During the time of dinosaurs in the Late Triassic, variations in the abundance and diversity of plant and vertebrate animal species cannot be causally related to the climate changes that occurred during that period. This is the conclusion of a new study led by the National Scientific and Technical Research Council in Argentina (CONICET) and the University of Utah in the United States.
By analyzing multiple independent lines of evidence drawn from sedimentology, clay mineralogy, and geochemistry, the researchers explored changes in paleoclimatic conditions, such as mean annual temperatures and precipitation, within the Ischigualasto Formation – a collection of fossil-rich sedimentary rocks deposited by rivers and streams during the late Triassic period (about 231 to 226 million years ago) in what are now the San Juan and La Rioja provinces in Northwestern Argentina. Although the scientists managed to identify a clear change from warmer and drier to more temperate and humid conditions, no concurrent major changes could be identified in the fossil record.
“We conclude that variations in the abundance and diversity of species, as recorded by their first and last appearances in the fossil record, are better explained by preservation and sampling biases than by changes in climate,” said study lead author Adriana Mancuso, a paleontologist at CONICET.
“What we see is that how many specimens collected from each interval of the sequence, and the chemical and physical characteristics that allow greater or lesser preservation of the remains of animals and plants, were significant factors. These two factors, collection and preservation, have more influence on the increase or decrease of abundance and diversity than the climate changes recorded.”
However, Dr. Mancuso and her colleagues managed to identify a relationship between climatic variations and two groups of reptiles: the rhynchosaurs, a group of herbivorous early archosauromorphs, and pseudosuchians, a type of crocodilian-line archosaurs. “We did find that the abundance of rhynchosaurs and extinction of a few pseudosuchian species appear to coincide with a climate shift,” said study co-author Randall Irmis, a paleontologist at the University of Utah.
This study highlights the importance of an explicit framework for testing hypotheses about the correlation between the fossil record and climatic changes. “In addition to the contribution on the relationship of biotic and climatic events in the Ischigualasto Formation, the work provides a methodological framework to test climate-biota associations, highlighting the data gaps that must be filled, and makes new testable predictions that can be tested in future studies,” Dr. Mancuso concluded.
The study is published in the journal Frontiers in Earth Science.