Herbivorous dinosaurs roaming the earth 200 million years ago were kept from reaching the equatorial zones by climate change.
Since the age of dinosaurs began on Earth and long after, the plant-eaters were inexplicably not found anywhere near the equatorial meridians. This territory is believed to have been populated solely by carnivorous dinosaurs, rather small in appearance compared with their plant-eating brethren.
Why were the low-latitudes of the equator so undesirable for the herbivorous giants remained a baffling question until recently.
A team of researchers from the University of Utah and the Natural History Museum of Utah, as well as the University of Southampton, UK, looked at the Ghost Ranch site located in the north of New Mexico and the wealth of fossils dating to the Late Triassic that are found here.
Based on the pieces of evidence at hand, the researchers concluded that what prevented the herbivorous dinosaurs from swinging right in the equatorial region like their carnivorous peers were the extreme and violent fluctuations in climate.
The tropical climate was constantly showcasing extreme events like drought, intense heat and ferocious wildfires that constantly changed the landscape and vegetation.
Randall Irmis, paleontologist at the Natural History Museum of Utah and co-author of the study explained:
“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”.
Specifically, the researchers looked at the fossils and charcoal that the wildfires left behind. To be able to reconstruct how the climate changed 200 million years ago, the scientists looked at carbonate nodules and stable isotopes found in organic matter at the Ghost Ranch.
During the Triassic Period, Ghost Ranch was as close to the equator as southern India is today.
In the first study of its kind, climate and ecology are put in the spotlight, shedding light on the implications of modern climate change as well. During the Late Triassic, the levels of carbon dioxide in the atmosphere were four to six times higher than modern day levels.
This may be indicative of the fact that if present trends continue and no changes are made to curb greenhouse gas emission, the climate we are creating will suppress the ecosystem of low-latitudes in a similar fashion to that of the Late Triassic.
University of Southampton’s Jessica Whiteside, lead author of the study, stated that each one of the datasets the researchers were working on are consistent with each other.
While the climate was changing violently, the pollen grains and the fossilized spores indicated different flora that grew around the equator at different times of the Late Triassic.
According to these findings, dinosaurs accounted for only 15 percent of the animal fossils found at Ghost Ranch. Of these, the majority were the carnivorous theropods. Sauropodomorphs or the giant, long-necked plant-eating dinosaurs did not feature at Ghost Ranch.
Knowing how the climate and vegetation looked at the time of Late Triassic makes it easier to understand why the equatorial regions were not a hospitable of desirable habitat for the herbivorous dinosaurs.
The study is published in its entirety in the journal PNAS.
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