Stegosaurus: Titan of the Jurassic

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Speaker 1 Hello and welcome to our latest Ancients episode.

Speaker 1 Today we're going to the time of the dinosaurs, but just before that, I wanted to do a quick shout-out because because a couple of weeks ago I got a message from one of our fellow ancients listeners Hugo and it was a video message and it featured Hugo and the youngest listener of the ancients two-month-old Aurelia Hugo and his wife's newborn daughter now Hugo sent me a wonderful message to let me know about Aurelia and how she's already been delving deep into the ancients archive her favorite episodes already being the Permian extinction and the fall of the Sumerians so Hugo well done you've already got already hooked on global prehistoric catastrophes and the falls of civilizations.

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Speaker 1 Anyways, on to today's episode, we're going back to the Age of the Dinosaurs to talk through the story of what is for many of us our favourite dinosaur, that iconic plated armoured dinosaur Stegosaurus.

Speaker 1 And to talk through it all, we've got one of the leading experts on armoured dinosaurs, none other than Dr.

Speaker 1 Susannah Maidment from the natural history museum now susie she came into our studio so we filmed it as well you can watch it on a youtube channel also featuring a fluffy stegosaurus toy steggy it is my own i must confess and i really do hope you enjoy let's go

Speaker 1 The Stegosaurus, one of paleontology's greatest icons. It was built like a tank, with hind legs like tree trunks, but its head held a brain no bigger than a walnut.

Speaker 1 It carried one of the most terrifying defensive weapons in history, in prehistory, four razor-sharp spikes swinging from a powerful tail, the legendary, so-called, Thagomizer.

Speaker 1 Today, we're delving deep into the world of Stegosaurus.

Speaker 1 We'll uncover the secrets of its incredible armor, explore the latest theories behind its bizarre anatomy, and journey back to the Jurassic to understand how this unique giant truly lived and fought.

Speaker 1 And I'm joined by the one and only Dr.

Speaker 1 Susie Maidman, paleontologist at London's Natural History Museum, which is home to Sophie, one of the most complete Stegosaurus fossil skeletons on display in Europe and indeed the world.

Speaker 1 Susie, it is great to have you on the show.

Speaker 15 Thanks very much for having me. It's a pleasure to be here.

Speaker 1 And we're talking about Stegosaurus today, and this feels like, for so many people, it is their favourite dinosaur. It is iconic today.

Speaker 15 It absolutely is. And, you know, every seven-year-old knows what Stegosaurus is.
And, you know, I give talks about Stegosaurus. And I ask in the audience first, you know, who's heard of Stegosaurus?

Speaker 15 Because this talk's going to go badly if you don't know what I'm talking about, right? And, you know, almost everyone puts their hand up. Everyone knows what Stegosaurus is.

Speaker 1 I guess we're quite fortunate to be in the UK with this study of Stegosaurus because we've got... one of the best preserved specimens at the Natural History Museum.
Is it Sophie?

Speaker 15 Yeah, we have the world's most complete Stegosaurus on display at the NHM.

Speaker 15 But actually, there are also two different species of stegosaur known from the uk included including the first one ever discovered which was found in swindon in swindon it was the swindon stegosaurus the swindon stegosaurus it's called dacentrurus armatus it's one of my favourite dinosaurs actually it's on display also in the natural history museum but it's in a kind of a cabinet like a like a slab mount and people just walk past it they don't notice it but it's the first stegosaur ever found anywhere in the world justice for the swindon stegosaurus absolutely needs to get more so maybe we'll talk about it a bit more as this episode goes along but i feel we need to address this first off.

Speaker 1 You mentioned the word stegosaurs there. We've already said stegosaurus.
So can you tell us the difference between the two words?

Speaker 15 Yeah, so stegosaurus is one type of stegosaur. Stegosaurs are a group of dinosaurs.

Speaker 15 So it's a bit like having antelope as a kind of, you know, group of animals that kind of look the same, evolved from a common ancestor and are quite diverse today.

Speaker 15 But then there's individual species within that that you can recognize. And it's the same with stegosaurs.
So we have a whole range of them. They lived all around the world.

Speaker 15 And of course, Stegosaurus is the one that everybody knows, but there are loads of others, actually.

Speaker 1 Does it have a particular scientific name?

Speaker 15 It's Stegosaurus.

Speaker 1 Stegosaurus is okay.

Speaker 15 Well, for most dinosaurs, we don't have kind of popular names. They are just the names that they're given.
But of course, our one at the Natural History Museum, Sophie, has a nickname.

Speaker 15 But yeah, no, it's Stegosaurus. Yeah.

Speaker 1 Well, we'll cover like Stegosaurus at large as well in this chat because it feels like the others, we can shine the spotlight on them at the same time.

Speaker 1 But when about in the age of dinosaurs do stegosaurs live?

Speaker 15 Yeah, so they first evolved in the middle Jurassic. So that's about maybe 167 million years ago, something like that.
And they really get going in the late Jurassic.

Speaker 15 So that's when they're most diverse and we know the most different types of stegosaur from.

Speaker 15 And then they really decline after that and actually go totally extinct by the end of the early Cretaceous, about 100 million years ago.

Speaker 1 Okay, so what types of dinosaurs should we be imagining living alongside them? Because sometimes you'll see...

Speaker 15 pictures of a stegosaurus defending against a tyrannosaurus rex or something like that but that feels like a misnomer yeah it's a really common you know misconception that all the dinosaurs were kind of mooching along together in the same ecosystem.

Speaker 15 And actually, of course, they weren't at all.

Speaker 15 I mean, aside from the fact they're living on different continents, although Stegosaurus and T-Rex did live on the same continent, they were actually separated in time by millions of years.

Speaker 15 So Stegosaurus was already a fossil when T-Rex lived. T-Rex lived 66 million years ago.
Stegosaurus lived 150 million years ago. So T-Rex is actually closer to us in time than it is to Stegosaurus.

Speaker 15 You stole the line.

Speaker 1 You stole the line. Exactly.
I love that fact, the fact that T-Rex lives closer to us than Stegosaurus Stegosaurus does. Okay, well, you mentioned location in the world.

Speaker 1 Where do Stegosauruses live in the Jurassic?

Speaker 1 In the world as it looks like at that time?

