Why the big dinosaurs steered clear of the tropics


The tropics were an inhospitable place 200 million years ago.
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Large dinosaurs remains have seldom been found near the equator. In fact few dinosaurs of any kind, apart from a few small-bodied meat-eating ones, appear to have lived there. Now scientist may finally be able to say why – the climate may have just been too hostile.

Having pieced together what conditions were like 200 million years ago, scientists working at Ghost Ranch in northern New Mexico, a site rich with fossils, say the tropical climate swung wildly with extremes of drought and intense heat.

"Our data suggest it was not a fun place," says scientist Randall Irmis of the University of Utah.

"It was a time of climate extremes that went back and forth unpredictably. Large, warm-blooded dinosaurian herbivores weren't able to exist close to the equator – there was not enough dependable plant food."

The study, led by geochemist Jessica Whiteside, now of the University of Southampton, is the first to provide a detailed look at climate and ecology during the emergence of the dinosaurs.

Atmospheric carbon dioxide levels then were four to six times current levels. "If we continue along our present course, similar conditions in a high-CO2 world may develop, and suppress low-latitude ecosystems," Irmis says.

The findings are reported in the journal Proceedings of the National Academy of Sciences (PNAS).

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