The Santa Maria Formation is a sedimentary

rock formation A rock formation is an isolated, scenic, or spectacular surface rock outcrop. Rock formations are usually the result of weathering and erosion sculpting the existing rock. The term ''rock formation'' can also refer to specific sediment ...

found in

Rio Grande do Sul Rio Grande do Sul (, , ; "Great River of the South") is a Federative units of Brazil, state in the South Region, Brazil, southern region of Brazil. It is the Federative_units_of_Brazil#List, fifth-most-populous state and the List of Brazilian st ...

, Brazil. It is primarily Carnian in age ( Late Triassic), and is notable for its fossils of

cynodont The cynodonts () (clade Cynodontia) are a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Cynodonts had a wide variety ...

s, " rauisuchian" pseudosuchians, and early dinosaurs and other

dinosauromorphs Dinosauromorpha is a clade of avemetatarsalian archosaurs (reptiles closer to birds than to crocodilians) that includes the Dinosauria (dinosaurs) and some of their close relatives. It was originally defined to include dinosauriforms and lager ...

, including the herrerasaurid ''

Staurikosaurus ''Staurikosaurus'' (Pronounced "STORE-ee-koh-SAWR-us", "Southern Cross lizard") is a genus of herrerasaurid dinosaur from the Late Triassic of Brazil, found in the Santa Maria Formation. Description Colbert (1970) described ''Staurikosaurus' ...

'', the

basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...

sauropodomorphs '' Buriolestes'' and ''

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 ...

,'' and the

lagerpetid Lagerpetidae (; originally Lagerpetonidae) is a family of basal avemetatarsalians. Though traditionally considered the earliest-diverging dinosauromorphs (reptiles closer to dinosaurs than to pterosaurs), fossils described in 2020 suggest that ...

'' Ixalerpeton''. The formation is named after the city of Santa Maria in the central region of Rio Grande do Sul, where outcrops were first studied. The Santa Maria Formation makes up the majority of the Santa Maria Supersequence, which extends through the entire Late Triassic. The Santa Maria Supersequence is divided into four geological sequences, separated from each other by short unconformities. The first two of these sequences (Pinheiros-Chiniquá and Santa Cruz sequences) lie entirely within the Santa Maria Formation, while the third (the Candelária sequence) is shared with the overlying

Norian The Norian is a division of the Triassic Period. It has the rank of an age (geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian. Stratigraphic defi ...

-age Caturrita Formation. The fourth and youngest sequence (the Mata sequence) is equivalent to the

Rhaetian The Rhaetian is the latest age of the Triassic Period (in geochronology) or the uppermost stage of the Triassic System (in chronostratigraphy). It was preceded by the Norian and succeeded by the Hettangian (the lowermost stage or earliest age ...

-age Mata Sandstone. The oldest sequence in the formation is the Pinheiros-Chiniquá Sequence (latest Ladinian-earliest Carnian, ~237 Ma), which is biostratigraphically equivalent to the '' Dinodontosaurus''

Assemblage Zone Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.Hine, Robert. “Biostratigraphy.” ''Oxford Reference: Dictionary of Bio ...

. It is followed by the shorter Santa Cruz Sequence (early Carnian-middle Carnian, ~236 Ma), biostratigraphically equivalent to the ''

Santacruzodon ''Santacruzodon'' is an extinct genus of cynodonts which existed in Brazil during the Triassic period. The type species is ''Santacruzodon hopsoni''. Species ''Santacruzodon hopsoni'', is a species that was collected in 1995 in Santa Cruz do Sul ...

'' Assemblage Zone. The final sequence, which is only partially present within the formation, is the Candelária Sequence (middle Carnian-latest Carnian, ~233-228 Ma). The lower portion of this sequence, coinciding with the upper part of the Santa Maria Formation, is equivalent to the ''Hyperodapedon'' Assemblage Zone.The ''Hyperodapedon'' Assemblage Zone is itself subdivided into ''Hyperodapedon'' Acme Zone (most of the zone, where the rhynchosaur ''Hyperodapedon'' is widely reported) and '' Exaeretodon'' Zone (restricted to about three known and sampled localities, where rhynchsaurs are almost completely absent, but the traversodontid cynodont ''Exaeretodon'' is widely reported). These subdivisions are also known as Lower and Upper ''Hyperodapedon'' Assemblage Zone, respectively. U-Pb radiometric dating of a locality in the Upper portion of the Santa Maria Formation found an estimated age of 233.23±0.73 million years ago, putting that locality 1.5 million years older than the Ischigualasto Formation and younger than Los Chañares Formation. The Santa Maria and Ischigualasto formations are approximately equal as having the earliest dinosaur localities.

Vertebrate paleofauna

Most of the information below was included on a revision of the Triassic faunal successions of the Paraná Basin, southern Brazil by Schultz et al.

Vertebrate paleofauna

Temnospondyls

Synapsids

Dicynodonts

Cynognathians

Probainognathians

Reptiles

Pseudosuchians

Avemetatarsalians

Other reptiles

Formations

See also

References