Guaibasaurus (Guaiba lizard)
Guaibasaurus (Guaiba lizard)
Named By : J. F. Bonaparte, J. Ferigolo, and A. M. Ribeiro - 1999
Diet : Uncertain
Size : Estimated 1.8 – 3 meters long
Type of Dinosaur : Small Theropod
Type Species : G. candelariensis (type)
Found in : Brazil
When it Lived : Late Triassic, 221-210 million years ago
Guaibasaurus is an extinct genus of basal sauropodomorph dinosaur known from the Late Triassic Caturrita Formation of Rio Grande do Sul, southern Brazil. It was possibly a basal theropod or sauropodomorph. 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).
Sergio kaminski, Public domain, via Wikimedia Commons
Guaibasaurus was originally named on the basis of the holotype, MCN PV2355, a well-preserved partial postcranial 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. A U-Pb (Uranium 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.
Specimen UFRGS PV0725T is articulated with hindlimbs tucked underneath its body and forelimbs flexed to the side. Although most of the neck is not preserved, the vertebrae at the base of the neck are present in UFRGS PV0725T and curve to the left, suggesting the entire neck was curved toward the left side of the body. The posture of this skeleton is similar to the resting position of birds, and is otherwise primarily known from advanced maniraptoran dinosaurs that are closely related to birds. It has also been observed in the dinosauriform Saltopus. Like living birds, Guaibasaurus may have rested in this position to conserve body heat.
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.