Speaker 15 Yeah, at that time. So we've really got two continents.
We've got a northern continent that's called Laurasia and a southern continent that's called Gondwana.

Speaker 1 Just after Pancheas split up at the end of the Triassic.

Speaker 15 That's right. And so we've got a big seaway between the two, but the Atlantic's only just beginning to open.

Speaker 15 So there is some separation between North America and Europe, but they're not fully separated. There's probably still kind of routes across and through Greenland Greenland and the top up there.

Speaker 15 And so we have stegosaurs living in North America, in the west, what is now the western US, most famously, of course, things like Stegosaurus. But then we have stegosaurs all across Europe.

Speaker 15 We have tons of stegosaurs in China. We've got them in Africa and South America as well.
So in fact, the only continents where we don't have stegosaurs at the moment are Australia and Antarctica.

Speaker 15 And I reckon they were probably there. It's just that we haven't got a really good sample of the fossil record from those continents yet.

Speaker 1 Do we have many fossil sites for stegosaurs surviving? Of all the dinosaur dinosaur species, are we quite blessed when it comes to stegosaurs?

Speaker 15 Yeah, no, not really, actually.

Speaker 15 Despite the fact they're very iconic and very well known, they're actually really quite rare as fossils.

Speaker 15 Now, Stegosaurus in North America is relatively well known, although we don't have very many complete animals, in fact, almost no complete skeletons at all, we do find lots of evidence that they were living there.

Speaker 15 They're much rarer. at other times and in other places, so much less common.

Speaker 15 I mean, we only have a couple from Europe, for example, and they're quite common in China, but China's a massive massive place with a long rock record.

Speaker 1 So, yeah. And also, last question before we delve into, I guess, head to tail of a Stegosaurus.

Speaker 1 We mentioned already how like T-Rex is not living alongside Stegosaurus, but in this period, like the late Jurassic, let's say, what are the key dinosaurs that would have been living alongside Ostegosaurus?

Speaker 15 The other dinosaurs that we see are long-necked, long-tailed dinosaurs primarily. So these are things like Diplodocus and Brontosaurus and Brachiosaurus and the giant ones.

Speaker 15 Yeah, the giants that you're very familiar with from, you know, when you're a kid, basically. And these, again, are all living in the western US alongside Stegosaurus.

Speaker 15 In fact, I think currently there's about 26 different types, different species of these sauropod, long-necked, long-tailed dinosaurs living alongside Stegosaurus.

Speaker 15 So they were the real kind of dominant herbivores in these ecosystems. Stegosaurus seem to be slightly more

Speaker 15 rare, not quite as common. And then we have predators, things like Allosaurus in North America,

Speaker 15 that are very well known from that time period. And it's really interesting because then we go into the into the Cretaceous period, so

Speaker 15 and these ecosystems completely change. And we don't have stegosaur and sauropod-dominated ecosystems anymore.
You know,

Speaker 15 that herbivorous kind of niche

Speaker 15 changes and we get ankylosaurs and iguanodontian dinosaurs occupying that instead.

Speaker 1 And also that shift from Jurassic to Cretaceous, it's not like a big world-ending cataclysm event that marks that shift, is it?

Speaker 15 Well, no, there's a faunal turnover. So the animals that characterize the ecosystems change.
And this is what early geologists and paleontologists recognise.

Speaker 15 This is why they drew that line, because they recognise that both in the sea, in the marine realm, and on land, we actually see a kind of turnover of animals.

Speaker 15 But what caused that turnover is a little bit unclear.

Speaker 15 And some people have suggested there might have been some sort of extinction event, but it's not really clear what might have caused it and whether this was true everywhere.

Speaker 1 And stegosaurs are one of those creatures that do...

Speaker 15 die out with the turning of that with that ecological change or gradually decline well it's a bit weird because in north america we don't see any evidence of stegosaurs after the Jurassic and we do have good terrestrial ecosystems from the Cretaceous.

Speaker 15 We have good Cretaceous rocks, good fossil records. So if they were there, you know, we would have found them, I think.

Speaker 15 In the rest, in Europe and Asia, we actually do see the stegosaurs continuing into the Cretaceous, although they're much more minor. They're quite rare part of ecosystems.

Speaker 1 Are these lush tropical habitats that they're living in, do we know much about the ecosystems of the Jurassic that they existed in?

Speaker 15 Yeah,

Speaker 15 in North America, we're looking at probably a seasonally arid environment, a bit variable because actually they, you know, the whole of the North American continent's big area, the area where they were living actually is, you know, covers 12 degrees of latitude.

Speaker 15 And in the north, it was probably a bit wetter. And then in the south, it might have been quite arid.
But yeah, probably

Speaker 15 seasonally arid, seasonally wet.

Speaker 15 Probably similar elsewhere. In Europe at this time, we actually have mostly marine rocks.
So the stegosaurs that we're finding are actually, we're probably kind of floating and bloating.

Speaker 15 So the animals are being washed out into the sea and their carcasses are floating out and then they're eventually falling to the sea floor.

Speaker 15 So we don't really know the environments on land very clearly at that time in the UK, for example.

Speaker 1 So some stegosaurs have been found at the bottom of Jurassic seaways, I guess then.

Speaker 15 Wow. There's a super cool specimen in the Natural History Museum.
It's one of my favourite specimens. I always show it to visitors to the collection.
It's not on display.

Speaker 15 But it's a couple of stegosaur tail spikes. I'm sure we'll come to that.

Speaker 1 We'll come to that, yes.

Speaker 15 And it's actually got bivalves, so you know, two shellfish are actually encrusted on it. So, like today, when you have whale falls, an animals kind of, you know, it forms a little ecosystem.

Speaker 15 The whale skeleton forms a little ecosystem with things living off the bones. It looks like the same was happening with this stegosaur skeleton way back in the late Jurassic.

Speaker 1 So, no wild theories that this particular type of stegosaur became a marine animal could swim.

Speaker 15 I don't think it was swimming, but to be fair, all we know of it is its two tail spikes. There's nothing else.
So, you know, I can't rule it out.

Speaker 1 Who knows? But it sounds like the general characteristics of a stegosaur, you can identify it whether it's in North America or the fossils are in China today.

