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- [00:00]
Podcast Host
Ever wondered why the Romans were defeated in the Teutoburg Forest? What secrets lie buried in prehistoric Ireland? Or what made Alexander truly great? With a subscription to History hit, you can explore our ancient past alongside the world's leading historians and archaeologists. You'll also unlock hundreds of hours of original documentaries with a brand new release every single week covering everything from the ancient world to World War II. Just visit historyhit.com subscribe.
- [00:33]
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- [01:05]
Podcast Host
Hello and welcome to our latest Ancients episode. Today we're going to the time of the dinosaurs. But just before that, I wanted to do a quick shout out 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 Aurelia hooked on global prehistoric catastrophes and the falls of civilization. So keep it up. Anyways, onto 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 favorite dinosaur, that iconic plated armored dinosaur, Stegosaurus. And to talk through it all, we've got one of the leading experts on armored dinosaurs, none other than Dr. 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. 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. It carried one of the most terrifying defensive weapons in prehistory. Four razor sharp spikes swinging from a powerful, the legendary so called Thagomizer. Today we're delving deep into the world of stegosaurus. 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. And I'm joined by the one and only Dr. Susie Maidment, palaeontologist 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. Susie, it is great to have you on the show.
- [03:38]
Dr. Susannah Maidment
Thanks very much for having me. It's a pleasure to be here.
- [03:40]
Podcast Host
And we're talking about stegosaurus today and this feels like for so many people it is their favorite dinosaur. It is iconic today.
- [03:47]
Dr. Susannah Maidment
It absolutely is. And you know, every seven year old knows what stegosaurus is and I give talks about stegosaurus and I ask in the audience first, you know, who's heard of stegosaurus? 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.
- [04:01]
Podcast Host
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?
- [04:10]
Dr. Susannah Maidment
Yeah. We have the world's most complete stegosaurus on display at the nhm. But actually there are also two different species of stegosaur known from the uk, including the first one ever discovered which was found in Swindon.
- [04:21]
Podcast Host
In Swindon it was the Swindon Stegosaurus.
- [04:24]
Dr. Susannah Maidment
The Swindon Stegosaurus. It's called Dacentrus 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.
- [04:37]
Podcast Host
Justice for the Swindon Stegosaurus. That 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, you mentioned the word stegosaurs there. We've already said stegosaurus. So can you tell us the difference between the two words? Yeah.
- [04:53]
Dr. Susannah Maidment
So stegosaurus is one type of stegosaur.
- [04:55]
Podcast Host
Right.
- [04:55]
Dr. Susannah Maidment
Stegosaurs are a group of dinosaurs. 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. But then there's individual species within that that you can recognise. And it's the same with stegosaurs, so we have a whole range of them. They lived all around the world and of course Stegosaurus is the one that everybody knows, but there are loads of others actually.
- [05:18]
Podcast Host
Does it have a particular scientific name?
- [05:20]
Dr. Susannah Maidment
It's Stegosaurus. 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, but. Yeah, no, it's Stegosaurus.
- [05:32]
Podcast Host
Yeah, well, we'll cover like stegosaurs at large as well in this chat because it feels like the others, we can shine the spotlight on them at the same time. But when about in the age of dinosaurs, do stegosaurs live?
- [05:43]
Dr. Susannah Maidment
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, so that's when they're most diverse and we know the most different types of stegosaur from. And then they really decline after that and actually go totally extinct by the end of the early Cretaceous, about 100 million years ago.
- [06:02]
Podcast Host
Okay, so what types of dinosaurs should we be imagining living alongside them? Because sometimes you'll see pictures of a Stegosaurus defending against a Tyrannosaurus Rex or something like that, but that feels like a misnomer.
- [06:12]
Dr. Susannah Maidment
Yeah, it's a really common, you know, misconception that all the, all the dinosaurs were kind of, you know, mooching along together in the same ecosystem and actually, of course they weren't at all, I mean, aside from the fact they're living on different continents. Although Stegosaurus and, and T Rex did live on the same continent, they were actually separated in time by millions of years. 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.
- [06:40]
Podcast Host
Stole the line. You stole the line.
- [06:41]
Dr. Susannah Maidment
Exactly.
