Australasian Science: Australia's authority on science since 1938

Were dinosaurs warm-blooded?

T. rex

There are several lines of evidence that the basal archosaurs were endotherms

By Roger Seymour

An analysis of muscular power reveals that cold-blooded crocodiles are poor models for our beliefs about dinosaur physiology.

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When thinking about dinosaurs, people typically think of large, powerful reptiles that were cold-blooded killers – just like modern crocodiles. The first dinosaur fossils were unquestionably associated with reptiles and just as unquestionably thought to be cold-blooded.

We call cold-blooded animals such as reptiles, amphibians and fish “ectotherms” because their body temperatures are influenced mainly by the outside environment. In contrast, warm-blooded birds and mammals are called “endotherms” because they heat their bodies internally. The strategies are so different that it makes us wonder what the dinosaurs were like.

We know that dinosaurs, crocodiles and birds form a group called the “archosaurs” (ruling reptiles), which evolved separately from the rest of the reptiles. Two lineages arose from the basal archosaurs – the crocodilian line and the dinosaurian line, the latter giving rise to birds.

The trouble is that the crocodilian line is represented today by cold-blooded crocodiles and alligators while the dinosaur line is represented by warm-blooded birds. This implies that either the dinosaur-bird line evolved endothermy from ectothermic basal archosaurs, or the crocodilian line evolved ectothermy from endothermic basal archosaurs.

I believe that all archosaurs, including all dinosaurs, were actually warm-blooded, while the crocodile...

The full text of this article can be purchased from Informit.