Riograndia

Riograndia Temporal range: Late Triassic, 225 Ma PreЄ Є O S D C P T J K Pg N ↓
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Synapsida
Order:	Therapsida
Suborder:	Cynodontia
Clade:	Prozostrodontia
Family:	†Tritheledontidae
Genus:	†Riograndia Bonaparte et al., 2001
Type species
†Riograndia guaibensis Bonaparte et al., 2001

Riograndia is a genus of tritheledontid cynodont from the Late Triassic of South America. The type and only species is Riograndia guaibensis. Remains have been found in the Caturrita Formation of the geopark of Paleorrota. It was a small non-mammalian cynodont several advanced features also present in mammals. Several specimens of Riograndia guaibensis have been found in the towns of Candelária and Faxinal do Soturno in the Caturrita Formation.

Classification

Riograndia is currently classified as a basal genus in the family Tritheledontidae. Other tritheledontids include the related Irajatherium, and two clades, a more basal group including Sinoconodon, Brasilitherium, Brasilodon, and Morganucodon, and a more derived clade of Chaliminia, Elliotherium, Pachygenelus, Diarthrognathus, and Tritheledon. The below cladogram was found by Martinelli and Rougier in 2007 and modified by Soares et al. in 2011, with Tritheledontidae added after Ruta et al. (2013):

	Brasilodon Brasilitherium Sinoconodon Morganucodon Tritheledontidae Riograndia Irajatherium Chaliminia Elliotherium Pachygenelus Diarthrognathus Tritheledon

Paleoecology

All specimens of Riograndia come from the Late Triassic aged Caturrita Formation. The formation dates to about 225 million years ago, and it based in the present-day country of Brasil. Dinosaurs from the formation only include the sauropodomorph Unaysaurus and the theropod Guaibasaurus. Non-dinosaurian animals include the dinosauriform Sacisaurus; the dicynodontid Jachaleria; an unnamed phytosaurian; isolated archosaurian teeth; an amphibian classified in Stereospondyli; and many common tetrapods smaller than 15 cm (5.9 in) long. Among the tetrapods is the procolophonid Soturnia; the sphenodontid Clevosaurus; the lepidosaurian Cargninia; the pterosaurian Faxinalipterus, and an assortment of mammaliamorphs including Riograndia, Brasilodon, Brasilitherium, Irajatherium, and Minicynodon.

External links

• Dinossauros do Rio grande do Sul. (in Portuguese)
• Sociedade Brasileira de Paleontologia. (in Portuguese)