The First Sharks

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Speaker 10 Hey guys, I hope you're doing well. Welcome to a very special episode of the Ancients because we are going back hundreds of millions of years to explore the story of the first sharks.

Speaker 10 Yep, you heard me right. I am really excited for this episode.

Speaker 10 I loved recording it with our guest today, a leading expert on prehistoric sharks, Professor John Long from Flinders University in Adelaide, Australia.

Speaker 10 And I just love the fact that we were able to explore a creature that we know today, that occupies the oceans today, whose ancestors also lurked in the seas and the rivers before the age of the dinosaurs.

Speaker 10 It's an extraordinary story and I really do hope you guys enjoy. Let's go.

Speaker 10 Sharks. They're older than the rings of Saturn.
They're older than trees.

Speaker 10 300 million years ago, sharks enjoyed a golden age. Dozens and dozens of different species spread all across the globe.

Speaker 10 These prehistoric predators occupied oceans, seas and rivers, seawater and freshwater habitats. And some sharks were more fearsome than others.

Speaker 10 One particular species even had a vertical buzzsaw-like wheel of teeth.

Speaker 11 Don't believe me?

Speaker 10 Just search the word Helicoprion. It's insane.
Today we're delving into this extraordinary world of the earliest sharks with our guest, Professor John Long.

Speaker 10 John, it is a pleasure to have you on the podcast today.

Speaker 11 Thank you, Tristan. It's great to be here.

Speaker 10 And we're literally doing this across the world. So you're in Australia at the moment, if I'm correct.
So it's bright and early in the morning here in Britain.

Speaker 10 You've taken some time out of your evenings to come on the Ancients today.

Speaker 11 Yeah, it's dark now.

Speaker 11 It's winter and it's very cold and i'm happy to be in a nice warm room to talk interesting things about fossil sharks with you exactly fossil sharks and this is a story that is correct me if i'm wrong but it feels it's older than the dinosaurs way older than dinosaurs we're talking older than trees older than insects and get this even older than the rings of saturn no really the rings of saturn yes rings of saturn are about 400 million years old and sharks go back 465 million years so that's a way long long time back.

Speaker 10 And for experts like yourself, are fossils the main tool of research for learning about these earlier specimens of sharks, for following the whole evolutionary cycle, the evolutionary journey of sharks?

Speaker 11 It is indeed, Tristan. I'm a paleontologist, so I study fossils to look at the history of life on Earth.

Speaker 11 As you get closer to the modern day, then genetics comes into it more and more because you've got living species that can bracket the extinct species.

Speaker 11 But when you go way back into deep time, hundreds of millions of years ago, it really is just fossils is all you've got.

Speaker 11 And the context of the fossil, like the geology of the rocks that the fossils are found in, the geochemistry of those rocks, you can do a lot of analyses that give you the environment that these creatures lived in.

Speaker 10 And John, you are one of the leading experts in the fields of early sharks and fossil fish in general.

Speaker 11 And your

Speaker 10 interest in this, it stems from quite a young age, you know, when you started collecting fossils.

Speaker 11 This has taken up almost all of your life yeah i started collecting fossils when i was seven at school because i met a schoolmate whose father collected fossils and used to take us out to local quarries and places where we could hit rocks and find little creatures like trilobites and fossil shells and then a year or two later i realized that right close to my home where i was living was a beach where we could find ancient fossil sharks teeth that were eroding out of the cliffs or you know you could just pick them up on the beach your listeners won't see this but here's a fossil shark tooth, a really large one.

Speaker 11 It's about six centimeters in size. And I found that when I was about eight years of age and kept it ever since.

Speaker 10 And how old do we think that shark tooth is, if I may ask?

Speaker 11 Well, that's from a site in Victoria called Beaumoris. It's about six million years.

Speaker 11 So it's kind of recent on the scale of, you know, sharks going back 465 million years, but it's still precious to me.

Speaker 10 Let's go right back to the beginning then. 450 million years ago, roughly 450 million years ago, what do we know about the origins of sharks, the earliest sharks?

Speaker 11 Well, sweet FA, actually, Tristan, all we had was a handful of scales, basically tiny little scales the size of a pinhead. Now, you might think, what can you do with scales?

Speaker 11 Well, think of a cake, you know, a lovely, delicious cake.

Speaker 11 If we only had crumbs, we could tell if from those crumbs, if it was a sponge cake, that's fairly boring, or a black forest cake, which is kind of interesting.

Speaker 11 And so those scales can be simple in terms of their structure, their histology, or they can be quite complicated.

Speaker 11 And so the first tens of millions of years of shark evolution is really told through these tiny little scales that become more and more complex.

Speaker 11 And they go from being the sponge cake of scales to the black forest cakes within 10 million years.

Speaker 11 And so sharks were starting to do a lot with their with their bones, with the structure of their scales, their dentine tissues that made those scales.

Speaker 11 But we know nothing about the animal, what they looked like, just that they were scales similar to living sharks. So we know they must be on the line leading to sharks.

Speaker 10 And how long is it before you start to see in the fossil record a bit more evidence and get a bit more sense of sharks actually as sharks?

Speaker 10 You have a bit more than just those scales and knowing FA about it.

Speaker 11 Well, during the, that was the 465 million years ago, was the Ordovician period. But you jump to the Silurian, which comes after it.
There's not much there, still mostly, you know, scrappy material.

Speaker 11 But when we go to the Devonian period, which started 419 million years ago and ended 60 million years later, we start getting abundant shark fossils from marine deposits and also freshwater like river deposits and an abundance of teeth because it was that point in time sharks developed their first great superpower, which was the ability to make lots and lots and lots of teeth quickly.

