Perceptions of climate change during the origin of dinosaurs.

The Triassic Period, about 252 to 201 million years ago, was a time of volatile change, particularly during an interval known as Carnian (about 237 to 227 million years ago). Three dramatic events occurred on Earth: the first dinosaurs appeared, gigantic volcanic eruptions called the great igneous province of Wrangellia spewed greenhouse gases, and the climate suddenly changed to warmer and wetter conditions that scientists call the Carnian Pluvial Episode (CPE ).

Recent work suggests that the Wrangellia eruptions caused the CPE, and that the resulting climate change may have stimulated early dinosaur diversification. But the lack of precise absolute dates for many Carnian sediments makes comparisons difficult. Furthermore, there is little detailed paleoclimatic data for many regions outside Europe, making it clear whether the EPC was indeed a global climate event or conclusively links it to dinosaur diversification.

In a new study in the magazine. Gondwana Research, an international group led by Adriana Mancuso, researcher at the National Council for Scientific and Technical Research (CONICET) of the Argentine Institute of Nivology, Glaciology and Environmental Sciences in Mendoza, Argentina, demonstrated that the CPE affected the southern hemisphere, specifically South America , which strengthens the case that it was a global climate event. The study was published online on June 15, 2020.

“There is a broad Triassic, and specifically Carnian, rocks and fossils in South America, and Argentina in particular, but until now there were no paleoclimatic studies that could conclusively demonstrate that the Carnian Pluvial Episode occurred in the southern hemisphere,” he said. Mancuso.

The team, which included researchers from the University of Utah and the Berkeley Geochronology Center, studied the Carniana rocks of the Los Rastros Formation, which are conserved in the Ischigualasto-Villa Unión basin in northwest Argentina. For the first time, the team accurately dated the volcanic ash preserved in the lake’s sediments and rebuilt the paleoclimate at this time.

“Our study focused on these rocks because they had the perfect combination of a good fossil record, dateable ash layers and rich climate data preserved in lake sediment,” said Randall Irmis of the Utah Museum of Natural History and the Department of of Geology and Geophysics from The University of Utah.

To date the ash layer, the scientists isolated tiny needle-shaped zircon crystals, minerals that act as time capsules. When the zircon crystallizes during an eruption, it traps the element uranium in its crystal structure, but never incorporates lead. Any lead preserved in the crystals today is the result of the radioactive decay of uranium. Because scientists know this rate of decomposition, they can measure the ratio of uranium to lead in each zircon crystal and calculate how long ago the crystals formed. In the present study, this measurement was performed on an accurate mass spectrometer at the Berkeley Geochronology Center.

The scientists then obtained paleoclimatic data by looking at detailed characteristics in the sediments: the types of clay preserved and the carbon and oxygen isotopes in the freshwater limestone layers. Using these measurements, the researchers estimated temperature, humidity, and aridity and observed a different range of particularly hot and humid conditions. Based on the absolute date of the same stratum, they concluded that it coincided with the CPE in the northern hemisphere. Using a variety of different analyzes, the resulting paleoclimatic inferences were stronger than previous claims made from a single line of evidence.

This warm / humid interval also incidentally includes layers that preserve the fossil footprints of the earliest dinosaurs or their closest relatives.

“Our study suggests that the emergence of dinosaurs in South America may be related to EPC, but the data available worldwide is inconclusive. Making a stronger global link between EPC and dinosaur diversification will require many More detailed paleoclimate studies with precise ages as we could do for the Los Rastros Formation in Argentina, “concluded Mancuso.