6. Dunkleosteus

Adele dives into the Devonian oceans to talk about the colossal armoured fish Dunkleosteus. An ancient apex predator about as big as a shark, with bone-crushing jaws. You're gonna need a bigger boat!

Plus tangents on coprolites and the accidental discovery of an ancient species of beetle from Triassic poop from Poland.

Links:
How Dinosaur Poop Got Its Name
What is a coprolite?

Dunkleosteus
Ecomorphological inferences in early vertebrates: reconstructing Dunkleosteus terrelli (Arthrodira, Placodermi) caudal fin from palaeoecological data

Feeding mechanics and bite force modelling of the skull of Dunkleosteus terrelli, an ancient apex predator

Giant, swimming mouths: oral dimensions of extant sharks do not accurately predict body size in Dunkleosteus terrelli (Placodermi: Arthrodira)

A Devonian Fish Tale: A New Method of Body Length Estimation Suggests Much Smaller Sizes for Dunkleosteus terrelli (Placodermi: Arthrodira)

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Transcript

Today on the show we are talking about the famous fish, Dunkleosteus. This episode we dive into the Devonian aged oceans, sink our teeth into placoderms, discuss the evolution of armor in fish and get down and dirty with claspers. 

Get ready to get wet 

Pals in Palaeo presents Dunkleosteus 

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This is Pals in Palaeo the show where we dive deep into the form, function and family groupings of your favourite fossils. 

I'm your host, paleontologist, PhD student and fish enthusiast Adele Pentland. You can stay up to date with me and the show by following @Pals in Palaeo on Instagram 

Ok, deep breath, and let's dive into today's episode. 

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Pals in Palaeo acknowledges Pals in Palaeo acknowledges the Traditional Custodians of the land throughout Australia, and recognises their connections to land, sea and community. 

We pay our respects to the Elders past, present and emerging, and extends that respect to all Aboriginal and Torres Strait Islander peoples today. This episode was recorded on Koa country and fossils of Dunkleosteus are known from parts of North America, Morocco, Belgium and Poland.

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Just wanted to quickly mention that the audio for one of our guests on today’s episode, Amanda McGee isn’t spectacular. It sounds like it’s been chewed up and spat out through a wormhole, but, we wanted to include it because Amanda has some really cool insights about Dunkleosteus so just bare with us on that. 

And I also just wanted to say thank you and acknowledge that this episode is a week late because I was at a conference. I was at Palaeo Down Under 3 which is something that I’ve been looking forward to for years and years, and I had a spectacular time but it also really threw my schedule out of whack, but hopefully, it’s been worth the wait and I hop you enjoy.

Random Fossil Fact 
Today I’m taking you to the Devonian, also known as the age of fishes and talking about one of the superstars from this time period, the famous armored fish Dunkleosteus. But before I start dunking on you, as is tradition, we’re starting this episode off with our Random Fossil Fact. It would be almost irresponsible of me to deprive you of this fact before we hear about Dunkleosteus.

Heaps of amazing palaeontology podcasts delve into the news and the discuss ground-breaking discoveries, but because there’s so much amazing research going on all the time, it’s easy to sometimes overlook some insanely cool discoveries. This is also just another excuse for me to info dump about palaeontology, but kind of zoom in and get into the nitty gritty details of something that’s a bit more obscure. 


Today's Random Fossil Fact is on the discovery of a new species of Triassic beetle, (wait for it) found in a coprolite.

We talked briefly about coprolites in episode 4, again, during the Random Fossil Fact, and if you missed that episode or haven't heard of coprolites before, they are a type of trace fossil, specifically fossil poo. We also talked about scanning coprolites in our bonus episode on VAMP, the Virtual Australian Museum of Palaeontology, with special guests Dr Aaron Camens, Dr Alice Clement and PhD candidate Jacob van Zoelen.

Getting back to coprolites though, I thought I remembered hearing in undergrad, that coprolites got their name when one scientist was being kind of petty and mean to another scientist. And as it turns out, that is FALSE.

Just a quick tangent here on the etymology, or the origins of the name coprolite, you might have heard of The Bone Wars and the famous rivalry between two toxic men Cope and Marsh. They absolutely HATED each other, and they both went to great lengths to throw shade, spill tea and sabotage their rivals research. It got pretty intense and was definitely a very bitter rivalry. 

If you want to hear about Cope and Marsh, these two pioneering but super problematic palaeontologists, I highly recommend episode 250 of I Know Dino. If you like facts on dinosaurs, that’s a great podcast to listen to. I've listened to hours of their show and also been a guest on that podcast a couple times now. Sabrina and Garret also visited the Winton area in 2019 so I got to meet them in person at our museum and hang out with them afterwards, and they are true dinosaur enthusiasts. 

Episode 250 is Sabrina's summary of the spat between Marsh and Cope is incredibly thorough and a solid 2 and a half hours long. So if you like listening to long podcasts, while you go about your day, that’s a great one to listen to. I'll have a link to it in the shownotes, along with other podcast recommendations and specific papers mentioned throughout this episode. 