Speaker 11 So sharks today, for example, are shedding their teeth all the time as new teeth pop up and keep that mouth full of really sharp, effective teeth so a shark can develop something like 20 000 teeth in its lifetime and keep shedding the old teeth into the the bottom of the sea floor so that's why sharks teeth make excellent fossils fantastic and where were these earliest shark teeth fossils found from some 419 million years ago well spain has got the oldest teeth that are actually belong to the the same type of replacement tooth as modern sharks have in the aragon mountains of spain which i was there in 2022, actually, on a field trip, and got to visit the beautiful mountains there with the limestones.

Speaker 11 You don't actually go and find teeth by spotting them with your eyes.

Speaker 11 You take big samples of rock, dissolve them up in weak acid, and then pick through the residue, and then you get the abundance of these micro-fossils, which include sharks' teeth and scales and other bits of fishes and things.

Speaker 10 Now, John, before we delve more into the evidence that we have and, you know, kind of their structure and size of these early sharks you mentioned there also this uh the devonian period and how it preceded by ordovician and silurian now i don't know too much but i know that this is long before as you mentioned at the beginning the times of that the triassic or the jurassic or the cretaceous with dinosaurs later yes but can you give us a sense of almost what was happening in the world you know between 450 and 420 million years ago that you go from that ordovician period to the devonian period where you see this kind of great leap in shark evolution?

Speaker 11 Well basically from the spines and scales we can see that sharks are developing a more complex kind of cartilage structure and are developing different hard tissues like dentines which forms the core of teeth and then when we get to the Devonian we start finding whole complete shark-like fossils as well with the whole body, the skulls, the head preserved and the whole dentition in place.

Speaker 11 And they look like modern sharks, but they're not yet anatomically the same as modern sharks in the same way as, you know, you've got early reptiles that look like dinosaurs, but they're not the same as living reptiles today.

Speaker 11 There had to be a lot of more evolution of sharks before we get to the modern groups, which, to be honest, don't really appear until the age of dinosaurs.

Speaker 11 And we'll talk about that later in this episode. But during the Devonian, sharks actually went from being tiny little things about

Speaker 11 half a meter long to creatures up to maybe six meters in length by the end of the Devonian, you know, the largest predatory creatures of that period.

Speaker 11 And to put the Devonian into a perspective, I think it's the most important period in the Earth's history. You have the pre-Devonian where not much happened, no life on land.

Speaker 11 During the Devonian, plants took over the land and grew to forests, you know, 30 meters high. Fish evolved arms and legs and started walking on land as the first land animals, vertebrates.

Speaker 11 Invertebrates invaded land and we have the beginning of the insect lineage and so on. So the modern world became shaped by that Devonian changes in the environment and what life was doing.

Speaker 11 And after that, life was more or less just changing towards the modern faunas we have today. But the Devonian was the revolution that really started it all.

Speaker 10 And why is it a revolution? Is it a change in the climate or for the sharks, obviously in the water? Do we know if the temperature changes that allows them to kind of grow and evolve? What do we know?

Speaker 11 Yeah, there were lots of changes going on in the atmosphere in the devonian from high levels at the beginning to low levels and then high levels again at the end so and i'm talking fluctuations from like 13 oxygen up to 28 oxygen you know today we have 21 oxygen so this

Speaker 11 changes in boosting the oxygen of the whole planet was how plants really got a a boost of energy and and life and started growing to, you know, the early Devonian, the beginning of the Devonian, the plant life life of the world was just mosses and bryophytes and lichens and things and very small weedy plants.

Speaker 11 But by the end of the Devonian, these forests had established made of lycophytes, which are horsetails, and ferns, gigantic ferns.

Speaker 11 And so we had the very first forests on the planet, as well as animals that were invading those forests to find food.

Speaker 10 Now, John, we've already covered a little bit of this in our chat already, but can we now actually kind of go through the kind of shape of these sharks and what we know of them when we are at the Devonian period?

Speaker 10 And, you know, those early adaptations, those early key kind of design improvements in the shark that we see at this period and how the shark comes to look pretty different to other fish at the time?

Speaker 11 That's right. Well, the fishes of the day included early bony fishes like, you know, we have salmon and trout today that have skeletons made of bone.

Speaker 11 And we had these ancient armoured behemoths called placoderms, which comes from the Greek meaning plated skin, because they had massive armoured plates covering their bodies.

Speaker 11 Some of these were enormous, like Duncalosteus, the Darth Veda of the Devonian, which was probably in the order of four or five meters in length, maybe bigger, but that's debatable.

Speaker 11 And at the time, sharks were mostly about a meter in length or smaller until the very end of the Devonian.

Speaker 11 But sharks were really just predators, but they weren't the apex predators because these placoderms had evolved before the sharks and occupied most of the environmental niches.

Speaker 11 But towards the middle of the Devonian, we get sharks that look a lot like modern sharks today with their triangular dorsal fins and wide pectoral fins at the front, mouths full of teeth in rows and files that could be replaced, and a shark-like streamlined body made of cartilage.

Speaker 11 And that's the critical thing about sharks. They have a cartilage skeleton.
Now, here's the rub. It's not the same cartilage as in your ear or your hip joint.

Speaker 11 They have their own unique kind of cartilage that no other creature has. It's called a globular calcified cartilage.
So it makes the skeleton very light, but also incredibly strong.

Speaker 11 So it's like a special type of cartilage that gave sharks an advantage to become more agile and faster in the water to outsmart these bony placoderms and other fishes.

Speaker 11 So I think that's a real advantage that sharks evolved at this time.

Speaker 10 And does it still have even these early sharks, even when they're quite small, do they still have the iconic fin on top that we think of as sharks today?

Speaker 11 Yeah, they do. They have that triangular fin.

