Jingmai O'Connor
Appearances
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Some Dinos Had Feathers. Did They Fly?
And that's why we can now tell you, sort of, what color some feathered dinosaurs were by looking at these melanosomes.
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Some Dinos Had Feathers. Did They Fly?
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?
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Some Dinos Had Feathers. Did They Fly?
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.
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Some Dinos Had Feathers. Did They Fly?
Is that right? 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. In fact, only three... Non-bird groups of dinosaurs had those types of feathers.
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Some Dinos Had Feathers. Did They Fly?
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.
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Some Dinos Had Feathers. Did They Fly?
Protofeathers basically just look like hair. They're very simple monofilamentous structures, right?
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Some Dinos Had Feathers. Did They Fly?
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.
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Some Dinos Had Feathers. Did They Fly?
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.
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Some Dinos Had Feathers. Did They Fly?
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.
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Some Dinos Had Feathers. Did They Fly?
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.
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Some Dinos Had Feathers. Did They Fly?
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.
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Some Dinos Had Feathers. Did They Fly?
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?
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Some Dinos Had Feathers. Did They Fly?
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.
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Some Dinos Had Feathers. Did They Fly?
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.
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Some Dinos Had Feathers. Did They Fly?
You know, they have very elevated metabolic rates and they have these very strange growth patterns 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.
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Some Dinos Had Feathers. Did They Fly?
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 it's this one group of birds just had evolved more advantage and characteristics and that allowed it to survive.
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Some Dinos Had Feathers. 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.
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Some Dinos Had Feathers. Did They Fly?
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.
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Some Dinos Had Feathers. Did They Fly?
And it's only the primary feathers that are usually very highly asymmetrical.
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Some Dinos Had Feathers. Did They Fly?
Yeah, so the asymmetry helps to create the cambered profile of the wing that then generates lift through Bernoulli's principle.
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Some Dinos Had Feathers. Did They Fly?
I was like, oh, that's why. Yeah, physics. This 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 paleontology. Yeah.
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Some Dinos Had Feathers. Did They Fly?
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 legs.
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Some Dinos Had Feathers. Did They Fly?
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 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 yeah great yeah exactly
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Some Dinos Had Feathers. Did They Fly?
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.
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Some Dinos Had Feathers. Did They Fly?
OK, 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.
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Some Dinos Had Feathers. Did They Fly?
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 this dinosaur, Microraptor, was found in 2003. Okay. It has wings on its arms and on its legs. asymmetrical feathers, it was flying. And people got really excited about this.
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Some Dinos Had Feathers. Did They Fly?
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? 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.
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Some Dinos Had Feathers. Did They Fly?
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? Amazing. I love it.
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Some Dinos Had Feathers. Did They Fly?
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.
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Some Dinos Had Feathers. Did They Fly?
And if we didn't have those fossilized soft tissues, I just can't imagine where we'd be right now, just lost in the dark, never able to tease out what these squished fossils are telling us.
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Some Dinos Had Feathers. Did They Fly?
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 organelles are extremely decay-resistant. So the keratin matrix of the feather is gone, but these pigment-containing mono-organelles get fossilized very easily.