Deep Dive
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Hey short wavers, Regina Barber here. I'm going to start today's episode with a question. When I say dinosaur, what do you picture in your head? Maybe a stegosaurus, like a chunky guy with diamond-shaped plates and a ridge along its back. Or a triceratops with like huge horns, kind of like a rhinoceros, but like a little kid had drawn it. Or a T-Rex, classic, big body, big teeth, tiny little arms. But what you might not think of
are feathers. It turns out many dinosaurs did have feathers. We found that out in the mid-90s when dinosaur fossils were discovered at the bottom of a lake in China.
In lakes, you have no scavengers and you have guaranteed burial. And so this leads to really exceptional preservation. And these fossils from China, the most common soft tissue they preserve are feathers. This is Jing-Mei O'Connor. She's a dinosaur paleobiologist and the associate curator of fossil reptiles at the Field Museum of Chicago. And she says that the structure of a feather is mostly keratin.
which is a protein that usually breaks down over time. But when feathers have pigment inside them, they have these pigment-bearing mono-organelles called melanosomes. They're in our eyes, they're in the ink sacs of squid, they're everywhere, right? So these organisms
Organelles are extremely decay resistant. So the keratin matrix of the feather is gone. But these pigment containing mono organelles get fossilized very easily. And that's why we can now tell you sort of what color some feather dinosaurs were by looking at these these melanosomes.
For the longest time, I admit, I thought that people at the museums or in the movies were like taking some creative license. Like how would they know that all of these dinosaurs had those specific colors, that stripe pattern, these feathers? Because the thing that always threw me off was that some dinosaur displays in the museums had feathers and others didn't have any. Like what gives?
But of course, they were as accurate as possible. The colors, the patterns, and even which dinosaurs had feathers. Because spoiler alert, not all of them did. So today on the show, the gorgeous, vivid world of dinosaur feathers. Which dinosaurs had feathers? Were they using them to fly? And once and for all, what are ancient dinosaurs' relationship to birds today? You're listening to Shortwave, the science podcast from NPR. ♪
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Okay, Jingmei, I'm really excited to talk to you about dinosaurs and flight and all of that. And I think we need to start with the basics. Feathers, did all dinosaurs have them? How do we know? So...
It's very likely that only smaller dinosaurs were feathered and theropods in particular. So basically, we know that the earliest dinosaur was a small, warm-blooded animal. And the earliest feathers evolved for the same reason as fur in mammals, in order to help with thermoregulation in a warm-blooded animal.
Right. If you are small and you're warm blooded and you don't have something to keep your body heat in, you're just shedding the body heat off your skin. It would take a ton of energy to maintain a high body temperature. So you need insulation. OK, so so then if dinosaurs got like bigger, they probably wouldn't need as much insulation. I'm guessing like cold blooded ones wouldn't either. Yeah. Right. So not all dinosaurs would have been fatigued.
been feathered. And also, when we talk about feathers and dinosaurs, we're talking about these early evolutionary stages and feathers. When we think about a feather in the modern sense, that is restricted to a very narrow group of theropod dinosaurs. In fact, only three...
non-bird groups of dinosaurs had those types of feathers. So it's a little bit semantics. When you say feather, do you mean even the earliest evolutionary stage of a feather all the way up to the very complex feathers we see today? Or do we restrict that term? That's why sometimes we'll call those primitive feathers proto-feathers and then
We'll refer to the modern, very complex feather as a panaceous feather. You were discussing about like why these protofeathers don't look anything like modern feathers. Can you get into that? Like what did they look like then? Protofeathers basically just look like hair. They're very simple monofilamentous structures, right? Got it. Developmentally, totally different than hair. But superficially, that's what they look like. And superficially, they probably both evolve for a similar purpose. Got it.
Why are they so different? So basically the difference between a feather, a proto feather, which looks like a hair and hair is in their development. Like feathers and hair, one of them starts by kind of
folding inwards in the skin and then forming the follicle. And the other forms first as a projection out of the dermis and then becomes this complex structure. Yeah. Also, feathers are the only keratinous structures that don't grow continuously throughout life. When that actually evolved, we're not sure because modern feathers are so complex that they can't keep growing, right? They have very distinct structures.
distal end and proximal end that are morphologically, like the shape of them is very different. Whereas a hair or a beak or fingernails are all just the same. So they can just continuously grow. Okay. So this brings me to a question I've been dying to ask.
Are birds descendants of dinosaurs or are they actually dinosaurs? Birds are dinosaurs. Okay. Birds are one group of dinosaurs. And I think when we think of a dinosaur, we think of Triceratops or Stegosaurus. And these are dinosaurs that are not closely related to birds. Like, for example, if you looked at an artist's reconstruction of something like Velociraptor or Microraptor, a small feathered theropod dinosaur, very closely related to
birds, you would see that it pretty much looks the same as a bird. I mean, there's some structural differences in proportions and some minor differences in the skeleton. But in terms of the plumage, like the soft tissues covering the body, it would have looked very, very bird-like.