- [06:42]
Podcast Host
I love that fact. The fact that T Rex lives closer to us than Stegosaurus does. Okay, well, you mentioned location in the world. Where do Stegosauruses live in the Jurassic? In the world, as it looks like at that time.
- [06:54]
Dr. Susannah Maidment
Yeah, at that time. So we've really got to continents, we've got a northern continent which is called Laurasia and a southern continent that's called Gondwana.
- [07:01]
Podcast Host
It's just after Panchaya split up at.
- [07:03]
Dr. Susannah Maidment
The end of the Triassic. That's right. And so we've got a big seaway between the two, but the Atlantic's only just beginning to open, so there is some separation between North America and Europe, but they're not fully separated. There's probably still kind of routes across through Greenland and the top up there. And so we have stegosaurs living in North America in what is now the western US Most famously of course, things like Stegosaurus. But then we have stegosaurs all across Europe. 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. 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.
- [07:41]
Podcast Host
Do we have many fossil sites for stegosaurs surviving of all the dinosaur species? Are we quite blessed when it comes to stegosaurs?
- [07:48]
Dr. Susannah Maidment
Yeah, no, not really actually, despite the fact they're very iconic and very well known, they're actually really quite rare as fossils. And 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. They're much rarer at other times and in other places so much less common. I mean we only have a couple from Europe for example and they are quite common in China. But China is a massive place with a long rock record. So.
- [08:16]
Podcast Host
Yeah, and also, last question before we delve into I guess head to tail of a Stegosaurus. 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 a Stegosaurus?
- [08:33]
Dr. Susannah Maidment
The other dinosaurs that we see are long neck long tailed dinosaurs primarily. So these are things like Diplodocus and Brontosaurus and Brachiosaurus and the giants. 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. In fact, I think currently there's about 26 different types, different species of the sauropod long neck long tailed dinosaurs living alongside stegosaurus so they were the real kind of dominant herbivores in these ecosystems. Stegosaurs seem to be, you know, slightly more, more rare, not quite as common. And then we have predators, things like Allosaurus in North America that very well known from that time period. And it's really interesting because then we go into the, into the Cretaceous period. So and these ecosystems completely change and we don't have stegosaur and sauropod dominated ecosystems anymore. You know, that herbivorous kind of niche, it changes and we get Ankylosaurs and Iguanodontian dinosaurs occupying that instead.
- [09:32]
Podcast Host
And also that shift from Jurassic to Cretaceous, it's not like a big world ending cataclysm event that marks that shift, is it?
- [09:39]
Dr. Susannah Maidment
Well, no, it's a, there's a faunal turnover. So the animals that characterize the ecosystems change. And this is what early geologists and paleontologists recognize, this is why they drew that line, because they recognize that both in the sea, in the marine realm and on land, we actually see a kind of turnover of animals. But what caused that turnover is a little bit unclear. 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.
- [10:06]
Podcast Host
And stegosaurs are one of those creatures that do die out with the turning of that, with that ecological change or gradually decline.
- [10:13]
Dr. Susannah Maidment
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. We have good Cretaceous rocks, good fossil records. So if they were there, you know, we would have found them. I think 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 are these lush tropical.
- [10:36]
Podcast Host
Habitats that they're living in. Do we know much about the ecosystems of the Jurassic that they existed in?
- [10:41]
Dr. Susannah Maidment
Yeah, in North America we're looking at probably seasonally arid environment, 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 and in the north it was probably a bit, a bit wetter. And then in the south it might have been quite arid, but yeah, probably seasonally. Seasonally arid, seasonally wet and probably similar elsewhere in, in Europe at this time we actually have mostly marine rocks. So the Stegosaurs that we're finding are actually were probably kind of floating and bloating. So their animals are being washed out into the sea and their carcasses are floating out and then they're eventually falling to the sea floor. So we don't really know the environments on land very clearly at that time in the uk, for example.
- [11:24]
Podcast Host
So some stegosaurs have been found at the bottom of Jurassic seaways. I guess, then, wow.
- [11:29]
Dr. Susannah Maidment
There's a super cool specimen in the Natural History Museum. It's one of my favorite specimens. I always show it to visitors to the collection. It's not on display, but it's a couple of stegosaur tail spikes. I'm sure we'll come to that.
- [11:39]
Podcast Host
We'll get to that. Yes.
