Definition and correlation of the Lamyan: A new biochronological unit for the nonmarine Late Carnian (Late Triassic)

The Sonsela Member of the Petrified Forest Formation at Petrified Forest, Arizona and the Tres Lagunas Member of the Santa Rosa Formation in east-central New Mexico yield vertebrate fossil assemblages (faunas) that are intermediate in composition between the Adamanian and Revueltian lvfs in that they include co-occurrences of the phytosaurs Rutiodon and Pseudopalatus and the unique taxon Typothorax antiquum. These faunas define an upper subdivision of Adamanian time that we refer to as the Lamyan sub-faunachron. The earlier Adamanian is distinguished as the St. Johnsian sub-faunachron. This refinement demonstrates the utility of defining biochronologic units in that it spurs detailed examination of biostratigraphy and lithostratigraphy. The Lamyan provides evidence that there is no major tetrapod extinction within the Late Triassic, specifically at the end of the Carnian.