Dinosaurs - from pipsqueaks to monsters

And now ... dinosaurs!

Robyn Williams: Legend has it that before the dinosaurs were wiped out 65 million years ago, we mammals were puny creatures the size of ferrets, slinking around the periphery, shy, but with lots to be shy about. But surely those dinosaurs began as proud beasts in the making, like baby Rockys or Schwarzeneggers showing what was there in store. But no, pipsqueaks says Steve Brusatte. How come?

Steve Brusatte: Well, the very first dinosaurs grew up in a world that was much, much different from today, and the biggest difference was there was just that one single supercontinent. All of the land was glued together into this one enormous landmass that stretched from the North Pole down to the South Pole, and it was surrounded by a single global ocean.

Now, the interior of Pangaea, the supercontinent, was many, many, many thousands of miles from the closest oceans, so these were harsh areas, desert areas, dry areas, areas where it was very hard to live. But there were some organisms that were well adapted to that world. There were some amphibians, there were various types of reptiles, there were early relatives of mammals that were thriving in the Permian period on Pangaea.

But then at the end of the Permian period these enormous volcanoes started to erupt in the north part of Pangaea in what is now Siberia, and those volcanoes erupted it seems like for a few million years, and these were volcanoes completely out of scale of anything humans would recognise. These were fissures in the Earth. It's like the Earth was sliced with a giant machete and it bled lava for millions of years. And the lava covered a land area that was larger than Western Europe. But that wasn't even the biggest problem, the biggest problem was all the poisonous gases that came up with the lava, the methane, the carbon dioxide, these greenhouse gases that warmed the atmosphere, led to a spike of global warming, and that caused a mass extinction, and so many of the creatures of Pangaea, maybe up to 95% of species died out, but it was that extinction that opened the gate for the dinosaurs.

Robyn Williams: Now, the dinosaurs, I would imagine, would have taken the stage and just been there and taken over for the next 150 million years. But they weren't naturally adapted like that as much as, well, the relatives of the crocs, they were the rivals. What were they like?

Steve Brusatte: So after that mass extinction you had essentially a wide-open world, a new playing field, and so all kinds of new animals started to evolve in that world, the first turtles, the first pterodactyls, the first true mammals, and the first crocodiles and the first dinosaurs. And you might think that the first dinosaurs were already things that looked like T. rex or brontosaurus because those are the dinosaurs we all think of when we think of dinosaurs, but in fact the first dinosaurs looked nothing like those later giant species. The first dinosaurs were humble animals, they were about the size of a house cat, they walked on all fours, you could hold them in your arms. They were rare animals as well, only a fraction of their ecosystems. And they were being eclipsed, they were being out-competed, essentially, by their crocodile cousins.

Crocodiles are close cousins of dinosaurs, and back in the Triassic period, which was the time after the mass extinction, you had all kinds of crocs. You had of course meat-eating crocs, you had plant-eating members of the croc family, you had ones that were getting close to the size of buses, you had ones with armoured plates on their bodies, you had ones that ate plants, you had ones that had beaks that lost all their teeth. All kinds of early crocs, and they were more diverse than the dinosaurs, they were doing more things than the early dinosaurs, they were eating more foods, they were living in more places. And so it really was a croc world at that time.

But that lasted for a few tens of millions of years, for quite a long time, but then there was another extinction at the end of the Triassic period when the supercontinent of Pangaea finally started to break apart. And of course it started to break apart, that's why we have separate continents today. And as it did so, as the land started to fracture, eventually water came to fill the gaps, the Atlantic Ocean opened up between North America and Europe, between South America and Africa. But before the water came in, once again the Earth bled lava, and once again there were these mega volcanoes and once again there was a mass extinction. And strangely enough, the crocs were decimated but the dinosaurs sailed right on through. And it was after that extinction when dinosaurs really started to take over the world.

Robyn Williams: What was their biological secret? What did they have that the other creatures didn't?

Steve Brusatte: That's a really good question, and that's the crux of this article I wrote in New Scientist, and it's also something I talk about in my book, in The Rise and Fall of the Dinosaurs, and in the book I call this the biggest mystery that remains about dinosaur evolution, which means I don't have a really good answer, it's not cut and dried. It's not clear that dinosaurs survived the extinction because they had a certain way of running or a certain way of growing or they had horns or a type of teeth or anything like that, it's not clear at all. And it is a wide-open question and it is something that I think somebody in the next generation of palaeontologists is going to solve. But there are a few ideas out there. One idea was it's just total dumb luck, you have this mass extinction, a lot of things die out really quickly, and from that carnage the dinosaurs just walk away quite randomly.

