MANOUSH ZOMORODI, HOST:
On the show today, ideas about breath. And we're going to go back now hundreds of millions of years before human history to dinosaurs.
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ZOMORODI: You know about their size...
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DAVID ATTENBOROUGH: The largest were plant eaters known as sauropods.
ZOMORODI: ...And their chompers.
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UNIDENTIFIED NARRATOR: With serrated teeth 16 centimeters long...
ZOMORODI: But there are still a lot of unanswered questions, namely...
EMMA SCHACHNER: Why did dinosaurs dominate in the beginning?
ZOMORODI: This is paleontologist Emma Schachner.
SCHACHNER: And why did they become the top predators, the top herbivores?
ZOMORODI: That's what Emma has been researching for the past several years, working to explore this hypothesis.
SCHACHNER: Their lungs may have played a role in this question.
ZOMORODI: Their lungs - and so at this point, we should say, Emma is not your typical paleontologist. Her job is to figure out how dinosaur lungs may have worked by looking for clues in animals that still exist today.
SCHACHNER: I personally am not doing a lot of the fossil work. I'm doing a lot more of pulling apart birds. I have a freezer filled with 80 hawks, owls and vultures.
SCHACHNER: And I have an 8-foot and 7-foot alligator in another freezer that we're going to CT and dissect. And...
SCHACHNER: I'm doing a lot more of the, like, validation of the modern animal because I find every time I dissect or CT a modern animal, we find discoveries of just anatomical structures that have not been seen before.
ZOMORODI: And so Emma is following these clues that she gets by dissecting all of these animal lungs and seeing if they can lead her to an explanation of how dinosaurs dominated the Earth starting about 220 million years ago.
SCHACHNER: The Triassic period - dinosaurs were not guaranteed to be the masters of the world at this point. So this is when the ancestors of mammals were evolving, and we have a really diverse array of other reptiles. We have all of these crocodilian-type ancestors that are running around - some had hooves; some had sails - a huge array of animals. And they were competing with dinosaurs at the same time. And then also, the atmosphere was really different. The oxygen levels were lower than they were today.
ZOMORODI: And Emma says not all animals have the same kinds of lungs or breathe the same way. And so she thinks since there was less oxygen, only some animals, like maybe dinosaurs, were easily able to breathe the Triassic air and flourish. Here's Emma Schachner on the TED stage.
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SCHACHNER: So how do we know what dinosaur lungs were even like since all that remains of a dinosaur generally is its fossilized skeleton? So we would look at the anatomy of birds, who are the direct descendants of dinosaurs. And we'd look at the anatomy of crocodilians, who are the closest living relatives. And then we would look at the anatomy of lizards and turtles, who we can think of like their cousins. And then we apply these anatomical data to the fossil record, and then we can use that to reconstruct the lungs of dinosaurs. And in this specific instance, the skeleton of dinosaurs most closely resembles that of modern birds.
ZOMORODI: So for Emma, birds are at the crux of her hypothesis and for two big reasons. The first...
SCHACHNER: Yes, so birds are the only living descendants of dinosaurs.
ZOMORODI: Birds are basically living dinosaurs. They come from the same family tree. And second...
SCHACHNER: The avian lung is specifically adapted to function under low-oxygen environments.
ZOMORODI: Birds fly up to where the air is thinner, but their lungs can handle it because they're built differently than ours.
OK, so, Emma, let's get into the lungs. Like, how do they actually work? And let's start with us mammals.
SCHACHNER: So the mammalian lung is really interesting. Our bronchial tree is shaped like an actual tree. So if you think about tree branches, they split and split and split until they get to the end as terminal branches that end in what are called alveoli. So with this mammalian lung, we have this common distribution of this gas exchange tissue that's all over the place.
ZOMORODI: And when you say gas exchange, that's oxygen moving from inside the lung and into the bloodstream, right?
SCHACHNER: Yes. Oxygen is going to flow across this membrane. Now, this is called the blood-air barrier.
ZOMORODI: Got it. OK.
SCHACHNER: So this blood-air barrier is really, really important. And because the entire lung is moving in mammals because it's this giant, flexible bag, it can't be too thin, or it'll break. Birds have done the opposite approach.
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SCHACHNER: So are you still with me? - because we're going to start birds, and it gets crazy. So hold on to your butts.
SCHACHNER: So in the bird, air passes through the lung, but the lung does not expand or contract. The lung is immobilized. It's inflexible and locked into place on the top and sides by the ribcage and on the bottom by a horizontal membrane. It is then unidirectionally ventilated by a series of flexible, bag-like structures beyond the lung itself, and these are called air sacs. Now, this entire extremely delicate set up is locked into place by a series of forked ribs. Also, in many species of birds, extensions arise from the lung and the air sacs, and they lock the respiratory system into place. And this is called...
ZOMORODI: So a bird lung is really elaborate. Every part is separated, spread out and super-specialized. And the blood-air barrier, that oxygenating membrane - it's protected by special ribs and bolted to the spine, which means it can be thinner and therefore transfer oxygen into the blood more efficiently. And Emma has found that dinosaur lungs were structured in a similar way.
SCHACHNER: So we're turning to dinosaurs. That's direct evidence that they had the infrastructural framework to thin the blood-air barrier.
ZOMORODI: And having lungs like that, like birds, would basically mean that in the low-oxygen environment of the Triassic - what? - 220 million years ago, dinosaurs would have had a huge advantage.
SCHACHNER: Yes. So the advantage of having the thin blood-air barrier is that oxygen can more easily cross the membrane, and then dinosaurs could breathe under the low-oxygen environment of the Triassic. And being able to breathe more easily means they can hunt more easily, run around more easily, reproduce more easily and ultimately just survive more easily in the Triassic period. And they could outcompete mammals, potentially lizards and everybody else that they live with in that environment.
ZOMORODI: So lungs might be the key to understanding how dinosaurs dominated the Earth. It's kind of amazing. I mean, I'm guessing that we humans, though, would never have made it back then.
SCHACHNER: (Laughter) So I think if a human was in the Triassic, we would not last longer than perhaps a few seconds.
ZOMORODI: That's paleontologist Emma Schachner. She researches and teaches animal anatomy. And you can find her full talk at ted.com.
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ZOMORODI: On the show today, ideas about the power of breath. I'm Manoush Zomorodi, and you're listening to the TED Radio Hour from NPR. Stay with us.
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