Speaker 11 And as I said, even though they're rather small, it was towards the end of the Devonian when there's a series of devastating mass extinction events that rock the Earth, that some of these placoderms go extinct just before the end of the Devonian, but others straggled on through.

Speaker 11 But at that point, which is about 10 million years, or actually... about yeah 15 million years before the end of the devonian sharks started to diversify rapidly and get larger and larger and larger.

Speaker 11 So that's when we get the rise of the first big, monstrous predatory sharks like Tenacanthus, which was probably in the order of seven or eight, probably six to seven meters in length, certainly bigger than a white shark today.

Speaker 10 Well, John, should we cover that evolutionary leap right now?

Speaker 10 Because it also feels, as you've hinted there, that that sharks, the fact that they've endured for so long, for so many hundreds of millions of years, that they are one of the great survivors of some of these biggest extinction events in the history of the earth and it feels like they are a beneficiary of this first big almost wave that decimates quite a few other fellow species at the time yeah and this was the second of the world's global mass extinction events so in the last 500 million years earth has gone through five major mass extinction events The first was at the end of that Ordovician period, about 455 million years ago, when all we had was sharks known by scales.

Speaker 11 But after that, we have an increase in the number of species of sharks, but they're still known from scant remains.

Speaker 11 But by the end of the Devonian, these two mass extinction events near the end of the Devonian shook the world up in a big way and paved the way for sharks to really go into their new golden age in the Carboniferous period.

Speaker 11 Because you know why? The placoderms went extinct. Their main rivals bump out.
Sharks can just walk in and take over all those vacant niches. And there's a parallel here with mammals and dinosaurs.

Speaker 11 I mean, the mighty dinosaurs went extinct 66 million years ago. There were mammals around the whole time with dinosaurs, but they couldn't really go anywhere until the dinosaurs were extinct.

Speaker 11 And so there were vacant ecological niches for them to then take over and expand. And sharks did exactly the same once the placoderms were extinct.

Speaker 11 And can we get a sense at this time that do you also see quite almost a growth in the area that we have evidence, fossil evidence for sharks, for these early sharks at that time do they seem to spread more across the world as you see them rising to the fore and taking the mantle of those species like the placoderms yeah i mean basically by the devonian we have remains of sharks all around the world but mostly from teeth and and a few sites with complete sharks but the carboniferous period which started 359 million years ago and went to about 300 million years ago There's excellent sites all throughout Great Britain and Scotland where some of the best fossil sharks in the world have been found, especially like around Glasgow, the Bears Den shark, whole, complete, perfect shark.

Speaker 11 It's called one of the great hero sharks of Scotland. There's even been poems written about it by Edward Morgan, who was a poet laureate in Scotland.
True, you know, this shark is a hero shark.

Speaker 11 It's in the museum in Glasgow in the Hunterian. I saw it only a couple of months ago when I was in Britain and I paid homage to it.
It's such a beautiful specimen.

Speaker 11 And it was found by a most incredible fossil collector called Stanley Wood, who is an absolute legend who found many new kinds of species of fossil fish and early amphibians, even fossil plants.

Speaker 11 And he's had like a dozen of these named after him as well. Unfortunately, he passed away about 2012, but he's left a lasting legacy for the collections up there in the museums.

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Speaker 10 You know, John, I'd never ever heard of the Bear's Den shark before. I'd heard of the Bear's Den Roman baths and the Roman fort up there on the Antonine Wall.

Speaker 10 I didn't know that Bears Den, like a suburb of Glasgow, was also famous for this skeleton, and correct me if I'm wrong, of a full Devonian shark.

Speaker 11 Yeah, or it's Carboniferous shark. Carboniferous lived in the seaways.

Speaker 11 It had this big anvil on its back like a massive bone that expanded out that had tooth-like structures on the top and the top of the head was covered in teeth as well tooth-like structures like denticles of the skin that have grown big and coarse and look like teeth so that this thing actually looked like it had a mouth sitting on top of its back which may have been a way of scaring away bigger predators which they actually were in the in the oceans and shallow seas of those days, giant bony fishes like rhizotas that grew to sort of six or seven meters in length.

Speaker 11 But nonetheless, there's another site in the Carboniferous of North America called Bear Gulch, not Bear's Den, but Bear Gulch in Montana. And get this.
This is a site with whole complete fossil fish.

Speaker 11 Literally thousands of them have been collected. But the most abundant fish in this fauna are sharks and their kin.

Speaker 11 So up until now, Sharks have very much been a small part of the overall fish faunas in the rivers and seas of the world.

Speaker 11 But in the Carboniferous, they take over and suddenly become the most abundant fishes in our seas and rivers and lakes, more so than the bony fish that today dominate our oceans.

Speaker 11 So I call this the golden age of sharks. And there are so many diverse forms of so many different shapes and sizes.
I could spend hours describing them all, but just take my word for it.

Speaker 11 There were every kind of shape and size of shark you could imagine at that time.

Speaker 10 I would like to explore some of that diversity because if there is such a rich multitude of sharks in that period, I mean, surely they can't therefore all be predators, John, or all carnivorous.

Speaker 10 I mean, because surely they all need to survive.

Speaker 11 That's exactly right, Tristan.

Speaker 11 This was a time when another lineage of sharks split off the main, shall we say, the main stem that leads to modern sharks, and it goes to a group called the rat fishes or holocephalans.

Speaker 11 These are like chamyrids and spook fishes that today live in the deep oceans.

Speaker 11 At that time, this split caused a great great radiation of these sharks with crushing toothplates in their mouth, like flat bricks for crushing up clams or rounded teeth for grinding things like corals and things.

Speaker 11 And there were hundreds of species of these holocephalans, and they were the most abundant shark-like fishes in the oceans at the time.

Speaker 11 But it also saw a radiation of the true sharks leading to the modern shark line and even more gigantic predators like Sabitus, which is found in Scotland and England, in the Carboniferous limestones.

