Our 84th episode kicks off with an interview featuring Dr. Scott Persons, who has a PhD in evolution and systematics from the University of Alberta, and still works there researching dinosaur biomechanics and evolution. He works for Dr. Philip J. Currie, who we interviewed back in episode 4. Dr. Persons has been on many dinosaur digs and he currently studies dinosaur locomotion. But the way that we found out about his work is that he presents all of the University of Alberta Massive Open Online Courses (MOOCs) on Coursera.org that came out this year, and he did a really amazing job.
You can reach Dr. Persons on Twitter @WScottPersons. And you can see the introduction to his Paleo 101 course on Youtube at https://www.youtube.com/watch?v=8jX4_mWAlUg as well as an awesome short video of the University of Alberta using a helicopter to lift a dinosaur skull out of the ground at https://www.youtube.com/watch?v=gJmHONyeLZ8&feature=youtu.be.
Episode 84 is also about Xixiasaurus, a troodontid with sickle claws and keen senses.
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In this episode, we discuss:
- The dinosaur of the day: Xixiasaurus
- Name means “Henan Xixia lizard“
- Not to be confused with Xixianykus, an alvarezsaur from the same formation (Majiacun Formation in China, Henan Province, Xixia County)
- Type species is Xixiasaurus henanensis
- Species name is in honor of the Henanon Province, where it was found
- Troodontid that lived in the late Cretaceous in what is now China
- Described in 2010
- Chinese scientists from the Chinese Academy of Geological Sciences in Beijing and the Henan Geological Museum in Henan described the fossil
- “From Lü, J.−C., Xu, L., Liu, Y.−Q., Zhang, X.−L., Jia, S.H., and Ji, Q. 2010. A new troodontid theropod from the Late Cretaceous
of central China, and the radiation of Asian troodontids. Acta Palaeontologica Polonica”
- Fossils found at the Xixia Basin
- Found a mostly complete skull, which resembles Bryonosaurus, a troodontid from the late Cretaceous in what is now Mongolia (both have no serrations on teeth)
- Bird like
- Estimated to be 3.9 ft (1.2m) long
- Had good hearing and a good sense of smell
- Very smart, one of the highest encephalization quotients of nonavian dinosaurs
- Skull is nearly complete, except for its posterior portion (part of braincase also missing)
- Skull is long and similar to Byronosaurus
- Had 22 maxillary teeth
- Xixiasaurus had fewer maxillary teeth than Byronosaurus, which had at least 30 (but still had more teeth than most other theropods)
- Troodontids were probably carnivores, based on their teeth. Though in 1998, Holtz et al. suggested they may have been herbivores because the size of the serrations on their teeth were more similar to other herbivores than carnivores (but not widely accepted)
- Lack of serrations on Xixiasaurus and Byronosaurus show their food sources may have changed (they could no longer slice meat with their teeth)
- So maybe Xixiasaurus was an herbivore or omnivore?
- Troodontidae is a group of bird-like theropods
- Troodontids have been found in the Northern Hemisphere only (North America, Europe, Asia)
- Largest one was Troodon, and the smallest was Anchiornis (known)
- They have closely spaced teeth in the lower jaw, sickle-like claws, and were pretty advanced
- Had long legs
- Had large brains and large eyes, and good hearing
- Had asymmetrical ears (one higher on the skull, like owls), which means they may have hunted similar to owls, using hearing to find prey
- Fun fact: It’s likely that Enantiornitheans lived in colonial nesting sites and unlike many modern birds they may have buried their eggs.
For those who may prefer reading, see below for the full transcript of our interview with Dr. Scott Persons:
Garret: Dr. Scott Persons has a PhD in Evolution and Systematics from the University of Alberta and he still works there researching dinosaur biomechanics and evolution. He works for Dr. Philip J. Currie, who we interviewed back in episode 4. He has been on many dinosaur digs and he currently studies dinosaur locomotion.
The way I found out about his work is that he presents all of the University of Alberta massive open online courses that came out this year, at least in the Paleontology department and he did a really amazing job, so I wanted to talk to him.
Dr. Scott Persons: Well thank you very much!
Garret: So, on Coursera where you presented those MOOCS it lists you as a dino maniac since the age of two and a half. So what first got you interested in dinosaurs?
