How Dinosaurs Loved: An Interview with Dr. Mark Norell on Dino Relations

Like almost any youngster, my love of dinosaurs was deeper than a tar pit and wider than the Cretaceous. Also like many, my love of dinosaurs and desire to learn about them faded before I reached the age when certain questions occurred to me. Sure it's cool to know how dinosaurs killed and how they died, but did you ever stop to wonder how they lived? And did any of your elementary school teachers ever tell you how dinosaurs loved?

Almost certainly not. But as you get older, taboos give way to titillation and finally it was time to learn how the progenitors of the birds (but not the bees) got it on.

My quest to get the lowdown on Pterandon Juans took me all the way to the dizzying heights of things buried in the ground—the American Museum of Natural History on Manhattan’s Upper West Side. I sat down for a chat with Dr. Mark Norell, the chairman of the paleontology division. He patiently explained what we know and what we're still guessing about when it comes to the life and death of terrible lizards, and brought me up to speed on the breakthrough in raptor coloration from just a few days ago. He didn't blink when I asked him to speculate on Apatosaurus penis size or kept bringing up what Tyrannosaurus probably tasted like, and he was more than polite when I made a Marc Bolan joke.

How much do we know about dinosaurs' lives and behavior?

We know a lot, but we don't know that much. When it comes down to it, we can find out about their behaviors through the fossil record. But the fossil record usually doesn't preserve acts—things that are going on. So we have to look at traces of those things.

One of the things people have looked at is footprints. From footprints you can tell whether these animals moved in herds, or flocks as we would call them. You can tell whether those flocks were structured in the way that elephants are today with the big ones out in front and the littler ones in the middle.

We can also tell a lot about these animals from model-based approaches. You build biophysical models and stuff and skeletons and subject it to a technique called "sensitivity analysis" and it can tell you some things about how fast these animals could move as well.

How do you do that based just off the skeletons?

You create a mathematical skeleton. Take the tyrannosaur for example, which most of the work has been done on. All the muscle attachments for a tyrannosaur are in exactly the same places as the muscle attachments in a chicken. You can just draw a line from the point of attachment in the two bones.

So you fill the whole thing in, all the muscles of the legs. And because strength in a muscle is proportional to its cross-sectional area, you can come up with a range of values. You would say, ‘Between 45 cm and 100 cm across would be reasonable for this muscle.’ And then you calculate all those values up within the range that you think the weight of that part of the animal would have been.

Then you let the values change. If it's between 45 and 80 you might let it change incrementally: 46, 47, 48, 49. Then you look at the forces of those muscles, and the forces generated by the proportions of that muscle. Then you can come up with an empirical demonstration of how fast that leg could have moved. The tyrannosaur's top speed, in a paper John Hutchinson wrote a few years ago, was said to be about 25 miles an hour. A reasonable speed would have been about 18. So between 13 and early 20s, it's a range.

Really the best way to understand anything about dinosaurs is by looking at living animals. You look at birds and then look at the closest living ancestor of birds, which is the crocodile. If you look at characteristics that birds and crocodiles have in common, the explanation is that the trait was in the common ancestor that birds and crocodiles had at one time.

So then you would predict, in lieu of any other evidence, that this was present in non-avian dinosaurs. Things like how parts of the brain work, and their four-chambered heart—things that are present in birds and in crocodiles—we would predict were present in dinosaurs.

Did Tyrannosaurus Rex move like a chicken in that halting jerky way?

No, if you saw a baby tyrannosaur you would probably think it was a weird looking bird. A full grown one might have had feathers too, maybe not on its whole body though, maybe more of an ornamental display sort of feathers. So traits in the theropod dinosaurs were more birdlike than say, crocodiles.

Also, if you look at crocodiles today, they aren't really representative of what the lineage of crocodiles look like. Crocodiles are represented by about 23 species, plus or minus a couple. Along that lineage the more primitive members weren't aquatic. A lot of them were bipedal, a lot of them looked like little dinosaurs. Some were armored, others had no teeth. They were all fully terrestrial. So this is just the last vestige of that radiation that we're seeing. And the ancestor of both dinosaurs and crocodiles would have, to the untrained eye, looked much more like a dinosaur.

So if you were to speculate on how a dinosaur might taste: actually like chicken?

Well, everything tastes like chicken. And chicken just tastes like alligator!

Now, if we can talk about a more sensitive topic… We can look at animals today and try to extrapolate some dinosaur mating behaviors, but of course what's unique about dinosaurs is that they're the largest land animals. So when a brachiosaurus got up on top of a brachiosaurus, wouldn't all her joints just splay outward?