Speaker 11 And this has monstrously large teeth, the size of your hand. And it was probably a shark that would have reached at least eight meters in size.
So the biggest predatory shark yet in our story.

Speaker 11 And it's found all over the world, not just Scotland and England and Ireland, but also remains have been found in North America and parts of Europe as well.

Speaker 10 I'd like to also ask, because you mentioned it in passing, and forgive me for going slightly further back in time, but at the end of the Devonian, you mentioned like one of those species that was bigger than the great white of today.

Speaker 10 And what was the name of that?

Speaker 10 Was that quite a, perhaps in the eyes of yourselves and fellow researchers today, was that quite a big moment in the story of the evolution of early sharks, this particular species?

Speaker 10 I mean, what do we know about this? Yeah.

Speaker 11 Because this was right near the end of the Devonian, about 360 million years ago, a million years before the end of that period.

Speaker 11 And between the two mass extinction events, we get a rise of diversity of sharks including many different kinds including even filter feeding sharks that weren't predatory as well as these ones with rounded tooth plates for crushing prey rather than or piercing and grabbing prey with sharp pointed teeth sorry john do you mean like basking sharks today or something like that with a big mouth open filter feeding sharks today like basking sharks and whale sharks filter by opening their mouths and catching food against their gill rakers or their gill arches like a sieve if you like but these sharks that they were filter-feeding Devonian sharks, that were small, not gigantic, they were probably about a meter in length, but they had teeth that were widely spaced to form like a sieve when the upper and lower jaws, like my fingers and my hands, where the fingers are loose between each other, not tight.

Speaker 11 And so they could then take a mouthful of planktons and get that into their gullet. So this is the first time in the history of life.

Speaker 11 in vertebrates anyway, backboned animals, we have filter feeding as a niche and sharks were the first to do it.

Speaker 10 Going back to what you were saying earlier, you know, between those two extinction events at the end of the Devonian, you get that bigger shark than the great white today.

Speaker 10 I forget the name that you said it was.

Speaker 11 It's called Tenacanthus. Okay.

Speaker 11 Yeah, and that would give rise to these bigger tenacanth sharks that go right through the next two periods, the Carboniferous and Permian, including Sabitus, the really gigantic one in the Carboniferous, was another member of the same family.

Speaker 11 It had teeth with many big cusps on a big, wide root, which means it had teeth that were very powerful for piercing and grasping prey but also at the same time in the same age rocks of the carboniferous we get the first sharks teeth that are broad and flat with serrated edges like a great white shark so we're getting an adaptation for tearing flesh off bigger prey so for me that's really significant because sharks were targeting creatures bigger than themselves at that time.

Speaker 11 Who knows what they were? They could be other sharks or they could be other types of bony fishes that were around that we don't really know of at this stage.

Speaker 11 But whatever it was, if you've got serrated teeth like a steak knife, it means you can grab prey and really take chunks out of it. Same way that white sharks can take chunks out of a dead whale today.

Speaker 10 You've probably therefore already answered another question that I had for you, but I'm going to ask you it anyway. It seems that, you know, shark teeth.

Speaker 10 they are so important for understanding the evolution of sharks over those millions of years and comparing the various shark teeth to understand how powerful a predator they were or the kind of diversity of the sharks that you had at the time.

Speaker 11 Exactly. The teeth are amazing because there's so many different forms and shapes of sharks' teeth, everything from adaptations for cutting, for piercing, for grinding, for crushing.

Speaker 11 It's just amazing how suddenly once they got this formula for different kinds of tissues that build a tooth, then you can build teeth in so many different ways.

Speaker 11 And it's kind of a superpower that sharks had that no other fishes at the time could do. Because all the bony fishes just had pointed, sharp teeth.

Speaker 11 They didn't vary that much, just like bony fish teeth don't vary that much today until you get into the specialized reef forms, you know, the brasses and things.

Speaker 11 But now at the time, sharks were, you know, took over the seas with so many different ways to feed with different shaped jaws and teeth.

Speaker 10 So let's kind of explore a couple more of these now. So you've already highlighted, yes, you've got the real dangerous predators in the golden age in the Carboniferous.

Speaker 10 You also mentioned about, you know, the herbivore ones almost, you know, that different strand. And then also the kind of basking shark-like ones as well.

Speaker 10 But were there certain other key, almost subspecies of shark that develop during the Carboniferous that have their own different modes of eating?

Speaker 11 Yeah, well, the most spectacular of these are the ones that aren't on the line to modern sharks, but go on the line towards the holocephalans or chimyroids.

Speaker 11 And we get groups called Aeneopterygians, which were totally bizarre. I mean, imagine a fish.
It looks like a little stubby shark with huge pectoral fins that come out the back of its neck.

Speaker 11 And they look like antlers of a moose. And they fly through the water like a butterfly.
And they have a club-shaped tail. I mean, and their mouth is just hardly any teeth except for one tiny little...

Speaker 11 jagged whirl of teeth like a like a buzzsaw at the end of the lower jaws. And these things, we know we've got them preserved whole from these sites in America, from Bear Gulch.

Speaker 11 And we know what they ate because they have remains of shrimp, they have remains of plants and conid worm-like creatures in their gullets and their stomachs.

Speaker 11 So we know these things were effective at hunting prey, but they weren't built for speed, that's for sure. So there were so many specialist types of shark-like creature around at that time.

Speaker 11 Some of these sharks even developed gigantic pectoral things so they could swim through the water like stingrays, but they weren't quite the first rays yet.

Speaker 11 They wouldn't evolve until the Jurassic period, much, much later. But they were trying to be stingrays, if you know what I mean.

