''Riograndia'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

tritheledontid Tritheledontidae, the tritheledontids or ictidosaurs, is an extinct family of small to medium-sized (about 10 to 20 cm long) cynodonts. They were highly mammal-like, specialized cynodonts, although they still retained a few reptile-like ana ...

cynodont The cynodonts () (clade Cynodontia) are a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Cynodonts had a wide variety ...

s from the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch ...

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 southe ...

. The type and only

species In biology, a species is the basic unit of 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 the appropriate s ...

is ''Riograndia guaibensis''. Remains have been found in the

Caturrita Formation The Caturrita Formation is a geological formation, 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 th ...

of 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 20 ...

of Paleorrota. It was a small non-mammalian

, with several advanced features also present in mammals. Several specimens of ''Riograndia guaibensis'' have been found in the towns of Candelária and

Faxinal do Soturno Faxinal do Soturno is a municipality in the state of Rio Grande do Sul, Brazil. See also *List of municipalities in Rio Grande do Sul This is a list of the municipalities in the state of Rio Grande do Sul (RS), located in the South Region of Br ...

in the Caturrita Formation. The genus defines the ''Riograndia'' Assemblage Zone.

Classification

''Riograndia'' is currently classified as a basal

in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Tritheledontidae Tritheledontidae, the tritheledontids or ictidosaurs, is an extinct family of small to medium-sized (about 10 to 20 cm long) cynodonts. They were highly mammal-like, specialized cynodonts, although they still retained a few reptile-like ana ...

. Other tritheledontids include the related ''

Irajatherium ''Irajatherium'' is an extinct genus of cynodonts, known only of the type species ''Irajatherium hernandezi''.Martinelli et al., 2005 It is named in honor of Irajá Damiani Pinto. Species ''Irajatherium hernandezi'' is a species known only by ...

'', and two clades, a more basal group including ''

Sinoconodon ''Sinoconodon'' is an extinct genus of mammaliamorphs that appears in the fossil record of the Lufeng Formation of China in the Sinemurian stage of the Early Jurassic period, about 193 million years ago. While sharing many plesiomorphic traits wi ...

'', ''

Brasilitherium ''Brasilodon'' ("tooth from Brazil") is an extinct genus of small, mammal-like cynodonts that lived in what is now Brazil during the Norian age of the Late Triassic epoch, about 225.42 million years ago. While no complete skeletons have been fo ...

'', ''

Brasilodon ''Brasilodon'' ("tooth from Brazil") is an extinct genus of small, mammal-like cynodonts that lived in what is now Brazil during the Norian age of the Late Triassic epoch, about 225.42 million years ago. While no complete skeletons have been foun ...

'', and ''

Morganucodon ''Morganucodon'' (" Glamorgan tooth") is an early mammaliaform genus that lived from the Late Triassic to the Middle Jurassic. It first appeared about 205 million years ago. Unlike many other early mammaliaforms, ''Morganucodon'' is well represe ...

'', and a more

derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...

clade of '' Chaliminia'', '' Elliotherium'', ''

Pachygenelus ''Pachygenelus'' is an extinct genus of tritheledontid cynodonts. Fossils have been found from the Karoo basin in South Africa and date back to the Early Jurassic. ''Pachygenelus'' had both an articular- quadrate and dentary-squamosal jaw joint ...

'', ''

Diarthrognathus ''Diarthrognathus'' ("Two joint jaw") is an extinct genus of tritheledontid cynodonts, known from fossil evidence found in South Africa and first described in 1958 by A.W. Crompton.Rieppel, Olivier. Evolutionary Theory and the Creation Controvers ...

'', and ''

Tritheledon ''Tritheledon'' is an extinct genus of cynodonts that lived during the Lower Jurassic. Fossils were found in the Elliot Formation, South Africa. Like all cynodonts, it had many traits shared by mammals. Tritheledonts were probably insectivores, ...

''. The below cladogram was found by Martinelli and Rougier in

2007 File:2007 Events Collage.png, From top left, clockwise: Steve Jobs unveils Apple's first iPhone; TAM Airlines Flight 3054 overruns a runway and crashes into a gas station, killing almost 200 people; Former Pakistani Prime Minister of Pakistan, Pr ...

and modified by Soares ''et al.'' in

2011 File:2011 Events Collage.png, From top left, clockwise: a protester partaking in Occupy Wall Street heralds the beginning of the Occupy movement; protests against Libyan dictator Muammar Gaddafi, who was killed that October; a young man celebrate ...

, with Tritheledontidae added after Ruta ''et al.'' (2013):

Paleoecology

All specimens of ''Riograndia'' come from the

aged

. The formation dates to about 225

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). ...

, and it based in the present-day country of

Brasil 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 an ...

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 ...

s from the formation only include the

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 lon ...

s ''

Unaysaurus ''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 ...

'' and ''

Guaibasaurus ''Guaibasaurus'' is an extinct genus of basal saurischian dinosaur known from the Late Triassic Caturrita Formation of Rio Grande do Sul, southern Brazil. Most analyses recover it as a sauropodomorph, although there are some suggestions that it ...

''. Non-dinosaurian

animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...

s include the

dinosauriform 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 lager ...

Sacisaurus ''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 ...

''; 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, typicall ...

Jachaleria ''Jachaleria'' was a dicynodont herbivore that lived from the Ladinian to Norian stages of the Middle to Late Triassic, from approximately 240 to 220 million years ago. ''Jachaleria'' was one of the last representatives of the dicynodonts, occ ...

''; an unnamed

phytosauria Phytosaurs (Φυτόσαυροι in greek) are an extinct group of large, mostly semiaquatic Late Triassic archosauriform reptiles. Phytosaurs belong to the order Phytosauria. Phytosauria and Phytosauridae are often considered to be equivalent ...

n; isolated archosaurian teeth; an

amphibia Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arbore ...

n classified in

Stereospondyli 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 ...

; and many common

tetrapods Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids (reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct therapsids ...

smaller than long. Among the tetrapods is 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, Antarc ...

Soturnia ''Soturnia'' is an extinct genus of procolophonid parareptile. It is known from rocks of the Late Triassic-age Caturrita Formation of the municipality of Faxinal do Soturno in the geopark of Paleorrota, Brazil. ''Soturnia'' was named in 2003 by ...

''; the sphenodontid ''

Clevosaurus ''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 ...

''; the

lepidosauria The Lepidosauria (, from Greek meaning ''scaled lizards'') is a subclass or superorder of reptiles, containing the orders Squamata and Rhynchocephalia. Squamata includes snakes, lizards, and amphisbaenians. Squamata contains over 9,000 species, m ...

n ''

Cargninia ''Cargninia'' is an extinct genus of basal lepidosauromorph from the Late Triassic of Brazil. The type and only known species is ''Cargninia enigmatica''. It is known from the holotype UFRGS PV 1027 T, a partial left dentary (lo ...

''; the pterosaurian '' Faxinalipterus'', and an assortment of mammaliamorphs including ''Riograndia'', ''Brasilodon'', and ''Irajatherium''.

References

External links

*
''Dinossauros do Rio grande do Sul''
*

{{Portal bar, Brazil, Paleontology Tritheledontidae Prehistoric cynodont genera Carnian genera Late Triassic synapsids of South America Triassic Brazil Fossils of Brazil Paraná Basin Fossil taxa described in 2001 Taxa named by José Bonaparte