Daniel and Kelly’s Extraordinary Universe - Was the Tyrannosaurus rex fast or slow? (Featuring Dr. John Hutchinson)

Episode Date: April 29, 2025

Daniel and Kelly talk to Dr. John Hutchinson about how large animals move. See omnystudio.com/listener for privacy information.

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comes driving up fast and just like screeches right in the parking lot i swear i'm not crazy but i think he poisoned me i feel trapped my breathing changes i realize wow like he is not a mentor he's pretty much a monster but these aren't just stories of destruction There are stories of survival. I'm going to tell my story, and I'm going to hold my head up. Listen to Betrayal Weekly on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. It's important that we just reassure people that they're not alone, and there is help out there. The Good Stuff Podcast, Season 2, takes a deep look into One Tribe Foundation, a non-profit fighting suicide in the veteran community.

September is National Suicide Prevention Month, so join us. host Jacob and Ashley Schick as they bring you to the front lines of One Tribe's mission. One Tribe, save my life twice. Welcome to Season 2 of the Good Stuff. Listen to the Good Stuff podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. When I was a kid, I was absolutely obsessed with Jurassic Park. It wasn't just because of the dreamy Ian Malcolm, but mostly was because of the dreamy Ian Malcolm, but mostly was because, I desperately wanted to be a paleontologist. The idea of bringing long, extinct animals back to

life through the magic of biology was absolutely enthralling to me. And I went to the cheap theater to watch Jurassic Park on the big screen as often as my mom was willing to take me. The scene where the T-Rex is chasing the Jeep carrying the injured Ian Malcolm to safety is burned into my memory. But even as a kid, I remember watching that scene and wondering to myself, could an animal that big, really go that fast? If so, why is the huge brontosaurus not similarly swift? This is a difficult question to answer. After all, how do you even go about figuring out how an extinct animal moved? They're not around to be videotaped anymore, and the muscles that hold keys to answering questions like these have long since decayed away. Well, on today's show, we're talking to Dr. John Hutchinson,

who studies the movement of long-dead animals while answering amazing questions like, can hippos get airborne and how do elephants run? This is the perfect topic for Daniel and Kelly's extraordinary universe because it's the happy intersection of biology and physics. Welcome to Daniel and Kelly's extraordinarily fast-moving universe. Hi, I'm Daniel. I'm a particle physicist, and I've always considered myself a large animal. Hi, I'm Kelly Weiner-Smith. I'm a biologist, and I sort of fluctuate between being a large and a larger animal.

Depends on how close we are to the holidays. But I always feel great about myself, so it's all good. And so, Kelly, what do you think is your top land speed? Or what could Kelly outrun? Let's put it that way. I've definitely outrun some turtles on the property. Okay, that's good. Let's start there. There are some fast frogs on the property, so maybe somewhere in between those things.

Wow. Are you telling me a swarm of frogs could take you down? Oh, I mean, they could catch up to me, but they're pretty tiny. You know, I think I could give them a couple good swift kicks. I have taken some Taekwondo, so maybe I can give them a couple of good swift kicks. Maybe I can give them a couple chops. All right. So all frog listeners, be warned.

Kelly can defend herself. Yeah. I'm not a very fast person. I could not outrun a cat or a dog or even a rat. I've chased a rat around our garage and lost that race. Wrath surprisingly fast. Yeah. But to my credit, I do have offspring that are surprisingly fast.

My son is a runner and he runs a mile in shockingly four minutes and 20 seconds or something. And so I think I want to take some credit for that, even though it's probably more. likely to be cosmic ray mutation or, you know, transcription errors or something that led to that. You're one of those parents whose children's accomplishments are your accomplishments. Absolutely. Why else have kids? I put his times on my CV for sure. Does that help with funding?

I can't imagine it would. No, it doesn't. It's wonderful to see your kids grow up and just have different skills and interest than you do. It's fantastic. and also surprising sometimes. Yes. No, my son has amazing abs. Like, you can put him in any position

and he can sort of lift himself up with his core. And it's crazy. And my daughter's starting her first math competition. Both of those things are just, my kids are amazing and I had something to do with it. But I don't know how much credit I get for either of those things. Turns out biology is complicated, right? Yeah.

Yep. It's true. And, you know, another thing that's complicated is how do you portray biology in movies and TV shows, especially when you're really pushing the boundaries of the biology. And we have a really great question about that today from a listener. Let's go ahead and hear it. Hi there, Daniel and Kelly.

It's Ben from Melbourne in Australia here, and I've got a question about large creatures, including giant people and how they move. So I've noticed in a lot of movies and TV shows when something giant is depicted like a giant, Ant-Man in the Marvel movies, they're often depicted as moving really slow, kind of like in slow motion. But then in other media, we've got giant things like the Ava units in the Evangelian anime, which move really, really fast. And it got me wondering, is there any

physics reason or any biology reason why one of those depictions is accurate as opposed to the gather or does it depend on the particular case? Really enjoy the podcast and really looking forward to what you might have to say. So this is an amazing question and I was so excited when we got this question because I had somewhat recently met a professor who studies very large animals and we were in a meeting with a bunch of other people and there were things going on and I didn't get a chance to ask him all the questions that I wanted to ask him about his research. So I was so excited to have an excuse to invite him on the show. And so today we have Dr. John Hutchinson on the show to tell us all about how very large animals move.

