An artist’s impression of dinosaurs that lived 200 million years ago. Photo: Victor Leshyk/PA WireDinosaurs that lived 200 million years ago have given scientists a dramatic glimpse of what may be in store for the world if greenhouse gas emissions are not held back.
The largest of the creatures were kept away from equatorial regions for more than 30 million years by extreme climate swings, droughts and devastating wildfires.
At the time, during the Late Triassic period, atmospheric carbon dioxide (CO2) levels were four to six times what they are today.
US expert Randall Irmis, from the Natural History Museum of Utah, said: “If we continue along our present course, similar conditions in a high CO2 world may develop and suppress low-latitude ecosystems.”
Why giant plant-eating dinosaurs took so long to populate the tropics has been a long-standing mystery.
The long-necked sauropods remained absent from the fossil record of equatorial regions until at least 30 million years after they first appeared on earth.
They did not make the move to the tropics until 10 to 15 million years after they had diversified and become abundant closer to the poles.
New research published in the journal Proceedings of the National Academy of Sciences suggests that climate was the reason. Long periods of drought, during which vegetation was scarce, would have made it impossible for the huge herbivores to satisfy their enormous appetites.
The findings show that in a high CO2 world the tropical climate swung dramatically between wet and dry years.
During the dry periods, vegetation die-offs fuelled raging wild fires that burned at temperatures as high as 600˚C, which in turn killed more plants and damaged the soil.
If we continue along our present course, similar conditions in a high CO2 world may develop
Lead scientist Jessica Whiteside, from the University of Southampton, said: “The conditions would have been something similar to the arid western US today, although there would have been trees and smaller plants near streams and rivers and forests during humid times.
“The fluctuating and harsh climate with widespread wild fires meant that only small two-legged carnivorous dinosaurs, such as Coelophysis, could survive.”
While the ancestors of famous plant-eating giants such as Brachiosaurus and Diplodocus avoided the tropics, their place was taken by early reptiles and crocodile relatives including long-snouted phytosaurs and armoured aetosaurs. These creatures were better able to withstand the wild and severe conditions, saidthe scientists.
The scientists studied rock samples from Ghost Ranch in New Mexico, where a large number of Triassic fossils have been discovered.
The rocks were deposited by rivers and streams between 205 and 215 million years ago. At the time, northern New Mexico was very close to the equator, at around the same latitude as the southern tip of modern India.
Analysing the samples allowed the researches to assess ecosystem changes and measure atmospheric carbon dioxide levels.
Fossilised bones, pollen grains and fern spores provided information about the types of plants and animals living at different times, while ancient charcoal remains made it possible to estimate wildfire temperatures. Dinosaurs accounted for less than 15 per cent of the animal fossils found. The findings will improve understanding of the consequences of human-caused climate change, said the scientists.
US co-author Nate Smith, from the Natural History Museum of Los Angeles County’s Dinosaur Institute, said: “Our study suggests that elevated CO2 and fluctuating plant diversity could fundamentally reshape vertebrate communities, and may account for the regional differences in dinosaur faunas that persisted for millions of years.”