Speaker 10 Carboniferous shark-like stingrays. I mean, I never thought I'd hear that sentence said on an ancients podcast ever.
So congratulations, John. That is quite something.

Speaker 11 Yeah, well, the amazing thing is that sharks tried out all sorts of different body plans.

Speaker 11 And even if they didn't work and that particular lineage went extinct at that time, it didn't mean they wouldn't try it again later.

Speaker 11 And later when they invented that same body plan again, it did work as rays became very successful later on.

Speaker 10 Can you give us a sense of the time scale with the Carboniferous period? How many millions of years are we talking about?

Speaker 11 We're talking from 359 million years ago when the Devonian ended to about 299 or 300 million years for the beginning of the end of the Carboniferous and the beginning of the Permian period, which comes after it.

Speaker 10 So just over those 50 million years, I mean, is it possible yet from the research that has been done by yourself and your colleagues to see whether some of these species of shark, you know, they experimented with different types of eating and different types of, I don't want to say equipment, but anatomy and how they were shaped.

Speaker 10 Do we see that some die out before the end of the Carboniferous and it's clear that some groups are more successful than others?

Speaker 11 Actually, no. Most of them that developed in the Carboniferous just keep going through to the Permian because there wasn't a mass extinction event at the end of the Carboniferous.

Speaker 11 There wasn't any reason why, you know, different species levels might go extinct, but the lineage keeps going, you know, as new species and new genera evolve from that same group.

Speaker 11 So we see a radiation of each of these groups into many different species, a great diversity of sharks by the Permian period.

Speaker 11 And including some of these forms evolved from Carboniferous forms with these rows of teeth in a single whirl, like a wheel, like a buzzsaw.

Speaker 11 Some of them evolved into the biggest and most spectacular sharks of all time in the Permian, the buzzsaw sharks like Helicoprion.

Speaker 11 Imagine a shark that's eight to ten meters in length and it has no teeth in the upper jaw, but the lower jaw just comes together as one gigantic wheel of death.

Speaker 11 Just all these teeth that are big and serrated but form a single wheel coming out the lower jaw.

Speaker 11 Now that wheel didn't move, it couldn't because it was teeth, you know, set in cartilage in the jaw, but it had this very elastic lower jaw joint, so it could swing that lower jaw forward and thrash it back.

Speaker 11 And that way it could catch gigantic squid and eat them.

Speaker 11 Even ammonites, which were squid-like creatures in a big shell, they might have had a special way of actually grabbing that ammonite and slipping the soft meat of the animal out of the shell and eating it and leaving the shell behind.

Speaker 11 Whatever they were doing, they were incredibly successful because we find these big wheels of teeth all around the world in the Permian period in nearly every country, even in Australia.

Speaker 10 But do we therefore have, because obviously squid is another word that we know well today, like alongside these very prehistoric sharks in the Carboniferous and Permian, you also had very prehistoric squid alongside them in almost another part of the food chain.

Speaker 11 Yeah, the first modern squid evolved in the Carboniferous.

Speaker 11 And by the end of the Carboniferous, we had many kinds of squid-like creatures called cephalopods, but some of them with big shells, they were ammonite-like creatures.

Speaker 11 We all know ammonites from the Jurassic, but the first ammonoids actually evolved in the Devonian that would evolve into the bigger ammonites of the Jurassic and so on.

Speaker 11 So there was an abundance of these squid-like creatures living in the oceans of the day, and they actually probably formed the main food source for many of the sharks.

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Speaker 10 And do we get a sense then at this time, it seems like there are sharks that are adapted to being deeper in the oceans, some the more shallow waters, but also with the Carboniferous, I think goes straight to my mind growing up watching things like Prehistoric Park and so on, of the big dragonflies, the big centipedes, and the big scorpions, and all, you know, the bigger insects on land, you know, that kind of warm climate, lots of carbon in the area, hence carboniferous.

Speaker 10 But in the like the shallow, in the rivers and the lakes near these, these beautiful, rich carbon landscapes, would you also have specially designed sharks just, you know, wallowing up and down those rivers and in the lakes?

Speaker 11 Oh, yeah. Oh, yeah.
We had a whole group of sharks called the Xenocanths, and that's from Xena. You know, Xena, the warrior princess? Xena meaning foreign in Greek.

Speaker 11 They had this foreign, xenacanth means foreign spine because the back of their neck had this whopping great spine sticking out the back.

Speaker 11 And these were kings of the rivers and lakes of the world, these xenacanths. And

Speaker 11 they appear in the early Carboniferous by their teeth and some whole complete sharks from Scotland and different places like that.

Speaker 11 By the Permian period, they're really taking off and getting to quite large sizes with really... quite large teeth.

Speaker 11 When I say large, you know, three to four meters in length, but one of them was really big, maybe five and a half meters, but it had tiny little teeth.

Speaker 11 And we believe this, even these xenocanths evolved a filter feeding line as well as a predatory line. So yeah, they were the rulers of the freshwater domain of the world.

Speaker 11 The first ones are found in the sea, but after that, they are only found in freshwater for the Permian, late Carboniferous, Permian, and Triassic.

Speaker 11 It was about a period of 100 million years or more, where they just dominated the freshwater rivers of the world.

Speaker 10 And they hunt on things like amphibians, if I'm thinking you have amphibians by that time, right? And they're quite big.

Speaker 11 Absolutely.

Speaker 11 In fact, in the book, I talk about a particular Permian turducken, you know, where we have a xenocanth shark that's just eaten two amphibians, two tetrapods, and in the bellies of one of those tetrapods is another fossil shark.

Speaker 11 Wow. You've got a stem shark.
So you've got three trophic levels all in the one fossil, which is so rare these days to find a fossil within a fossil within a fossil kind of thing.