And what a giraffe burger taste like. Mmm. Dr. John Hutchinson is a professor of evolutionary biomechanics and a fellow of the Royal Society. His research straddles the fields of evolutionary biology and biomechanics with an emphasis on how very large animals stand and move and how locomotion evolved in different groups of land vertebrates. Welcome to the show, John. Thank you very much, Kelly.

Kelly, in your introduction, you neglected to mention that John also has an incredible array of heads on the wall behind him. Well, I didn't know that when I wrote the intro. What's going on there? Yeah, it's my mask collection. Oh, cool. Which got particularly ironic early in the COVID pandemic, but it only encouraged my collection of masks.

So for those of you just listening, we see octopus and what else is going on? Thulhu, giraffe. Are these all from places that you've visited? Oh, just random places, often just gifts from people, or I find them at an arts sale kind of thing or whatever. I don't know why you don't just wear them when you jump onto a Zoom call. That'd be very dramatic. Yeah, some of them would fit. All right, well, let's pull back and talk about what got you interested in studying the movement of very large animals. It really goes back, I think, to being a high school student in a physics class. And I remember my teacher had like a bulletin board with some news articles or something on it.

That's the way I remember it. And one of them explained why King Kong and Godzilla were physical impossibilities because they were just too big to support their own weight. And I was a big, big monster movie fan, just way too early for my years, really, into kaiju type movies and that was really interesting to me because it made me grapple with my growing interest in science and my longstanding interest in the arts and fiction so I had to think about oh wow that actually really makes sense but too bad and you were like one day I'm going to crush dreams just like the author of that article yes walk us to the argument

Why does physics say that biology can't get too big? The simplest explanation is what they call the square cube law. Well, there's various terms for it. But as animals get bigger, their wet mass or their weight goes up by a linear dimension cubed. So you have a length, a width, and a height. That's your mass, your volume, so forth. So that increases with your size overall. Mass is a metric of size, more or less.

But as your mass increases, your area, your linear dimension squared, so cross-sectional area, only goes up proportionately by the linear dimension squared. So very quickly, the amount of weight you support on a given area gets higher and higher and higher unless you do something to change your mechanics of movement. So let me interpret that. assume, for example, we have a spherical Godzilla, right? Because this always like to assume spherical monsters. Yes. Then you're saying the volume of that sphere goes with the radius cubed, right? It's like four-thirds pi-r cubed.

But the surface area of the sphere is four pi-r squared. And so when you double the radius, the volume goes up by eight, but the surface area only goes up by four. And as that continues, as the radius goes up and up and up, and you get to actual Godzilla sizes, the ratio gets larger and larger of volume to surface area. But why is that a problem? Like, why is it a big issue to have a lot of wet mass inside your surface area? Because of biology. Because animals are made of the same stuff that has intrinsically the same mechanical properties, the same strength, fundamentally. That's the most important thing.

See, the amount of force per unit area a bone or a muscle can support is fairly constant across vertebrates that move on land in particular, because this is all operating under gravity is the assumption. Once animals get into the water, all bets are off. It's effectively zero gravity, more or less. So then this square cube law is not such a concern. On land, the strength of tissue becomes fundamental. Is the limiting factor there mostly bone or mostly muscle or it has to be both? What limits what an animal can hold? I think this is still a big question in science that you would think it might be bone because bones are there to support body weight against gravity, but bones form joints that muscles act around to support animals. So there's the living component, the contractile component of support, which is muscle, but then there's all the other passive stuff, bone, ligaments, and cartilage and so forth that also provide support.

And what we don't really understand yet is how much of a role each of those things plays and how that balance changes as animals get bigger. One thing we do know is that as animals get bigger, land animals, I should specify, land vertebrates, as they get bigger, they tend to straighten their legs. So that shifts their mechanics of support to using their legs more and more and more like pillars, which transmits more of the force down the long axis of the bone. So like when we stand, we're using our legs like pillars more or less. We're quite unusual, actually, for animals of our size in the way we do that.

It's very efficient providing a lot of passive support. So mostly the bones are providing a lot of support once you get to a very, very pillar-like posture. Whereas intermediate postures with more bending of the limbs would involve presumably more muscle activity. But, you know, this is hard to figure out because there are so many components acting around each joint in any real organism. It's a really difficult mathematical problem. So my takeaway is that it's not necessarily impossible to have any given size of animal, but that the task of the animal, the sort of biological engineering needed, changes as the animal gets bigger or smaller because of these different ratios. And the strategies that we have are vertebrates on Earth might not scale to like really big Godzilla's. But does that mean, for example, you couldn't have a fundamentally different biology, you know, some crazy hollow thing or different kind of biological engineering or no joints or, I don't know, something, you know, really out of this world that could allow for much, much larger animals?

