|Fossil skeleton (UFRGS PV0725T), with head and neck based on Herrerasaurus|
Bonaparte et al., 1999
Bonaparte et al., 1999
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 geopark of Paleorrota. Later, two additional specimens were referred to G. candelariensis: UFRGS PV0725T is an articulated and nearly complete postcranial skeleton missing one forelimb, both feet and the neck, and MCN PV 10112 is still being unprepared block containing articulated parts and some isolated elements of which, 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 geopark of Paleorrota. 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 known only from advanced maniraptoran dinosaurs that are closely related to birds. 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.
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 primitive sauropodomorphs, or an assemblage of forms close to the common ancestor of the sauropodomorphs and theropods. Overall, Bonaparte found that both Saturnalia and Guaibasaurus were more theropod-like than prosauropod-like. However, all more recent cladistic analyses found the members of Guaibasauridae to be very basal sauropodomorphs, except Guaibasaurus itself which was found to be a basal theropod or alternatively a basal sauropodomorph.
The Anchisauria were a clade of sauropodomorph dinosaurs that lived during the Late Triassic and Early Jurassic. The name Anchisauria was first used by Galton and Upchurch in the second edition of The Dinosauria. Galton and Upchurch assigned two families of dinosaurs to the Anchisauria: the Anchisauridae and the Melanorosauridae. The more common prosauropods Plateosaurus and Massospondylus were placed in the sister clade Plateosauria.
However, recent research indicates that Anchisaurus is closer to sauropods than traditional prosauropods; thus, Anchisauria would also include Sauropoda.The following cladogram simplified after an analysis presented by Blair McPhee and colleagues in 2014.Averostra
Averostra, or "bird snouts", is a clade that includes most theropod dinosaurs that have a promaxillary fenestra (fenestra promaxillaris), an extra opening in the front outer side of the maxilla, the bone that makes up the upper jaw. Two groups of averostrans, the Ceratosauria and the Orionides, survived into the Cretaceous period. When the Cretaceous–Paleogene extinction event occurred, ceratosaurians and two groups of orionideans within the clade Coelurosauria, the Tyrannosauroidea and Maniraptoriformes, were still extant. Only one subgroup of maniraptoriformes, Aves, survived the extinction event and persisted to the present day.Avetheropoda
Avetheropoda, or "bird theropods", is a clade that includes carnosaurians and coelurosaurs to the exclusion of other dinosaurs.Buriolestes
Buriolestes (meaning "Buriol's robber") is a genus of early sauropodomorph dinosaurs from the Late Triassic Santa Maria Formation of the Paraná Basin in southeastern Brazil. It contains one species, B. schultzi, named in 2016. The type specimen was found alongside a specimen of the lagerpetid dinosauromorph Ixalerpeton.Carnian
The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic series (or earliest age of the Late Triassic epoch). It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followed by the Norian. Its boundaries are not characterized by major extinctions or biotic turnovers, but a climatic event (known as the Carnian Pluvial Event) occurred during the Carnian and seems to be associated with important extinctions or biotic radiations.Cerapoda
Cerapoda ("ceratopsians and ornithopods") is a clade of the dinosaur order Ornithischia.Chromogisaurus
Chromogisaurus is a sauropodomorph which existed in Argentina during the Late Triassic (Carnian) period. It was a herbivore about 2 metres (6 ft 7 in) in length, and was optionally quadrupedal.Dinosauriformes
Dinosauriformes is a clade of archosaurian reptiles that include the dinosaurs and their most immediate relatives. All dinosauriformes are distinguished by several features, such as shortened forelimbs and a partially to fully perforated acetabulum, the hole in the hip socket traditionally used to define dinosaurs. The oldest known member is Asilisaurus, dating to about 245 million years ago in the Anisian age of the middle Triassic period.Guaibasauridae
Guaibasauridae is a family of basal saurischian dinosaurs, known from fossil remains of late Triassic period formations in Brazil and Argentina.Haya griva
Haya is an extinct genus of basal neornithischian dinosaur known from Mongolia.Jingshanosaurus
Jingshanosaurus (meaning "Jingshan lizard") is a genus of sauropodomorph dinosaurs from the early Jurassic period.Neotheropoda
Neotheropoda (meaning "new theropods") is a clade that includes coelophysoids and more advanced theropod dinosaurs, and the only group of theropods who survived the Triassic–Jurassic extinction event. Yet all of the neotheropods became extinct during the early Jurassic period except for Averostra.Orionides
Orionides is a clade of tetanuran theropod dinosaurs from the Middle Jurassic to the Present. The clade includes most theropod dinosaurs, including birds.Orodrominae
Orodrominae is a subfamily of parksosaurid dinosaurs from the Cretaceous of North America and Asia.Saturnalia tupiniquim
Saturnalia is an extinct genus of basal sauropodomorph dinosaur known from the Late Triassic Santa Maria Formation of Rio Grande do Sul, southern Brazil and Pebbly Arkose Formation, Zimbabwe.Saturnaliinae
Saturnaliinae is a clade of sauropodomorph dinosaurs found in Brazil and Argentina.
In 2010, Martin Ezcurra defined the subfamily Saturnaliinae for the clade containing Saturnalia and Chromogisaurus, which were found to be close relatives in several studies. While they are sometimes found to be a subgroup within the Guaibasauridae, other studies have found the saturnaliines to form an independent lineage at the very base of the sauropodomorph family tree. Langer and colleagues (2019) recovered Pampadromaeus and Panphagia as relatives of Saturnalia and Chromogisaurus, elevating Saturnaliinae to family rank as Saturnaliidae. They recovered Guaibasaurus as a basal theropod.Sauropodomorpha
Sauropodomorpha ( SOR-ə-POD-ə-MOR-fə; 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 long necks and tails, were quadrupedal, and became the largest animals to ever walk the Earth. The "prosauropods", which preceded the sauropods, were smaller and were often able to walk on two legs. The sauropodomorphs were the dominant terrestrial herbivores throughout much of the Mesozoic Era, from their origins in the mid-Triassic (approximately 230 Ma) until their decline and extinction at the end of the Cretaceous (approximately 66 Ma).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 known. It is closely related to plateosaurid dinosaurs found in Germany, which indicates that it was relatively easy for species to spread across the giant landmass of the time, the supercontinent of Pangaea.The fossils of Unaysaurus are well preserved. They consist of an almost complete skull, complete with a lower jaw, 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.Xixiposaurus
Xixiposaurus is a genus of prosauropod dinosaur which existed in what is now Lower Lufeng Formation, China during the lower Jurassic period. It was first named by Sekiya Toru in 2010 and the type species is Xixiposaurus suni.