|Fossil skeleton of Guaibasaurus candelariensis|
Bonaparte et al., 1999
The exact makeup and classification of the Guaibasauridae remains uncertain. The family was originally named by Jose Bonaparte and colleagues in 1999 to contain a single genus and species, Guaibasaurus candelariensis. When a second specimen of Guaibasaurus was described from better remains in 2007, it became easier to compare it to other enigmatic early saurischians, which are often difficult to classify because they combine characteristics of the two major saurischian groups, Theropoda and Sauropodomorpha. Bonaparte and colleagues, in light of the information gained from this second specimen, found that the genus Saturnalia (which is anatomically very similar to Guaibasaurus) could also be assigned to the Guaibasauridae, though they did not conduct a phylogenetic analysis or define Guaibasauridae as a clade. The researchers also tentatively assigned the poorly understood genus Agnosphitys to this family. However, the latter assignment was not supported by the results of the phylogenetic analyses of early dinosaurs that were carried out by Baron, Norman & Barrett (2017).
Bonaparte and colleagues (2007) found that guaibasaurids have more characteristics in common with theropods than they do with early sauropodomorphs (or "prosauropods"). Because of this, according to Bonaparte, they are most likely either a very basal group on the stem leading toward sauropodomorphs, or a group ancestral to both sauropodomorphs and theropods. Furthermore, the authors interpret this as evidence that the common ancestor of both saurischian lineages was more theropod-like than prosauropod-like.
Ezcurra (2010) 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 of guaibasaurids, 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.
Agnosphitys (; "unknown begetter"; sometimes mistakenly called Agnostiphys or Agnosphytis is a genus of silesaurid dinosauriform that lived during the Late Triassic. It contains only one species, the type species A. cromhallensis. Its remains include an ilium, maxilla, astragalus and humerus, which date variously from the Norian and Rhaetian stages of the Late Triassic.
The type species, Agnosphitys cromhallensis, was described by Nicholas Fraser, Kevin Padian, Gordon Walkden and A. L. M Davis in early 2002. The fossils, consisting of a partial skeleton including referred material, were found in Avon, England.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.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.Guaibasaurus
Guaibasaurus is an extinct genus of basal dinosaur known from the Late Triassic Caturrita Formation of Rio Grande do Sul, southern Brazil.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.Nambalia
Nambalia is a genus of basal sauropodomorph dinosaur. It lived during the Late Triassic period (late Norian to earliest Rhaetian) in what is now Andhra Pradesh, central India. It is known from the holotype ISI R273, parts 1-3, partially articulated postcranial material and from the paratypes ISI R273, parts 4-29, including partial postcrania of at least two individuals of different sizes found closely associated and one of them is nearly the same size as the
holotype. ISI R273 was discovered and collected from the Upper Maleri Formation within the Pranhita–Godavari Basin,
north of Nambal village. It was first named by Fernando E. Novas, Martin D. Ezcurra, Sankar Chatterjee and T. S. Kutty in 2011 and the type species is Nambalia roychowdhurii. The generic name is derived from the Indian village of Nambal which is close to the type locality. The specific name honors Dr. Roy Chowdhuri, for his research on the Triassic vertebrate faunas of India. A cladistic analysis by Novas et al. found that Nambalia is basal to Efraasia, Plateosauravus, Ruehleia and Plateosauria, but more derived than Thecodontosaurus, Pantydraco, and Guaibasauridae. Nambalia was found along with the plateosaurid Jaklapallisaurus, a guaibasaurid, and two basal dinosauriforms.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).Unaysauridae
Unaysauridae is a family of basal sauropodomorphs from the Late Triassic of India and 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.Yueosaurus
Yueosaurus is an extinct genus of basal ornithopod dinosaur known from Zhejiang Province, China.