Speaker 1 But because the ecosystems differ in those areas, you can notice how the species had unique little characteristics that differed them between other ones depending on where they lived.

Speaker 15 Exactly.

Speaker 1 And so if we focus on, I guess, the overarching features of a stegosaur, and then we can delve into kind of like little details and how they change.

Speaker 1 If we go from head to tail, let's start with the head.

Speaker 15 What should we be thinking of with the iconic stegosaur head well they're very small and actually stegosaurs are kind of famous i think it's true that they have the smallest brain volume per body mass unit of body mass of any terrestrial animal that's ever lived wow so i their brains are about the size of a walnut they're very small and they you know these are animals that are four five six meters long, something like that.

Speaker 15 So yeah, they have very small heads and they have tiny teeth, actually only about half a centimeter. The crowns of the teeth are only about half a centimetre tall.

Speaker 15 So, I mean, I always thought this was probably suggested they were kind of slurping some soft material, soft pond weed or something like that.

Speaker 15 But actually, some of my colleagues have done some kind of bite force modeling and some engineering, using some engineering techniques to look at the strength of the skull.

Speaker 15 And we think actually they were, you know, they could probably bite through twigs. They probably had the same bite force as a sheep.
But maybe they had this sort of keratinous.

Speaker 15 sheath kind of beak covering, which is actually quite common in these herbivorous dinosaurs. So it's almost a bit like a turtle's beak and that they were using this to sort of crop vegetation.

Speaker 1 So quite a strong beak, even with those small teeth. And do we have lots of stegosaurus teeth surviving or stegosaur teeth?

Speaker 15 No, not really. And we've not got very many stegosaur skulls, actually, and not very many isolated teeth either.

Speaker 15 So we have a few skulls from North America and a few from China, which preserve teeth in the jaws. So we can see, you know, where they fit and what they were like.

Speaker 1 Such a fascinating part of Stegosaurus' story, isn't it?

Speaker 1 The fact that this massive, bulky herbivore, like a bulldozer today, and yet in comparison to the rest of its body, like its brain size is the size of a pea. Yeah, well, maybe a walnut.

Speaker 1 Let's not be unfair to it. Sorry, okay, maybe I'm being into it.
Yes, you can tell me off if I'm being a bit too strict, but that's amazing.

Speaker 15 Yeah, I mean, I guess, you know, they did what they needed to do, which was to eat and mate, basically. And, you know, that's what stuff needed to do.
Make sure you don't get eaten.

Speaker 15 So, yeah, it was obviously smart enough to live for millions of years and be successful in its ecosystems.

Speaker 1 But I'm guessing we don't know much about like the eyes or the nose or anything like that.

Speaker 15 No, it's quite difficult.

Speaker 15 Although we have calves of the inside of the brain case so reptiles the brain is encased in a kind of bony casing right called the brain case so we can ct scan a skull and we can look at that space that's you know inside which would have been occupied by the brain and in meat-eating dinosaurs people have done this and you can see kind of big olfactory lobes which relate to your sense of smell.

Speaker 15 So a big olfactory lobe might indicate very good sense of smell or optic lobes which might indicate a very good eyesight.

Speaker 15 But in the the herbivorous dinosaurs, the Ornidisian dinosaurs, we think that the brain probably didn't leave that quite as good impressions on the inside of the bones.

Speaker 15 So it's a little bit more hard to see those features in these sorts of dinosaurs. There's certainly nothing particularly remarkable when we look at that brain case, those endocasts, as they're called.

Speaker 15 There's nothing that you go, wow, you know, that was an amazing, had amazing eyesight or anything like that. It just kind of looks kind of average, to be honest.

Speaker 15 So, yeah, we don't have a good idea about its senses, really. I mean, pretty much, I've told you about bite forces.
I guess we know that it wasn't processing food.

Speaker 15 Stegosaurus didn't process food in their mouths. So we chew and we break down our food in our mouth and then we swallow.
Lots of reptiles don't do that.

Speaker 15 They just swallow the food down and then that digestive processing takes place in the stomach. And birds, for example, will do this and then they eat stones, which help grind up.

Speaker 15 food in their stomachs. Lots of the herbivorous dinosaurs actually evolved chewing like us, convergently to us, of course, you know, separately from us.
But the stegosaurs didn't.

Speaker 15 There's no evidence that they were, you know, doing lots of kind of food processing in their mouths or anything like that.

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Speaker 1 Well, let's go towards the body then. So, should we be imagining a long neck or quite a thick neck, I guess?

Speaker 15 Well, actually, different stegosaurs, there might be different answers for that. We have Stegosaurus, which we know very well, which has a kind of totally average-sized neck, I'd say.

Speaker 15 You know, I mean, it's got to be able to reach the ground, otherwise it couldn't drink and eat. But yeah, it's not particularly long.
It's not particularly notable.

Speaker 15 And then we have a dinosaur from Portugal, a stegosaur called Miragaia. And that actually has more neck vertebrae than most

Speaker 15 long-tailed dinosaurs. It has 17 neck vertebrae, which is loads relative to most stegosaurs, which have between 11 and 13.
So that one looks like it had a bit of a longer neck.

Speaker 15 So we, when we described that, we actually described that back in 2009 and named it. And we suggested that it was kind of mimicking a sauropod, sauropod, a long-tailed dinosaur.

Speaker 1 Do you think the primary purpose of that would be to reach higher up foliage, that idea?

Speaker 15 Possibly. It's a bit difficult to tell.
There's this idea that stegosaurs might have been able to rear up onto their hind limbs and use their tail as a kind of bit like a tripod.

Speaker 15 It's called the tripodal stance. And maybe this helped them reach higher into trees.
So it's possible that they were doing something like that.

Speaker 15 And there's a little bit of evidence in terms of where their center of mass is that suggests they might be able to do that.

Speaker 15 So your centre of mass is like, you know, it's like the balance point of your body. So you can imagine it's like the balance point of a seesaw.

Speaker 15 And in stegosaurs, that seems to be over the hips, which means it would be quite easy for them to kind of push off and adopt that kind of position. It's a bit circumstantial.

Speaker 15 We don't really know whether they did it or not, of course. But yeah, they might have used it to reach higher into the trees.