That is a great question, like, in terms of, like, other worlds or such. Certainly we don't know what tissue could achieve. We only know it's there. So Daniel was asking, are there different ways to get bigger? Like, can you hollow out your insides or something? You mentioned in water is effectively zero gravity. Does that mean that blue whales, like we could have something a hundred times bigger than that? Or does something else limit size in the ocean? This is another big question we don't understand.

We don't understand what the upper limit of size is on land or in water or anything. We only know what we see. And the largest animal ever so far is the blue whale. There are some fossils that kind of seem to maybe come close to that. in size, but blue whales are the biggest. But it doesn't mean that animals can't get any bigger than that. It's just that that's what evolution has produced. And certainly, there are other mitigating factors like physiology, cardiovascular issues, breathing, ecology, ecology. So food is a huge constraint on body size. If you don't have enough food around, if you're in an unstable

environment where food resources are crashing all the time, like in the face of environmental change, then being big is a very terrible biological strategy, so to speak. So large body sizes has many limits, not only the physical. There is a whole different body plan out there that we can look to in nature to ask questions about mechanics of size and support, and that's arthropods. What's really interesting is that even in the most extreme cases in the fossil record, we see no gigantic arthropods. Remind me what's an arthropod? Animals with exoskeleton, so insects, crabs, crustaceans, spiders, so forth. Things with their skeleton on their outside. So no lobsters, the size of blue whales so far. Yeah, yeah. So they keep their muscles

on the inside, which constrains how big their muscles can be because they've got to have not only all their muscle on the inside, but all the other stuff, their circulatory system, so on and so forth. So that constrains them to a certain degree, but also other factors like their circulatory system constrain their size. So they are weirdos, but also arthropods are weirdos because their muscles break all the rules of what muscles can do. I talked about vertebrate muscle having pretty much the same properties across any size of vertebrate, but insect muscles have tremendous variation in what kind of properties they can have, but they still could not enable like a 50-ton ant.

Oh, there was a movie when I was a kid that had a giant aunt after a nuclear war. And yeah, them. Oh, you've crushed my dreams. I was really hoping that that would be a silver lining. I think I specifically chose that to crush your dreams. Oh, man. Well, good job. Good job.

Spot on. A little taste of your own medicine there, Kelly. Oh, ouch. Could you tell us a little bit more about the different kinds of insect muscles? How do they break the rules or arthropod muscles? Okay, this is getting outside of my expertise a bit, but they have really different sizes and proportions of proteins that make up muscle. There are three major proteins that make up muscle, actin, meosin, and titan. And those three molecules interact to produce these sliding filaments that lengthen and shorten the muscle unit called the cyrus.

in vertebrates, they're all kind of made the same. But in insects, they're built in different ways. They can contract at different rates. They can do all kinds of crazy stuff. And I can't explain that to you. I'm not an insect muscle physiologist. I have huge respect for them because they study things that are really weird to me. Can I admit something that may be embarrassing?

Yeah. I didn't know until this conversation that insects had muscles. My mental image was that they just basically had some sort of hydraulic goo in the inside their exoskeletons and I had no idea how they moved. So that's fascinating. Are you saying it's like differentiated inside there? Like if I cut into a 50 tonne ant, it's not just like a fire hose of goo that's going to spray out?

No, no, no. They have plenty of internal structure. Spiders do move using a largely hydraulic limb structure. So they have muscles, but they're mostly powering their leg movements through a hydraulic movement that's coupled to their circulatory system. so they're pumping fluid around their bodies and using that fluid to move their legs. So are muscles conserved across all animals? Like everything that's mobile on Earth uses some kind of muscle?

Yeah, every animal. There are other things that do weird stuff. I guess once you get down to a single cell, it becomes a question of what really is a muscle. It becomes a little weird. I mean, you're using proteins to spin a flagella, a little whip-like structure in bacteria and other. small, small organisms. So I think if we're talking about muscle in the way we're familiar with it, with the three major components actin myocin and Titan,

then that's an animal thing more or less. And so on that topic, why don't we have like macroscopic sized bacteria? Why don't we see the ocean filled with like blue whales and then like bacteria the size of a blue whale with a massive flagella behind it? Oh, boy. And how come nobody's made that monster movie yet?

That's the real question. Yeah. Yeah, well, I mean, the blob was kind of in that direction. I loved that, too. I don't know how you classify the blob, although if you know your H.P. Lovecraft lore, it was probably a shagoff. Anyway, yeah, bacteria, I don't know if I could give you an easy answer there. I think diffusion would be a big problem for them. They've got this big, tough cell wall, and they're one cell that relies on,

stuff to get in and out of that cell wall and move around the organism. They have no respiratory, circulatory systems, anything like that. They just rely purely on diffusion. So I think that's going to be a big constraint on any single-celled organism is diffusion. And maybe the support of their cell wall itself might just crumple under its own weight. And they can't really move. I mean, it would take a huge phlegelum to move a big bacterium through the water. I can't even imagine how the mechanics of that would work. I'm sure you can imagine it. Mr. Monster Movie over there, for sure, has the mental image.

