-most populous state and the List of Brazilian s ...

, 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 Saturnalia is an Roman festivals, ancient Roman festival and holiday in honour of the List of Roman deities, god Saturn (mythology), Saturn, held on 17 December in the Julian calendar and later expanded with festivities until 19 December. By t ...

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

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

(like the ''

Eoraptor ''Eoraptor'' () is a genus of small, lightly built, Basal (phylogenetics), basal sauropodomorpha, sauropodomorph dinosaur. One of the earliest-known dinosaurs and one of the earliest sauropodomorphs, it lived approximately 231 to 228 million yea ...

''), 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 Rosa described ''Unaysaurus tolentinoi'' as a new genus and species on the basis of the

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

specimen UFSM 11069. The generic 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 specific name, "''tolentinoi''" honors 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. It was only long, tall, and weighed about ). In 2023, Müller and colleagues described the remains of a juvenile specimen of ''Unaysaurus'' 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.

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 considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

, but rather ''

Plateosaurus ''Plateosaurus'' (probably meaning "broad lizard", often mistranslated as "flat lizard") is a genus of plateosaurid dinosaur that lived during the Late Triassic period, around 214 to 204 million years ago, in what is now Central and Northern Eu ...

'', which lived about 210 million years ago in

. However, in 2018, ''Unaysaurus'' was found to belong to the newly erected clade Unaysauridae, alongside ''

Macrocollum ''Macrocollum'' is a genus of unaysauridae, unaysaurid sauropodomorph dinosaur that lived during the Late Triassic period (geology), period (early Norian) in what is now Brazil. It is one of the oldest dinosaurs known. Discovery and naming ''Mac ...

'' and '' Jaklapallisaurus'', the former of which was from

Paleoecology

''Unaysaurus'' lived between about 225 to 200

million years ago Million years ago, abbreviated as Mya, Myr (megayear) or Ma (megaannum), is a unit of time equal to (i.e. years), or approximately 31.6 teraseconds. Usage Myr is in common use in fields such as Earth science and cosmology. Myr is also used w ...

, in the

Carnian The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227.3 ...

or Norian

age Age or AGE may refer to: Time and its effects * Age, the amount of time someone has been alive or something has existed ** East Asian age reckoning, an Asian system of marking age starting at 1 * Ageing or aging, the process of becoming older ...

of the late

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

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. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

. 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 Pa ...

in the north, and

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

in the south. A U-Pb (

Uranium Uranium is a chemical element; it has chemical symbol, 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. Ura ...

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 the silesaur '' Sacisaurus agudoensis'', and the coeval

'' 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 herbivores that typically bore a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, t ...

'' Jachaleria candelariensis'', an unclassified

phytosaur Phytosaurs (Φυτόσαυροι in Greek, meaning 'plant lizard') are an extinct group of large, mostly semiaquatic Late Triassic archosauriform or basal archosaurian reptiles. Phytosaurs belong to the order Phytosauria and are sometimes ref ...

, 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

tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...

s have been recovered from the Caturrita Formation, which is quite surprising. They measure less than long. Species preserved are the procolophonid '' Soturnia caliodon'', the lepidosaur '' Cargninia enigmatica'', the sphenodontid ''

Clevosaurus brasiliensis ''Clevosaurus'' (meaning "Gloucester lizard") is an extinct genus of rhynchocephalian reptile from the Late Triassic and the Early Jurassic periods. Species of ''Clevosaurus'' were widespread across Pangaea, and have been found on all continents ...

'', and some small therapsids coexisting with '' Faxinalipterus minima'', 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 Unaysauridae Dinosaur genera Norian dinosaurs Taxa named by Alexander Kellner Fossil taxa described in 2004 Dinosaurs of Brazil