Dinosaur eggs reveal: most were warm-blooded

Adam Murphy’s been looking at some cracking, cutting edge science with Yale University's Robin Dawson: using eggshells to take a dinosaur’s temperature…

Adam - Jurassic park is one of my favourite films. I watch it several times a year. But as the years go on, the picture on screen gets further and further from reality, and the scary lizard-like thing peering in the window of a Jeep probably didn't match what dinosaurs look like - as dinosaur expert Robin Dawson was quick to point out to me.

Robin - I think for as long as we've named dinosaurs, we've gone from thinking they're lizard-like and reptile-like, to now over the years learning the group of dinosaurs which includes the scary Velociraptor that's in all the movies, this group of dinosaurs that birds evolved from. The more we learn about them, the more characters they seem to have that are kind of bird-like.

Adam - We know T-Rex had feathers, for example. We also know that T-Rex was warm-blooded like a bird, not cold-blooded like a crocodile. But Robin's been working on a different technique to measure dino temperature by looking at the eggshells of dinosaurs. Eggshells contain carbon and they contain oxygen, and sometimes these elements will have an extra particle called a neutron inside them - and that makes them heavier. If a heavy carbon binds with a heavy oxygen, it makes a much stronger bond and it takes more heat to pull them apart. So if you look at the egg shell and it's got none of those kinds of bonds, that means that when mama dinosaur was making the eggs, she must have been running hot enough to stop them forming. And if she was cooler, there'd be more of those bonds.

Robin - There's more energy in the system, and so those bonds are able to break and move around and exchange in the lattice with each other. So the thing that is really cool about this technique is, since for example a dinosaur eggshell grows within the mother dinosaur, the temperature at which that calcite mineral shell of the egg is growing is the internal body temperature of the mother dinosaur.

Adam - And recent work has shown that it's not just the dinosaurs that evolved into birds that were warm-blooded. Other, more distantly-related dinosaurs were as well. But what does that mean for what we know of dinosaur evolution?

Robin - Dinosaurs sit at this interesting evolutionary point between living reptiles and living birds, and reptiles are cold-blooded and birds are warm-blooded, and so this question about what dinosaurs were - you know, extinct dinosaurs - I think people have been wondering for a while, and there've been various attempts to try to get at this. What's really fascinating is that the dinosaurs we've studied which represent all these major groups, we've actually found that all of them had body temperatures warmer than their environment, which would suggest that they had capabilities to use their metabolism to raise their body temperatures above the ambient. And so if all major groups of dinosaurs have this, what it suggests, what's the most reasonable assumption then is that this is really something they acquired early on in their evolution. It's an ancestral trait if it's representative of the whole group.