Some Dinos Had Feathers. Did They Fly?

When you picture a dinosaur, what does it look like? For Jingmai O'Connor https://paleontologista.com/, paleobiologist and associate curator of reptiles at the Field Museum of Chicago, the dinosaurs she studies look a lot more like birds. "If you looked at an artist's reconstruction of something like Velociraptor or Microraptor ... you would see that it pretty much looks the same as a bird," Jingmai says. "In terms of the plumage, the soft tissues covering the body, it would have looked very, very birdlike." In this episode, Short Wave delves into the dinosaur-avian connection. Which dinosaurs had feathers? Were they using them to fly? And once and for all – what are those ancient dinosaurs' relationship to birds today? Have other dinosaur questions you want us to unravel? Email us at [email protected] mailto:[email protected] — we'd love to hear from you! Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:00Speaker 00

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• 0:27Regina Barber?

  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?

• 0:38Regina Barber?

  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.

• 0:51Regina Barber?

  Or a T-Rex, classic, big body, big teeth, tiny little arms.

• 0:58Regina Barber?

  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.

• 1:12Speaker 02

  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.

• 1:23Regina Barber?

  This is Jingmai 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.

• 1:37Speaker 02

  But when feathers have pigment inside them, they have these pigment-bearing monoorganelles called melanosomes. They're in our eyes, they're in the ink sats of squid, they're everywhere, right? So these organelles are extremely decay-resistant. So the keratin matrix of the feather is gone, but these pigment-containing monoorganelles 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 melanosomes.

• 2:10Regina Barber?

  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?

• 2:39Regina Barber?

  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 Short Wave, the science podcast from NPR.

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• 4:28Regina Barber?

  Okay, Jingmei, I'm really excited to talk to you about dinosaurs and flight and like all of that. And I think we need to start with like the basics. Feathers, like, did all dinosaurs have them? Like, how do we know?

• 4:40Speaker 02

  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 thermo regulation in a warm-blooded animal. Right? If you're 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.

• 5:11Regina Barber?

  Okay, 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, is that right?

• 5:20Speaker 02

  Yeah, so not all dinosaurs would have been feathered. And also, when we talk about feathers in dinosaurs, we're talking about these early evolutionary stages in 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 I just like, like, it's a little bit semantics. Like, do you, when you say feather, do you mean even the earliest evolutionary stage of 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 penicious feather.

• 6:00Regina Barber?

  You were discussing about like, why these proto-feathers don't look anything like modern feathers? Can you like, get into that? Like, what did they look like then?

• 6:07Speaker 02

  Proto-feathers basically just look like hair. They're very simple, monofilamentous structures, right?

• 6:14Regina Barber?

  Got it.

• 6:14Speaker 02

  Developmentally, totally different than hair. But superficially, that's what they look like. And superficially, they probably both evolved for a similar purpose.

• 6:23Regina Barber?

  Got it. Why are they so different?

• 6:26Speaker 02

  So basically, the difference between a feather, a proto-feather, which looks like a hair, and a hair is in their development.

• 6:33Regina Barber?

  Okay.

• 6:34Speaker 02

  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 coratidus 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 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.

• 7:13Regina Barber?

  Okay, so this brings me to a question I've been dying to ask. Are birds descendants of dinosaurs, or are they actually dinosaurs?

• 7:21Speaker 02

  Birds are dinosaurs.

• 7:22Regina Barber?

  Okay.

• 7:23Speaker 02

  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, like, you know, differences in proportions, and some, you know, 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.

• 7:58Regina Barber?

  Okay, but let's, 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, how did these dinosaurs, that were basically birds, survive?

• 8:14Speaker 02

  Probably the million-dollar question in my area of dinosaur paleobiology is, you know, understanding the selectivity of the end-cretaceous mass extinction. Like, 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- Survived.

• 8:37Regina Barber?

  Oh.