Getting back to Marsh and Cope, it's tempting to think that Marsh named fossil faeces after his rival, to besmirch his name, and basically give him a crappy reputation forever and ever. Again, it sounds kind of convincing and honestly on brand for how much these two hated each other, but it is not true.

Coprolite, has Greek origins and is based on two words: 'kopros', which means dung, and 'lithos', which means stone. The person who coined the word coprolite was in fact, William Buckland, an English geologist and palaeontologist who is credited for writing the first description of a dinosaur fossil when he named Megalosaurus. He was working on stuff before Marsh and Cope's time so again, the name coprolite, isn't related to their famous feud.

Coprolites come in different shapes and sizes. If they're more spiral-shaped, then there's a chance that it belongs to a shark or other fish, since they have spiral-shaped intestines. Another random fact for ya. They come in other shapes too but I’ll leave it up to you to use your imagination.

Coprolites are incredibly useful trace fossils, since they can reveal clues as to how different species in an ecosystem interacted with one another. Normally it's almost impossible to work out that kind of information and reconstruct potential food webs from the fossil record.

But, if you look through a coprolite, you can find undigested material: if that animal was a predator, you can find bits of bone shards, and fur. Similarly, if an animal was herbivorous and mostly ate plants, depending on the efficiency of its digestive tract, you can find remnants of whatever it was eating, or plant-shaped voids.  

Coprolites can also contain parasites and their eggs, as well as bacteria, and fungal remains, which again, are incredibly rare in the fossil record. 

By the way, if the idea of studying coprolites is grossing you out, rest assured they don’t smell. At this point, they're basically rocks. While I’m no microbiologist, the surface of a coprolite probably has about as much bacteria, as your phone does. 

Getting back on track to discuss the actual science of today's Random Fossil Fact, a team of scientists studying coprolites wanted to see if there was anything interesting inside them and accidentally discovered a new species of extinct beetle from the Triassic. 

This beetle looked a little worse for wear, but it still had its legs and antennae attached. It was essentially on par with insects preserved in amber, which is absolutely incredible, when you consider what this insect went for a rollercoaster ride through the guts of another animal and out the other end! 

The paper is titled "Exceptionally preserved beetles in a Triassic coprolite of putative dinosauriform origin" and that was published by Martin Qvarnström and colleagues in 2021 in Current Biology and that paper is free to access.

Just to be clear, this isn't the first record of an insect in a coprolite, but it is the first insect species named from fossil faeces. And of course this means that there might be more species of insects discovered from coprolites in the future. 

Getting back to the specific details of this study though, these beetle remains were identified when the material was scanned at a Synchrotron. 

The scans are similar to x-rays in that show what's going on inside a fossil. More accurately a Synchrotron is like a CT scanner at a hospital, but they are able to detect really subtle differences in density and produce hi-res images. 

And in case you’re wondering HOW a Synchrotron works, it scans objects by accelerating particles in a massive loop, and focusing a beam of energy at the test subject. I should also add, Synchrotrons are massive. The whole building is shaped like a massive donut and everything else is built onto it. At least, that's what the Synchrotron in Melbourne is like. There are other facilities like this in other places around the world, and synchrotrons can be used to help study all kinds of fossils, everything from specimens in limestone, to amber and in this case, fossil poop.

You're probably wondering at this point: “if these paleontologists discovered an almost-complete beetle, how big can this turd be?!” Well, it's actually not that big. The coprolite at the centre of this study was actually a partial poop about 2cm in diameter which is... little over three quarters of an inch. And just 1.5 cm long, so just over half an inch in length. 


But good things come in small packages: Inside that one fragment of fossil faeces, they found tons of beetle fragments, and relatively complete individuals too. Most of the fragments were elytra which are the tough shield-like coverings that protect the flight wings in most beetles, as well as other bits and pieces. If you’re struggling to imagine what elytra are, think of a ladybug with their spotty wings. Those are elytra and they cover and protect a second pair of wings, which are used during flight.

So, in this coprolite, there were 9 good specimens, and out of those, 2 were almost complete beetles with their antennae still attached. These beetles were just 1mm long, so they're absolutely tiny. 

The team of researchers named this beetle Triamyxa coprolithica. The species name, coprolithica is obviously a reference to the discovery of this insect inside fossil poo and Triamyxa is a portmanteau, so it’s a combination of the words, Triassic, which is the time period this little bug came from, and Myxophaga which is the suborder this insect belongs to. 

Modern day members of the Myxophaga are also incredibly small, and aquatic to semi-aquatic mostly feeding on algae.  

It’s nothing short of a miracle that the near-complete beetle specimens survived the trip through the digestive tract of another animal, but those fragments I mentioned before? They came in clutch and helped Martin Fikáček, a co-author on the paper and expert in modern beetles, determine that this was a new species of fossil beetle, AND the taxonomic family it belonged to.


Beetles, like other insects and arthropods have an exoskeleton. Essentially, they walk around wearing a suit of armor. The bits that make up a beetle's exoskeleton, are called sclerites, and are kind of like the plates that make up a suit of armor. 

As it turns out, beetle experts define different species based on the sclerites. And since the coprolite had a lot of different examples of sclerites, this really helped Martin Fikáček, piece everything together, plus he was able to then compare these against the almost complete beetles. 

