Scientists Can't Agree If Dinosaurs Were Warm-Blooded or Cold-Blooded

Illustration for article titled Scientists Can't Agree If Dinosaurs Were Warm-Blooded or Cold-Blooded

Paleontologists have spent a vast amount of time digging up dinosaur fossils, studying them, and then slating Jurassic Park. But despite the effort, some questions still remain about our predecessors on this planet — including whether or not they were cold-blooded.


One of the most recent papers to tackle this question was a 2014 study, published in Science, which came to the rather middle-of-the-road conclusion that dinosaurs were mesotherms, somewhere between warm and cold blooded. But, as Live Science documents in an excellent article, some scientists aren’t happy with the conclusions.

The study involved counting rings in fossilized dinosaur bones, which show signs of aging in rings, just like trees. By examining the growth rate of dinosaurs, and comparing it to that of modern-day warm-and-cold-blooded animals, the team came to the conclusion that dinosarus were mesotherms — a conclusion disagreed with by Michael D’Emic, the author of a new study. He contends that the original authors didn’t analyze the data correctly, and that dinosaurs were really warm-blooded, just like mammals.

Naturally, the authors didn’t agree with his suggestions. The full back-and-forth — including some excellent (but very polite) scientific trash-talk — is over on Live Science, and is well worth a read.

[Live Science]

Art by R.J. Palmer

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The truth (as if we could actually get to it) is probably a mixture of all three. I’d say that many, if not most of the smaller species would be warm-blooded. The larger animals, and perhaps the oldest species, could very likely be mesothermic or even cold-blooded.

Consider the larger herbivores such as Apatosaurus— they would have to be constantly grazing to get enough energy to maintain their large bodies (I imagine herds of them cutting huge swathes through the countryside, like enormous bison), but to process that raw vegetation, they likely had a digestive system analogous to modern ungulates, where much of the energy-extraction is done by gut fauna.

Having a stomach the size of your living room full of active compost would generate enough heat to keep the entire animal going, without the need for the biological overhead of being a warm-blooded animal.