Dr. Scott Persons: Ok, so I’m told I’ve been interested in dinosaurs since I was two and a half. I don’t actually remember that far back, but the story goes that it all began in Las Vegas where my dad was on a business trip—legitimate business trip and he wanted to bring me back something. And there weren’t a lot of child-friendly venues in Vegas at the time, but where there was a place called the Desert Museum and he went there while he was in Vegas and like all good museums he was forced to exit through the gift shop. And there in the gift shop he found a very small paperback book entitled The Big Little Dinosaur. It’s a story about a baby sauropod, a baby longneck. And he brought that book home and I had him read it to me, and read it to me again, again and again and apparently I was just hooked from there. It’s a great story—it’s got a whole Jurassic cast of characters. There’s sort of a smart-alecky pterosaur, there’s a very heroic stegosaur, and then the big villain is purple Allosaurus.
Garret: Oh cool. That’s interesting, they pick and Allosaurus rather than the typical T-rex.
Dr. Scott Persons: Yeah they kept it Jurassic.
Garret: Yeah, that’s rare, actually. That people realize that dinosaurs didn’t all co-exist in one big crazy hodgepodge.
Dr. Scott Persons: Right.
Garret: So, do you have a favorite dinosaur? Is it one of the ones from that book?
Dr. Scott Persons: No—so I’d like to say that my favorite dinosaur will be the one that I discover. But right now my favorite dinosaur, if I had to pick just one, is an individual we call Hannah.
Garret: Okay. That name is familiar—is that a Styracosaurus?
Dr. Scott Persons: So—Hannah is a particular individual, it’s a skeleton that I found last summer in the Dinosaur Park Formation, and when we first found her, we found the nose first. So the horn was just poking up out of the sediment—we got the whole skull, and we first thought it was going to be actually a Centrosaurus. So another kind of horned dinosaur because of the shape of some of the ornaments on the frill just as you get to the very back of it. So just as you reach the shield. it looked very much like a Centrosaurus but then as we continued to work around the skull we found these great big spikes—the classic Styracosaurus horn dew sticking out there at the back. Then it because very, very clear that it was a strange critter that mostly looks like a Styracosaurus, but it’s got those few horn ornamentations that seem more in line with Centrosaurus.
So right now we’re thinking it’s probably Styracosaurus, maybe possibly it’s a different species of Styracosaurus—who knows. It’s ceratopsians, you might try to split that up even as far as genus level. Maybe it turns out this is a critter that helps to bridge an evolutionary gap between Centrosaurus and Styracosaurus. But we really don’t know yet and we’re continuing to excavate Hannah.
Garret: Gotcha. Last week we were talking to Dr. David Hone.
Dr. Scott Persons: Oh yeah.
Garret: Oh, ok so you know about his zoology background I guess?
Dr. Scott Persons: Yep.
Garret: And I asked him “How come there are so few dinosaur genus even predicted?” And he pointed out when you’re doing paleontology, it’s a lot harder to break down the nuance between species, so it makes me think maybe that one that you found will eventually be classified as something we already have by some people, and other people might say “Well it’s actually a bridge specimen, in between them.” I keep seeing that debate over and over again.
Dr. Scott Persons: The lumpers and the splitters, yeah.
Garret: Yeah exactly. I like that, lumpers and splitters. So another area you did some research was near Glenrock, Wyoming.
Dr. Scott Persons: That’s right. Yes, yes Glenrock, Wyoming that’s with the Paleon Museum in Glen Rock which is a really cool place.
Garret: Cool, there are some T-rex tracks there that you looked at and you, kind of, worked on determining its speed. Can you talk a little bit about how that worked?
Dr. Scott Persons: Sure, sure. So I did not find these tracks. These tracks were found by the Glen Rock Paleon Museum’s head paleontologist, Sean Smith and they are a short series of tracks. They’re in the land’s formation, so they’re latest Cretaceous. They’re big, so they’re… they probably are tyrannosaur. And they’re a little bit too small to be an adult T-rex so they may be a juvenile Tyrannosaurus rex, or—speaking of lumpers and splitters—maybe they belong to a critter called Nanotyrannus which a lot of people think is just a juvenile Tyrannosaurus rex. But yeah so we’ve got a whole series of tracks there.
