Only a few small-bodied meat-eating dinosaurs eked out a living near the equator around 200 million years ago, reports the study, which is published in the Proceedings of the National Academy of Sciences.
“Our data suggest it was not a fun place,” co-author Randall Irmis, curator of paleontology at the Natural History Museum of Utah and assistant professor at the University of Utah, said in a press release. “It was a time of climate extremes that went back and forth unpredictably and large, warm-blooded dinosaurian herbivores weren’t able to exist nearer to the equator — there was not enough dependable plant food.”
The researchers, led by geochemist Jessica Whiteside of the University of Southampton, focused on Chinle Formation rocks, which were deposited by rivers and streams between 205 and 215 million years ago at Ghost Ranch in northern New Mexico. (This site in the subtropics is well known to art admirers too, as it’s where artist Georgia O’Keeffe lived and painted for much of her career. The multi-colored rocks of the Chinle Formation are a common sight on the Colorado Plateau at places such as the Painted Desert at Petrified Forest National Park in Arizona.)
The rock layers contain multiple clues for what the environment was like in the tropics and subtropics back in the dinosaur era. These include fossils, charcoal left by ancient wildfires, stable isotopes from organic soil matter, and carbonate nodules, which formed in ancient soils.
“Each dataset complements the others, and they all point towards similar conditions,” Whiteside said. “I think this is one of the major strengths of our study.”
Fossilized bones, pollen grains and fern spores revealed the past flora and fauna of the site, or lack thereof. Dinosaur remains were surprisingly rare for the time, given that they were much more prevalent then in more northern and southern latitudes. Here, closer to the equator, however, their remains accounted for less than 15 percent of all animals. Reptiles that later gave rise to today’s crocodiles and alligators instead dominated the food chain.
The dinosaurs that did manage to live at the site were small, carnivorous ones. Big, long-necked plant-eating dinosaurs were completely absent.
The charcoal remains discovered in the sediment layers show that numerous wildfires occurred, with some being incredibly intense. The scientists suspect that plant die-offs, due to climate change, fueled hotter fires, which in turn killed more plants, damaged soils and increased erosion.
Read more at Discovery News
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