Dinosaurs in Argentina and in what is now the western United States moved toward the equator due to increasing levels of carbon dioxide in the atmosphere at about the same time. This is the conclusion of research conducted by Dennis V. Kent from Rutgers University in Piscataway, New Jersey and colleagues. The analysis was published in the May 19, 2014, edition of the journal Proceedings of the National Academy of Sciences.
The researchers used magnetochronology to estimate the age of 52 sites in the fossil bearing Los Colorados Formation in Argentina. The researchers compared the age of the Argentinean fossil site with the North American Chinle Formation using the same technology. Magnetochronology estimates time based on the reversals of the Earth's polarity as displayed in the polarity of the rocks in fossil bearing strata and in the fossil themselves. The method produces a highly linear correlation with paleontological time frames that is superior to isotope comparison methods.
The fossils in the Los Colorados Formation in Argentina and the North American Chinle Formation date to between 227 and 213 million years in age. The methods allowed the researchers to determine the movement of dinosaurs in both regions over at least 30 million years in time. Dinosaurs in both regions moved in response to polar shifts, continental drift, and carbon dioxide content of the atmosphere.
Dinosaurs in both North America and South America preferred a humid tropical climate. Over millions of yeas the levels of carbon dioxide in the North American Chinle Formation and the Los Colorados Formation in Argentina forced dinosaurs and other animals to move toward what are now more equatorial regions. Similar movement in response to climate has been documented in dinosaurs in Iceland, Canada, and Europe. This is the first research that shows a congruent movement of dinosaurs in the Americas in the same time periods.