Give me a few million in VFX budget, and I can imagine it, yeah. Done and done, yes. Oh, yeah, because we've got loads of money. James Cameron. There you go. Welcome to Daniel and Kelly's production studio. There you go. So the conversation we've been having has gone between physics and biology a lot.

So you clearly know a lot about both. And so after the break, I'm going to ask you to explain why biology is better than physics. Oh, dear. All right. If possible. The gauntlet has been thrown down. Imagine that you're on an airplane and all of a sudden you hear this. Attention passengers.

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I do love the intersection. I love intersections of fields in general. I like to defy boundaries. I like to think about how a lot of boundaries we erect with our minds are false. And they're just there as conveniences. So, however, I mean, physics is physics. it's very easily circumscribable, much like mathematics is, whereas biology is fuzzier. I like that aspect of biology, maybe because I like fuzziness.

Although physics can get pretty fuzzy, I guess, down at the weird end of scales. Maybe Daniel, you can agree that or not. That's where Daniel lives, yeah, at the weird end. I'm at the weird end of everything. That's right. But you ended up a biologist. I mean, by name you're in the evolutionary biomechanics department. you're not like in a physics department doing biophysics and i completely agree with you that these are

artificial dotted lines that we draw on a smooth spectrum of natural curiosity but i am curious why you ended up on one side of that than the other like why are biologists more likely to hire you than physicists oh my training very much is in biology into my PhD i am a biologist fundamentally i can't claim to be a physicist it's just not my training i'm not an engineer or anything like that. I did do a postdoc in an engineering laboratory, which gave me a bit of street cred with that crowd and did teach me a lot about that kind of perspective

with Newtonian mechanics. But, yeah, I couldn't go work at a physics department. They could tell that I was an imposter. No, you'd just be like, hey, what happens if we have a really high-energy collisions of very large animals? Two elephants running at each other at high speeds. Let's do that experiment, right?

It's easy to be in the physics department. Well, can we get into the details of your day-to-day life studying this stuff? So, like, when I think about studying movement in small mammals, I can imagine, for example, putting them in a CT scanner or an x-ray machine. But you study animals that are just absolutely massive. And so presumably they don't stay still in those machines or there's no machines big enough. So how do you get your data? Well, I'm interested in the size spectrum of animals in general,

because I don't think you can understand big animals without also understanding. smaller ones. It's just that we do have a lot of knowledge of how smaller animals work, and just up until my work, there haven't been that much research on how the biggest land animals worked. So I do work on living animals using like x-ray machines. We have multiple x-ray video cameras, as you can loosely call them, where you can have an animal moving through two planar x-ray systems with high-speed video cameras attached to them, and use those in animation software to reconstruct how the skeleton moved in the living animal. That's really cutting edge stuff in our field that allows us to see inside the animal and see its skeleton moving

in life. It's been a big game changer over the last 20 years. But yeah, we can't do that with big animals. The biggest size you can image is about soccer or football sized for Americans soccer ball sized roughly. And technology for reasons I don't understand or maybe just demand has not created any machine that can do a volume bigger than that. So doing even small parts of big animals is impossible with that kind of stuff. We do more conventional kinds of study of larger animals with motion capture or just high speed video or whatever. We use other devices to measure how hard they exert force against their environments of what we call force platforms and pressure pads that measure the force per unit area they apply to the ground. We have lots of cool toys.

to measure what we would call the kinetics, so the forces and related things, and the kinematics, the motions of organisms. I'm confused when you say that you can only image something the size of a soccer ball, because you can put a whole human inside a CT machine, and there are some pretty big humans out there. Why can't we do that with animals also? You can't have them moving around with like a video camera going on, capturing data.

In a CT scan, you have to have an individual remaining still. Because you're taking serial slices, serial x-rays of the individual to then piece together the whole 3D person. So if they move, actually, your image gets screwed up. I see you can't convince an elephant to stay still. Yeah, yeah. What's the biggest animal that you've studied? I've worked a bit on the big starpot dinosaurs. I'm not so well known for doing that, but I have published a bit on them with some colleagues.

I'm more well known for studying the big carnivorous dinosaurs like T-Rex. I really made my name with an early study I did showing that T-Rex couldn't run quickly. Again, smashing dreams, making some paleontology fans rather upset, but it was well-received scientifically, so I'm very pleased about that. I've worked with elephants a lot about as much as I've worked on T-Rex and its kin. I've worked on living elephants from zoos around the U.S. and the UK to more wild-type elephants in Thailand, working with elephants that were either previously used in logging or tourism or even used in racing.

So I got to measure how the fastest elephants could move, which was really, really cool. How fast can the elephant move? They can go up to almost 15 miles an hour, which might not sound that fast, but that's a challenge for me to keep up with that pace. It's still pretty impressive to see like a 4,000 kilogram animal traveling at 15 miles an hour.

That's a lot of kinetic energy. I bet it feels really fast if it's chasing you. Oh, yeah. What we found with that work was that even though elephants don't go airborne at any time when they go quickly, which is kind of what we thought, they do sometimes only have support on one limb while the other three limbs are airborne, kind of doing the splits in midair. So that was really cool to see how extreme the gate of elephants could be. They really do move in rather extreme ways, even though they're not. don't go fully airborne. That's fascinating.