Now, for the skeptics out there who might be wondering “well, could this beetle be behaving like the modern day dung beetle?”, you’ve got a good point, and this was actually something raised during the peer review process. Peer review by the way is when you get other scientists to check your paper for scientific accuracy, every scientific paper goes through this process and it happens before the research is posted online and is announced to the press.

So this team of researchers is confident that the beetle inside this coprolite was digested, because there's at least 50 fragments of the same species, and most of these are pretty badly broken up. Which is what we'd expect to see for stuff that's been eaten by another animal. On the flip side, if these beetles had crawled into that poop after it came out the other end, we'd expect to see more whole specimens of this beetle, and potentially, fewer of them.

The coprolite is from the Late Triassic, about 230 million years ago from southern Poland. So at this time there are dinosaurs, but they haven't diversified and really taken off yet. And if we zoom in, at this particular locality, there aren't many dinosaurs, but it’s believed that Silesaurus probably made the coprolite in question. 

Silesaurus by the way is a bit of a contentious character, depending on who you ask it's either: a dinosauriform, so not actually a dinosaur but very close to that lineage, or, a very early, basal dinosaur. 

According to lead author Martin Qvarnström, Silesaurus was probably omnivorous and would've eaten other things aside from beetles.

If you’re keen to learn more about this research, you can check out episodes 127 and 128 of Palaeocast, which features interviews with two of the palaeontologists on that paper, Dr Martin Qvarnström and Dr Martin Fikáček. Palaeocast is another great paleontology podcast that has experts on to talk about their research, and if you want to hear more from me, there’s a Palaeocast episode with me on Ferrodraco. 

If however, you’ve been waiting patiently to hear me talk about Dunkleosteus, don't go anywhere, because I’m about to give you the facts on the form, function and family grouping of this fantastic fossil fish.



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So If this is your first time listening to Pals in Palaeo, we talk about fossils through the lens of Form, Function and Family Grouping. And then I normally sneak in some pop culture references at the end. 

Before we get into all that, let's talk about some basic info first, and set the scene a little bit.

This is normally the part of the show where I would mention how old Dunkleoseus is in years, but since there’s 10 species within this genus, the waters are a little murky, but, we’re swimming around the geologic time period spanning 382–358 million years ago. 

Like I said before, we’re hanging in the Devonian today, which is also called the age of fishes. That’s not to say there weren’t other cool things alive during this time period, but the oceans were absolutely popping off during this time and the diversity of fossil fish is at an all time high.

The Devonian is the period in earth history that gave us ammonites which persisted for millions of years and I’ll undoubtedly cover ammonites in future episodes, but, during the Devonian, the continents looked completely different compared to today, and life on the land was starting to heat up: we see vascular plants, plants out of water and on the land form the first forests in the Devonian. They’re soon followed by arthropods which explode in numbers and species diversity during the Devonian. And it wasn't long before arthropods were terrorised by amphibians who also came onto the scene during the Devonian. 

So, there's lots of cool stuff going on during the period in Earth history, but today we're going to get the facts on fish.

And as far as ancient prehistoric fish go, Dunkleosteus is kind of a big deal. It's a type of placoderm, which I'll touch on later when we talk about Family Grouping, but for now, all you need to know is that there are ten species in this genus. The most famous species belonging to this genus, is Dunkleosteus terrelli. There’s a lot of buzz surrounding this species in particular because it’s absolutely massive, not just for the genus, but compared to fish in general including modern day sharks. 

Dunkleosteus terrelli is also the state fossil for Ohio in the US, and has been since March 2021, so again, it’s another fossil emblem birthed from the absolute mess that was the COVID-19 pandemic. 

The name Dunkleosteus literally means, Dunkle's Bone. Osteous means bone, which you might recognise from the word osteoderm which means bony skin, and Dunkle as you might have guessed is actually someone's name. 

Dunkleosteus was in fact named in honour of David Dunkle, a former curator of vertebrate paleontology at the Cleveland Museum of Natural History, in Ohio. 

Even though there are 10 species within this one genus, just assume that I'm talking about Dunkleosteus terrelli, just to keep things nice and simple and because there is some cool research that I want to discuss a little bit later.

You’ll also be hearing from two guest experts on this episode, both from the Cleveland Museum of Natural History in Ohio, in the United States. They are Amanda McGee, the collections manager in vertebrate palaeontology, and her colleague, the assistant curator of vertebrate palaeontology, Dr Caitlin Colleary. 

Again, the Cleveland Museum of Natural History is the museum that David Dunkle worked at, so it was a no-brainer to have Amanda and Caitlin talk to us about this incredible fossil. Plus they have a bunch of fossils of Dunkleosteus on display and in their collections, and in there collections and some new displays planned for the future.




FORM


For now let’s focus on the Form of this fossil fish, and discuss the shape of its body, and the all important size, because I did tease before that this is basically one of the biggest things in the oceans during the Late Devonian.

Like modern fish today, and a bunch of other marine creatures Dunkleosteus has a torpedo shaped body. This is a case of convergent evolution, which is when things that are unrelated evolve similar adaptations. So from the outside, two things look the same on the outside, but when you “look under the hood”, or at their skeletons, they are actually quite different. I’ll also talk about this later in Family Grouping but Dunkleosteus isn’t related to modern fish either, it belongs to a group that is now completely extinct, with no modern day descendants.

