Herbivorous, giant plant eaters have first emerged in the Middle Triassic, some 230 million years ago, their absence in the low altitudes persisted for almost 30 million years, even after they have become abundant in north and south. Now, researchers think they know why.
To solve this long mystery, a team of paleontologists scoured the famed New Mexico fossil site, Ghost Ranch, which during the time period in question was only about 12 degrees north of the equator, on the supercontinent, Pangea. They hoped the evidence they gathered would enable them to reconstruct the ancient environments of the Triassic.
Jessica Whiteside, a paleoclimatologist at the University of Southampton and lead researcher of the study said, “For several decades, researchers noticed [that] large, plant-eating dinosaurs seemed to be much more common at high latitudes during the Triassic. However, in the past 10 years we’ve realized that they’re completely missing from the tropics, where only a few small carnivorous dinosaurs dwelled.”
Researchers have analyzed the carbon and oxygen isotopes within the rocks recovered at Ghost Ranch, they were able to reconstruct the ancient environment, and they found that carbon dioxide level were four to six times higher than today’s. they evidence also suggested persistent wildfires that ravaged the leafy vegetables on which large plant eaters relied.
Whiteside said, “Rapid climate swings, extremes of drought, and intense heat continually reshaped the vegetation available for warm blooded plant-eating dinosaurs, suppressing their ability to live in the low-latitudes for millions of years. These data suggest there are profound consequences for our modern world if they enter the high CO2 conditions that are predicted to occur in the next 100 years.”
This is the first multiproxy study to examine the interplay between climate change and ecosystem evolution at low latitudes.
Randal Irmis, a vertebrate paleontologist at the Natural History Museum of Utah said, “This is the first really detailed look tying together climate and paleoecology in the Late Triassic of western North America. There have been previous related studies from eastern North America where we find early dinosaur footprints, but this is really the first study of its kind from a Triassic site known for its abundant fossil bones of early dinosaurs and other reptiles.”
Irmis hopes that their research will inspire further interdisciplinary studies linking climate, habitat, and species range in order to further elucidate the complex evolutionary processes of the dinosaurs.
Irmis said, “I think it really emphasizes the interplay between climate and dinosaur evolution. Our results go to show that the rise of dinosaurs was a multi-faceted event that occurred in several stages, and occurred at different rates in different areas of the supercontinent Pangaea.”
The study appeared in the Proceedings of the National Academy of Sciences.