You talk about the gait of elephants, like whether they're ever have all four legs off the ground, what animals do ever have all four legs off the ground? Pretty much everything, except like tortoises and other really slow animals. And just this past summer we showed with another paper that when hippos go really quickly, they leave the ground with all four feet, which elephants don't. So that was a nice thing to find, which had never been reported scientifically. We know that rhinos, which get very, very big. to 3,000 kilograms or so, so rivaling the size of some like Asian elephants.

They can gallop. They can leave the ground with all four feet. So they are kind of in that zone of being big and being athletic that is apparently hard to achieve. You discovered flying rhinoceroses. That's amazing. The rhino thing was known, but the flying hippo thing, that was a small new contribution that I'm still proud of.

And got a lot of news attention. I was really kind of pleasantly surprised by that. I want to come back to dinosaurs in a minute, but first I have a question about elephants because I've always heard this story about elephants that the reason elephants have really big ears is because of this volume surface area question, and you know, you've scaled up the elephant to be so big,

it's got so much meat, it's hard for it to stay cool. And so having really big, flappy ears is like a cheap way to increase your surface area without increasing your volume. Is that pop science nonsense or is that real science? There is some truth to that. There's big differences in ear size in Asian versus African bush elephants. The bush elephants in Africa have much bigger ears that corresponds to being out there in hotter temperatures in the open, exposed to sunlight and so forth.

I think it's pretty well accepted that that difference in ear size and just the overall large ear size in elephants overall relates to them using the ears as the cooling mechanism. And they do wave their ears, so they get convective cooling, moving the air quickly passed to ensure that there's always more air to unload the heat onto as they keep airflow going. And mammoths had little ears, right? Some woolly mammoths did. So, yeah, there are quite a few different species of mammoths. The woolly mammoth is the one we know best from animals preserved in frost in Siberia. Those had a lot of body parts reduced to avoid frostbite, probably. You know, I noticed that in Farside, Farside, the mammoths always have kind of little cute ears.

And I remember as a kid being like, is that right? So it's amazing Gary Larson ahead of his time. Oh, he knew his science. Yeah, he paid attention. Can I dig in a little bit more to your elephant study before we go to dinosaurs? So how did you figure out that the elephants had one foot on the ground at all time? Was it just a really good camera? And how do you make an elephant run on command?

That sounds scary. It was just using pretty conventional cameras. or not very high-speed cameras. We did eventually get hold of some good cameras that helped confirm it even better, but when I was just a postdoc, or even a grad student, yeah, I was just like in my mid-20s,

I started working on elephants trying to answer the question, well, do they leave the ground with all four feet or not? We didn't think so, but I wanted to test that empirically. And so I just took a video camera out to some zoos, couldn't get them going quickly, and then got in touch with a guy in Thailand

he was interested in this kind of question. I went out there with just a conventional video camera, and he knew all the elephant keepers and just got them together and made it into kind of a game for them or a contest. So each elephant has its own companion, a Mahout, or a rider, who pretty much grows up with the elephant, and they have a very strong bond in Thailand.

And so the Mahout would encourage the elephant by whatever means he thought was reasonable, like calling to it, usually, or having someone run in front of it or have it go toward a friendly elephant, and that would motivate it to go quickly. Cool. It certainly did work in Thailand. We got much faster elephants than we ever did elsewhere.

I love the idea of explaining your thesis advisor. I couldn't answer the question. I couldn't get the elephants to go fast enough. Like, that's a very unique problem. This is animal research. Yeah, motivating animals, very challenging. It's true. Do you have to get an IRB there?

Like, do elephants get grumpy if you make them run or can you possibly hurt them or something? Yeah, there's always stringent ethical approval involved because even just stress is a concern. So you have to explain how are you going to mitigate stress. What are you going to do if an animal seems stressed while you terminate the experiment? What does stress look like? Those are important questions. And avoiding fatigue also is really important. So you give animals lots of rest because we don't want to study fatigue.

We want animals that are fresh. Let's go back to dinosaurs. You mentioned T-Rex right after we had finished talking about methods for looking at animal movement. But when you're studying dinosaurs, of course, you can't see them move at all. So how do you study animal movement in long dead animals? So we have kind of two things. We have the fundamental principles of animal movement that we know from living animals, which tell us some pretty good, reliable general rules that we can use as expectations.