Dunkleosteus would have had fins, including a dorsal fin on its back, a caudal fin or tail fin, pectoral fins which are what we think of as its arms for lack of a better word, and possibly more fins but long story short, we don’t know. 

You might also be wondering, well is the tail kind of asymmetrical like a shark, or is it crescent-moon shaped like in tuna and swordfish? Again, we just don’t know.

That’s because Dunkleosteus fossils are often just the head and shoulders, and the rest doesn’t preserve. I wanted to make sure I didn’t get it twisted, so let's bring in the experts.

Caitlin: I am Dr Caitlin Colleary, I am the associate curator of vertebrate palaeontology at the Cleveland Museum of Natural History, and I didn’t know who Dunkleosteus was until I started working here. But I have very quickly become obsessed by looking at all of the fossils we have here in the collection and going out looking for more.

One of the many things I asked Dr Caitlin Colleary about were her thoughts were on the size and what the rest of the body looked like and again, but as she points out, without any direct evidence, it’s really a mystery just waiting to be solved. 

Caitlin: We don’t really know! I think the short answer is we don’t really know what the rest of Dunkleosteus looked like, we only find their heads preserved which were bony plates so they preserve really well, the rest of their body was cartilaginous. Estimates of the length of Dunkleosteus range from 4 to 10 metres, so it’s an absolutely huge range and it’s because we just haven’t found their bodies preserved and this group of fish is extinct and we really don’t know exactly what they looked like. So, there have been some ideas about how big it was or the rest of its body looked like but until we actually find its body preserved, we really can’t say for sure.

So in terms of the maximum size of Dunkleosteus, there’s still a bit of mystery surrounding the size of this colossal fish. 

Just this year alone there’s been at least two papers published, trying to grapple with this research question: just how big was this fish?

One of those was published by Russell Engelman​ in PeerJ, which is an open access paper, and they wanted to see whether sharks were something that could be used to accurately determine the size of the ancient armoured fish, and the bigger group Dunkleosteus belongs to.

So in the past, the jaws of Dunkleosteus were found, and then they estimated the length of the body, as if it were a shark. But since sharks aren’t modern day descendants of the arthodire, this might not be the best idea? 

Anyway, to work out whether it gave accurate results or not, Engelman applied this method to arthodires that are complete, and basically this study wanted to verify whether this actually worked. And as it turns out, it’s not that great… 

The article was titled “Giant, swimming mouths: oral dimensions of extant sharks do not accurately predict body size in Dunkleosteus terrelli (Placodermi: Arthrodira)” I’ll pop a link to that paper in the shownotes, but yeah, they found that Arthrodires, these ancient armoured fish have proportionally larger mouths than sharks, and they’re actually more similar to catfishes. 

Russel Engelman also published another paper that came out this year, and yes, I realise that this now sounds like a Russel Engleman fan podcast, but, they then came up with a solution to this problem of, well “how do we accurately estimate the size of Dunkleosteus now?” 

So they came up with a mathematical equation, to estimate size and they put this together using multiple different species of arthrodire, as well as some modern fish, in total, they made 3169 observations, and included 972 species in their study. 

Basically, what they worked out is that if you can pinpoint the position of where the eye was in the skull, which is called the orbit, and then measure the distance between the orbit to where the gills sat, you can work out body length. 

And then they used some math to backup this equation by working out the statistical significance and quantify using numbers that yes, this is pretty reliable.

And if you want to check out that paper, it was called “A Devonian Fish Tale: A New Method of Body Length Estimation Suggests Much Smaller Sizes for Dunkleosteus terrelli (Placodermi: Arthrodira)”

And that was published in the Multidisciplinary Digital Publishing Institute, which is abbreviated to MDPI.

So based on that 2nd paper, Dunkleosteus terrelli, which again, is like, the biggest species in this genus. Adults would been about 3.4 m which is equal to 11 feet or so. So overall, suggesting a somewhat chunkier body for this Devonian aged fish. So less of a cigar shape, and more like a nugget, with fins.


The whole situation is kind of like, why we don’t know a lot about fossil sharks, because we only find teeth. Sharks are mostly made up of cartilage, but their teeth are made from the usual stuff which is dentine, so they’re a lot harder and can be fossilised a lot easier. 

Same same with Dunkleosteus, the skull is made of bone and there’s other bony plates around that near the shoulders, but beyond that, the rest of their body was made up of cartilage. 

If you’re not familiar with cartilage by the way, just touch the tip of your nose, that is made up of cartilage, so it still holds its shape, but it’s not as hard as bone. Like you can smoosh it a decent amount and it’ll just bounce back.

Anyway, all this to say that scientists actually have no idea what body length is FOR SURE, but also the shape of the fins on Dunkleosteus. There’s been a bit of guesswork, and as it turns out, most of the palaeoart depicting Dunkleosteus is based on a close cousin, called Coccosteus. 