Speaker 1 We're talking about the legs. So my classic image of a stegosaurus from cuddly toys to...
shows that walking with dinosaurs and the like is a big body and then stumpy legs. Is that the idea we have?

Speaker 15 Yeah, well, all of these four-legged herbivorous dinosaurs, in fact, all the four-legged dinosaurs, evolved from two-legged ancestors. So, unlike with mammals, where often we see kind of,

Speaker 15 well, you know, we as mammals evolved from four-legged ancestors, you know, the mammals often have quite even length hind and forelimbs.

Speaker 15 Because the two-legged dinosaurs that were the ancestors of the four-legged ones had shorter forelimbs than hind limbs, what we see in a lot of the herbivorous dinosaurs, the bird-hip dinosaurs, things like Stegosaurus and Triceratops and that, they actually have much shorter forelimbs than they do hind limbs.

Speaker 15 So I think, you know, sometimes we put a very mammalian kind of view on what looks normal.

Speaker 15 And I suspect actually some of these dinosaurs would look quite weird to us, you know, very, very short forelimbs, quite crouched posture.

Speaker 15 So they couldn't straighten their forelimbs and they couldn't have. kind of I can't do this without miming.

Speaker 15 It's absolutely impossible to talk about dinosaur locomotion without miming, but they couldn't move their forelimbs forwards and raise their arms in the air if you like.

Speaker 1 So almost this idea that a stegosaurus in its natural pose potentially could be kind of leaning over a little bit because the front legs are a bit shorter than the hind yeah absolutely so it's its back would have been angled downwards interesting so interesting if we move up the body we've got to talk about one of the two most iconic parts of stegosaurs which are these plates First off, I mean, what is the usual number of plates that we see on a stegosaur?

Speaker 15 Well, do you know, this is an interesting question because stegosaurs are so rare as fossils, particularly complete individuals, that actually we didn't know the answer to that question until we got Sophie the Stegosaurus at the Natural History Museum, the Natural History Museum's one, because we had no stegosaur that preserved all the plates in the right place down the spine.

Speaker 15 But now we, well, Sophie at least has 19 plates and spikes down its back. So obviously we don't know whether that's typical for other stegosaurs.
And there's a difference with Stegosaurus.

Speaker 15 Stegosaurus and some of its very close relatives seem to have plates that are offset. So they're not paired down the back.
They're two rows of plates, but they're offset offset from one another.

Speaker 15 Whereas most other stegosaurs appear to have paired plates because we've actually got, although we haven't got the whole array, we've actually got plates from the left and right that are identical to each other.

Speaker 1 So it's not just one line of plates along, which is also a classic image you get. There are multiple lines of plates.

Speaker 15 Well, there's two lines, yeah. Oh, sorry, there's two.
Two rows of plates, yeah. Right, that's so interesting.

Speaker 1 And so what are they made out of?

Speaker 15 They are bone, which is why they preserve, why they fossilise. If they were soft tissue, they wouldn't fossilise.
So they have a bony core.

Speaker 15 However, However, when you look at them, they've got blood vessel channels running all over the surface. So it looks like they had a good blood supply.

Speaker 15 And they probably had some sort of keratinous covering. So this would be a material a bit like our fingernails, you know, something like that, kind of a horny covering.

Speaker 15 So they would have been bigger than are preserved as bone. The bone would have been kind of the core of the plate, if you like.

Speaker 1 And are they directly connected to the backbone, to the spine?

Speaker 15 No, not at all. They're just embedded in the skin.

Speaker 15 And this is similar to, actually, we see, they're called osteoderms, skin bone, right?

Speaker 15 So they're they're very very hypertrophied they're very elongated osteoderms and we see these in alligators actually in crocodiles as well today so they have them embedded in their skin and their backs and actually all through throughout the mesozoic throughout evolutionary history of lots of different groups of animals we actually see osteoderms cropping up time and again so it's not particularly unusual or unique to have bony bits in your skin but what's interesting about the stegosaurs and of course they're close relatives the ankylosaurs is that they really took this to kind of extremes and and really hypertrophied them and made them extremely elaborate and elongate and large and flashy.

Speaker 1 Yeah, and absolutely extraordinary. And you said one of the most iconic images we have in our heads today, which leads to the big question, what do we think that these plates were used for?

Speaker 15 Yeah, well, this is not a trivial question, actually, and not easy to answer because, you know, actually being able to test ideas around the function of this, you know, we call it armor.

Speaker 15 is really difficult. There's been a number of different suggestions of what the function might have been.

Speaker 15 I mean, so I refer to it as armor, and you know, it could be armor, it could be for protection against predators.

Speaker 15 You know, if you've got a load of spikes and plates sticking up off your back, um, Allosaurus isn't going to want to come down and take a big chunk out of your back.

Speaker 1 I guess the fact isn't it? You've got the carnivores of the time, which are, you know, they can stand taller than a stegosaurus.

Speaker 15 Yes, they would have been taller. But of course, you know, Stegosaurus' flanks are entirely unarmoured.
So it doesn't seem like great as a form of armor, I would have said.

Speaker 15 But, you know, yeah, it would have, it would have put off the big ones from coming down on your back, presumably. You've then got ideas that they could be for display.

Speaker 15 So, you know, often when we see in today's animals features of the animals which don't seem to have any obvious function, look like they might be quite energetically expensive to produce.

Speaker 15 They often are related to some sort of display. Now, this could be to try to attract a mate, you know, to show off to try and attract a mate.

Speaker 15 It could be, you know, think about a peacock's tail, for example. It could be for some sort of intra-specific combat.

Speaker 15 So if you think about the horns of an antler, the antlers of a deer even, or the horns of a big horn sheep or something like that, they are, you know, fighting each other for mates.

Speaker 15 It's usually something to do with mating. But, you know, it could also be, we know that lots of these stegosaurs were living alongside each other in the same ecosystems.

Speaker 15 So it could be that, you know, you're making sure you're mating with the right people. So we'd, you know,

Speaker 15 it could be some sort of display function.

Speaker 15 Not quite clear what that might be, but it could be be a number of things and then there's this idea of thermoregulation so this is being able to control your body temperature and of course the closest living relatives today to the dinosaurs are the birds and the crocs and if we want to understand features that aren't preserved in the fossil records then we tend to look at the closest living relatives and say well what you know what was the common ancestor of this animal doing and and metabolism is one of these with these warm-blooded or cold-blooded animals and actually this is problematic because crocs are cold-blooded they're ectothermic birds are warm-blooded So we don't know what the common ancestor of crocs and birds was doing, and we don't know what the dinosaurs were doing.

