Dinosaurs: Were They Cold Blooded?

Dinosaurs: Were they cold blooded?

While dinosaurs were traditionally presumed to have been cold blooded (ectothermic), the behavioural implication of this that they were slow and docile creatures has now been thoroughly discredited. These days, dinosaurs are regarded as highly adapted and sophisticated animals that lived very active lives.

Whats more, recent discoveries suggest many small theropods (the dinosaurs from which birds are descended) possessed metabolisms closer to warm-blooded (endothermic) birds than cold-blooded reptiles. For example, fossilised remains of hairs and feathers covering their body would have insulated them from heat loss, just like on mammals and birds today.

And even if the larger, slower dinosaurs were cold blooded, their large body volume relative to their skin surface area means that body heat loss through their skin would have been slow. In other words, they had a built-in system for retaining body heat (this is known as inertial homeothermy or, more appropriately, gigantothermy).

Did you know?

In all, around 700 distinct species of dinosaur have been discovered and named over the past 185 years, and it is thought that just as many new species are still waiting to be discovered in fossil sites around the world. By comparison, 10,000 distinct species of bird have been identified as living on the planet today, as well as almost 8,000 species of lizard and snake, 5,400 species of mammal, and (dwarfing everything else completely), 900,000 distinct species of insect.

18-21, M
3 Responses Mar 3, 2010

Then again, none of the dinosaurs inhabited cold regions. Any snow raptors?

Did you know they discover on average 10 new species of insect every month! So 900000 is a definate understatement. Anyway, back to dinosaurs. Back in the Mesozoic, the earth's climate was around 10 degrees warmer on average than it is now. The atmosphere was much more dense and contained a higher concentration of O2 (which is what allowed such large creatures to be energetically feasable) taking all this into account it's easy to see that retaining heat wouldn't be the difficulty, but rather, keeping cool would be the chalange. That's why many species of dinosaur and synapsid had those huge fans on their backs, to emit the excess heat. Or at least that's the leading theory. Wether or not they were endo or ectothermic, I can't say for sure, I would need to see their hearts for that, but they definatly had physiological adaptations for temperature regulation. On another note, did you know that birds are not believed to be monophyletic, and that most biologists just concider them as dinosaurs. I.e. There's no class aves, all birds are just class reptilia, order theropoda. Trippy eh?

yes, very interesting, thanks for sharing. :)