We know a lot more about Coccosteus purely because complete fossils of this fish have been found, as Amanda McGee from the Cleveland Museum of Natural History explains:

Amanda: So most of the reconstructions you see of Dunkleosteus are based off of another placoderm that is preserved, called Coccosteus. So Coccosteus is a little, much smaller fish with the head plates are preserved and as well as the soft tissue and the rest of the body. It’s a fish that’s been found in Scotland and other places in Europe. So a lot of the reconstructions on the tail shape and the fin shape are based on this other placoderm, one that’s preserved.
However, Coccosteus was a lot smaller and it lived in freshwater, so there’s been debate as to whether it had the same fin shape as Dunkleosteus, but it’s the best-preserved placoderm that we have to date.

This happens a lot in palaeontology by the way, since the fossil record is often incomplete, you need to connect the dots as it were and fill in gaps, make educated guesses and estimate what the rest of the animal looked like, based on other organisms in that group. Which is fine, 99% of the time but every now and then you get a weirdo that just defies all logic and reason. 

Anyway, even though we don’t know for certain how long or big Dunkleosteus was, we can learn a lot about how it lived, based on the fossils we do have.


What puts Dunkleosteus head and shoulders above all other fish species, is the bony armour that makes up its skull and shoulders. Not only does this protect Dunkleosteus from predation, but it’s jaws are highly modified, to the point where the lower jaw bone is basically a DIY knife. What is mean by that, is

Placoderms lacked teeth but possessed dermal bones associated with the jaws known as gnathal bones, and there’s a silent ‘G’ at the start of gnathal, and these differ from the teeth you and I have because our teeth are in sockets, also known as alveoli, whereas these gnathal bones are more like bones, pretending to be teeth if that makes sense. It’s all connected together, it’s bones, doing their best impersonation of teeth. And by the way, this has evolved independently in other groups, of the top of my head there’s Pelagornis which is an extinct pseudo-toothed bird which had a beak with these spikes arranged almost like teeth which it probably used to help catch fish.

Rather than having a series of spikes, Dunkleosteus kind of had these fangs instead which were obviously, still super effective and got the job done.

Caitlin: I always like to say that they basically made their own teeth, because they didn’t have teeth.
We think about teeth, they sharpened their jaw bones which is just a wild thing for an animal to do, and they also had an incredibly hard bite, and a very fast bite, so it was definitely not a fish that you wanted to run into, in the ocean.

Yeah, not gonna lie it kind of looks like a fish dressing up as Dracula for Halloween, like, those fangs aren’t massive but they’re still giving vampire energy, in my opinion. 

And the final point I want to touch on, since we’re talking about the form of Dunkleosteus is that it probably had something claspers! We don’t have direct fossil evidence for claspers in the genus Dunkleosteus but this was something other placoderms and fish in this group called arthodire had, so it’s pretty well accepted that the same is true for Dunkleosteus.

I feel like I’ve spent ages talking about the form, trying to paint you a word picture so you get an idea of what this sea beast looks like, and I don’t want to bore you so let’s now pivot to talk about Function. What exactly is it doing with its body, and how does it fit into the bigger picture, what’s its role ecologically in the Devonian Ocean?


FUNCTION 


The million dollar question right now is: if Dunkleosteus had these incredible jaws made for chomping, how good can it bite? And more importantly, how can you look at the bones of an animal, and work out how strong the jaws were and how do you measure bite force?

Gooood question, so if you’ve done a little bit of physics, you might remember that force is measured in Newtons, which of course, is named after Sir Isaac Newton, and if you combine the mass of an object with how fast it’s accelerating, the product of that equation, is force.

So, in terms of bite force, a bigger animal has a larger mass, but the secret ingredient to a strong bite is moving quickly. Of course this would also put you at an advantage since you’d have the element of surprise and potential prey would have less time to get away, BUT on top of that, you can actually crunch through bone, if your fast enough.

And it looks like Dunkleosteus would have been able to bite through things like other armoured fish and bite through their bony plates, as well as the shells of things like ammonites and arthropods. 

They did this with something called a four bar linkage system, which is a term that pops up in machinery, and robotics, and basically you have four bars connected by four links, there’s different types, that move in different ways… but yeah, as it turns out you can also study fossils from this same perspective to understand how things move and the physics behind them.

Just FYI, I am not good at biomechanics and studying how fossils move. In fact, Physics was my worst subject in Year 12! It didn’t help that the boys in my Year 11 class constantly bullied me, because I was the only girl in my class but yeah, it’s not something that I’m naturally good at so I don’t study fossils from this angle.

And it’s quite complicated! It’s not like, you 3D scan the fossil though and a computer program does all the work, you still need to look at the fossil and work out where can pinpoint where on the bone muscles attached. But once you map out where the muscles connected, and compare these with modern day animals to estimate the thickness of that muscle, then you can work out bite force.

So bringing this back to Dunkleosteus, yes it was probably one of the largest fish during the Devonian, but the fact that it was able to rapidly move its jaws, that was key to the success of this fossil fish.

There’s a couple different papers that have studied the bite force of Dunkleosteus terrelli, but part of that equation is the total length of the body, which, as we’ve touched on in this episode can vary anywhere between 4 to 10 metres, depending on who you ask, which is 13 to just shy of 33 feet.  

