How Did Giant Pterosaurs Fly?
Hey smart people, Joe here.
So my friend Emily Graslie from The Brain Scoop came to visit a while back, and we did
what you do when you're hanging out with Emily, which is go look at some bones from
some awesome prehistoric creatures.
That big thing above our heads? That's a giant pterosaur named Quetzalcoatlus.
Seeing that up close kinda blew my mind. I mean this was a giant winged reptile that
stood as tall as a giraffe and probably weighed as much as a grizzly bear, which would make
it the largest and heaviest animal that's ever flown.
To put that into perspective, this is a wandering albatross, the largest flying animal alive
today. And this is Argentavis, an extinct bird of prey and the largest flying bird that
ever lived. And that is Quetzalcoatlus. It's closer in size to an F-16 than a bird.
Now, I don't know about you, but it's pretty hard for me to imagine a creature that
huge taking to the skies. I mean, you can't argue with the laws of physics, and just because
something has wings, doesn't mean it can fly.
It turns out scientists have been trying to solve this mystery of whether giant pterosaurs
could fly for decades. And they might have finally done it, by thinking not just like
paleontologists, but also by looking to aerospace engineering and mathematics.
[MUSIC]
Michael Habib is one of those scientists, so I called him up to get some answers.
I am a paleontologist, what we call a biomechanist, which is to say I study the motion and physics
of living and fossil animals.
Can you give us an idea of, what is a pterosaur
So, pterosaurs represent an extinct group of flying reptiles. They can be found in small
toys marked “dinosaurs” which is terribly misleading because they were not in fact dinosaurs.
There are such a thing as flying dinosaurs, we call them birds and there are 12,000 living
species of them. But the last pterosaurs perished at the end of the Cretaceous with the last
of the non-bird dinosaurs.
These guys were by far the earliest flying vertebrates. The earliest pterosaur fossils
go back to about 230 million years ago, and they owned the skies for almost 160 million
years. Birds have only existed for about 150 million years, so that's pretty impressive.
But pterosaurs are not dinosaurs. I just want to emphasize that again. Not dinosaurs. They're
their own thing. The Dinobots have some explaining to do.
Where were we?
The average pterosaur was around, say, one to two meters wingspan. The smallest one could
fit in the palm of your hand
Sounds cute!
Which is very cute. And when you're talking about the largest pterosaurs I'm talking
about a three-way tie between Quetzalcoatlus, which is the first giant discovered. More
recently rediscovered one called Hatzegopteryx from Transylvania, and then just recently
named is Cryodrakon “The frozen dragon,” from Alberta, Canada.
Ok, Cryodrakon is hands down the coolest name ever given to any extinct reptile. I mean
“frozen dragon”! Eat your heart out George R. R. Martin.
Based on what we see alive on Earth today, it's pretty hard to imagine one of these
giants actually flying. So, how could they have done it? Well, it turns out, to fly,
you really need to master two things: being able to generate lift to stay in the air,
and also, getting into the air in the first place.
Now, staying in the air is actually not the hardest part for a giant flying creature.
The wings of birds, bats, and pterosaurs are shaped like airfoils, thick at one end, where
the bones of the limb are, and thinner at the trailing end where it's either feathers
or the wing membrane. The flapping draws this airfoil through the air, creating both lift
and thrust. Turns out a big animal with big flapping muscles, like Quetzalcoatlus, would
have more than enough power to create sufficient lift and thrust to fly.
You know, to show you what I mean, I think we should take a closer look at some bones.
Some old bones. Luckily, Quetzalcoatlus was discovered in my home state of Texas and those
bones happen to be just down the road at the University of Texas Vertebrate Paleontology
Library.
Yeah, so these are the actual bones of Quetzalcoatlus.
Wow
And this really heavy drawer is full of some of the wing bones from this giant flying pterosaur.
So there are a lot of adaptations throughout the skeleton of the pterosaur that allowed
it to fly. And one of the things that jumped out when people look at this humerus is there's
this big prong that sticks up here, out of the bone that is the source for all the muscles
to attach and stretch across the chest where they attach to the breast bone basically.
So the bones tell us these things had massive arm and chest muscles in order to provide
enough force to cut that giant airfoil wing through the air. But that's not the only
flight adaptation we can see in pterosaur bones.
I know one of the things that birds did, an adaptation, is they have partially hollow
bones?
Yeah that's right, and pterosaurs did the same thing. So we can take a look at the smaller
species to compare the cross section of broken bones.
Ugghhh (I work out)
So this is the ulna from the small animal. So if we look at this in cross section, you
can see there is a thin rim of dark gray bone about 2 mm wide.
All that lighter part in the middle would have been hollow when this pterosaur was alive,
just like bird bones.
But that bone's not much thicker than a large egg shell. And it had to support the
weight of all those muscles, and a grizzly bear-sized body in flight, without snapping
in half. How did it do that?
So, if you're a pterosaur, you have the weirdest hands that ever evolved. They only
had four fingers, they did not have a fifth finger, so your pinky finger would be absent.
And your thumb, middle, and index finger would be basically normal for a reptile. And then
the fourth finger, your ring finger would be enormous. It would be as thick as your
wrist and as long as your entire leg.
It's … that's tough to even imagine. I'm sitting here looking at my own hand
thinking, ok that first part makes sense. But you lost me with the ring finger.
Imagine how much rings would cost!
J: I know!
The weight support for this animal is essentially hanging off this finger. Which is crazy. All
of their wing bones, including that ring finger, are hollow. But it has that large diameter
which makes it surprisingly strong.
