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Dinosaurs Were Neither Warm-Blooded Nor Cold-Blooded

Update Date: Jun 13, 2014 07:53 AM EDT

The debate among paleontologists over whether dinosaurs were warm- or cold-blooded seems to be ending with an unusual conclusion - the famous (infamous?) animals may have been both, according to a new study. 

"Our results showed that dinosaurs had growth and metabolic rates that were actually not characteristic of warm-blooded or even cold-blooded organisms. They did not act like mammals or birds, nor did they act like reptiles or fish," said University of Arizona evolutionary biologist and ecologist Brian Enquist, according to NBC News.

"Instead, they had growth rates and metabolisms intermediate to warm-blooded and cold-blooded organisms of today. In short, they had physiologies that are not common in today's world."

Researchers evaluated the metabolism of numerous dinosaurs with the help of a formula based on their body mass, as revealed by the bulk of their thigh bones. They also estimated their growth rates as reflected by the rings seen in fossilized bones. 

"Most dinosaurs were probably mesothermic," said University of New Mexico lead researcher John Grady in the press release. "A thermally intermediate strategy that only a few species - such as egg laying echidnas or great white sharks - use today."  

"[W]hen the effects of size and temperature are considered, dinosaur metabolic rates were intermediate to those of endotherms and ectotherms and closest to those of extant mesotherms," Grady and his team wrote.  

"Our results suggest that the modern dichotomy of endothermic versus ectothermic is overly simplistic," investigators wrote in a journal article detailing the results of their study. 

The article has been published in the journal Science

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