And what’s neat about it is you’ve got a left right left right pattern of tracks you can do a rough calculation of how fast the animal is moving. And this is not a dinosaur that is racing—it doesn’t record a running tyrannosaur by any means. But it’s cool to give a sort of baseline for how the animal is walking. And one neat thing that seems to show is that for their size, tyrannosaurs are taking, as most meat-eating dinosaurs were, relatively longer steps than equivalently sized ornithopods. So the Glen Rock trackway shows that these tyrannosaurs are at least walking faster than the duck billed dinosaurs that they were hunting were walking.
Garret: Yeah, so I think I read somewhere that we’ve found several tracks of tyrannosaurs walking, but prints of running don’t really fossilize well, or maybe just aren’t common enough.
Dr. Scott Persons: Yeah they’re just not very common. So there are a number of factors that play into that. And really here we can talk not just about tyrannosaurs but we can talk about dinosaurs in general. We just don’t have very many convincing running tracks for dinosaurs. There are a couple reasons for that. One is strictly a probability argument, right? Think about the amount of time you spend or an animal spends walking vs. the amount of time that they spend running, right? You’re running for only very short periods of time—so just the odds are that if you’re going to find an animal’s track, it’s going to be doing what it’s normally doing which is walking. And then added on top of that, is the fact that in order for you to get tracks preserved, you need to be walking on sediments surface that’s conducive to preserving footprints. So usually that means walking of very soft, squishy sediments.
Dr. Scott Persons: And when you’re moving on soft squishy stuff, you know, normally you’re not, you’re not trying to run, right? You may even be walking slower than you normally would because you’re being careful not to slip or to get stuck.
Garret: Makes sense. So do you know if there have been any running fossilized footprints?
Dr. Scott Persons: There had been some controversial ones. So the prime example of that are some tracks that have been found down in Australia that are supposed to preserve possibly some dinosaurs running—possibly even a chase between a carnivorous dinosaur and its prey. But there has been so recent controversy about that.
Garret: Controversy always seems to pop up with new and exciting, so…
Dr. Scott Persons: Absolutely.
Garret: So you also describe Carnotaurus as having an exceptionally long, or large—I guess maybe long caudofemoralis muscle which may have helped it sprint but it may not have been able to turn very well. So what do you think it might have hunted? Or—how do you think it might have hunted?
Dr. Scott Persons: Yeah, so Carnotaurus is a really weird, really cool critter and it’s got the single most bizarre dinosaur tail I think I’ve ever seen. That’s including things like Ankylosaurus and stegosaurs. So Carnotaurus’ tail is so bizarre because of what we can call the transverse processes or caudal ribs. And so the tail of course is an extension of the backbone, so it’s composed of a series of vertebrae and the caudal ribs are bones that stick out from the vertebra usually to the sides. So on any respectable meat-eating dinosaur’s tail you’ve got a nice long series of these ribs on either side. But on Carnotaurus, they get freaky. They point way the heck upwards, so not so much out as up. And on the ends of these ribs, they’ve got these weird hooks to them so it looks like the dinosaur’s almost got a row of question marks running down it’s spine. And the way that those hooks, when you articulate the tail skeleton, they line up one directly behind the other and they sort of overlap and make contact with the ones in front of and behind them.
So you’ve got this tight interlocking series and we also see some evidence on the lateral surface of those caudal ribs giving us—we think—some indication of where the different muscles attached. And based on my research looking at dissections of modern-day reptiles, we think that the muscle that is most reasonably filling that space on the sides of the tail is the muscle called the caudofemoralis which is actually a muscle that is tied to the leg. So it’s a big muscle in the tail that’s attached to the femur—the upper leg bone—by the tendons. When the muscle contracts it pulls the leg backwards or if you’re planting your foot and your contracting that big caudofemoralis muscle it’s was pulling your body forward, is what’s giving you your power stroke. By angling the caudal ribs upwards in Carnotaurus you’re expanding the size for this muscle, which implies Carnotaurus has an increased locomotive oomph. It’s just got more power in it’s trunk, which like a Volkswagen beetle is the engine and so that presumably would give it more power, let it to run faster.