- [11:40]
Dr. Susannah Maidment
And it's actually got bivalves, so, you know, two shelled shellfish are actually encrusted on it. So like today, when you have whale falls and animals kind of, you know, it forms a little ecosystem, 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.
- [11:58]
Podcast Host
So no wild theories that this particular type of stegosaur became a marine animal, could swim?
- [12:03]
Dr. Susannah Maidment
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.
- [12:09]
Podcast Host
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. 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 live.
- [12:29]
Dr. Susannah Maidment
Exactly.
- [12:30]
Podcast Host
And so if we focus on, I guess, the overarching features of a stegosaur, and then we can delve into kind of little details and how they change if we go from head to tail. Let's start with the head. What should we be thinking of with the iconic stegosaur head?
- [12:47]
Dr. Susannah Maidment
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.
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Podcast Host
Wow.
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Dr. Susannah Maidment
So their brains are about the size of a walnut. They're very small and they, you know, these are animals that are 4, 5, 6 meters long, something like that. 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 centimeter tall. 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. But actually some of my colleagues have done some kind of bite force modeling, some engineering, using some engineering techniques to look at the strength of the skull. 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 gratinous 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.
- [13:47]
Podcast Host
So quite strong beak, even with those small teeth. And do we have lots of stegosaurus teeth, surviving or stegosaur teeth?
- [13:52]
Dr. Susannah Maidment
No, not really. And we've not got very many stegosaur skulls actually, and not very many isolated teeth either. 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.
- [14:06]
Podcast Host
Such a fascinating part of stegosaur's story, isn't it? 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.
- [14:20]
Dr. Susannah Maidment
Well, maybe a walnut, let's not be unfair to it.
- [14:22]
Podcast Host
Sorry. Okay, maybe I'm being into, yes, you can tell me off if I'm being a bit too strict, but that's amazing.
- [14:26]
Dr. Susannah Maidment
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. So yeah, I was obviously smart enough to live for millions of years and be successful in its ecosystems, but I'm.
- [14:39]
Podcast Host
Guessing we don't know much about like the eyes or the nose or anything like that.
- [14:42]
Dr. Susannah Maidment
No, it's quite difficult. Although we have casts of the inside of the brain case. So reptiles, the brain is encased in a kind of bony casing 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. So a big olfactory lobe might indicate very good sense of smell or optic lobes which might indicate a very good eyesight. But in the herbivorous dinosaurs, the ornithischian dinosaurs, we think that the brain and probably didn't leave that quite as good impressions on the, on the inside of the bones. 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. There's nothing that you go, wow, you know, that was an amazing, had amazing eyesight or, or anything like that. It just kind of looks kind of average to be honest. So yeah, we don't, 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. Stegosaurs 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. 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 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. There's no evidence that they were, you know, doing lots of kind of food processing in their mouths or anything like that.
- [16:32]
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- [17:16]
Podcast Host
Well, let's go towards the body then. So should we be imagining a long neck or quite a thick neck? I guess.
- [17:22]
Dr. Susannah Maidment
Well actually different stegosaurs, there might be different answers for, for that.
- [17:25]
Podcast Host
Great.
- [17:25]
Dr. Susannah Maidment
We have Stegosaurus which we know very well, which has a kind of totally average sized neck I'd say, 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. And then we have a dinosaur from Portugal, stegosaur called Miragaia and that actually has more neck vertebrae than most long necked 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. 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, a long tailed dinosaur.
- [18:04]
Podcast Host
Do we think the primary purpose of that would be to reach higher up foliage that idea?
- [18:08]
Dr. Susannah Maidment
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. 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. 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. So your center 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. 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. 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.
- [18:51]
Podcast Host
We're talking about the legs. So my classic image of a stegosaurus, from cuddly toys to shows up walking with dinosaurs and the like is a big body and then stumpy legs. Is that the idea we have?
- [19:03]
Dr. Susannah Maidment
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, well, you know, we as mammals evolved from four legged ancestors. You know, the mammals often have quite even length hind and forelimbs 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. So I think, you know, sometimes we put a very mammalian kind of view on what looks normal. And I suspect actually some of these dinosaurs would look quite weird to us. You know, very, very short forelimbs, quite crouched posture. So they couldn't straighten their forelimbs and they couldn't have kind of, I can't do this without miming it's absolutely impossible to talk about dinosaur locomotion without miming, but they couldn't move their forelimbs forward and raise their arms in the air, if you like.