So the numbers vary a little bit, but it looks like bite force is strongest at the back of the mouth, or the rear dental plates, compared to the tip of the jaw. And I’m just gonna read a little bit from one of the scientific papers I looked at, it says:

“Jaw closing muscles power an extraordinarily strong bite, with an estimated maximal bite force of over 4400 N at the jaw tip and more than 5300 N at the rear dental plates, for a large individual (6 m in total length). This bite force capability is the greatest of all living or fossil fishes and is among the most powerful bites in animals.”

Again, like I said though, the bite force gets bigger in larger sized animals, so if Dunkleosteus was bigger than 6 m or 20 feet long, it would have an even stronger bite.

By the way those numbers were pulled from:

“Feeding mechanics and bite force modelling of the skull of Dunkleosteus terrelli, an ancient apex predator”
And that was written by Philip Anderson and Mark Westneat and, published in Biology Letters in 2007, and it’s in open access if you want to check it out.

So Dunkleosteus has a strong bite, and even though the numbers vary a bit, it has a bite more powerful than a hyenas. Since Hyenas have a reputation for being able to crush bone, just about everything would've been on the menu for Dunkleosteus. So that would mean that it’s an apex predator! Since nothing is hunting Dunkleosteus and it’s in what most would consider the best position in the food web. Well… for an adult anyway. 

I’m guessing that if Dunkleosteus ate other placoderms, as in other armored fish, there might have been some cannibalism going on.

But Dunkleosteus not only had these funky jaws, they also had armor protecting their heads, which is great because that’ll protect the brain, as well as their shoulders but the torso and tail aren’t covered in bony plates. 
I think this is actually really clever and a good trade-off, because it offers protection but isn’t too bulky so you can still move around with ease and have a bit of speed.


Especially if the movement of the tail is really important for moving through water.

And the final thing I want to talk about in terms of Function, are claspers. I mentioned them before, but didn’t say what they were used for specifically…

I have done my best to not swear on this podcast and keep it rated PG but I can't not talk about Dunkleosteus without talking about sleeping with the fishes. 

Not how the Mafia define it, but the way Troy McClure defines, sleeping with the fishes. Things are about to get hot and steamy up in here so if you don't want to hear how fish get down and dirty or you don't want to answer uncomfortable questions from your kids, feel free to skip the next couple of minutes because we are gonna be talking about claspers. You've been warned. 

So, when I was studying second year biology I was shocked to discovered that some fish are viviparous meaning they give birth to live young. Meaning that there's internal fertilisation in some species of fish. Which just goes to show how little I knew about fish back then.

Now, you might be wondering, "how do they pull it off when they're in water?". Good question. 

That's where claspers come in.

The PG explanation is that… OK just imagine 2 ships and they’re next to each other. Or maybe submarines is better in this analogy. The point is, claspers kinda stabilise the two vessels and allow passengers from one ship to hop onboard the other. 

This is why I shouldn't be a sex educator, because I'm talking about the birds and the bees, but I've complicated things with fish and ships. This might be the first and last time I take about reproductive organs on the podcast. *** And If you are relying on me to accurately explain how reproduction works, don't. 

Anyway, this is kinda what modern sharks do today but with similar structures, which have evolved independently in what is known as convergent evolution. Convergent evolution is kinda like when you and someone else come up with the same idea and you both get in trouble with your teacher, even though it was just purely a coincidence. 

Feel like there's a lot of convergent evolution, especially in the oceans but normally it affects the overall shape of the body but there you go. A hyper specific example, that absolutely no one asked for and may even result in some complaints. We’ll see how we go. 

And on that note, let’s move on from Function and talk taxonomy with the Family Grouping.

- - - 

Family Grouping 

Dunkleosteus is a type of fish, but it doesn't belong to any of the modern groups. It is in fact a type of placoderm, or armored fish.

Since this is also our first time on the podcast talking about a fish, and we’re discussing taxonomy, I am obliged to tell you at this point that there is no such thing as a fish. Even though, yes, you probably know what a fish is. You know where to find them, and if you ask a small child to draw a fish, they’ll hopefully draw a blob with at least a tail fin, possibly a dorsal fin, and maybe gills for good measure.

But fish aren’t monophyletic, which is something I’ve mentioned before when talking about reptiles. If we included the descendants of fish, that would include you and me, dinosaurs, mammals, birds, amphibians… you get the picture. Just about every other vertebrate living on land shares a fish ancestor.

No matter how hard I try though people don’t like it when I call them a fish, so for all intents and purposes, we’re going to use fish in a casual sense, but yeah, just keep that in mind going forward. Don’t forget your roots and where you came from, OK?

Before we talk about Dunkleosteus specifically, I also just want to quickly run through the types of fish we find today. Broadly speaking, there are two major classes: Chondrichthyes and Osteichthyes.

Chondrichthyans are cartilaginous fishes, so things like Sharks, skates, rays and sawfish. So rather than having a skeleton mostly made of bone, most of the skeleton in these fishes is made up of cartilage, but there is still some bone in the body. And just to clarify, the ancestral condition is a bony skeleton, but sharks and skates have opted to use cartilage to build their bodies, since it’s lightweight but still strong. Generally speaking, these fish have five to seven pairs of gills, which are exposed. So if you see one of these in an aquarium, you can easily see their gills on the side.