When we say I don’t think it can turn particularly well, it’s just because by having that tight interlocking series of tail vertebrae, it means your tail is less flexible and you probably have to turn the whole thing more as a unit, which may increase your rotational inertia, making it harder for you to pivot quickly. Now in terms of what Carnotaurus was actually hunting, that’s a tricky question. We don’t have any good direct evidence of that. But one bit of speculation that we put forth in our paper describing Carnotaurus is that, as with all bazaar dinosaur adaptations, this one didn’t just pop into existence overnight. We see in some of Carnotaurus’ other South American relatives, we think is a fairly gradual progression leading up to this bizarre tail form. And during that time, at least when these ancestors of Carnotaurus were around, you know, some of them were coexisting with some of the great big predators of South America. So things like Mapusaurus and Giganotosaurus—the really big guys. And were thinking well maybe this represents a little bit of niche partitioning.
So that is Carnotaurus and its ancestors might be becoming more specialized to run really fast and in turn both avoid being eaten by those other big super predators but maybe they’re also better at catching some of the smaller faster critters. So maybe going after some of the abundant South American ornithopods and possibly may be leaving the big sauropods there for Giganotosaurus and its crew to tackle. Now that being said, we don’t have direct evidence of Carnotaurus itself coexisting with some of those other big predators. But that may very well be just a function of sample size. Because we really don’t know a lot about the other animals that share the particular environment, the particular point in time with Carnotaurus.
Garret: So it makes Carnotaurus look more like a cheetah and some of these other guys look more like lions or something.
Dr. Scott Persons: Yeah, maybe that’s a good comparison.
Garret: Okay. Cool, yeah. I’m also kind of surprised, like you mentioned the book that you had as a kid, that the Carnotaurus doesn’t pop up more as a big villain—because it’s even got the horns and everything.
Dr. Scott Persons: It does, it does. Well Carnotaurus has been the villain in pop culture a little bit, right? If you think back to Disney’s Dinosaur, with the iguanodons and the big migration story, Carnotaurus is the big bad.
Garret: You’re right.
Dr. Scott Persons: In that film, in fact they make them bigger and badder than the animal was. Right? They blow it up to the size of a tyrannosaur. So it has gotten to be villainous in that way. Carnotaurus makes a cameo in the second Jurassic Park novel, where it’s a scary critter looking in the dark and it’s got camouflage powers, I think.
Garret: I’ll have to re-read that. It’s been a long time since I’ve read the Jurassic Park books. Do you think that it might have been the fastest large carnivore? Or do you think of something more like a Dakotaraptor or something would have been quicker?
Dr. Scott Persons: OK, so actually I would argue to you that although the raptors, the dromaeosaurs at least, get a lot of publicity for being fast, thanks in large part to Jurassic Park. Actually when you look at their limb proportions, most of them, say when you look at the length of the lower leg, the length of the shin, and the length of the metatarsal—so some of the foot bones which count effectively as leg bones in these guys because of course they are standing on their toes so the foot is raised up and contributing to the length of the leg. They are actually not that elongate—they don’t really have the legs of a sprinter.
I tend to think of a classic raptor dinosaurs or the dromaeosaurs as maybe being more like wolves and coyotes in terms of their athleticism than like cheetahs or other big cats that are really, really good sprinters. Now if I had to bet, you know, I probably wouldn’t say that Carnotauruses, even among the big theropods was necessarily the fastest. We don’t have a complete lower leg of the Carnotaurus, so it’s a little hard to say that. Maybe it does. Maybe when we find the full leg it will surprise all of us. But you might want—you’d have to go out to the Dino Derby and place a bet, you might go for a small to medium sized tyrannosaur actually…
Dr. Scott Persons: Of the big predators because it got really, really long legs. Tyrannosaurus are super leggy—sort of the Radio City Rockettes of the dinosaur world.
Garret: Have you talked it all to the group that’s making the game Saurian at all?
Dr. Scott Persons: No I haven’t.
Garret: They describe T-rex in almost the exact same way. It’s just—they say Sue has legs for days, she can just run so fast super easily. Cool—so other than running ability, or perhaps how quickly they can change direction, what else can we learn about dinosaur locomotion from fossils?
Dr. Scott Persons: Ok, so as I said a big part of my work focuses on looking at dinosaur muscles and trying to figure out from the skeletons where they are attached. And as far as we talked about looking at just the proportions of the limbs as they relate to speed and also looking at the size of the tail muscle. One other thing that I look at, which is sort of a combination of those two, is trying to think a little bit about the leverage involved in the muscle and skeletal system.
