South American Triassic geochronology: Constraints and uncertainties for the tempo of Gondwanan non-marine vertebrate evolution

Gondwanan sedimentary deposits preserve a rich archive of Triassic non-marine vertebrate evolution. This fossil record is integral to understanding early Mesozoic global change events, including the end-Permian and end-Triassic mass extinctions, Carnian Pluvial Episode, and macroevolutionary events such as the origin of dinosaurs. Until very recently, almost all of these fossil assemblages were dated by exclusively biostratigraphic means, which made robust correlation to the GSSP-defined timescale difficult. Furthermore, recent advances in radioisotopic dating and magnetostratigraphy have demonstrated that many of these biostratigraphic schemes were imprecise and that key index taxa have different first and last appearances across geographic space. Thankfully, over the past ten years, new radioisotopic and magnetostratigraphic age constraints from fossiliferous sequences in South America have allowed the revision of the absolute ages and relative correlation of key Gondwanan vertebrate assemblages.