to apply to extinct animals, or at least give boundaries for here's what this could be like, here's how big the muscles might be relative to the limbs, that kind of thing. And then we have physics. So we can, and this is what I did in my PhD thesis, we can build either a very simple or a very complicated mechanical model of a dinosaur for its own sake. So actually try to reconstruct, like in a computer, usually, what the animal looked like, its dimensions, and give those dimensions, physical properties, mass, center of mass, inertia, so forth, stuff that physicists would care about. And then ask questions of that model, basically,

what can you do? What is possible with this representation of a dinosaur? And then you can test hypotheses like, well, given this set of assumptions about a T-Rex, could it run quickly or not? How much muscle mass, would it have needed to run quickly? And is that reasonable, given how much we could fit on the skeleton or not? And I tested that and found that no, it couldn't run very quickly, not like a racehorse, like 25 miles an hour, but still possible to do more like kind of elephant speeds, maybe 15 miles an hour, which for an animal that could get bigger than an elephant, it's still pretty darn good. So what you're doing here is sort of like imagining how you might build a dinosaur, saying, like, well, how do reptiles move and how do current animals move,

and you know the sort of shape of a dinosaur? So you're sort of imagining a biological model of a dinosaur and then studying that. It's setting up a set of constraints. So here's what's possible, given what we know from living animals, the range of variation we see in living animals, which sometimes can be pretty conservative. And using that as inspiration to make assumptions about extinct animals so we have the bones that's direct information sometimes we have fossil footprints that we can use to kind of give an idea okay this animal stood on two feet with the feet very close together not sprawled out to either side and yeah so ultimately then we can for example reconstruct muscles attaching from bone to bone to guide their lines of action and that can be done

by looking at living animals and seeing, okay, where are the muscles of living animals attach? And I did a lot of that in my Ph.D. work and found that if you look at living animals, especially the closest relatives to dinosaurs, like living birds and crocodiles and other reptiles, the leg muscles are really conservative. So you can pretty well predict where the muscles attach from the shape of the bones, from marks on the bones, which reveal the actual interface between the muscle or tendon and the bone itself. When you say conservative, you mean similar across species, not in small government. Yes. Yeah, similar across species. So, yeah, consistent and probably predictable,

that we can make assumptions about the anatomy of extinct animals that are reasonable. They're not going to be perfect, but they're pretty well grounded in actual evidence. And we can be very explicit. Well, I think it was this way, of these data that we have from living animals and this information that we have directly from the skeleton. The physicist in me likes that you're like building a model and exploring, you know, the speed and motion of that model. But then also wonders, like, what do we know about how that model might differ from real dinosaurs, right? You are making assumptions and extrapolations. Then along with that, you might develop, like, some uncertainty window or some band of your

knowledge and confidence to say, like, well, we're pretty sure. Or is that something you can quantify or is the information so sketchy that we can just sort of like make qualitative arguments about how well we know this stuff? It is difficult to make very specific predictions and any quantitative arguments are always in some very rough bounds of possibilities. So like trying to predict the speed of an extinct us or we don't even know for sure what the bounds can be, but we can do what we call sensitivity analysis. So the different inputs we put into the model. so how big are the leg muscles where they attach to, so on and so forth, and then see what the output of the modeling analysis is.

So how does that change running speed if we change these assumptions in the model? Another thing we do that's really important, and this is where my training in biology really comes to bear in my work with living animals, is we can apply the same methods to a model of living animals and see, can we predict how a living animal works based on the same kind of modeling approach as we apply to an extinct animal. And comfortingly, when we do those kinds of tests, they usually do pretty darn well.

So we can predict that a bird can run bipedally, whereas a crocodile that doesn't run bipedally cannot. That's very cool that you apply your mechanism to animals where you can check yourself. That's very cool. Very important. But also as a complete non-expert in biology or in dinosaurs, I have the sense that our mental imagery of how dinosaurs stood and moved and looked has changed over the last 50 or 100 years, you know, like D-Rex used to look more like standing up and now we think dinosaurs might have all had feathers or something. Doesn't that tell us that a lot of what we're assuming that the assumptions

we're making might be changing with time and might have uncertainties we haven't accounted for? Yeah, and I think that's the great thing about science is these things can always be updated. Everything's provisional. They need to be revisited. I mean, someone might come along and show that my work that I did 20 years ago is wrong, and that's just the way it goes. The key thing I think is to be explicit to say, here's my set of assumptions, here are the data that go in, here are the data that go out, here's the methods that are used, so it's all reproducible, and someone can go back and say, oh, no, I found some other information that changes the inputs completely or changes the way we should even model the whole thing completely

the way the whole system might work, and so they could repeat or do a completely new invention of that kind of analysis. I think that's the key. And sorry if I missed this earlier, but what was the thing that limits T-Rexes to not going much faster, or what was the thing that we learned about T-Rexes that changed people's minds about why they couldn't go quickly? Living land animals, no matter of what their size is, can only devote so much of their body mass to muscle that supports the body weight. You have to have not only muscles, but bones, skeletons, lungs, brains, so on and so forth. And the upper limit of that muscle mass that we can see in nature appears to be ostriches. Large fraction of ostrich is leg muscle that supports them. You think

about an ostrich, it's got a long, skinny neck, tiny little head, tiny little wings, no tail to speak of. A big torso, but really most of it is these big, long, long, meaty legs. And no dinosaur was really built like that. Nothing like a T-Rex was built to have a body devoted to muscle like an ostrich does today. So we could use an ostrich as like an upper limit for what we know of in terms of how much muscle a dinosaur might have had. And even that that would be a bit straining credulity if we did say a dinosaur had that much muscle. Are you saying an ostrich would beat any dinosaur in a foot race? Yeah, yeah, I think it probably would