So for instance, one cool topic that my advisor Dr. Phil Currie and I try to tackle is the mystery of the successful duck-billed dinosaurs. So if we imagine a video game, right where we get to travel back to the Hell Creek, the most common dinosaur, […] I would imagine, that they’d have you encounter is probably going to be, at least of the big ones, is going to be a duck-bill. Because duck-bills are like everywhere. In North America at least they easily outnumber all the other kinds of big dinosaurs—they’re really, really successful. Which is also really, really weird because, I mean, as a video game character goes it would seem like the duck-bill dinosaurs would be like the safest thing you could try to attack, right? That’s like level one. It’s just a duck-bill. It doesn’t have horns, it doesn’t have armour, and for big animals that’s something that’s really weird.
So there’s this idea in modern ecology and thinking about the evolution of ecosystems that says, you know, as an animal gets larger, as it increases in body size, it’s environment becomes progressively more two-dimensional. Ok, because if you’re a really, really big animal there are fewer objects in the environment that are, number one, an obstacle for you, right? Everything gets progressively flatter—there are very few things that you can not cross. They you can not simple step over if you’re the size of a big dinosaur. Ok, and that has implications for predator avoidance strategies, right? If you are a little critter, then your world is filled with rocks and bushes and grass and things that you can hide behind. You’ve got the option—you can burrow and make your own hidey hole, you climb up trees and things like that. If you were a big dinosaur, those really weren’t options for you and so strategies based on crypsis and concealment—so hiding from your predators probably doesn’t work because they can see you. There’s no place to hide.
And so you need more direct methods for dealing with your predators and we see that today if you look at big megafauna like in Africa, for example. You see a couple different strategies. You can do what elephants do, you can just get to be so big that a predator can’t tackle you—certainly not one on one. You can be a warrior, like a cape buffalo or rhinoceros—you can develop a weapon that makes it dangerous for a predator to try to muck with you. You can be a fortress, like a crested porcupine, or a giant ground pangolin—so you’re so well armoured and pointy that you’ve got no vulnerable spots. Or you can be a speedster like a gazelle or antelope. You can match your predator step for step and make it so that they can’t catch you. If we look back on dinosaurs, we see a lot of parallels, right? We’ve got huge sauropods, they’re giants, we’ve got ceratopsians, which certainly seems to take the warrior strategy, you’ve got some fortresses in the case of the big Ankylosaurus, obviously you’ve got speedsters with some of the small ornithopods or the Ornithomimus and of course the big predators in that scenario would be the tyrannosaurs. But duck-billed dinosaurs—they don’t seem to fit into any of those, right?
They’re not super big, most of them at least. They overlap with the size of their predators. They don’t have very big horns, they don’t have armour, they’re certainly not fortresses. The question is—well, okay, are they speedsters? Can they be as fast as their predators? Well, when we look at the length of a duck-billed dinosaur’s leg, turns out, no, it’s much shorter. The same sized Edmontosaurus has got a much shorter than the same sized tyrannosaur’s. It doesn’t look like they could outrun them, but one thing my research suggests that the attachment side for the caudalfemoralis is really, really high up on the femur. It attaches very high up on the femur—it attaches very high up on the tyrannosaur. That’s great for high speed running, right?
You have it attached high up so a very short contraction of the muscle is enough to swing the leg back and forth through one entire power stroke. So very quickly, contact, contract, contract. Your tyrannosaur can swing its leg very, very quickly—great for sprinting—cool. In a duck-billed dinosaur though, it’s attached really, really far down. So you’ve got a slow contraction, or else very short steps. Again, that parallels with what we see in the dinosaur footprint record—duck-billed dinosaurs taking shorter steps. That makes you slower. But by positioning it lower down, right, you’re extending the moment arm. You’re giving yourself a lot more leverage for that muscle, right? It’s like—imagine a door. You put your door handle far away from the hinge, it makes it nice and easy to open. If you put it really, really close to the hinge, you got to really work in order to swing the door open. Same thing would be true for these dinosaurs and their legs.
So the idea is well, whether or not a tyrannosaur can catch a duck-billed dinosaur might really depend on what kind of a race you’re running. In a short sprint, sure. The tyrannosaur can overtake it easy, but if it’s a long race, if the duck-billed dinosaur sees you coming from a distance, well then it can run and run and you’ll gain on it for the first little while, but then your caudofemoralis is going to be aching and burning and the duck-billed dinosaur, with it’s superior leverage you know, it’s slow but steady would win that race.