Speaker 15 We think that warm-bloodedness must have evolved somewhere on the line to birds, but where we don't know.

Speaker 15 So we generally think based on a few different lines of evidence, and particularly how fast the stegosaurs were growing, they appeared to be growing quite slowly relative to other dinosaurs, that maybe they had a relatively slow metabolism.

Speaker 15 They were more at the kind of cold-blooded end of the spectrum than the warm-blooded end. And thus, the problem for them, being massive multi-ton animals was actually losing heat.

Speaker 15 So they would have generated lots of body heat from moving around and eating and digesting things. And how you get rid of that heat is difficult when you're a great big animal.

Speaker 15 So people have suggested that maybe the plates were increased their surface area. You know, they would be able to flush hot blood into these plates and it would radiate heat out.

Speaker 1 It's almost kind of like a ventilation kind of thing.

Speaker 15 Yeah, or like a radiator, yeah.

Speaker 1 Radiator to cool themselves.

Speaker 15 So the problem with all of these ideas, though, is actually how do you test them?

Speaker 15 You know, it's really, really difficult, particularly given the fossil record that we have so we might be able to test some ideas around display for example if we had a very large fossil record we could say well do juvenile animals have really tiny plates and then they sort of grow really big and elaborate as they become adults because we know that that features that juveniles tend not to have and adults tend to have tend to be something to do with sex tend to be something to do with mating likewise do we see differences in males and females and now we don't have any juvenile stegosaurs and we can't tell sex.

Speaker 15 We can't tell which are the males and which are the females. And we don't even have, you know, we would need an enormous sample size.

Speaker 15 We would need hundreds of individuals to be able to tell, you know, do one set have small plates and one set have big plates, for example, or different shape plates.

Speaker 15 And we simply don't have the sample size in stegosaurs to tell that. In fact, we don't really have it in any dinosaur, I would argue, to be able to tell that.

Speaker 15 it's really difficult to test these ideas.

Speaker 15 And actually, I think it's kind of, it's a slightly made-up question, really, because because when we look at animals that are alive today that do have osteoderms, so things like crocs and alligators, what we know is they use them for loads of different reasons.

Speaker 15 So alligators use them to stiffen their spine, so it helps when they're walking on land, which they don't do that much, but when they do, it helps them stiffen their spine.

Speaker 15 They use them as calcium reservoir when they're making eggshell. And they actually do appear to use them.
for some parts of, you know, for thermoregulating.

Speaker 15 So they actually use them to help lose heat. So I think it's very likely that stegosaurs might have used them for all of these different reasons.

Speaker 15 And actually, you know, there's not, it's not really a debate about what they used them for. They probably used them for all of them.

Speaker 1 Yes, and you can't take away the idea that, you know, in a tricky situation, if it had to defend itself, it was still quite a good, you know, piece of armor at the same time, wasn't it? Absolutely.

Speaker 1 But is it very much the fact that, you know, the primary purpose of the plates of stegosaurs could well have differed depending on where in the world they lived and at what time in the Jurassic they lived.

Speaker 15 Yeah, absolutely. And we do see really different armor and different types of stegosaurs.
So Stegosaurus from North America had very big, wide, flat plates.

Speaker 15 And as I said, they were offset from each other, whereas other, most other stegosaurs actually had much smaller armor and they were much more spine-like. So maybe not quite as good as heat radiators.

Speaker 15 Probably still would have had some, well, they definitely would have still had some function in, you know, thermoregulation, but maybe not as great.

Speaker 15 But they might have been better as actual, you know, protection. If you've got a big spike sticking out your back rather than a very thin plate, it might be more useful.

Speaker 15 You know, I sometimes say that I think that Allosaurus could have chomped through Stegosaurus's plates like us eating Doritos, but

Speaker 15 I don't know whether that's true or not, but you know, yeah.

Speaker 1 But do some stegosaurus, we're going to get to the spiky tail very soon, I promise, building up to it. But do some stegosaur types, do they have spikes on their body as well instead of plates?

Speaker 15 Yeah, so some, actually quite a lot, we think, had shoulder spikes.

Speaker 15 So spikes, they again embedded in the skin, but over the shoulder blades and then sticking out backwards. So there's one in China called Gigant Spinosaurus.
And as you might guess,

Speaker 15 it has a gigantic spine. It's about a metre and a half long that sticks out from its shoulder region.

Speaker 15 And that one was, actually, we know that they were shoulder spites because that one, they were actually found in place alongside the arms. And lots of Stegosaurus seem to have this.

Speaker 15 Stegosaurus doesn't. I think we've got so many or we've got several pretty good specimens of stegosaurus.
If they had them, I think we would have found them by now.

Speaker 15 There are some individuals of Stegosaurus that seem to have kind of throat armor, these kind of, it's almost like chain mail these little tiny ossicles like little tiny like beads almost of bone in the throat region and we haven't found them in any other stegosaur but we haven't got such a good fossil record of other stegosaurs so it's possible that some of them did to protect that vulnerable area maybe well yeah it's a vulnerable area isn't it so wow and so and and the skin on the body of a stegosaur generally that's less armoured than the plates and the spikes yeah just scaly skin just scaly skin there we go well then let's go on to the last part of the stegosaur which is of course the tail region And what is this other iconic part of a stegosaur that you have with the tail?

Speaker 15 So stegosaurs have spikes at the end of their tail. Stegosaurus has four.
Some people refer to these as thagomizers.

Speaker 1 Thagomizers. That's the word I've seen.

Speaker 15 Okay, well, so this word comes from a far side cartoon.

Speaker 15 And it is a caveman who is being, he's called thag.

Speaker 15 and he meets his demise thanks to a stegosaur tail spike so it becomes a thagomizer and this i i have actually seen it being used in one scientific paper i'm kind of against it like it's used in the sort of dino nerd world i'm against it on the basis that we have enough terminology in science like we don't need any i mean they're just spikes let's just call them what they are guys spikes we don't need

Speaker 15 yeah we don't need it and then people try and say oh no isn't a thagomizer the whole no no no it's not it's literally a made up word that was made up in a comic it's nothing it's not a thing but anyway Yeah, so they're spikes at the end of the tail.

