The American Museum of Natural History's latest exhibition, Pterosaurs: Flight in the Age of Dinosaurs, opens today (check out just a few of the things we learned at the exhibit here). At the media preview, we spoke with pterosaur flight expert Dr. Michael Habib about figuring out how these reptiles flew.
When you and other scientists are trying to figure out how pterosaurs flew, do you start with the fossils? Or do you start with an animal alive today because we know the flight mechanics and work backward?
We do a little bit of both. Mostly, you start with fossils. Then you go to the principles of physics—things that are fundamentals that you know are true, because physical laws make them true and they're going to be true for everything. Then you build models from that and validate them using the living things: Does the model make good predictions in birds? Does it make good predictions in bats? If it does, I'm relatively confident that it will make good predictions in pterosaurs.
The trick, of course, is the predictions all have to do with anatomy, and make predictions about the anatomy. To say, "Alright, if this hypothesis is true, then it would look like this and if it was false, it would not look like this." And then you test to see if that is what the anatomy looks like in the animals you have. That's kinda tricky, and part of what you do to make it reasonable, is you pick the tractable questions and tractable approaches. An intractable question for pterosaur flight is "Exactly how fast does a Quetzalcoatlus fly?" And a tractable question is, "Would quetzalcoatlus fly faster or slower than a living large bird?" Comparable questions are more tractable than absolutes.
That question is actually not completely intractable. I can get a good idea of how fast it could probably fly. But I couldn't give you an absolute answer because we don't know exactly what the wing shape was on the animal. So actually the answer would be—it would vary. Flying animals change their speed based on how much fat they've burned on that long trip, for example. They start off as a big fat bird and show up as a little skinny bird. So there is no single answer to that anyway. But I can give you an idea of range. What I can say with more confidence is how pterosaurs would fly relative to certain first principle models and relative living animals.
Pterosaurs came in a huge array of sizes. How would you say the 10 inch little guy, Nemicolopterus cryptus, flies compared to something bigger like Quetzalcoatlus?
Small things tend to be more maneuverable. They fly slowly in terms of mass of speed, but they tend to be more maneuverable. And landing and takeoff is less energetic for them. In this particular case, the animal is not just smaller, it also has other wing characteristics that are associated with highly maneuverable flights, so it would be less efficient but more maneuverable. Quetzalcoatlus would be a faster flyer, overall, because it's so much larger. It would probably be a flat glider that would flap in bursts and they would glide for long periods; it would probably be a soaring animal. Soaring is what we call it when you have an external source of lift—you're gliding, but you're not dropping relative to the ground because you've got some rising air, which is your source of external lift. Quetzalcoatlus probably hunted on the ground and flew between places to eat or escape predators or things like that.
Would there be differences in take off and landing, too, depending on the animal's size?
We have some good ideas. Take off is sort of my specialty. It turns out that in all fliers—including unpowerfliers like gliding snakes, for example, even flying squirrels, things like that—in all the ones we've measured, launch is effectively ballistic. So the launch is not initiated with the wings. You don't flap yourself into the air, you jump yourself into the air. And then you engage your wings. Now, we don't see that. It's so fast. What it looks like to us is that a pigeon is pulling himself into the air with his wings, but he's actually pushing his feet and then pulling himself higher with his wings. Which might seem like a nitpick, but in terms of physics, it is fundamentally different.
Some animals run into the jump—especially on water; that's mostly where you see them running—some just jump. For pterosaurs, we're fairly certain they would leap as well. Since they walked on both feet and hands, the expectation is that they would probably leap with all four limbs—we call it a quadripedic launch. I have not run the test for all known pterosaurs by any stretch of the imagination. For all the ones I have done analysis on, it appears that that is true, so I would expect small and large ones use quadripedic launch.
That said, a little guy has a much larger room for error than a big one in the sense of, it doesn't have to put as much "oomf" into it. It could, from a power perspective, maybe launch bipedally, but there's no reason to think that it would. A small pterosaur wouldn't have to leap nearly as hard [as a big one] before it could engage its wings. It would probably get relatively much higher, launch more vertically, if it wanted, when it took off.
Big guys would have to launch at a much more shallow angle. That means they need some clearing in front of them in order to take off, which limits their habitat a little bit, and they're going to have to devote a lot of their muscle power to launch, which means you would expect those animals—as per the predictions I’ve mentioned before—if this model were true, you'd expect that there'd be certain anatomical features related to launch that would be exaggerated in big pterosaurs that wouldn't be in small ones. And that seems to hold true. Big pterosaurs are devoting more of their anatomy to that initial takeoff phase because it's a more rigorous phase for them.
What kind of computer programs are you using to model pterosaur flight?
For me personally, I do a lot of my stuff on a Matlab. It's the big bruiser on the market, but it's flexible. The equations it collapses through are surprisingly simple structures. The best expressions are the ones that are as simple as possible. I spend most of my time on a white board, quite frankly.
There's another Jurassic Park movie coming out. What would you want the director to get right about the pterosaurs in that movies if they include them?
Take off is my personal bias. Might as well see if they get that right. And it would actually be kind of embarrassing if they didn't, because they’ve done TV shows and gotten it right. So if Jurassic Park 4 didn't get it right, that would be embarrassing.