And indeed, if you then apply that back to our African analogue, you see that, well, what’s the number one, reasonable sized herbivore that you often encounter on the plains of the Serengeti? Well, it’s things like zebra, and wildebeest. And the zebra is a fast critter, can move 30-35 miles per hour. But the lion can do 50, cheetahs which do attack zebras can do 60 and up. So those big cats are faster, but the zebra has got superior endurance such that the cat can only overtake them if they get into a very narrow striking distance.
Now imagine you’re a duck-billed dinosaur. You’re not having to be on the lookout for a stealthy cat moving through the tallgrass. Instead you’re on the lookout for a predator that’s literally the size of a billboard sign and you’re a herding animal, so you’ve got multiple eyes and ears and noses—all on the alert. For a predator with the ability to alert you if they’re spotted. So we would argue that an endurance based strategy might be very viable for duck-billed dinosaurs. And maybe that was at least partially key to their success and certainly for their continued survival alongside tyrannosaurs.
Garret: Yeah, that makes a lot of sense.
Dr. Scott Persons: You know maybe, maybe in the video game the duck-billed dinosaurs aren’t even an animal you get to interact with. Maybe they’re just sort of a background critter that runs away as soon as you get close and you never made any progress.
Garret: Yeah, because sneaking up as a T-rex is going to be a little tricky.
Dr. Scott Persons: Yep.
Garret: So you were involved in the discovery of the “Romeo and Juliet” find which is believed to be a mating pair of Oviraptors. Can you tell us a little about what you did there?
Dr. Scott Persons: So I should clarify—first off I was definitely not involved in the discovery of those specimens. I was not even on the same continent—they were found in Mongolia. What my role has been is that after a bunch of hard working folks found the specimens, cleaned them up, and brought them for study at the American Museum of Natural History, I was one of many researchers that was allowed to come in and have a look at them and study them. So as background goes, yeah—Romeo and Juliet are a pair of Oviraptors. They were found very, very close together, they’re beautifully preserved. It looks like they may have died in the same event. Maybe they got buried as a big sand dune came down over top of them. So it looks like they died almost in each other’s arms and so that gave them the nickname Romeo and Juliet. It was one of a couple of nicknames they got. They were also nicknamed Sid and Nancy, and also Batman and Robin.
Romeo and Juliet was the name that really stuck because it conjures up the image of “Oh, what a tragic death for these dinosaurs, maybe they were in love.” Okay, so what I did was, I was interested in tails, and although these two critters are basically identical in every regard, the one that’s named Romeo is slightly larger. But they’re basically identical except when you go to look at their tails. So the tail vertebrae are very different as are the chevrons, and chevrons are the little tailbones that stick down below.
And in the specimen that’s nicknamed Juliet she’s got a fairly standard series of chevrons—Oviraptors didn’t have many flexible tails, they were actually pretty beefy tails too. But she’s basically a par for the course, wasn’t a big surprise. But then when you look at Romeo, he’s got these chevrons that really start to change shape very radically as you move past the base of the tail. And it develops this almost spearhead like shape to it which I took as indication of, “Wow, what a strong attachment point for some muscles that you’ve got going on there.” Those caudal ribs are proportionately longer in Romeo as well.
And the reason that we can think about relating tales to romance in oviraptorosaurs is that many of them have got what we call pygostyles—so a series of fused vertebrae right there at the tip of the tail which is something you also see in birds. And we think that those pygostyles were there to support a fan of feathers. So a little bit like the fans of feathers you see in modern day birds. And we know from a critter called Caudipteryx actually preserved in China one of the specimen’s beautiful asphalt specimens where you actually physically see a fan of tail feathers. So we know that these critters have got this structure.
And if you think about modern day birds with big fans of feathers do with them when they’re not using them to help them fly—and indeed these oviraptors are flightless—one function is that you use them as a sexual display structure, right? You flaunt them, you flash them in mating dances. You use them to attract the opposite gender. And of course, as is often the case, these sexual signalling devices tend to be sexually dimorphic meaning they’re bigger, they’re more exaggerated in one sex than in the other. And of course because it is usually the males that have to do the advertising, it’s to the males that the onus of doing the mating dance, of doing the convincing, that responsibility falls to. It tends to be the males that have got the more elaborate display structure.