• 8:37Speaker 02

  Why did they make it through and and nobody else? We don't really have the answer. Like you 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 in 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 they have incredibly efficient respiratory system. They have a incredibly efficient digestive system that is shorter, more lightweight, more efficient than a mammalian digestive system. You know, they have a very elevated metabolic rates and they have these very strange growth pattern,

• 9:22Speaker 02

  where almost all birds grow to adult size in a matter of weeks to a couple of 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.

• 9:43Regina Barber?

  Okay.

• 9:43Speaker 02

  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 advantageous characteristics and that allowed it to survive.

• 9:58Regina Barber?

  Okay, so birds are dinosaurs. And we know that these dinosaurs had feathers. But how do we know that they actually like flew? Like, did they fly?

• 10:07Speaker 02

  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.

• 10:50Regina Barber?

  Oh, because you need lift.

• 10:52Speaker 02

  Yeah, so the asymmetry helps to create the cambered profile of the wing that then generates lift through Bernoulli's principle.

• 10:59Regina Barber?

  Yeah, physics. I was like, oh, that's why.

• 11:01Speaker 02

  Yeah, physics.

• 11:03Regina Barber?

  This I understand.

• 11:05Speaker 02

  You probably understand this way better than me. But basically, if you look at the feathers, the primary feathers in all these non-flying dinosaurs, the feathers are symmetrical, so they don't have, they're not generating lift.

• 11:16Regina Barber?

  This is so cool. This is so cool.

• 11:17Speaker 02

  Yeah, so yeah, we use physics in paleontology. 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, um, all Mesozoic birds also have asymmetrical feathers.

• 11:54Regina Barber?

  You have no idea how happy this is making me. I'm like, I know how lift works. This makes complete sense. If you find a symmetrical feather, it didn't fly.

• 12:01Speaker 02

  Yeah.

• 12:02Regina Barber?

  Great.

• 12:02Speaker 02

  Yeah, exactly.

• 12:03Regina Barber?

  Okay, okay, let's get, 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.

• 12:16Speaker 02

  Yeah.

• 12:17Regina Barber?

  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?

• 12:29Speaker 02

  Okay, like, it's a little bit of a story, and I'll try to tell it quickly. In like 1915, this researcher named William Beebe was just like kind of pontificating about the evolution of flight in birds. And he hypothesized that in the evolution of avian flight, that it would have gone through a four-winged gliding stage. And he did this little drawing of what he thought this animal would look like, just like a made up animal, right?

• 12:54Regina Barber?

  Just from his noggin.

• 12:55Speaker 02

  Yeah, it just, you know, just hypothesizing what might have happened.

• 12:58Regina Barber?

  Yes.

• 12:58Speaker 02

  And then this dinosaur, Microraptor, was found in 2003. It has wings on its arms and on its legs, asymmetrical feathers, it was flying. And people got really excited about this. People thought Microraptor was proving that he was right about the evolution of flight. So we hypothesized that one origin event of flight in dinosaurs produced both Microraptor and birds, right?

• 13:20Regina Barber?

  Yeah.

• 13:21Speaker 02

  Now, let's enter this dinosaur, Echi. Echi, basically a little like flying squirrel dinosaur, right? So it's also a flying dinosaur, but it flies not with wings made out of feathers. It flies with wings made out of flaps of skin, like a flying squirrel. So now you have drastically 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?

• 13:57Regina Barber?

  Amazing. I love it.

• 13:59Speaker 02

  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 the 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.

• 14:27Regina Barber?

  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.

• 14:34Speaker 02

  Awesome. Well, my job here is done then.

• 14:38Regina Barber?

  This episode was produced by Hannah Chen. It was edited by showrunner Rebecca Ramirez. The engineer was Jimmy Keely. Betson Ivan is our senior director, and Colin Campbell is our senior vice president of podcasting strategy. I'm Regina Barber. Thank you for listening to Short Wave from NPR.

• 14:58Speaker 00

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