Maybe not. It's just that these animals didn't weigh nearly as much as people think they did. When people look of non-avian dinosaur they're thinking of extrapolating a cow up to that size. Mammals are much much denser than birds are, because a lot of the skeletons of sauropods (the big, long-necked ones—Apatosaurus, Brachiosaurus and the like) and theropod dinosaurs are just air. Theropods don't have solid bones like we do; they have hollow bones. Sauropods don't, but they have tremendous air sacs that fill up a lot of their bodies. And thus they weigh way less than a mammal scaled up to that size.

So an elephant comparison isn't totally apt?

No, it's not apt at all. If you look at a lot of sauropod dinosaurs—a diplodocus for example—the trunk region is about the same size as a very large African elephant. Then they've got a long neck and long tail that stick out from it. But they wouldn't have weighed much more, if not the same, because there's so much air in the air sacs of the body.

Can you speculate on sauropod mating?

Yeah, it would pretty much be like modern terrestrial birds like ostriches and stuff like that.

Well, the size and practical considerations like tails don't really apply to ostriches.

Well crocodiles, big lizards.

Would it have to take place in the water?

Probably not. I don't think a lot of these animals ever went into the water. Some did, but I'm sure a lot didn't. And I think the majority probably didn't. These things would've had to be eating all the time. I just don't think you could get enough food if you're spending most of your time in the water.

Didn't some dinosaurs have had webbed feet and spent time in the water? Maiasaura?

That was something people said a long time ago, but that's probably not the case. Those things that look like webbing on the feet support a pad-like structure more like a hoof. There's no clear adaptation, to my knowledge, in any extinct dinosaur that suggests that it was aquatic or primarily aquatic.

Ah. Well I was wondering because aquatic birds usually have adaptations to (ahem) assure that the sperm makes it over…

Well the presences of penises in birds is thought of as aquatic because people are just more familiar with ducks and geese, but it's just as present in ratites like ostriches and cassowaries and all these things are fully terrestrial.

So could we speculate on sauropod penis size on a scale from bicycle to Econoline van?

I think the best thing to do would be to do some scaling from crocodiles.

That's a very mature answer.

In case you were wondering: A 15 foot crocodile's penis measures about 4 inches (2 percent of body length). So a 40-foot Tyrannosaurus comes in at about 9.5 inches. It's also worth noting that while something like a diplodocus was around 90 feet long, a solid 71 feet was the disproportionate (relative to crocodiles) neck and tail, so adjust your calculations accordingly. I'm guess what I'm saying is that people who want to use euphemisms should stick to horses.

What do we know about the mating process outside of just the actual act? A lot of birds have mating dances. Is it possible to speculate on that at all?

It's not even possible to speculate on. We have no idea. Of course we would think that there may be some sexual behaviors that were apparent, because those sexual behaviors are really common in birds.

It's everything from all sorts of different plumage displays, all sorts of different hormonally based sort of displays where the plumage or head color changes in the year seasonally. And there's lots of vocalization that occurs. And that diversity through birds is incredible. In crocodiles, on the other hand, there isn't a lot known. We do know some vocalizations happen—big male alligators for instance vocalize to attract females. We can't measure any of those things directly in the fossil record, but we can say that because these sorts of behaviors are widespread within both birds and crocodiles that non-avian dinosaurs undoubtedly had some, we just don't know what they are.

Is there much post-mating cannibalism in the avian or reptile world?

There is some in birds and a lot in crocodiles.

Does that implicate dinosaurs?

Some people have said that's true, but we haven't found a specimen that clearly shows it yet. Some people think we have, but I think those specimens are a little bit controversial, in the sense that there have been small tyrannosaur bones that have been found in or around the body cavity of a Tyrannosaurus Rex. I'm not convinced that they actually originally were in the body cavity and weren't things that were washed in after the animal had died. Certainly we see lots of juvenile dinosaurs' bones that have bite marks on them, but it's hard to say if they were being predated on by their own species or by someone else. It wouldn't surprise me at all if they were though.

A lot of attention has been paid attention to dinosaurs as mothers— Maiasaura for instance. How uniform was that across dinosaurs? Would an Apatosaurus herd raise their young differently than a theropod?

A couple things that we do know about theropods—the ones that most closely related to birds—is that they brooded their nests. If you go deeper in the tree, what you see is that for sauropods, we have no direct evidence that they returned to the nest after the eggs were laid. Most of the evidence for that comes from an excavation in Argentina called Auca Mahuevo. What's thought with sauropods is that they'd just lay a bunch of eggs and leave them alone—the turtle model. Few of those would ever reach adulthood.

Does contradict the idea of them being herd animals?

Not really. They could still herd together and be around each other. It's a big group, and it spanned a huge amount of time. Sauropods themselves are a very large group that lived from 200 million years ago to 65 million years ago so a lot longer than even primates have existed and they existed on all continents.

Thanks so much for talking to me. Any final thoughts?

Not really, except that people should remember that when you're thinking about dinosaurs, it's better to think of a bird than a crocodile when you think about how they behaved and what their physiology is.

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