So when we saw that these two dinosaurs seemed to show what might be sexual dimorphism in their tails, we figure most likely the one that’s got the butcher tail, the one that seems better adapted to swing and flaunt and wave its tail about is more likely the male. As it happens, that’s the one that did get the nickname of Romeo. So we suggested, “Yeah, you know Romeo and Juliet may in fact be a male-female pair. Maybe this really is the tragic dinosaur love story that the press originally made it out to be.”
Garret: Cool, yeah. That’s sometimes not the case that the press jumps on a cool title.
Dr. Scott Persons: Oh, yeah.
Garret: Especially whenever tyrannosaurs get involved, but… So one other paper that I found really interesting is on Sinocalliopteryx.
Dr. Scott Persons: Oh, yes.
Garret: And the paper describes it as likely a stealth hunter.
Dr. Scott Persons: Mhmm?
Garret: Can you talk a little bit about what clues there were for that conclusion?
Dr. Scott Persons: Sure, sure. Ok so Sinocalliopteryx is a very cool critter for China. It is related to a very small […] (00:28:18) dinosaur although it’s actually fairly large for its group, so it’s pushing wolf size. And the reason there was discussion about it being a stealth hunter is because inside the preserved ribcage of some Sinocalliopteryx specimens we find the remains of some early primitive birds. Inside the specimen of another one we actually found the leg of a raptor—a little raptor. So like a relative of, like Microraptor. And these are critters that have got wings in the case of birds. They’re certainly at least critters that were capable of flight. And so that’s sort of an unusual prey choice for a land bound predator to be going after. Apparently, with some regularity, right?
Multiple instances show these kinds of prey preserved. Based on that, we can suggest, well maybe we can compare Sinocalliopteryx to some modern day predators that are good at catching prey that can fly. So that’s something that, say, foxes can do. Obviously that’s something that a lot of cats do and they wa… that do… that is, they are really, really good at sneaking up stealthily and then pouncing on their prey before they seem them and they’re able to take off. And so Sinocalliopteryx seem to have an abnormal preference for flighty prey. We suggest that maybe it was particularly good at that.
Garret: Ok, so just looking at the stomach contents alone you can draw the conclusion, you didn’t have to look too much at… I guess it helps that it’s small, probably.
Dr. Scott Persons: It helps that it’s relatively small, when we think about the limb proportions of Sinocalliopteryx. Actually it’s got a really, really long lower leg—it was also a pretty fast critter. So you can definitely imagine it finding its feathery prey and then sprinting in a big lunge, or big pounce to nab it.
Garret: Ok, very cool. One other dinosaur study question that I have for you is you have talked a little bit about a non avian theropod swimming in China and we saw a similar track that came out of the UK recently.
Dr. Scott Persons: Mhmm?
Garret: What do you think would make a dinosaur want to swim? Or where would they be swimming?
Dr. Scott Persons: Oh, so I’ll tell you—when I was growing up, on of the big movies before Jurassic Park was of course the Land Before Time.
Garret: Mhmm, that’s probably our favorite.
Dr. Scott Persons: All right, cool. Well you remember the big climax in the Land Before Time is when Littlefoot and his posse make the big stand against Sharptooth the tyrannosaur. And the way they defeat him is they just sort of knock him into a puddle. And they say it’s so deep down there that he won’t be able to swim with those scrawny little arms. And for a long time there was this sort of idea that, you know, unless a dinosaur had clear adaptations or what we thought were clear adaptations for being able to swim, you know, they were land bound critters. They didn’t go into the water and maybe Tyrannosaurus rex and what not couldn’t even swim. It’s actually a pretty silly thing to think, I would argue.
If you look at modern day critters—even animals that mostly hang out on land, if you put them in water, they float—they are perfectly capable of swimming. Some may actively try to avoid the water but there are also plenty of big mammals today that are perfectly happy to go for a swim. And there are many reasons why they might choose to do that. Could be as simple as, “Ah, we need to cross this river, this body of water to get to the other side.” It may be, “It’s nice to take a nice refreshing dip.” Maybe it’s good for getting rid of parasites, maybe it’s just a good way to cool off.