Speaker 15 And actually, people have done some modeling to look at if the stegosaur swished its tail from side to side like what would be the forces that would be generated at the end of the spikes and we know that they would be pretty bone crushing so you know it could do allosaurus's legs some damage i think if it was swinging its tail from side to side so yeah probably a weapon

Speaker 2 Hi folks, it's Mark Bittman from the podcast Food with Mark Bittman.

Speaker 7 Whole Foods Market is your holiday headquarters with everything you need, whether you're a guest guest or hosting the big dinner with show-stopping centerpiece means like bone-in spiral cut ham or bone-in rib roast or even king crab.

Speaker 11 And if you want to take a few shortcuts, no one is looking after all, try the heat-neat sides from the prepared foods department.

Speaker 14 Shop for everything you need at Whole Foods Market, your holiday headquarters.

Speaker 19 Hey, it's Mark Marin from WTF here to let you know that this podcast is brought to you by Progressive Insurance.

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Speaker 1 And the stegosaurus has four of them. Yep.
But does the number of spikes on the tail differ between the other stegosaurs?

Speaker 15 It seems to. We don't know.
We haven't got complete articulated skeletons of other stegosaurs, but many of them seem to be much more spiky, as I said.

Speaker 15 And there's one called Kentrosaurus, for example, which is well known from Tanzania. And that seems to have spikes all the way up its tail.

Speaker 1 Yes, Kentrosaurus is another interesting example. I had in my notes down here, but it wants to mention it as well, because, and that is another type of stegosaur, is it?

Speaker 1 It just looks a bit different than your classic Stegosaurus image.

Speaker 15 Yeah, it's a different, it's a different species, yeah. I mean, it lived in, it lived in Tanzania, southern Africa, but at the same time as Stegosaurus, roughly.

Speaker 1 And is this idea like the swinging of the tail, should we be imagining almost like kind of the big hip motions of today to generate that power?

Speaker 1 Or is it more that the tail had more flexibility almost to kind of go almost to a right angle and then be swished that way?

Speaker 15 Or is it the whole body bringing that kind of weight in an attack do we think the tail could flex side to side not up and down so much but side to side so i think it would have swung its tail but also remember again you know we do tend to have a very mammalian focused view of what things look like and and

Speaker 15 the tail of a dinosaur would have been much more like that of a croc so they have these incredibly long muscles that run all the way along the tail and very very chunky very robust so very muscular and those probably would have been used to swing the tail.

Speaker 1 Got to ask because I mean, if you haven't, I want to be there if you do it at any time.

Speaker 1 But have you guys at the NHM or have paleontologists tried to recreate a tailed swing, you know, kind of get this idea of the body mass and then recreate some spikes and then have a dummy or something there, maybe like a piece of pork or whatever, a piece of meat, and to kind of test just how brutal.

Speaker 1 a swing could have been.

Speaker 15 So we have not done that.

Speaker 15 Although my colleague Heiruk Mallison, who was at the Museum Fanaticunde in Berlin, where a Kentrosaurus is, but most of the fossils of Kentrosaurus are housed and is on display there.

Speaker 15 He has done it digitally. So he's done it computationally and calculated those forces at the end of the tail spike.

Speaker 15 And that's why we know that they could have kind of impacted bone is because he's actually calculated the forces.

Speaker 15 So yeah, analogue models are more difficult to come by, but doing it digitally is a little easier.

Speaker 1 Come on, Susie, we've got to make it happen. It's going to be hilarious.
I'd love to see it. But that is kind of the classic anatomy of a stegosaurus, isn't it? Of a stegosaurus.

Speaker 1 Is there anything we've missed that we should also mention about how its body functioned?

Speaker 15 Oh, well, you know, there's so much we don't know, really. So I don't think so.

Speaker 15 You know, there's loads we don't know about the paleobiology of stegosaurs because we just don't have that good a fossil record.

Speaker 1 Well, it was also interesting what you mentioned there that we don't have any juvenile stegosaurs surviving.

Speaker 1 So do we not know much about young stegosaurs or how they raise their young and the kind of when the plates developed and stuff like that?

Speaker 15 Yeah, no, we know virtually nothing. I actually should say there is one juvenile that I'm aware of, at least, that was from Dinosaur National Monument in Utah, in the US.
And it's very incomplete.

Speaker 15 So it's just some hind limbs and some forelimbs and a little bit of pelvis. I don't think there's any plate.
There might be one tiny plate, but there's it's very, very fragmentary.

Speaker 15 And that is the only baby stegosaur that we have. And as I say, very, very fragmentary remains.
So very difficult to say anything about it. We don't have any nests of stegosaurs.

Speaker 15 We don't have any eggs.

Speaker 15 Actually, I think probably we think now that for these sorts of dinosaurs, the bird-hip dinosaurs, that

Speaker 15 primitively, you know, and stegosaurs are fairly early members of this group, that they were probably had soft-shelled eggs.

Speaker 15 So they weren't laying eggshells, they weren't laying eggs with calcite eggshells. And it's the calcite that preserves in the fossil record.

Speaker 15 So when we found dinosaur eggs, they tend to be, you know, they're calcite ones.

Speaker 15 Yeah, and that there has been some pretty recent discoveries of more of softer, kind of more leathery shelled eggs from some of these herbivorous dinosaurs.

Speaker 15 So I think that's probably a good explanation for why we don't have more nests or evidence of them. But, you know, even so, we might expect to have more young ones, but we don't.

Speaker 15 So we don't really know whether they were living in family groups. We don't know whether they were herding.
We don't know whether they had kind of, you know, they sometimes call them nursery herds.

Speaker 15 You know, this idea that maybe all the babies were living together. and maybe a separate environment from the adults, we really don't have any clue about anything.

Speaker 1 When you read my next question, Richard, was going to be like, like you imagine the big herds of Iguanodon or even the sauropod herds, isn't it?

Speaker 1 It seems like Stegosaurus, the question is still out there.

Speaker 1 But I guess also with their armor, I mean, do you see with like ankylosaurs later in the like that they are more individualistic, I guess, or more on their own?

