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Were dinosaurs warm-blooded?

One approach to this question is to look at the microscopic structure of bone. In many cold-blooded animals, bone grows in dense, concentric rings. In warm-blooded animals, a complex system of closely spaced cavities, called the Haversian system, permeates the bone. By cutting bones of extinct, non-avian dinosaurs into thin slices and examining them under the microscope, we can look for these characteristics. In most non-avian dinosaurs, the microstructure of the bone looks more like that of warm-blooded animals, but the evidence is not conclusive. Created by American Museum of Natural History.

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Video transcript

There are two different kinds of metabolisms we ascribe to animals today, warm-blooded like us humans are creatures that control their body temperatures, body temperatures tend to be warm, we're at ninety eight point six and our body temperature doesn't vary, unless we're sick, it doesn't vary with the outside temperature. Lizards, and a lot of other kinds of animals, of course, are what we call cold-blooded, not really cold-blooded technically, but what that means is their body temperatures, internal body temperature is much more labile, much more sensitive to the environment, when it's cold outside, their body temperature is cold, when it's hot their body temperature warms up. What were dinosaurs? Well we don't really know the answer to that question, actually based on some of the evidence of posture and locomotion we actually think that some of these more predatory dinosaurs might've been warm-blooded, whereas some of the larger vegetarian animals might have been cold-blooded, but we don't know that directly. But one thing is certain, that birds are warm-blooded animals and birds are a kind of dinosaur so somewhere in the evolution of dinosaurs warm-bloodedness eveolved. Maybe in those dinosaurs that aren't strictly classified as birds, maybe Tyrannosaurus was warm-blooded, we don't know that for sure but it's a good supposition.