Guaibasaurus is an extinct genus of basal saurischian dinosaur known from the Triassic Caturrita Formation of Rio Grande do Sul, southern Brazil.[Langer MC, McPhee BW, Marsola JCdA, Roberto-da-Silva L, Cabreira SF (2019) "Anatomy of the dinosaur Pampadromaeus barberenai (Saurischia—Sauropodomorpha) from the Late Triassic Santa Maria Formation of southern Brazil". PLOS One
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/ref> In 2016 Gregory S. Paul estimated it at 2 meters (6.6 ft) and 10 kg (22 lbs), whereas in 2020 Molina-Pérez and Larramendi listed it at 3 meters (10 ft) and 35 kg (77 lbs).
Discovery
Guaibasaurus was originally named on the basis of the holotype, MCN PV2355, a well-preserved partial skeleton and the paratype, MCN PV2356, an articulated and nearly complete left hindlimb, which were discovered in the "Sesmaria do Pinhal 2" locality near Candelária, Rio Grande do Sul, in Brazil, in the upper portion of the Candelária Sequence or the Caturrita Formation.
Later, two additional specimens were referred to G. candelariensis: UFRGS PV0725T (an articulated and nearly complete postcranial skeleton missing one forelimb, both feet and the neck), and MCN PV 10112 (a not-fully-prepared block containing articulated parts and some isolated elements, including a partial hand). The referred materials were collected from the "Linha São Luiz" locality near the town of Faxinal do Soturno, Rio Grande do Sul, also in the upper portion of the Candelária Sequence or the Caturrita Formation.
All specimen were collected in these two localities from the lower portion of the Caturrita Formation (Rosário do Sul Group, Paraná Basin) or alternatively the uppermost Santa Maria 2 Sequence, dating to the early Norian faunal stage of the Late Triassic.
Guaibasaurus was first named by José F. Bonaparte, Jorge Ferigolo and Ana Maria Ribeiro in 1999 and the type species is Guaibasaurus candelariensis. The generic name is named after the Rio Guaíba hydrographic basin where the holotype was found as a part of the "Prό-Guaíba Project", a scientific program supporting research on fossils from the Triassic period. The specific name is named after Candelária, a city near the fossil locality in which the holotype was found.
Classification
José Bonaparte and colleagues, in their 1999 description of the genus, found it to be possible basal theropod and placed it in its own family, Guaibasauridae. Bonaparte and colleagues (2007) found another early Brazilian dinosaur Saturnalia to be very similar to it, and placed the two in the Guaibasauridae which was found to be a primitive saurischian group. Bonaparte found that these forms may have been "prosauropods" (primitive Sauropodomorpha), or an assemblage of forms close to the common ancestor of the sauropodomorphs and theropods. Overall, Bonaparte considered that both Saturnalia and Guaibasaurus were more theropod-like than "prosauropod"-like.
More recent cladistic analyses have disagreed on the placement of Guaibasaurus. Some analyses have found it to be a basal theropod,[Bittencourt Rodrigues, 2010. Revisao filogenetica dos dinossauriformes basais: Implicacoes para a origem dod dinossauros. Unpublished Doctoral Thesis. Universidade de Sao Paulo. 288 pp.] while others consider it a basal sauropodomorph.
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