Speaker 15 Again, I don't think that we have a great answer to that. And I don't think that all of them...
They might have been doing different things.

Speaker 15 So we have loads of different, I mean, the ankylosaurus, there must be 60 or 70 of different types of ankylosaurs. And it's possible that, you know, different ones were doing different things.

Speaker 15 I think it seems quite likely that these dinosaurs were living in herds or you know groups of some form, just because it's a really sensible way to defend yourself from predators.

Speaker 15 And I think we're very clear that these animals were not running very far. You know, these are not fast-moving animals.
They're not running away from predators.

Speaker 15 These big, big predators would have been slow moving and the herbivores would have been probably slower moving. So I think there wasn't any pursuit predation going on.

Speaker 15 So they had to come up with different ways to defend themselves. And that could be why, one of the reasons why we see these very kind of of elaborate structures on all these sorts of dinosaurs.

Speaker 15 So this armor in ampylosaurs and stegosaurs. And then we have things like the horns and frills in the ceratopsines and the triceratops-like dinosaurs.

Speaker 15 So, you know, it could be that they're using these kind of bizarre display or, you know, possibly defensive structures to help defend themselves from predators because they can't run away.

Speaker 15 But I think, you know, herding is kind of, it makes sense. We just don't have any evidence for it.

Speaker 1 And talking about predators quickly, we've already mentioned Dallasaurus, but do we think that there were any other kind of big predators that would have been the main, I guess, enemies, the main threats to Stegosaurus?

Speaker 15 Yeah, there are other big meat-eating dinosaurs around at the same time. So in North America, we've got Ceratosaurus, Martiosaurus, Torvosaurus living alongside them.

Speaker 15 Yeah, I mean, Allosaurus, certainly in North America, living alongside Stegosaurus, Allosaurus is by far the most abundant predator, you know, by miles.

Speaker 15 The other meat-eating dinosaurs are much, much rarer.

Speaker 15 So really, you know, the Morrison formation where these dinosaurs are found, where Stegosaurus and Allosaurus found, you know, Allosaurus ruled the Morrison.

Speaker 15 It was doing all the eating of everything, I think.

Speaker 1 Well, I have in my nose one particular type of stegosaur that I know is close to your heart. They've done work around, but please forgive me if I mispronounce the wording of it.
Adraticlet Bulafa.

Speaker 15 Pretty good. I mean, I don't really...
We named it in Amazia, which is the language of the Berbers in the Middle Atlas Mountains in Morocco. And so I'm not going to pretend that I speak Amazir either.

Speaker 15 So you can go nuts and pronounce it however you want. It doesn't mind.

Speaker 1 I'm not going to try again.

Speaker 1 I'll say once again, Adraticlit Bulafa. So can you tell us about this particular stegosaur? This is a name I've never heard before.

Speaker 15 Yeah, so this is a stegosaur that we named back in 2020. And it's from the Middle Atlas Mountains of Morocco.
It was the first stegosaur found in North Africa. And it's from the Middle Jurassic.

Speaker 15 So it's really early on in the evolution of the stegosaurs.

Speaker 15 So when we first came across these fossils, which were actually for sale, they were for sale in a commercial fossil dealers in Cambridge actually, and we spotted them and my colleague at the Natural History Museum is before I worked there, but he decided to acquire them for the museum, rescue them, if you like, from the commercial market and bring them into public ownership.

Speaker 15 And so we worked on these specimens. When you buy specimens on the commercial market like this, you often lose the contextual data that comes with them.
So

Speaker 15 it said that they were from the middle Jurassic of the Middle Atlas Mountains of this town called Bulmain.

Speaker 15 But of course, we didn't know whether those rocks were accurately dated. We didn't know whether that was all that information was correct.

Speaker 15 So I decided to go and try and find out where this specimen was from. And I went with a colleague who's a shark guy.
He collects sharks' teeth.

Speaker 1 Oh, we love, we love fossil shark guys as well. Don't worry.

Speaker 1 That's good to hear. That's good.

Speaker 15 So he had been to Morocco a bunch of times because there's loads of sharks. You can collect sharks' teeth in Morocco.

Speaker 15 And anyway he knew all of the commercial dealers and so he and I basically worked our way back down the commercial supply chain to the guy who dug the specimen out of the ground and it was amazing it was a farmer who lived on the side of a hill and I showed him the picture of the specimen and he was able to just kind of take me to the hole and was like this is where I got it from and I worked with a geologist from the local university who is

Speaker 15 an expert in the rocks of the area.

Speaker 15 And so he was able to come with us and then say, yeah, this is all Middle Jurassic, this is this formation, you know, these are these rocks, because he'd been working on these rocks for his entire career.

Speaker 15 And that was fantastic because we were able to demonstrate, you know, exactly where the specimen was from, that it was indeed Middle Jurassic, making it one of the oldest stegosaurs we know in the world.

Speaker 15 And it's actually gone on to result in a really long-term collaboration between myself and the geologist and his group now.

Speaker 15 We've set up Morocco's first vertebrate paleontology labs at his university and doing lots and lots of work with them and training students there to be vertebrate paleontologists.

Speaker 15 So it's been an incredible project that started with a few stegosaur bones for sale in a fossil shop in Cambridge.

Speaker 1 That's great. And to discover the first known stegosaurs in North Africa today, in the Atlas Mountains in Morocco.

Speaker 15 Yeah, that's right. Yeah.
And it's a very fragmentary specimen. I mean, we just have the forelimb, part of the forelimb, and some vertebrae.
And that's it.

Speaker 15 So, you know, we hope that we're going to find more there.

Speaker 15 Do you think it's almost certain then that there are still so many different species of different types of stegosaurs from the jurassic and maybe into the early cretaceous that we just don't know about yet yeah definitely uh africa is virtually unsampled you know relative to north america and europe we just haven't been looking there very long and there's lots of you know geopolitical and sociopolitical reasons why it's sometimes difficult so they have middle jurassic rocks it's a time period that i'm really interested in because it's when we really see you know all of these different groups of dinosaurs get going um and really radiate and diversify and sort of take over.

Speaker 15 Middle Jurassic rocks are present in places like Niger as well as Morocco, but it's difficult. It's dangerous.

