Short Wave - Some Dinos Had Feathers. Did They Fly?

Episode Date: January 15, 2025

When you picture a dinosaur, what does it look like? For Jingmai O'Connor, 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 [e-mail] — 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.See 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

You're listening to Shortwave from NPR. Hey, Shortwaiver is Regina Barbara 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 t-saurus. 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 May 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-bearing mono-organelles 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 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 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 gifts? 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.

Okay, Jingme, 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? 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 and mammals in order to help with thermoregulation 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. 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. Yeah. So not all dinosaurs would have 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. Okay. In fact, only three non-bird groups of dinosaurs had those types of feathers. So it's a little bit semantics. Like, 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 panaceous feather. You were discussing about why these proto feathers don't look anything like modern feathers. Can you get into that? What did they look like, then? Proto feathers 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 a 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 caratness 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. 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 Microwpter, 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. 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. 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 survives. So why did they make it through 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 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 a very elevated metabolic rates and they have these very strange growth pattern where almost all birds grow to adult size in the 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 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 this one group of birds just had evolved more advantageant characteristics than 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 like flew? Like 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, physics. I was like, oh, that's why. Yeah, physics. You're like, I understand. 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 phalientology. Yeah. We're not just digging in the dirt. Like, there's a dinosaur called Microraptor. And actually, Micropter has like huge aerodynamic surfaces create 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.

Yeah. 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 1915, this researcher named William Beebe was just like kind of pontificating about the evolution of flight and 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? Just from his noggin. Yeah, just, you know, just hypothesizing what might have happened. Yes. And then its 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 micropter and birds, right? Yeah. Now let's enter this dinosaur, Ichi. Ichi, 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? 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-wing 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 like can't imagine where we'd be right now, just like lost in the dark, never able to tease. out with 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 Keely. Beth Donovan is a 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. Thank you.