Speaker 10 Well, it shows so much more, isn't it, to the fossil record for these sharks. It isn't just scales early on.

Speaker 10 It isn't just teeth, although the teeth are really interesting, as you've highlighted, for tracking the evolution and the different kind of strands of sharks at this time.

Speaker 10 You can also find, as time goes on,

Speaker 10 evidence of shark killings, you know, deep in the Permian and Carboniferous and so on.

Speaker 11 Yeah, these xenocats are also the first record of shark cannibalism, where they're eating their own species and other xenocanths. So that's really nice to record.
They just ate anything.

Speaker 11 You know, sharks today, they only have one parental mechanism, and that is a hormone that kicks in when the females give birth, so they don't eat their young straight away.

Speaker 11 And that's as good as parental care you get with a shark.

Speaker 10 Sorry, I'm going to kind of go on a bit of a myth bust here and a bit of a silly one as well. There's that saying that sharks can't swim backwards or they always have to keep swimming forwards today.

Speaker 10 I mean, do we have any idea about that with the prehistoric sharks?

Speaker 11 Oh, absolutely, because their skeletal structures are the same as living sharks.

Speaker 11 And we even have beautifully preserved fossil sharks from the Devonian Carboniferous with the livers and soft tissues preserved in some deposits.

Speaker 11 And sharks have these gigantic livers, which gives them buoyancy in the water.

Speaker 11 And it's also a huge store of energy from squalene oil that those livers are full of, which enables sharks to do large migrations around the globe without feeding if they don't need to.

Speaker 11 They can draw energy from those livers.

Speaker 11 So, yeah, the point is that sharks can't respire by sitting still in the water.

Speaker 11 They need to either have a current moving through their mouth so they can breathe to get the oxygen out of the seawater, or they have to keep swimming to breathe.

Speaker 11 So they tend to keep moving, or if they rest, they tend to rest in areas where there's a moving current flowing over them.

Speaker 10 Also, another question, kind of keeping on those rivers, and you mentioned amphibians earlier, and also, you know, these different strands, these different family lines that come from the shark line and then diverge.

Speaker 10 Do we get any sense during this time time of almost experimental, you know, so many different strands of sharks in the Carboniferous and Permian, whether any of the groups did ultimately become amphibians?

Speaker 11 No, no, the amphibians are line that evolved from the bony fishes, from the lobe fin fishes. Today we have the coelacanth and the lungfish.

Speaker 11 that are more advanced than the rest of the ray fin fishes like the trout and salmon.

Speaker 11 But we had a whole host of intermediate prehistoric forms like titalik, for example, which is, like we call it a fissure pod.

Speaker 11 It's got a bony skeleton like a fish, but it's got very well developed limbs, paired limbs, pectoral fins that have a humerus, ulna, radius, carpal bones, and we even found digits in one of them, a fish called Elpistostinghi from Canada.

Speaker 11 We found the first evidence of a fish fin that had finger bones or digit bones in it. So that's been sealed.

Speaker 11 very clearly that we know that that's evolutionary story going from fishes to land animals via these intermediate forms like tiktalik.

Speaker 11 So sharks don't have anything to do with evolving into land animals, but what they do tell us is the early part of the vertebrate body plan developing parts of the skeleton that would then carry on through to the rest of evolution, like developing backbones and paired fins and things like that.

Speaker 10 And such an important part of the story, of course, isn't it? The development of the backbone. One other question to ask after you mentioned it earlier, you mentioned migrations.

Speaker 10 So with this great diversity of shark types at this time, should we imagine that some species, maybe the more predatory ones, were they more solitary creatures?

Speaker 10 And were other ones, did they keep together in larger packs and were following kind of migratory movements? Do we get any ideas of that from the record?

Speaker 11 We get vague ideas about it, really, Tristan, because fossil sites are so rare to get whole complete sharks, let alone to get a massive sharks preserved as a fossil in one bed is very rare.

Speaker 11 We do get that with bony fishes different deposits around the world, but we know from some of these sites where shark fossils are common, like the Bear Gulch site in Montana that has yielded thousands of well-preserved fossil shark remains, that some sharks tend to be more common than others, which does kind of suggest that in one layer you can get an aggregation of sharks.

Speaker 11 And this is not unlike sharks today that many of them are solitary, but you'd have aggregations of large numbers of them at certain times of the year when there's abundance of of food resources around, like masses of hammerheads or rays all, you know, bonding together.

Speaker 10 John, are there any particular fossil discoveries of sharks that date to the golden age of sharks? And for you that are particularly special or particularly memorable?

Speaker 11 Most of my discoveries go back a little bit before that.

Speaker 11 I did discover, if I can jump back to the Devonian, my most comfortable time of life, I did discover a shark at Gogo, which is an incredible fossil site in the Kimberley, the northwest of Australia, where normally fishes that are 380 million years old are kind of squashed flat like kippers between rock.

Speaker 11 But Gogo, we get perfect three-dimensional skulls and brain cases and jaws, and sometimes even soft tissue preserved. The muscles have been preserved.

Speaker 11 I've even discovered embryos with the umbilical cord still attached to some of these fossil placoderms.

Speaker 11 But I did discover the first shark from that deposit that was ever found there after 60 years of collecting by the British Museum in the 60s and by me since about the mid-80s onwards.

Speaker 11 I've spent nearly 40 years collecting at that site and made many interesting discoveries, shall we say.

Speaker 11 But this particular shark, the first one found, had three-dimensional jaws and cartilage and teeth and shoulder bones. And basically, we discovered something that we didn't expect to find.

Speaker 11 We did some histology study on the actual cartilage, which was three-dimensionally preserved so we could etch it out of the rock, you know, with weak acid.

Speaker 11 And then we cut thin sections of that cartilage. And we found bone cells between the layers of cartilage, osteocytes.

