New research challenges assumptions about climate-controlled ecosystem change during the origin of dinosaurs in Argentina

Newswise — A group of researchers from CONICET and the University of Utah have demonstrated that during the time of the first dinosaurs, variations in the diversity and abundance of plant and vertebrate animal species cannot be linked to the climatic changes recorded throughout its deposit, in contrast with the previous hypotheses.

In the new study, published in the open-access journal Frontiers in Earth Sciences, the team of scientists studied several independent data sources (sedimentology, clay mineralogy, and geochemistry) to elucidate changes in paleoclimatic conditions (such as mean annual precipitation and mean annual temperature) within the Ischigualasto Formation. These fossil-rich sedimentary rocks were deposited by rivers and streams approximately 231–226 million years ago during the Upper Triassic period in what is now northwestern Argentina ( provinces of La Rioja and San Juan). In the middle of the formation, researchers observed a clear change in conditions, moving from approximately hotter, drier conditions to more temperate, humid conditions, but no major concurrent changes could be identified in the fossil record.

“We conclude that variations in species abundance and diversity, as recorded by their first and last appearances in the fossil record, are better explained by preservation and sampling biases than by climate change. “said Adriana Mancuso, lead author and CONICET. independent researcher at the Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales in Mendoza, Argentina.

“What we see is that the number of specimens collected at each interval of the sequence, and the chemical and physical characteristics that allow greater or lesser preservation of animal and plant remains, were important factors. These two factors, collection and preservation, have more influence on whether abundance and diversity increase or decrease than recorded climate change,” Mancuso explained.

However, although the evolution of the ecosystem does not generally show a biotic response associated with climate change, the research group observed a relationship between climatic variations and two groups of reptiles, the rhynchosaurs (early herbivorous archosauromorphs) and the pseudosuchians (archosaurs of the crocodilian lineage). . “We found that the abundance of rhynchosaurs and the extinction of a few species of pseudosuchians seem to coincide with a changing climate,” said Randall Irmis, co-author of the U and the Natural History Museum of Utah.

Beyond findings about this specific fossil and paleoclimate record from Argentina, the new research highlights the importance of an explicit framework for testing hypotheses about the link between climate change and the fossil record. “In addition to contributing on the relationship of biotic and climatic events in the Ischigualasto Formation, the work provides a methodological framework for testing climate-biota associations, highlighting data gaps that need to be filled, and makes new testable predictions that can be tested in future studies,” concludes Mancuso.

Other authors include Tomás Pedernera and Cecilia Benavente of the Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (CONICET), Leandro Gaetano of the Instituto de Estudios Andinos (CONICET) and the Departamento de Ciencias Geológicas of the University of Buenos Aires, and Benjamin Breeden of the University of Utah.

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