But even ostriches have more muscle devoted to their limbs Than like fast animals like cheetahs Or big animals like rhinos or elephants do They're super muscular animals All right, so let's take a break And when we get back, we're going to hear about some weird stuff That's been in John's freezer Oh

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12th season of Family Secrets. With over 37 million downloads, we continue to be moved and inspired by our guests and their courageously told stories. I can't wait to share 10 powerful new episodes with you, stories of tangled up identities, concealed truths, and the way in which family secrets almost always need to be told. I hope you'll join me and my extraordinary guests for this new season of Family Secrets. Listen to Family Secrets Season 12 on the IHeart Radio, app, Apple Podcasts, or wherever you get your podcasts. As someone who is married to biologist and has weird stuff in his freezer, as a result,

I am terrified to learn what John might have in his freezer. So, John, you have a really great blog called What's in John's Freezer, and I decided I shouldn't look at it with my husband around because it might turn his stomach too much, but you've had some cool stuff in your freezers. Can you tell us about some of the cool stuff that's in your freezer and what you've done with it? The glory days are gone. You used to have cooler stuff, although I mean, there's still some cool stuff there. I've been trying to get rid of stuff lately because it just got too full and became kind of a hazard with piles of frozen stuff, getting up to the ceiling of this walk-in freezer. But yeah, I mean, over the years, I've had a lot of parts of elephants.

because elephants die in captivity, and zoos give parts of them, at least, to me, to study for research. And then we take those parts and use them to help us understand, like, the anatomy of elephants and how things can go wrong in elephant feet, which are a big cause of mortality in elephants. They have a lot of problems with their feet. We can use the information from cadavers to actually contribute to taking care of animals like elephants. A lot of elephant parts, rhinos, never had a hippo, lots of giraffes. lots of crocodiles of all kinds of different species. I love crocodiles. I'm crazy about them and have done a lot of research on crocodiles.

What's to love about crocodiles? Sorry, I got out. Oh, they're so bizarre. I've just shocked two biologists. Everybody out there should have seen their faces. The horror, the outrage, just a surprise. Really tell me, I'm imagining crocodiles like eating dogs and like snatching babies. What's amazing about crocodiles?

Why do we love them? Well, just that. It means that's pretty good right there. That's pretty good. Wow, you're coming out as anti-baby on the podcast. That's amazing. Seriously. What's cool about them is that I think they got in the short stick in terms of being just dismissed as living fossils,

which, yeah, they look a lot like they did back in the Cretaceous when dinosaurs were around. They've remained somewhat conservative over time, although there have been some groups of crocodiles that have come and gone, even since the dinosaurs went extinct, that were pretty darn weird. And just to be clear, you're not making a political statement that conservative animals eat babies. No, not yet.

Daniel. Sorry. Yeah, so crocodiles are just bizarre. They're not some sort of primitive thing. Everywhere you look at them, their body plan is incredibly specialized and modified. They're not like some holdover from some unspecialized,

imperfect body plan. They're really amazing at what they are able to do. The way they breathe is really remarkable. They have this muscle that attaches to their pelvis that pulls their liver forwards and backwards, working like a piston to pull air in and out of their body. Kind of like we use our diaphragm, but with a totally different mechanism. And they can produce the largest bite forces of pretty much any animal we know of. So they have gigantic jaw muscles toward the back of their jaws that can produce lots and lots of force. As I showed in some of my research, most species of crocodile can use these really extreme bounding and galloping gates that we would normally think of as mammalian-like kinds of movement. So they bend their backbones up and down

instead of side to side and go airborne for substantial periods of time and can go pretty quickly overground. When they're small, at least. Once they get big, they seem to lose that ability. But Yeah, they can be pretty great athletes and so on and so forth I could go on and on about this. I just think they're really neat and you might look at them and think oh, that's just another lizard. Lizards are great in their own right, but

a crocodile is not just an armored lizard or something like that. It's completely different. It's its own thing. I'm going to say I'm a little jealous. In my field, the calls that we get are like, oh, hey, Kelly, I saw some really fresh roadkill. Do you want to come grab it? And like, the answer is always yes, because there's probably some really great parasites in there. This is a bunch of tapeworms from a road-killed porcupine.

I know good stuff in my office here, but I don't have anything as cool as what you've got in my freezer. Well, you can always come visit and have a tour. I'd be glad to show you around. I've got ostriches, emus, there's a buffalo somewhere in there. I got a very Gary Larson image of your freezer going on right now with like, you know, ostrich head sticking out and giraffe limbs everywhere. Is that pretty accurate? It's kind of like a frozen Noah's Ark, I guess you could say. That's awesome. I'm going to see you in May.

Oh, okay. Great. Yeah, I'm coming back to town in May. I'm going to visit your freezers. Great. So what are the big open questions in your field right now? Oh, oh, boy. Some of the ones we touched on earlier is like what really limits size in animals, what limits speed in animals, how flexible is that? How flexible are those things?