- [20:02]
Podcast Host
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 legs.
- [20:10]
Dr. Susannah Maidment
Yeah, absolutely. So its back would have been angled downwards.
- [20:13]
Podcast Host
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, what is the usual number of plates that we see on a stegosaur?
- [20:28]
Dr. Susannah Maidment
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. 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. 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 from one another. 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.
- [21:13]
Podcast Host
So it's not just one line of plates along, which is also a classic image you get. There are multiple lines of plates.
- [21:19]
Dr. Susannah Maidment
Well, there's two lines.
- [21:20]
Podcast Host
Yeah, sorry, there's two.
- [21:21]
Dr. Susannah Maidment
Two rows of plates, yeah.
- [21:22]
Podcast Host
Right. That's so interesting. And so what are they made out of?
- [21:25]
Dr. Susannah Maidment
They are bone, which is why they preserve, why they fossilize. If they were soft tissue, they wouldn't fossilize, so they have a bony core. 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 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. 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.
- [21:51]
Podcast Host
And are they directly connected to the backbone to the spine?
- [21:55]
Dr. Susannah Maidment
No, not at all. They're just embedded in the skin. And this is similar to. Actually we see. They're called osteoderms. Skin bone. Right. So they're very, very hypertrophy. 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 throughout the Mesozoic, throughout evolutionary history of lots of different groups of animal, 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 their close relatives, the Ankylosaurs, is that they really took this to kind of extremes and really hypertrophied them and made them extremely elaborate and elongate and large and flashy.
- [22:36]
Podcast Host
Yeah, and absolutely extraordinary. As you said, one of the most iconic images we have in our heads today, which lead to the big question, what do we think that these plates were used for?
- [22:45]
Dr. Susannah Maidment
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, is really difficult. There's been a number of different suggestions of what the function might have been. I mean, I. So I referred to it as armor and, you know, it could be armor, it could be for protection against predators. You know, if you've got a load of spikes and plates sticking up off your back, Allosaurus isn't going to want to come down and take a big chunk out of your back.
- [23:13]
Podcast Host
I guess the fact isn't it, you've got the carnivores at the time, which are, you know, they can stand taller.
- [23:18]
Dr. Susannah Maidment
Yes.
- [23:18]
Podcast Host
Than a stegosaur.
- [23:19]
Dr. Susannah Maidment
Yes, they would have been taller. But of course, you know, stegosaurs flanks are entirely unarmoured. So it doesn't seem like great as a form of armor, I would have said. 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. 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. 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. It could be, you know, think About a peacock's tail, for example, it could be for some sort of intraspecific combat. So if you think about the horns of an antler, the antlers of a deer even, or the horns of a bighorn sheep or something like that, they are, you know, fighting each other for mates. 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. So it could be that, you know, you're making sure you're, you're mating with the right people. So we, you know, it could be some sort of display function. Not quite clear what that might be, but it could 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 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. We think that warm bloodedness must have evolved somewhere on the line to birds, but where, we don't know. 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. 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. 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. 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.
- [25:52]
Podcast Host
It's almost kind of like a ventilation kind of thing.
- [25:54]
Dr. Susannah Maidment
Yeah, or like a radiator. Yeah, absolutely.
- [25:56]
Podcast Host
To cool themselves.
- [25:57]
Dr. Susannah Maidment
So the problem with all of these ideas though is actually how do you test them? 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 sexual. Tend to be something to do with mating. Likewise, do we see differences in males and females. Now we don't have any juvenile stegosaurs and we can't tell sex. 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. 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? And we simply don't have the sample size in stegosaurus to tell that. In fact, we don't really have it in any dinosaur, I would argue, to be able to tell that. So it's really difficult to test these ideas. And actually I think it's kind of, it's a slightly made up question really, 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.
- [27:10]
Podcast Host
Yes.
- [27:11]
Dr. Susannah Maidment
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. 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. 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. And actually, you know, there's not, it's not really a debate about what they use them for. They probably use them for all of them.
- [27:38]
Podcast Host
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?
- [27:46]
Dr. Susannah Maidment
Absolutely.
- [27:46]
Podcast Host
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?