The other idea is that there was something special about dinosaurs that helped them survive the catastrophe. Whatever special thing this was or series of special things, they didn't necessarily help dinosaurs overtake the crocs during the normal time of the Triassic but once the extinction hit, the dinosaurs had something special. So maybe they did grow faster than the crocs, maybe they could run faster, maybe they had feathers on their bodies and they could control their body temperature better.

Maybe they had these really special birdlike lungs, and this is something that I talk about in the article because there's a couple of young palaeontologists, Emma Schachner in the US, and Cecilia Apaldetti in Argentina, who make a really strong case that many dinosaurs had the same lungs that birds have today, and those lungs are very efficient, they can take in more oxygen than mammal lungs and they also have air sacs connected to them that reach throughout the body and can lighten the body, can cool the body down, that factors into metabolism and growth and so on.

So I think there's something promising about the lungs. I don't want to anoint it just yet and say the lungs are the answer, but I think this is getting down the right track.

Robyn Williams: Would that make it lighter in the body, and also you can do things like the birds do which is almost breathe in and breathe out at the same time. So, even though you're huge, you're not weighing quite so much, and you get more energy turnover quickly.

Steve Brusatte: Exactly, exactly. So the bird lungs really are a superpower because you bring in more oxygen with those lungs, much more than mammals because you are bringing in oxygen when you're breathing in, of course, but also when the birds breathe out they take in oxygen, it's a feat of engineering, it's enabled by those air sacs that store oxygen-rich air. Some of that oxygen-rich air during the breath in is shunted off to the air sacs, and then when those deflate, when the bird breathes out, that air still has oxygen, it passes across the lungs again, so birds get twice the bang for their buck when it comes to breathing.

But also, as you say, those air sacs, they have other benefits, they extend throughout the skeleton, even into some of the bones, they lightened the bones, they allowed these dinosaurs to get big while still having lightweight skeletons, that's something mammals have not been able to do and probably why no land mammals have ever approached the largest dinosaurs in size.

And those air sacs can cool the body down, they are like an air-conditioning system. So I really do think there's something to the lung and maybe it wasn't only the lung that explains what happened at the extinction but I think the lung is probably a big part of the story. It might be part of a winning hand of cards that the dinosaurs had compared to their crocodile competitors.

Robyn Williams: Yes, it's fascinating stuff. You mentioned two of your colleagues, one in Argentina and one in the States. Are you looking these days in the field for evidence from fossils like that?

Steve Brusatte: I am. Not so much in the Triassic anymore, I must say. I did do a lot of fieldwork earlier in my career when I was a student in the Triassic rocks at places like Portugal and Poland and Lithuania looking for early dinosaurs and some of these early croc animals. I moved on to other things. Really I'm doing a lot more fieldwork nowadays here in Scotland, we have Jurassic-age rocks on the Isle of Skye where there are dinosaur footprints and dinosaur bones preserved, in one of the most gorgeous settings you can imagine. And I also do a lot of work now on what happened right after the asteroid came down and killed off the dinosaurs and how mammals seized the crown from the dinosaurs.

Robyn Williams: Because I think the mammals at that stage when the thing hit, they were almost as meek and mild as, well, the dinosaurs were way back, as you describe, by the side of the lake, running around, the size of a pussycat.

Steve Brusatte: Yes, that's right. This is a recurring theme in evolution; from small things great things come. And when you think about it, it really has to work that way, evolution isn't just going to just produce a T. rex out of nowhere or a brontosaurus out of nowhere or an elephant or a whale out of nowhere. All of these groups that went on to become dominant animals, they had to start somewhere, they had to start small, in the shadows, in the marginal niches, in worlds that were dominated by other animals. And they had to bide their time, and oftentimes they had to get lucky, oftentimes there have been these extinctions that have wiped the slate clean, that have cleared the deck, and that happened with dinosaurs, and that then later happened when the dinosaurs were wiped away, giving way to the mammals.

Robyn Williams: It's an exciting story, thank you very much, Steve.

Steve Brusatte: Always a pleasure, Robyn, always a pleasure.

Robyn Williams: One of the great writers on dinos, Steven Brusatte is Professor of Palaeontology at the University of Edinburgh. His latest book is The Rise and Fall of the Dinosaurs.

-Australian Broadcasting Corporation