Santa Maria Formation

The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It has a Late Anisian to Early Norian age (Early to Late Triassic), and is notable for its fossils of early dinosaurs and other dinosauromorphs, including the herrerasaurid "Staurikosaurus", the basal sauropodomorphs "Buriolestes" and "Saturnalia," and the lagerpetid "Ixalerpeton". It received this name because it was discovered first in the city of Santa Maria, on the central region of Rio Grande do Sul state.
The distinguished English paleontologist Arthur Smith Woodward determined the age of Santa Maria Formation dated Mesozoic Era, Upper Triassic period (about 220 million years). A U-Pb (Uranium decay) dating of a locality of the Upper portion of the Santa Maria Formation dated around 233.23±0.73 million years ago, putting that locality 1.5 million years older than the Ischigualasto Formation, instead being in the temporal range of the Los Chañares Formation, and making the two formations (Santa Maria and Ischigualasto) approximately equal as having the earliest dinosaur localities.
The Santa Maria Formation is part of the Candelária Sequence, and is biostratigraphically subdivided into "Dinodontosaurus" (latest Ladinian-earliest Carnian), "Santacruzodon" (earliest Carnian-middle Carnian), and "Hyperodapedon" (middle Carnian-latest Carnian) Assemblage Zones (from the oldest to youngest). Moreover, the "Hyperodapedon" Assemblage Zone is subdivided into "Hyperodapedon" Acme Zone (most of the zone, where the rhynchosaur "Hyperodapedon" is widely reported) and "Exaeretodon" Sub-Zone (restricted to 3 known and sampled localities, where "Hyperodapedon" is almost absent, but the traversodontid cynodont "Exaeretodon" is widely reported). These subdivisions are also known as Lower and Upper "Hyperodapedon" Assemblage Zone, respectively.