Missing Tropical Dinosaurs Mystery Finally Solved

Scientists believe that they now know why the biggest dinosaurs on the planet stayed away from the tropics for millions of years.

Fluctuations associated with high atmospheric carbon dioxide, new findings suggest, may have prevented the establishment of a diversified populations of large dinosaurs such as sauropods and their relatives.

The giagantic long-necked plant eaters known as sauropodomorphs were, by the mid-Triassic some 212 million years ago, commonly found in northern latitudes such as present-day Europe, and southern latitudes such as what is now Argentina, but according to fossil records, were totally absent in the tropics.

Why did take around 30 million years after the origin of dinosaurs, well into the early Jurassic period, for these big creatures to start to show up in lower latitudes closer to the equator?

In a paper published Monday in Proceedings of the National Academy of Sciences, a team of researchers concludes that high atmospheric carbon dioxide levels in the Triassic period resulted in an unstable and hostile environment in the lower latitudes of the continent Pangaea.

Co-author Dr Randall Irmis of the University of Utah and the Natural History Museum of Utah, said:

“Our data suggest it was not a fun place. 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 team discovered that extreme climate swings during the Late Triassic Period correlate with changes in plant eco-structure. The community went from a seed fern dominated system to a conifer dominated one, and individual plant groups repeatedly cycled from rare to common through time.

“The conditions would have been something similar to the arid western United States today, although there would have been trees and smaller plants near streams and rivers and forests during humid times,” said study lead author Dr Jessica Whiteside of the University of Southampton, UK.

Jessica H. Whiteside et al.
Extreme ecosystem instability suppressed tropical dinosaur dominance for 30 million years.
PNAS, published online June 15, 2015; doi: 10.1073/pnas.1505252112

Illustration credit: Victor Leshyk