Okay, but let's talk about birds then. What made them so well-equipped for the modern world in a way that, like, these other dinosaurs, they were not equipped? How did these dinosaurs that were basically birds survive? ♪
Probably the million dollar question in my area of dinosaur paleobiology is, you know, understanding the selectivity of the end Cretaceous mass extinction. Why did only birds survive? And it's not just that birds survived. There were lots of birds that go extinct alongside non-avian dinosaurs. It's really just one group of birds that survives. So why did they make it through and nobody else?
We don't really have the answer. Like I said, if we did, I'd have that million dollars. I'm kidding. But we have a lot of hypotheses. And one of them is because birds are the most modified group of amniotes on our planet.
Now, every single biological system of making up the bird's body has been modified in some way for powered flight, which is the most physically demanding form of vertebrate locomotion. So they have incredibly efficient respiratory system. They have an incredibly efficient digestive system that is shorter, more lightweight, more efficient than a mammalian digestive system.
You know, they have very elevated metabolic rates and they have these very strange growth pattern where almost all birds grow to adult size in a matter of weeks to a couple months. I mean, there's just so many weird things about the biology, about the physiology of
birds. And it's probably these features that allowed them to survive this environmental crisis. But I would, I would guarantee you that it is not a single factor that you can point to and say, this is why. Evolution is incredibly complex and it's probably never just one reason that we can point to. It's probably a bunch of different reasons. And so we think it's this one group of birds just had evolved more advantage and characteristics and that allowed it to survive. Okay. So
Birds are dinosaurs, and we know that these dinosaurs had feathers, but how do we know that they actually flew? Did they fly?
Okay, this is a cool question because I mentioned that we know that the wing-like structure was already present in non-avian dinosaurs and inherited by birds, right? So how do we know that those dinosaurs weren't flying? The key characteristic for us is the vein asymmetry in the primary feathers. So the primary feathers are the ones that attach to the hand. They form the distal part of the wing and they are primarily responsible for generating the lift that allows birds to fly.
And on one side, the vein is very narrow. And on the other side, it's very wide so that the feather itself is asymmetrical. All other feathers are symmetrical, like all the feathers on the body. Unless the feathers are used for flight, they're always symmetrical. And it's only the primary feathers that are usually very highly asymmetrical. Oh, because you need lift. Yeah. So the asymmetry helps to create the cambered profile of the wing that then generates lift through Bernoulli's principle. Yeah, exactly. It's super cool. Yeah, physics.
You're like, I get this. You probably understand this way better than me. But basically, if you look at the feathers, the primary feathers and all these non-flying dinosaurs, the feathers are symmetrical. So they don't have, they're not generating lift. This is so cool. This is so cool. Yeah. So yeah, we use physics and paleontology. Yeah.
We're not just digging in the dirt. Like there's a dinosaur called Microraptor. And actually Microraptor has like huge aerodynamic surfaces created out of feathers on its arms and its legs. Right. But not only does it have proportionately large aerofoils attached to its arms and legs, but the feathers are clearly highly asymmetrical.
So this allows us to make a strong hypothesis that Microraptor was not just a feathered dinosaur with proto wings, but that it actually was flying. And all Mesozoic birds also have asymmetrical feathers. You have no idea how happy this is making me. I'm like, I know how Lyft works. This makes complete sense.
If you find a symmetrical feather, it didn't fly. Great. Yeah, exactly. Okay. Okay. Let's get back to flight. Earlier you said like in the era when most of those dinosaurs died out, one group of these like small, these avian dinosaurs survived the Cretaceous mass extinction and they became the birds we see today. Right.
But was there like one dino ancestor that evolved to fly? And then like, that's why we're seeing all these flying dinosaurs. Or could the evolution of flight have happened in like different animals at different times, like independently? Okay, like it's a little bit of a story and I'll try to tell it quickly.
in like 19 different forms of flight in dinosaurs, which poses the question that perhaps flight evolved multiple times in dinosaurs. This is a big debate right now. Did flight evolve once in the common ancestor of all flying dinosaurs?
Or did flight evolve independently multiple times? Amazing. I love it. It's like really exciting to think about the fact that there are all these different flying dinosaurs around during this certain period of time, like four-winged flying dinosaurs, little flying squirrel dinosaurs. But the other cool thing is that we only know what the wings of these dinosaurs look like because they preserve soft tissues. And if we didn't have those fossilized soft tissues, I just can't imagine where we'd be right now. Just like...
lost in the dark, never able to tease out what these squished fossils are telling us. Jingmei, thank you so much for coming on our show. I think I love dinosaurs more than I did before, and it's all because of you. Thank you so much. Awesome. Well, my job here is done then. This episode was produced by Hannah Chin. It was edited by showrunner Rebecca Ramirez. The engineer was Jimmy Keeley. Beth Donovan is our senior director, and Colin Campbell is our senior vice president of podcasting strategy.
I'm Regina Barber. Thank you for listening to Shortwave from NPR.
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