Speaker 11 So it kind of showed that earlier sharks had a lot more bone in their skeleton, but as they developed this highly specialized kind of cartilage,

Speaker 11 they were getting rid of bone and they just had random bone cells here and there, but not an abundance of them. So that was a really cool, cool discovery.

Speaker 11 And we call that shark Gogo silicus, meaning shark from Gogo.

Speaker 10 And sorry, did you find in the similar context placoderms as well? So you almost have those two titans of the time up against each other?

Speaker 11 Yeah, I've spent a lot of my time working on placoderms and that's where we found the motherfish with the embryo in it that Martipisus Attenborough I that I named after Sir David Attenborough, which was the earliest evidence of sex in the vertebrate lineage.

Speaker 11 And Sir David, when I met him, was very happy about it, but he said now they'll always remember me for being associated with the origin of sex.

Speaker 10 We'll get you on for that podcast next where we explore more about the placoderms, I guarantee you that. After Megalodon, of course.

Speaker 11 Yeah.

Speaker 10 There is one particular expedition that I'd like to ask you about that you do mention also in your book, which is a venture down to Antarctica for a particular shark fossil.

Speaker 10 Now, can you elaborate on this extraordinary venture?

Speaker 11 Yes, well, I've had four expeditions to Antarctica over the last 30 years, but the one you're referring to, which is the opening pages of my book, is basically happened in 1991-92 in the early days when we still did big sledging expeditions.

Speaker 11 They don't really do that that anymore today. It's considered too dangerous and too difficult.

Speaker 11 But we had a sledge and we'd go to completely unknown territory and we'd set up a camp and we'd then climb mountains and look for fossils in the exposed layers of rock, you know, between the ice and the snow.

Speaker 11 And I had a very close call, almost falling down a crevasse on one of those expeditions, but I did get to the mountain.

Speaker 11 I was out by myself that day and I was looking at the geology of this area is known for fossil sharks' teeth collected 20 years earlier by an older geology expedition.

Speaker 11 And then a small avalanche tumbled down and hit me and rolled me in the snow, but it was only a small one.

Speaker 11 I got back safely to the camp and the next day we all went back, the whole expedition, all four of us, to get onto the mountain and collect fossils. But we used a crevasse probe.

Speaker 11 to walk through my footprints, tracing exactly where I'd been.

Speaker 11 And we found out that I'd actually walked over seven crevasses that day, the day before and only broke through one so I was very very lucky to be here but we did find lots of good sharks teeth once we got to the mountain so that would that was that was good and did those sharks teeth did some of those data in Devonian as well is Antarctica a good place for Devonian fossils it is indeed the reason why we go there is because there are no plants there is no soil it's just sheer rock and snow and when you get rock outcrop it's really clean and you can see exposures of rock for miles and miles and and find the fossils quite easily because you just see them there you know standing out in the layers so we collected a number of new species of sharks from there and it denoted a time when we studied it all in the lab i named a new shark from those teeth from that mountain portal mountain called portalotus and these teeth were huge they're up to like two and a half centimeters high indicating that even back in the devonian where that's a turning point where sharks went from being maybe half a meter to a meter in length to up to maybe three to four meters in length in those big river ways.

Speaker 11 That's a huge chunk of the time, right? Yeah, yeah. So that was a very interesting discovery.
And I wrote the paper on that and got to name all those new species from that expedition.

Speaker 10 Is it quite interesting? I'm sorry that we focus more on the golden age of sharks and less time on the Devonian, which is

Speaker 10 your biggest period. So we can certainly go back there a little bit now if there's anything we've missed.

Speaker 10 But is it so fascinating having a look at seeing those earlier steps where it almost goes from half a metre to a a metre, then evidence of going from a metre to two metres, and then it almost kind of explodes in the size.

Speaker 10 Is it fascinating looking at the fossil records to understand those kind of key jumps in shark evolution at the time of the Devonian and into the Carboniferous afterwards? It is.

Speaker 11 It's not just the jumps in size. Although you get these standout forms that are quite large, the vast majority of sharks in the seas at that time are still quite small.

Speaker 11 So it's not like you have suddenly all sharks get big. It's like you've got one or two that are big predators, but the vast majority of them are still about a meter or less in size.

Speaker 11 Until you get to the Carboniferous, then you start getting a large increase in the whole shark fauna getting bigger kind of thing. So the Devonian was a very interesting time.

Speaker 11 Sharks also occupied new environments for the first time, invading freshwater rivers and lakes for the first time, and going into deep water.

Speaker 11 And we know from certain sharks' teeth that only occur in the deep ocean basins, that they were starting to occupy the areas areas well away from the continental shelves.

Speaker 11 So up until this point in the story, most sharks were found in the shallow seaways where there was an abundance of food, abundance of invertebrates and fish and other things, but not much in the open oceans kind of thing.

Speaker 11 But yeah, we start finding their remains in deep water, deep ocean deposits, shall we say. So they're starting to expand out.

Speaker 11 And I think that's what saved them through those extinction events, that there were a whole range of different environments sharks occupied.

Speaker 11 So So these extinction events heavily hit the shallow seaways the most, the hardest. And so sharks could then repopulate from deeper water to come back in again.

Speaker 10 Yeah, so it's not this popular idea of, you know, when the extinction event happens, all of the sharks go deeper and they all survive.

Speaker 10 It's that there are certain strands of shark that survive because they've learned to adapt before that happens. And so they escape the worst effects of the well one of the mass extinction events.

Speaker 11 Yeah, and the other way is that when a mass extinction event happens, it might hammer the shallow seaways with anoxia, lack of oxygen and algal blooms that suck the oxygen out of those basins and things.

Speaker 11 But it wouldn't affect every single shallow seaway of the whole world. It probably just selectively hits a number of areas.