Ok, so that's how giant pterosaurs were adapted to staying in the air, but remember,
there's a second thing an animal has to master in order to fly: Actually getting up
in the air. They need to give themselves enough of a speed boost so that the combination of
the forward speed from takeoff and the flapping speed from the wings creates enough lift.
And that turns out to be the hard part for giant flyers.
Now, when I was a kid, the first time I ever saw a pterosaur was in the Disney movie Fantasia.
So I grew up thinking pterosaurs lived on cliffs and basically jumped off the edge to
start flying. Well… my childhood is a lie.
It does not actually help to drop off a cliff to get that speed. You're accelerating one
gravity down at that point, and you really want to be accelerating a couple of gravities
up. And the way that an animal, say on the ground, it's going up and forward quickly,
is to jump.
I have a confession: I've gone my entire life thinking birds launched themselves into
the air by just flapping their wings and lifting themselves into the air. But if you watch
a bird in slow motion, it turns out they start with their wings up, and jump into flight.
H: It all happens so fast by our standards that it looks like they're wing launching,
but they're not. They're leg launching, so about 80-90% of the power for takeoff in
most birds comes from the legs. It turns out most flying animals are good jumpers, and
that's not coincidental. It's because they need that to take off.
But pterosaurs aren't birds. In fact, when it comes to taking off, they have an advantage
that birds don't have. And it goes back to those really weird wings.
We know that they walked on folded wings. And they were probably good jumpers for their
size. A giraffe can't jump very high, it's actually quite heavy, it has a big torso.
A pterosaur might be that height, but it's a fraction of the weight. And it would have
more muscle in its limbs. These things should be able to jump a couple of meters. That is
more than they need to get the clearance and speed they need to start flapping.
Unfortunately, we don't know exactly what it would have looked like to see a big giraffe/bear/dragon
jump several meters into the sky, but we can get an idea thanks to another flying animal.
Bats that take off from the ground, walk on their wings and their feet. So they're walking
quadrupedally, on all four limbs. Which means that all four are available for jumping. So
when they jump, they get a little bit of force off the hindlimbs, and they get most of the
force from the forelimbs, because the wings are bigger than the legs, it's a flying animal.
And they can REALLY take off like a rocket.
Birds - they're also tetrapods, they have four limbs, but they basically said “two
of you are only going to be used for this special thing.” And it sounds like pterosaurs
were like, “we're going to combo our arms, we're going to get two good things out of
this. We're going to get leaping and flying.”
Yeah, they're taking the combo approach. It ends up giving a lot more room for getting
big. Because birds end up getting stuck. You've got one motor that's specialized for swimming,
running, and jumping, and taking off. And the other one is okay, once we get up, you're
going to take over and do the flapping and to keep us up.
And this is the key thing that has kept birds from getting to be giraffe-sized. If you make
your flapping muscles bigger, that's more payload you have to push up with your launching
muscles, so they have to be bigger. But if you make the launching muscles bigger that's
more payload you have to carry in the air with your flapping muscles. At some point
you're either too heavy to launch or too heavy to keep in the air. But if you use the
same motor for your flapping and your takeoff then you can be way heavier before physics
keeps you on the ground.
That also explains, rather nicely, why the largest pterosaurs have enormous forelimbs
but shockingly small hindlimbs.
One of my favorites, called Anhanguera, from Brazil, this animal has a 4 to 5 meter wingspan,
a head that is well over a meter long, the neck is not too far off from that. The body
- it has a big chest but the rest of the body is like an afterthought, it's a tiny thing.
And the hindlimbs are so small that feet will fit in one eye socket.
Wow! I mean, I don't want to laugh at pterosaurs, but they do have really goofy body ratios.
So much head, and so much neck, and the farther you go back, you're right, it's like somebody
ran out of energy and was like, I'll finish this later.
Yeah, my joke is always that they skip leg day.
They definitely skipped leg day.
So that's how we think the largest flying animal ever took to the skies. What I love
about this is scientists wouldn't have solved this mystery if they hadn't combined different
kinds of science together. Not just paleontology, but aerospace engineering and mechanics and
computer modeling too.
So it would used to be that we'd have to sit down with the fossils or casts of the
fossils because the bones are too delicate to try and figure out how these animals moved,
and what we've done a lot of lately is CT scanning or laser surface scanning of the
bones, and we can study those quantitatively, making computer models so we can test how
these animals might have moved around in their lifetime.
You build that pterosaur inside the computer, put it in a wind tunnel, throw it off of a
cliff, put it in an attack dive, all kinds of cool stuff.
We've had people who work on designing gliders and other aircraft come in and look because
when they're trying to find efficiencies and make faster planes and more fuel efficient
planes, looking at the fossil record is something we can apply.
We've only been working on flight for like a century and a half…
Yeah, we haven't been working at it very long!
And they had tens of millions of years of practice.
But as incredibly adapted as pterosaurs were to flying, they were no match for a rock the
size of a small city falling out the sky and setting the atmosphere on fire. So unlike
birds, all we know of pterosaurs is from their bones. And honestly, after seeing those bones
up close, I can't decide if it would be really cool, or completely terrifying to have
pterosaurs around today.
I think it would depend on which ones. I think i would be perfectly happy seeing a little
fit-in-the-palm-of-my-hand pterosaur perched on my porch, but, Quetzalcoatlus is circling,
we can't go outside today because it might eat the kids… that would be…
It's like in game of thrones. The dragons were cute when they were babies, but later
on they became real problem children.
I'm kinda glad we got chickens instead.
Stay curious.