- [27:56]
Dr. Susannah Maidment
Yeah, absolutely. And we do see really different armor and different types of Stegosaurus. So Stegosaurus from North America had very big, wide, flat plates 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 probably still would have had some. Well, they definitely would have still had some function in, you know, thermoregulation, but maybe not as great, 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. You know, I, I sometimes say that I think that Allosaurus could have chomped through Stegosaurus plates like us eating Doritos. But, you know, I don't know. I don't know whether that's true or not, but, you know.
- [28:39]
Podcast Host
Yeah, but do some stegosaurs. 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?
- [28:50]
Dr. Susannah Maidment
Yeah, so some actually quite a lot, we think had shoulder spikes. 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, it has a gigantic spine, it's about a meter and a half long that sticks out from its shoulder region. And that one was actually, we know that they were shoulder spikes because that one, they were actually found in place alongside the arms. And lots of stegosaurs seem to have this. 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. There are some individuals of Stegosaurus that seem to have kind of throat armor. These kind of. It's almost like chainmail. 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.
- [29:44]
Podcast Host
Did to protect that vulnerable area, maybe?
- [29:46]
Dr. Susannah Maidment
Well, yeah, it's a vulnerable area, isn't it?
- [29:48]
Podcast Host
Wow. And so, and the skin on the body of a stegosaur, generally that's less armored than the plates and the spikes.
- [29:55]
Dr. Susannah Maidment
Yeah, just scaly skin.
- [29:56]
Podcast Host
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?
- [30:08]
Dr. Susannah Maidment
So stegosaurs have spikes at the end of their tail. Stegosaurus has four. Some people refer to these as thagomizers.
- [30:15]
Podcast Host
That's the word I've seen, yes.
- [30:17]
Dr. Susannah Maidment
Okay, well, so this word comes from a far side cartoon and it is a caveman who is being. He's called Thag. And he meets his demise thanks to a stegosaur tail spike. So it becomes a thagomizer. And this 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 this. Yeah, we don't need it. And then people try and say, oh, no, isn't the 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 there's spikes at the end of the tail. 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, could do allosaurus legs some damage, I think if it was swinging its tail from side to side. So yeah, probably a weapon.
- [31:24]
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- [32:08]
Podcast Host
And the stegosaurus has four of them. Yeah, but does the number of spikes on the tail differ between the other stegosaurs?
- [32:14]
Dr. Susannah Maidment
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. 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.
- [32:26]
Podcast Host
Yes. Kentrosaurus is another interesting example I had in my notes down here that wanted to mention it as well, because. And that is another type of stegosaur. Is it? It just looks a bit different than your classic Stegosaurus image.
- [32:36]
Dr. Susannah Maidment
Yeah, it's a different. It's a different species. Yeah. It lived in Tanzania, so in Africa, but at the same time as Stegosaurus, roughly.
- [32:43]
Podcast Host
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? Or is it more that the tail had more flexibility almost to kind of go almost to a right angle and then be switched that way? Or is it the whole body bringing that kind of weight in an attack?
- [33:01]
Dr. Susannah Maidment
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 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.
- [33:31]
Podcast Host
Got to ask, because if you haven't, I want to be there if you do it anytime, but have you guys at the NHM or have palaeontologists tried to recreate a tail 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, piece of meat, and to kind of test just how brutal a swing could have been.
- [33:54]
Dr. Susannah Maidment
So we have not done that. Although my colleague Heiri Mallison, who was at the museum for Naticender in Berlin, where Kentrosaurus is, is most of the fossils of Kentrosaurus are housed and is on display there. He has done it digitally, so he's done it computationally and calculated those forces at the end of the tail spike. And that's why we know that they could have kind of impacted bone, is because he's actually calculated the forces. So, yeah, analog models are more difficult to come by, but doing it digitally is a little easier.
- [34:22]
Podcast Host
Come on, Susie, we got to make it happen. It's going to be hilarious. I love to see it. But. But that is kind of the classic anatomy of a stegosaurus isn't it? Of a stegosaur. Is there anything we've missed that we should also mention about how its body functioned?
- [34:34]
Dr. Susannah Maidment
Oh, well, you know, there's so much we don't know really, so I don't think so. But 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.