Speaker 11 There's always going to be patches where certain species will survive and then be able to repopulate back. And that's the way it seems to work.
Otherwise, everything would get wiped out.

Speaker 11 But, you know, certain things go extinct, but other groups just bounce back and eventually repopulate those vacant niches.

Speaker 10 I apologize, this is a slightly vague question, but before we completely wrap up, with the Devonian period, is there anything that we haven't covered so far that you feel is instrumental, is critical that we should talk about with these sharks and their rise and things that are really important to their story?

Speaker 11 Yeah, well, one of the most iconic Devonian sharks, which is known from deposits in Ohio and New York State, is called Cladosalaki. And it's known from beautiful complete specimens.

Speaker 11 We see these in museums. You can see them in the British Museum in London or virtually any big natural history museum will have them on display.

Speaker 11 And it looks like a typical shark, you know, like a typical modern shark.

Speaker 11 But we've just recently discovered that many of these fish that look, sharks that look like modern sharks living in the Devonian were not actually on the line to living sharks, but they were the beginning of that line going to the ratfish and chimyards.

Speaker 11 So the thing that when I wrote the book and I researched this whole topic very thoroughly, I spent four years writing this book, The Secret History of Sharks, that fundamentally it was a revelation to me that most of the sharks I thought were typical sharks were not.

Speaker 11 They were actually members of this early Holocephalan radiation going towards the ratfishes today.

Speaker 11 And that there's very, very few sharks in the Devonian that are actually on that line that lead to modern sharks.

Speaker 11 But Tenacanthus, the great big predator, was one of them, as was another common shark called Phebidus, which is mostly known from isolated teeth, but we have whole complete specimens of it from the mountains of Morocco at this time.

Speaker 10 So it's Tenacanthus, is it?

Speaker 11 Tenacanthus. Ct tenacanthus.

Speaker 10 Well, if you want a prehistoric jaws, you could do a tenacanthus versus the placoderms, right? You know, one of the great sea battles.

Speaker 11 That would be a great battle scene. In my book, I do reconstruct scenes where there are battles, and I have a giant Duncal osteus attacking some phytosalike sharks.

Speaker 11 And then I talk about what's the evidence we have for all these kind of interactions based on the fossil record.

Speaker 11 But throughout the book, I create lots of different scenes where we have these living snapshots of what was happening in our oceans at the time.

Speaker 10 John, this has been such a fascinating insight into the early millions of years into shark evolution, you know, from the Silurian and the Ordovician, as you say, with just scales into the Devonian and then into the Carboniferous with the golden age of sharks.

Speaker 10 Lastly, on that, do we know how long, if we can even say that the golden age of sharks lasts? Does it endure into the Triassic and Jurassic and the time of the dinosaurs?

Speaker 11 No, that's the biggest mass extinction of all time would come at the end of the Permian period, about 252 million years ago.

Speaker 10 And that's

Speaker 11 the boundary, the Great Dying indeed, the boundary between the Paleozoic era and the age of dinosaurs, what we call the Mesozoic era.

Speaker 11 And that's the first major mass extinction event that did have an effect on sharks. It did wipe out a number of shark and holocephalan groups.

Speaker 11 And so we see sharks are very subdued for about 140 million years after that extinction event. They're mostly small.

Speaker 11 They don't get very big. There's one or two species that might get to three meters in length, but the vast majority of them, you know, 99% of them, are under a meter in length.

Speaker 11 So they did still diversify into many different groups, but one group called the hybridonts took over most of the niches in the Triassic and Jurassic period.

Speaker 11 So that's a very interesting time in shark history because out of that group of hybridonts, we get the first of the Neo-Silarchians. And Neo means new and Silarchi means fish, shark.

Speaker 11 So it means the beginning of the modern lineage of sharks that would populate the oceans today. comes out bang in the Jurassic period.
So forget Jurassic Park. Jurassic shark is where it all happened.

Speaker 10 Jurassic shark, what a way to end this. And also a hint as to where we're going to be going in our next episode together, John.

Speaker 10 How long is it between, let's say, the golden age of sharks or even Jurassic shark and the megalodon, the meg that's arguably perhaps the most famous prehistoric shark of all times?

Speaker 11 I've got at least 150 million years from the Jurassic to the first megalodon, but sharks didn't have it easy during the Jurassic period or the Cretaceous that came after it because they weren't top dogs again.

Speaker 11 They were top dogs during the golden age of sharks and the Carboniferous and Permian, but then reptiles decided to invade the seas.

Speaker 11 And we get these big predatory reptiles, way bigger than any of the sharks, taking over the oceans. And sharks had a pretty hard time of it during that era.

Speaker 10 The rise of reptiles. I always think of walking with dinosaurs and like Pleurodon and so on and so forth.

Speaker 11 Yes, indeed.

Speaker 10 John, this has been really fantastic.

Speaker 10 Last but certainly not least, you have written a book about all of this in so much more detail, which is called The Secret History of Sharks, The Rise of the Ocean's Most Fearsome Predators.

Speaker 10 John, it just goes for me to say thank you so much for taking the time to come on the podcast today.

Speaker 11 My pleasure, Tristan. It's been a lot of fun today.

Speaker 10 Well, there you go. There was the one and only Professor John Long exploring the story of the first sharks millions of years ago before before the age of the dinosaurs.

Speaker 10 I hope you enjoyed the episode just as much as I did recording it. It was such a fun interview to do.

Speaker 10 And don't you worry, John will be back on the podcast very soon to continue the story of prehistoric sharks and the super predator that once lurked beneath the waves. The one and only Megalodon.

Speaker 10 Thank you for listening to this episode of the Ancients. Please follow the show on Spotify or wherever you get to your podcasts.
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