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.

Fauna

Synapsids

Archosauromorphs

Formations