Vertebrate succession in the Ischigualasto Formation

A comprehensive analysis of the Ischigualasto Formation in Argentina reveals that vertebrate diversity and abundance gradually declined over time due to climatic deterioration, with only one abrupt faunal shift. The study, based on 848 fossil specimens representing 29 taxa, identified two new basal dinosauromorphs—an unnamed lagerpetid and a silesaurid, Ignotosaurus fragilis—expanding the known fauna of this Upper Triassic ecosystem. Radioisotopic dating of ash layers provided a precise chronological framework, enabling the detection of subtle changes in faunal composition across three biozones. Notably, the dominant cynodont Exaeretodon was replaced by the rare dicynodont Jachaleria at the end of the second biozone, marking the only abrupt shift in this otherwise gradual decline.

Martínez, R. N., Apaldetti, C., Alcober, O. A., Colombi, C. E., Sereno, P. C., Fernandez, E., Malnis, P. S., Correa, G. A., & Abelin, D. (2012). Vertebrate succession in the Ischigualasto Formation. Journal of Vertebrate Paleontology, 32(sup1), 10–30. https://doi.org/10.1080/02724634.2013.818546