As the old saying goes though, there are plenty of fish in the sea and 
The other type of fish are Osteichthyes which are bony fish. The most obvious difference between the two is that osteichthyes have proper bone throughout the body, so their skeletons are like ours, but they also differ from cartilaginous fishes in that they have something called an operculum. This is a flap that protects their gill slit, which is super important because this is how they breathe and get oxygen out of the water. Cartilaginous fishes don’t have the flappy operculum, OK?  


Getting back to the Devonian though, there was a huge variety of fish, hence why it’s sometimes called ‘the Age of Fishes’. The first osteichthyans and chondrichthyans pop off in the Devonian, but there were also jawless fishes (which includes things like hagfish), and armored jawless fishes. The most famous group of fish from the Devonian though has gotta be the placoderms, which is the class Dunkleosteus belongs to. 

And then, if we zoom in, within placoderms, there’s another group called Arthodira, and that’s another group that Dunkleosteus fits within.

Adele: Now, I’ve been a bit slack with your subliminal Latin lessons, but in case you were wondering what Placoderm means, derm means skin and plac or plax means flat, so together the word placoderm actually means “flat plates”

The earliest placoderms are from the early Silurian, and there are currently over 200 species of placoderm identified from the fossil record, but this group went extinct at the end of the Devonian, roughly 358.9 million years ago. 

I just want to highlight something here: there was more than one extinction event in the Late Devonian, but the one that was the last straw for placoderms and wiped them out, once and for all was the Hangenberg event, also referred to as the Hangenberg crisis. 

Placoderms actually survived an earlier mass extinction in the Late Devonian, called the Kellwasser event (I’m guessing it’s German? It looks German so I’m pronouncing the W as a V, I hope that’s correct). Then, another 13 million years later, the oceans were depleted in oxygen and honestly that’s how a lot of marine species get wiped out during mass extinction events because like us, they need to breathe oxygen, it’s just that they get their oxygen from water and we get ours from air. 

Amanda: So one of the really cool things about Dunkleosteus and the other fish fossils we find in right in Cleveland is they preserve an ecosystem right before one of Earth’s major mass extinctions, so right before the Devonian mass extinction about 350 million years ago and Dunkleosteus was the top predator was wiped out, and all the other fish were wiped out. And because of that, well sharks survived the and then sharks were able to go on and diversify and get much larger than they had previous, and that never would have happened if that mass extinction hadn’t happened then and Dunkleosteus was wiped out.


Adele: The poor placoderms had to deal with low oxygen levels in the oceans as I mentioned before, but on top of that, they also had to deal with global cooling and glaciation which extended down to the south pole, so for species that are adapted to living in warmer waters, there was no escape.

Within the Placoderms, Dunkleosteous belongs to the order Arthrodira which were originally thought to be bottom-dwellers, living life in the slow lane but athrodirans have torpedo shaped bodies that are built for speed. 

And you might be thinking that they were all sort of predatory, but as it turns out there a bunch of different ecological niches that these fish filled during the Devonian. Here's Dr Caitlin Colleary to tell us a little bit more about some of the other fish in the sea.

Caitlin: Yeah, and there were a lot of other fish related to Dunkleosteus that were around at the time and I think that Dunkleosteus gets a lot of the lime-light, and the other arthrodires are in the background, a little bit, but there were other weird bony armoured fish back then too living with Dunkleosteus. And they were in every niche and some of them were slower-moving shell-eating creatures, there was a big filter-feeding fish called Titanichthys that was Dunkleosteus-sized but was more similar in personality to a whale shark, so it was just a filter-feeder, hanging out. So Dunkleosteus was a super cool fish but it was also part of an ecosystem and there were a lot of other cool fish at that time too.

Adele: If we zoom in, Dunkleosteous belongs to Pachyosteomorphi which are interpreted as open ocean fish and long-distance swimmers, which ties in with the extensive geologic record for this genus. I mentioned at the beginning of the show that fossils of Dunkleosteous are known from parts of North America, Morocco and parts of Europe so their active lifestyle helped them disperse to new areas and be successful across different parts of the world. 

Now we’ve known about Dunkleosteous for 250 years, so, unsurprisingly, the family and superfamily are both named for this fish. So, Dunkleosteous belongs to the superfamily, Dunkleosteoidea and the family, Dunkleosteidae. If this podcast thing doesn’t work on, maybe I’ll start a YouTube channel where I pronounce scientific names and then give that up.

Speaking of YouTube, let’s wrap things up and talk about where else you can learn about Dunkleosteous and how this fossil fish has influenced popular culture.


- - - 

To round out the show, I’ve searched high and low across the Internet for video games, TV shows and other media featuring our fishy friend: Dunkleosteous. I guess if we want to stay on theme with the Form, Function and Family, this is the Fandom section? Am I using this word right? I don’t know sometimes, as I get older my understanding of stuff like that gets worse and worse.