- [34:44]
Podcast Host
Well, it was also interesting what you mentioned there, that we don't have any juvenile stegosaurs surviving. 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?
- [34:56]
Dr. Susannah Maidment
Yeah, no, we know virtually nothing. I, 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. 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. 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, we don't have any eggs. And actually I think probably we think now that for these sorts of dinosaurs, the bird hip dinosaurs that primitively, you know, and stegosaurs are fairly early members of this group that they were probably had soft shelled eggs. 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. So when we found dinosaur eggs, they tend to be, you know, like calcite ones. Yeah. And that there, there has been some pretty recent discoveries of more, of softer, kind of more leathery shelled eggs from some of these herbivorous dinosaurs. 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. 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. 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 any of that.
- [36:27]
Podcast Host
When you read my next question, which was going to be like you imagine the big herds of Iguanodon, even the sauropod herds, isn't it? It seems like Stegosaurus, the question is still out there. But I guess also with their armor, I mean, do you see with Ankylosaurs later and the like that they are more individualistic, I guess, or more on their own?
- [36:44]
Dr. Susannah Maidment
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. So we have loads of different, I mean Ankylosaurs, there must be 60 or 70 of different types of Ankylosaur. And it's possible that, you know, different ones were doing different things. I think it seems quite likely that these dinosaurs were living in herds or, you know, groups of some form just because it's, it's a really sensible way to defend yourself from predators. 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, from predators. These big, big predators would have been slow moving and the herbivores would have been probably slower moving. So I think, you know, there wasn't any pursuit, predation going on. 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 elaborate structures on all these sorts of dinosaurs. So this armor in Ankylosaurs and stegosaurs and then we have things like the horns and frills in the Ceratopsians, in the Triceratops, like dinosaurs. 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. I think, you know, herding is kind of, it makes sense, we just don't have any evidence for it.
- [37:52]
Podcast Host
And talking about predators, quickly, we've already mentioned Allosaurus, 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 Stegosaurs?
- [38:04]
Dr. Susannah Maidment
Yeah, there are other big meat eating dinosaurs around at the same time. So in North America we've got Ceratosaurus, Marshasaurus, Dwarvosaurus living alongside them? Yeah, I mean, Allosaurus certainly in North America living alongside Stegosaurus, Allosaurus is by far the most abundant predator, you know, by miles. The other meat eating dinosaurs are much, much rarer. So really, you know, the Morrison Formation where these Dinosaurs are found where Stegosaurus Allosaurus found. Yeah, Allosaurus roared the Morrison. It was doing all the eating of everything, I think.
- [38:33]
Podcast Host
Well, I have in my nose one particular type of stegosaur that I know is close to your heart. They done work around, but please forgive me if I mispronounce the wording of it. Adra Tiklit Boullafa.
- [38:49]
Dr. Susannah Maidment
Pretty good. I mean, I don't really. We named it in Amazigh, 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 Amazigh either. So you can go nuts and pronounce it however you want. It doesn't mind.
- [39:04]
Podcast Host
I'm not going to try again. I'll say it once again. Adratiklitz Bulafa. Can you tell us about this particular stegosaur? This is a name I've never heard before.
- [39:12]
Dr. Susannah Maidment
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. So it's really early on in the evolution of the stegosaurs. So when we first came across these fossils which were actually for sale, they were for sale in a commercial fossil dealership 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. 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 it said that they were from the Middle Jurassic of the Middle Atlas Mountains of this town called Balmain. 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. 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 shark's teeth and.
- [40:20]
Podcast Host
Oh, we love, we love fossil shark guys as well. Don't worry. That's good to hear.
- [40:23]
Dr. Susannah Maidment
That's good. So he had been to Morocco a bunch of times because there's loads of sharks. You can collect sharks teeth in Morocco. 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. It was amazing. As 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 an expert in the rocks of the area. 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. 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. And it's actually gone on to result in a really long term collaboration between myself and the geologist and his group. Now we've set up Morocco's first vertebrate paleontology labs at his university and doing lots and lots of work with them and training, training students there to be vertebrate paleontologists. So it's been an incredible project that started with a few stegosaur bones for sale in a fossil shop in Cambridge. That's great.
- [41:40]
Podcast Host
And to discover the first known stegosaurs in North Africa today in the Atlas Mountains in Morocco.
