The Late Triassic Ischigualasto Formation at Cerro Las Lajas (La Rioja, Argentina): fossil tetrapods, high-resolution chronostratigraphy, and faunal correlations

A new high-resolution chronostratigraphic framework for the Late Triassic Ischigualasto Formation at Cerro Las Lajas, Argentina, reveals that rhynchosaur-dominated faunas persisted into the earliest Norian. The study, combining detailed lithostratigraphy and U-Pb geochronology from three intercalated tuffs, constrains the formation's deposition between 230.2 ± 1.9 Ma and 221.4 ± 1.2 Ma, with its fossil-bearing interval dated to 229.20 + 0.11/- 0.15-226.85 + 1.45/- 2.01 Ma. This precise dating allows for biostratigraphic correlations across South American basins and provides a ca. 229 Ma age assignment to the ornithischian Pisanosaurus mertii, partially filling a ghost lineage in early dinosaur evolution. The research also introduces two new biozones, the Hyperodapedon and Teyumbaita, based on rhynchosaur ranges.

Desojo, J. B., Fiorelli, L. E., Ezcurra, M. D., Martinelli, A. G., Ramezani, J., Da Rosa, Átila. A. S., von Baczko, M. B., Trotteyn, M. J., Montefeltro, F. C., Ezpeleta, M., & Langer, M. C. (2020). The Late Triassic Ischigualasto Formation at Cerro Las Lajas (La Rioja, Argentina): fossil tetrapods, high-resolution chronostratigraphy, and faunal correlations. Scientific Reports, 10(1). https://doi.org/10.1038/s41598-020-67854-1