Guaibasauridae is a

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

of basal sauropodomorph

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

s, known from

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

remains of late

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest per ...

period formations in

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

and

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the List of South American countries by area, second-largest ...

Classification

The exact makeup and classification of the Guaibasauridae remain uncertain. The family was originally named by

Jose Bonaparte Jose is the English transliteration of the Hebrew and Aramaic name ''Yose'', which is etymologically linked to ''Yosef'' or Joseph. The name was popular during the Mishnaic and Talmudic periods. * Jose ben Abin * Jose ben Akabya *Jose the Galil ...

and colleagues in 1999 to contain a single

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

and

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

, ''

Guaibasaurus candelariensis ''Guaibasaurus'' is an extinct genus of basal saurischian dinosaur known from the Late Triassic Caturrita Formation of Rio Grande do Sul, southern Brazil. Most analyses recover it as a sauropodomorph, although there are some suggestions that it ...

''. When the 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 Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally ...

and Sauropodomorpha. Bonaparte and colleagues, in light of the information gained from this second specimen, found that the genus ''

Saturnalia Saturnalia is an ancient Roman festival and holiday in honour of the god Saturn, held on 17 December of the Julian calendar and later expanded with festivities through to 23 December. The holiday was celebrated with a sacrifice at the Temple ...

'' (which is anatomically very similar to ''Guaibasaurus'') could also be assigned to the Guaibasauridae, though they did not conduct a

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups ...

analysis or define Guaibasauridae as a

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...

. 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).Baron, M.G., Norman, D.B., and Barrett, P.M. (2017). A new hypothesis of dinosaur relationships and early dinosaur evolution. ''Nature'', 543: 501–506. 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 Saturnaliidae is a family of basal sauropodomorph dinosaurs found in Brazil, Argentina and possibly Zimbabwe. It is not to be confused with Saturnalidae, a family of radiolarian protists. Classification In 2010, Martin Ezcurra defined the subfa ...

for the clade containing ''

'' and ''

Chromogisaurus ''Chromogisaurus'' is an extinct genus of saturnaliid sauropodomorph which existed in Argentina during the Late Triassic (Carnian) period. It is from the Cancha de Bochas, Valle Pintado member of the Ischigualasto Formation. It was a herbivore ...

'', 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.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 14(2): e0212543. https://doi.org/10.1371/journal.pone.0212543 ''Guaibasaurus'' has since been recovered as a sauropodomorph, possibly allied with Unaysauridae, with Saturnaliidae representing a group of more basal sauropodomorphs. Among taxa at one point considered guaibasaurids, ''Agnosphitys'' has been reassigned to

Silesauridae Silesauridae is an extinct family of Triassic dinosauriforms. It is most commonly considered to be a clade of non-dinosaur dinosauriforms, and the sister group of dinosaurs. Some studies have instead suggested that most or all silesaurids compri ...

, and ''Eoraptor'', ''Panphagia'', ''Saturnalia'' and ''Chromogisaurus'' are considered basalmost sauropodomorphs possibly in a clade of their own.

References

Sauropodomorphs Carnian first appearances Late Triassic extinctions Prehistoric dinosaur families {{Sauropodomorph-stub