- [41:46]
Dr. Susannah Maidment
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. So, you know, we hope that we're going to find more there.
- [41:57]
Podcast Host
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?
- [42:07]
Dr. Susannah Maidment
Yeah, definitely. 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 all of these different groups of dinosaurs get going and really radiate and diversify and sort of take over. Middle Jurassic rocks are present in places like Niger as well as Morocco. But it's difficult, it's dangerous. The risk assessment that I would have to write would be so long to be able to be able to work in some places that, you know, we can't go there many places. As I say, you know, Morocco had no vertebrate paleontologists working in the country in university. So we, we set that up. So there are lots of reasons why these places aren't sampled.
- [42:57]
Podcast Host
And the African continent today, if going back into that kind of the Jurassic mindset, are we thinking the, the north of the emerging Atlantic Ocean or the south? Where should we be thinking?
- [43:06]
Dr. Susannah Maidment
Yeah, south. So southern hemisphere.
- [43:08]
Podcast Host
And that's the area where there haven't been stegosaurus or known of until now.
- [43:12]
Dr. Susannah Maidment
Well, Kentrosaurus, which we, that's from Tanzania. So that's been long known about. That was first discovered by the ger in the 19, early part of the 20th century. And there's also a little bit of material from Argentina. 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. 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. 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. We all do this to each other's papers, we all read each other's papers and comment on them. And it's part of our job as scientists to review what other people have written and make comments on it. And I got this paper and I went, well, that's a stegosaur. And so did my two other colleagues. And we all sent our papers back independently of each other, of course, not knowing this, saying, well, we think these are stegosaurs. And then the authors came back and said, you know, we think it's a stegosaur too. But we keep, we keep doing these, these quantitative analyses that look at the evolutionary relationships of these different animals. And we can't make it be a stegosaur. 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. Looks exactly like a stegosaur. It's definitely a stegosaur, but it's very, very early. It's the world's oldest, so it's quite primitive. And that means it has a number of features that, you know, kind of bridge the gap between some of these early dinosaurs and some later stegosaurus.
- [44:39]
Podcast Host
Well, it's really exciting having you on because you know, you're someone at the forefront of the developing story of stegosaur. You know, now in the 21st century, many of us growing up would have heard of Stegosaurus since, you know, since we were kids and TV programmes. 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. So it's 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 armored dinosaur that comes to the forehead?
- [45:16]
Dr. Susannah Maidment
Yeah, we don't. They went extinct, so they don't evolve into anything. Our evolutionary trees, we make evolutionary trees. We, you know, we reconstruct evolutionary relationships in kind of a semi quantitative way, I will say. And yeah, the evidence from that is that, yeah, they just go extinct.
- [45:31]
Podcast Host
Susie, this has been such a fun chat growing up. I've already mentioned that 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 in the 2000s, and stegosaurus depiction there. I mean, what do you think of the depictions of Stegosaurus in the media world and their attempts to give us an idea of what Stegosaurus looks like?
- [45:58]
Dr. Susannah Maidment
I think generally they're very good. You would have to show me what Stegosaurus looked like in the original walking of dinosaurs. I can't remember what they did with it.
- [46:05]
Podcast Host
Quite like the classic with the big plates and the very small head. And I think it's a fight against an allosaurus in a narrow kind of ravine.
- [46:13]
Dr. Susannah Maidment
Yeah, I think 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. 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 and there was the recent Walking with Dinosaurs. They had. They had. Triceratops is running around and I was like, no, no, no, no, no, they weren't doing any of that. There was no. There was no 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. You know, the thing with Stegosaurs is that we know so little about them that you've got a lot of latitude.
- [46:47]
Podcast Host
You know, which makes them really fun and great as kids toys and you know, from everything and then in the media today, Suzie, this has been absolutely great. We've covered so much. But is there anything else you'd like to mention about stegosaurs before we finish?
- [46:58]
Dr. Susannah Maidment
Oh my God. I think I've told you everything I know. Good.
- [47:00]
Podcast Host
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.
- [47:05]
Dr. Susannah Maidment
Thanks for having me on.
- [47:09]
Podcast Host
Well, there you go. That was Dr. Susie Maidment 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 while. 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 the new release every week. Sign up@historyhit.com subscribe. That's all from me. I'll see you in the next episode.
- [47:54]
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