And how has that flexibility or the constraints on animals evolved over time with like changes in ecosystems, changes in animal tissues or what have you. I think there's still a lot that we can learn about what the range of possibilities is in animals. And the goal of my work that I've been really pushing on for a long time. And I think a good general goal for paleontology is that paleontology should be able to teach us things about biology and contribute to theories in biology as a whole, not just be a slave to biology where we're always looking to biology, looking to nature today to try to solve questions about the past, but contributing to broader theories about animals in general through looking at the past

and the present. So like my studies of how big animals are limited by their size and how athletic they can be, it's all about all these different groups, living and extinct. I don't care if they're living or extinct. I want to know what the principles are that we can derive from them. and I want to be able to prove to colleagues, regardless of what field they're in, that I can answer those questions and that we can learn something from a T-Rex that isn't just, you know, a variant of what we already could learn from an elephant. That's a selfish example, just explaining what I would say is big questions. Do you think there are big surprises waiting for us underground? You know, is it a possibility we could find a new huge dinosaur that blows your mind?

I mean, I know we found, like, the supersaurus and the gigantosaurus and the titanosaurus. Is there the possibility of some, like, uber megasaurus to be discovered? Or do you think we've sort of maxed out the size of dinosaurs? Or a hollow earth, like, filled with giant sorbods? Exactly. No on the latter point, a very firm no there. But in terms of finding giant dinosaurs, yeah, I mean, over the last 20, 30 years, there have been larger and larger sorpods that have been found.

including more and more complete ones, there's like seven skeletons of one really giant animal called Patega Titan that I've worked with a small amount with colleagues on, and that's one of the biggest land animals ever. It's up there as a contender, and yeah, to have seven skeletons of that is really remarkable. But discoveries are pushing the boundaries continually, and we suspected that dinosaurs were feathered, but it wasn't until almost 30 years ago that we actually found out that many dinosaurs were feathered. dinosaurs were from some pretty startling discoveries in China. So we know from the history of paleontology that there can be shocks there in terms of revolutions that can happen. Going up and digging fossils is always the primary

lifeblood of paleontology. That's where discoveries ultimately come from. I don't do that kind of work. It's just not my skill set. I do the more lab or computer-based work where I'm trying to unravel what it all means. But yeah, I'm sure there's more surprise to come. It's time for the alien question, Daniel. Well, it's always inspiring, I think, for listeners to hear that there are lots of mysteries left to unravel. And one mystery I think about a lot is what life might look like on another planet. And I wonder if you might speculate with us, because everything you've learned about comes from the experience here on Earth. And we don't know, of course, if this is typical,

if we've explored all the effective possibilities that biology allows, or if life on Earth went down some weird little nook and most of life in the universe is different it's all weird in hollow bubbles or something so if we are about to land on an alien planet and you're a biologist on board what are you expecting to see in terms of large animals on an alien planet and you know as an aficionado of monster movies feel free to go weird and crazy in science fiction what would i expect to see i'd be surprised if there were large animals well it depend on what we would know about the planet. If it had been a place where the environment had been fairly stable for some time, given a long enough time for large animals to have evolved at all, and not having mass

extinctions that screw it all up, then I might be more inclined to expect that. But anyway, all right, if I was expecting a big animal, well, I'd be wondering what's it supporting itself with. Are we going to learn something entirely new about supportive tissue? Like, is it going to just not have anything remotely like muscle, some other thing. Is it even a protein that it's using to provide an active support, or is it, I don't know, this, boy, the boundaries, the possibilities there get so interesting and certainly depends on whether you are a carbon-based life form ultimately or silicon or whatever else they're using as their building blocks.

And if they have DNA, what kind of DNA is it double-banded? triple-banded, is it following the same curvature as our DNA or the opposite handedness? Does that even matter? I don't know. Or are they using something totally different as heritable material? That would be a game changer for what evolution can even do. But I'm not sure I can give you a very satisfying answer for what I would expect in terms of animal life. It's so wide open for possibilities. That's a pretty satisfying answer, honestly, to think that it's very wide open and we could be very surprised. I'd still expect the fundamental principle of the square cube law probably would hold if you got a wide enough size range of animals that ultimately, if you push

size to a large enough extreme on land where gravity's affecting organisms, then they're going to hit a limit and something's going to have to change. They're going to have to slow down or really change their shape or something like that, that would be a prediction that's really rooted in physics and fundamental theory of animal size and shape change. I'd feel pretty confident in that, but I don't know, biology can screw things up and maybe they change their molecules that they're made of as they go from small to big and just break the rules of what we think is normal. Leaving on a high note here for Daniel, we can be sure about the physics, but the biology can screw things up. All right.

As usual, with biology, it depends. It depends. Yes, that's the rule in ecology, at least. All right, well, John, thank you so much for being on the show. That was a ton of fun, and I really hope I get to check out your freezer one day. Please do come. Yes, it's an open invitation for you both. And if John ever serves you dinner, you should ask, what's in this burger?

Or don't ask. Yeah, I think don't ask is the way to go. You can ask. I won't be offended. Daniel and Kelly's Extraordinary Universe is produced by IHeart Radio. We would love to hear from you. We really would. We want to know what questions you have about this extraordinary universe.

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