The Santa Maria Formation is a

sedimentary Sedimentary rocks are types of rock formed by the cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or deposited at Earth's surface. Sedime ...

rock formation A rock formation is an isolated, scenic, or spectacular surface rock (geology), rock outcrop. Rock formations are usually the result of weathering and erosion sculpting the existing rock. The term ''rock Geological formation, formation ...

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 s ...

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

. It is primarily

Carnian The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227.3 ...

in age (

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...

), and is notable for its

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 preserve ...

s of

cynodont Cynodontia () is a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 Megaannum, mya), and extensively diversified after the Permian–Triassic extinction event. Mammals are cynodonts, as are their extin ...

s, " rauisuchian"

pseudosuchia Pseudosuchia, from Ancient Greek ψεύδος (''pseúdos)'', meaning "false", and σούχος (''soúkhos''), meaning "crocodile" is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely relat ...

ns, and early

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

s and other dinosauromorphs, including the herrerasaurid '' Staurikosaurus'', the basal sauropodomorphs '' Buriolestes'' and ''

Saturnalia Saturnalia is an Roman festivals, ancient Roman festival and holiday in honour of the List of Roman deities, god Saturn (mythology), Saturn, held on 17 December in the Julian calendar and later expanded with festivities until 19 December. By t ...

,'' and the lagerpetid '' 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 In mathematics, a sequence is an enumerated collection of objects in which repetitions are allowed and order matters. Like a set, it contains members (also called ''elements'', or ''terms''). The number of elements (possibly infinite) is call ...

, separated from each other by short

unconformities An unconformity is a buried erosion surface, erosional or non-depositional surface separating two Rock (geology), rock masses or Stratum, strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer ...

. 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 geological period, Period. It has the rank of an age (geology), age (geochronology) or stage (stratigraphy), stage (chronostratigraphy). It lasted from ~227.3 to Mya (unit), million years ago. It was prec ...

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

Rhaetian The Rhaetian is the latest age (geology), age of the Triassic period (geology), Period (in geochronology) or the uppermost stage (stratigraphy), stage of the Triassic system (stratigraphy), System (in chronostratigraphy). It was preceded by the N ...

-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. It is followed by the shorter Santa Cruz Sequence (early Carnian-middle Carnian, ~236 Ma), biostratigraphically equivalent to the '' Santacruzodon'' 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 Cerro da Alemoa (the type locality of '' Saturnalia tupiniquim'') 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.'' (2020).

Vertebrate paleofauna

Temnospondyls

Fish

Synapsids

Dicynodonts

Cynognathians

Probainognathians

Reptiles

Pseudosuchians

Avemetatarsalians

Other reptiles

Formations

See also

References