Speaker 15 The risk assessment that I would have to write would be so long to be able to work in some places that we can't go there.

Speaker 15 Many places, as I say, Morocco had no vertebrate paleontologists working in the country in university. So we set that up.
So there are lots of reasons why these places aren't sampled.

Speaker 1 And the African continent today, if going back into the Jurassic mindset, are we thinking the north of the emerging Atlantic Ocean or the south? Where should we be thinking?

Speaker 15 Yeah, south. So southern hemisphere.

Speaker 1 Yeah, and that's the area where there haven't been stegosaurs or known of until now.

Speaker 15 Well, Kentrosaurus, which we mentioned earlier, that's from Tanzania. So that's been long known about.
That was first discovered by the Germans in the 19th, early part of the 20th century.

Speaker 15 And there's also a little bit of material from Argentina.

Speaker 15 And it's quite cryptic in Argentina because the specimen was originally described not as a stegosaur but as a kind of general early ornithischian bird hip dinosaur.

Speaker 15 The bird hip dinosaurs are part of the group that stegosaurs belong to. And actually myself and two other colleagues got the paper to review.

Speaker 15 So you know when we publish a scientific paper the first part of the process is you submit it to a journal and the journal goes well this looks interesting but we're going to send it to some other experts to see what they think and this is the process of peer review.

Speaker 15 We all do this to each other's papers.

Speaker 15 We all read each other's papers and comment on them and it's part of you know our job as scientists to review what other people have written and make comments on it.

Speaker 15 And I got this paper and I went, well, that's a stegosaur. And so did my two other colleagues.

Speaker 15 And we all sent our papers back independently of each other, of course, not knowing this, saying, well, we think these are stegosaurs.

Speaker 15 And then the authors came back and said, you know, we think it's a stegosaur too, but we keep doing these quantitative analyses that look at the evolutionary relationships of these different animals.

Speaker 15 And we can't make it be a stegosaurus. It just doesn't want to be a stegosaur in our analyses.
But anyway. you know, subsequently we've shown that this animal is almost certainly a stegosaur.

Speaker 15 It looks exactly like a stegosaurus. It's a stegosaurus.
It's definitely a stegosaur. But it's very, very early.
It's the world's oldest. So it's quite primitive.

Speaker 15 And that means it has a number of features that, you know, kind of bridge the gap between some of these earlier dinosaurs and some later stegosaurus.

Speaker 1 Well, it's really exciting having you on because you're someone at the forefront of the developing story of stegosaurs and how now in the 21st century, many of us growing up will have heard of stegosaurus since, you know, since we were kids and TV programs.

Speaker 1 But to think that actually more is being known about them, you know, all the time, thanks to people like yourself and other papers writing about them and new discoveries being made.

Speaker 1 So it's a really exciting feel for the future i must ask although the evolution question is it a fair question to ask what we think stegosaurs evolve into in the cretaceous or do we think it just kind of dies out and then there's just a new type of armoured dinosaur that comes to the fore yeah we don't we that they went extinct so we they don't evolve into anything um our evolutionary trees we we make evolutionary trees we you know we we reconstruct evolutionary relationships in kind of a semi-quantitative way i will say and yeah the evidence from that is that yeah they they they just go extinct susie this has been such a fun chat growing up i've already mentioned the the series the original series walking with dinosaurs as being a big influence and i think it's been a big influence on so many of us like at the end of the 1990s beginning of the 2000s and stegosaurus's depiction there i mean so what do you think of like the depictions of Stegosaurus in the media world and their attempts to give us an idea of what Stegosaurus looks like?

Speaker 15 I think generally they're very good.

Speaker 15 You would have to show me what Stegosaurus looked like in the original Walking with Dinosaurs.

Speaker 1 I can't remember what they did. They're quite like the classic with the big plates and the very small head.

Speaker 1 I think it's a fight against an Allosaurus in a narrow kind of ravine.

Speaker 15 I think, you know, all of this is entirely plausible. I think the things that I see sometimes where I go, oh, that's a bit wrong, is when they make them run.

Speaker 15 So it's actually less common with Stegosaurus than you sometimes see with something like Triceratops, where you saw them, you see them kind of galloping.

Speaker 15 And there was the recent Walking with with dinosaurs they had they had triceratopses running around and i was like no no no no no they weren't doing any of that there was no there was a galloping around this is ludicrous but so that is one thing that gets my goat but generally i think they do pretty well with stegosaurs like you know i the thing with stegosaurs is that we know so little about them that you've got a lot of latitude you know which makes them really fun yeah and uh greatest kids toys and you know from everything and then in the media today Susie, this has been absolutely great.

Speaker 1 We've covered so much, but is there anything else you'd like to mention about stegosaurs before we finish?

Speaker 15 Oh my God, I think I've told you everything I know.

Speaker 1 good well i've done my job well then it just goes to me to say thank you so much for taking the time to come on the show thanks for having me

Speaker 1 well there you go there was dr susie maisman talking all things stegosaurus i hope you enjoyed the episode thank you for listening please follow the ancients on spotify or wherever you get your podcasts that really helps us and you'll be doing us a big favor if you'd also be kind enough to leave us a rating well we'd really appreciate that now don't forget you can also sign up to History Hit for hundreds of hours of original documentaries with a new release every week.

Speaker 1 Sign up at historyhit.com slash subscribe. That's all from me.
I'll see you in the next episode.

Speaker 2 Hi folks, it's Mark Bittman from the podcast Food with Mark Bittman.

Speaker 7 Whole Foods Market Market is your holiday headquarters with everything you need, whether you're a guest or hosting the big dinner, with show-stopping centerpiece means like bone-in spiral cut ham or bone-in rib roast or even cane crab.

Speaker 11 And if you want to take a few shortcuts, no one is looking after all, try the heat-neat sides from the prepared foods department.

Speaker 14 Shop for everything you need at Whole Foods Market, your holiday headquarters.

Speaker 19 Hey, it's Mark Marin from WTF here to let you know that this podcast is brought to you by Progressive Insurance.

Speaker 19 And I'm sure the reason you're listening to this podcast right now is because you chose it.

Speaker 23 Well, choose Progressive's name your price tool, and you could find insurance options that fit your budget so you can pick the best one for your situation.

Speaker 22 Who doesn't like choice?

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