So I actually imagine that a lot of dinosaurs had many reasons, many opportunities to get their feet wet, to go for a nice little swim. And even though Tyrannosaurus rex has got those tiny little arms, it’s got huge lungs. It would be very, very buoyant. It would be hard to sink a Tyrannosaurus. Plus, it’s got giant feet and really powerful legs. The animal could certainly swim, it could do this sort of duck paddle, which is some of what we think those tracks show—the dinosaur just touching bottom and scratching along as it moves. And of course, it’s also got the great big tail that it could certainly move from side to side to help propel it through the water. So I don’t think you could kill a tyrannosaur by dropping it in the water.
Garret: So are most of these swimming tracks really that transitional, where they go from walking to clawing a little bit at surfaces because they’re starting to float?
Dr. Scott Persons: Yeah, so I mean—and that’s not surprising, right? Because the only place that you could get a swimming track is when the dinosaur is just beginning to start to swim, because after that it’s just padding through the water. And the water won’t fossilize it to give you a track. So where you tend to get it is right where you’re moving into the deep end.
Garret: That’s amazing to me, especially it’s so hard to find running tracks, but we can find these swimming tracks periodically.
Dr. Scott Persons: Sure, sure. And that again relates to the kind of environment, right? You need to have somewhat wet moist sediment for you to get a track that gets to be preserved, and of course you have those around watery environments. And watery environments are also where you’re going for a swim. So that really increases the probability of it.
Garret: Cool. Do you have any plans for making any other paleontology MOOCS? Or maybe now that you’re an official doctor, somebody else is taking that over?
Dr. Scott Persons: We do actually have plans to do some quick revisions, maybe add in a few things, touch on some stuff we either didn’t get a chance to do, or didn’t get a chance to do justice to. So there are some revisions, some update additions to the Paleo MOOCS that are scheduled. Currently though, there are no big plans that I’m involved with for the moment. But you know, they’ve just come out, there’s going to be a period of time of waiting to see how they’re received.
Garret: They are great. Probably the best MOOCs I’ve taken, so—excellent work.
Dr. Scott Persons: Ok, thank you! That’s great to hear.
Garret: Yeah, I often recommend it on the course for everybody to take the Dino 101 and the Early Theropod.
Dr. Scott Persons: Theropods and the Origins of Birds, yeah.
Garret: Yes. I also took the other ones, even though they’re not about dinosaurs. Just because you did such a good job.
Dr. Scott Persons: Thank you!
Garret: So, one final question.
Dr. Scott Persons: Okay?
Garret: We’re going to be visiting the Philip J. Currie Museum and the Royal Tyrrell Museum in a couple of weeks on a road trip.
Dr. Scott Persons: Oh, cool. Now you’ve been before, right. To the Royal Tyrrell, I mean?
Garret: We haven’t been at all, which is…
Dr. Scott Persons: Oh, you haven’t! Oh my gosh—well you’re in for a treat.
Garret: Is there anything in particular that we should know about or anything?
Dr. Scott Persons: I tell you what, when you go through the very first gallery at the Royal Tyrrell Museum, once you come out of the beautiful room that’s got these life-sized albertosaurs you’ll enter into what looks like an art gallery almost. The skeletons are behind little portraits in the wall, and you’ll come to two beautiful death posed skeletons. One of them is a juvenile Gorgosaurus, the other one is a ornithomimid—and they’re gorgeous and you’ll be blown away with the Gorgosaurus’ teeth and its claws. Pay attention to the back end. Have a look at the tail and have a look at the chevrons, again those little bones that stick down on the underside. And see if you can spot the point where those chevrons begin to change their shape.
So they’ll go from looking like elongate finger-like projections up to more sort of a boat shape to them. And right when you see that transition, you’ll be able to see a little series of scars, of little ridges running down the surface of those chevrons. And that, as I’ve argued in the literature before may very well represent the point where that caudal femoralis muscle, that big muscle that was powering that juvenile Gorgosaurus and that ornithomimid as they were running and sprinting through the Cretaceous landscape. You can see the point where it begins to taper out and some of the muscle moves in to take over it’s position. So look for that.
Garret: I will! Now that you’re a doctor I’m sure you have a very bright future, and an excited to see the first dinosaur that you get to name.
Dr. Scott Persons: Ok, well thank you very much and thanks for having me on the podcast!
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