Global Triassic Tetrapod Biostratigraphy and Biochronology: 2007 Status

The global Triassic timescale based on tetrapod biochronology remains a robust tool for both global and regional age assignment and correlation. The Lootsbergian and Nonesian land-vertebrate faunachrons (LVFs) are of Early Triassic age; cross correlation of part of the Lootsbergian to the Olenekian and all or part of the Nonesian to the Anisian lacks support. In the South African Karoo basin, both the Lootsbergian and the Nonesian can and should be subdivided into sub-LVFs. The upper part of the South African Cynognathus zone, previously considered Nonesian in age, is younger, of Perovkan age. We redefine the beginning of the Perovkan as the first appearance datum of the temnospondyl Eocyclotosaurus, which resolves uncertainties in the correlation of Eocyclotosaurus assemblages and shansiodont assemblages. The Berdyankian LVF equates to parts of Ladinian and Carnian time. Rejection of recent cladotaxonomy of phytosaurs and an incorrect claim of a Revueltian record of the temnospondyl Metoposaurus, as well as newly established stratigraphic ranges and new taxonomy of aetosaurs, have improved correlation and temporal resolution within the interval Otischalkian-Apachean. This further supports separation of the Otischalkian and Adamanian and runs contrary to suggestions to merge the two LVFs as a single Ischigualastian LVF. Though readily recognized and correlated in western North America, the Apachean LVF remains the most problematic LVF for global correlation. A recent purported test of the Triassic LVFS based on GIS is rejected as invalid because it is replete with internal inconsistencies, factual errors and questionable interpretations. Continued careful biostratigraphy in the field and improved alpha taxonomies that are not cladotaxonomies will further develop, elaborate and test the Triassic timescale based on tetrapod evolution.