Anyway, first thing’s first, I am a mad Animal Crossing fan, have been since it came out on the Gamecube, and since the very beginning you can dig up fossils in that game. There’s also always been a museum in your town where you can donate fossils to, which again is pretty cool when you start donating stuff in game and can see it on display. There is, a Dunkleosteus in the latest incarnation of the game, Animal Crossing New Horizons which you can play on the Nintendo Switch. 

I mentioned at the start of the episode that Dunkleosteus is the state fossil for Ohio, and that there’s 10 species within this genus, but I reckon the Dunkleosteus fossil as it appears in New Horizons is based on Dunkleosteus terrelli. The reason why I say that is it’s a dead ringer for specimen CMNH 5768 from the Cleveland Museum of Natural History. Chances are, if you’ve seen a replica of the Dunk at any museum, it’s based off this one fossil.

Getting back to the game though, in New Horizons, some fossils are made up of multiple pieces, as in there’s a T rex head, torso, and tail... But there’s just the one Dunkleosteus fossil, so once you find it, you can hear a bunch of facts about it from Blathers the curator of the museum in the game who is a great horned owl.  

Speaking of Blathers, if you want to hear what Blathers has to say about Dunkleosteus, I highly recommend you check out the podcast Beyond Blathers, hosted by Olivia deBourcier and Sofia Osborne. 

They've done an episode on this armored fish and on other episodes they cover the fish, insects and fossils that appear in New Horizons, so if you love that game and want to learn about science, check it out, it's literally a match made in heaven.
 
By the way, having done a guest episode on Beyond Blathers, I can tell you hand on heart, Olivia and Sofia are some of the sweetest science communicators you'll ever meet, when we recorded our episode it literally just felt like hanging out with friends and talking about science. 

It was so much fun. And if you want to check out our conversation which was on amber, just search for Beyond Blathers, Amber, Adele Pentland and it'll pop up. Otherwise, it’s in the show notes along with the other podcasts I’ve mentioned today.

-
In terms of other video game references there is a Dunkleosteus Pokémon... but, wait, there’s more. 
So in the eighth generation of Pokémon, Sword and Shield which is loosley based on the UK, there are fossil Pokémon. 

This is something Pokémon's explored since first gen, I mentioned it in our episode on Anomalocaris but in case you missed all that, you can find fossils as items, but you revive these and have fossil Pokémon join your team. Cool concept right? Very, very 90's because at that point there was this zeitgeist surrounding fossils and extracting DNA from fossils, following the success of Jurassic Park. 

In Pokémon Sword and Shield, they played around with this concept so instead of finding a complete fossil, you were then set with the task of combining two halves together. 

Which is again, fine, that's how palaeontology is a lot of the time? What makes me salty though, is that there are no right answers, and you end up with these Frankenstein creations and dumbass Pokédex entries, trying to explain why these creatures went extinct. 

The closest you can get to a Dunkleosteus Pokémon is Dracovish, which like a reverse mermaid with a fish head but then a dragon body, or Arctovish which is all fish but still messed up because the head is upside down and facing the wrong way. 

I'm gonna be really real here: I hate this concept so much I was geared up to buy Pokémon Sword and Shield, found out about the mechanics of fossil Pokémon in this game and went: yeah nah. Do not want. 

I don't play a ton of video games, I used to when I was younger but between you know running the farm and doing my PhD, a full on RPG is a big time commitment so I'm super picky about what games I get into these days. 

And if I'm gonna invest in a game, I want to enjoy every second of it. You know, if I’m trying to chill and relax, I don’t want fossils to become the butt of some sick joke. Like, this is gonna sound super cheesy, but palaeontology is one of the things I love most in the world. I can’t even describe how grateful I am that I get to study ancient life and uncover their secrets. Especially because, after I finished my Honours degree I thought I would never get to do a PhD. But that’s a story for another time.

Getting back to Pokemon though, they could've made it so that if you pieced together the fossil incorrectly, the revival process didn't work. I could get behind that. But the fact that, you have these straight up, dumb Pokédex entries trying to explain why this thing went extinct? It literally makes me so mad. 

Listen to this one for Dracovish:
*clears throat*
“Its mighty legs are capable of running at speeds exceeding 40 mph, but this Pokémon can't breathe unless it's underwater.”
What a mess… And the one for Arctovish isn’t much better:
In Pokemon Sword the Pokedex entry reads:
“Though it's able to capture prey by freezing its surroundings, it has trouble eating the prey afterward because its mouth is on top of its head.”
And in Shield version it reads:
“The skin on its face is impervious to attack, but breathing difficulties made this Pokémon go extinct anyway.”

*deep sigh*

I think the most upsetting part is that because of this mechanic, they effectively ruined a whole generation of fossil Pokémon. Like, fossil Pokémon are some of my favourite, but speaking as a palaeontologist, these ones suck. They’re absolutely terrible. Which is so unfortunate because Dunkleosteus is such a cool species of fish, they could've done something really amazing with the design but instead they did Dunkleosteus dirty. 


I get it, right now I sound like a curmudgeon complaining that the new Pokémon suck and first gen was the best when out of the first 150, 2 were literally piles of sentient goo but, this? They went too far. 

Like, I’ve loved Pokémon ever since I was a little kid, like, just ask my brother about it, but yeah, as it turns I'm now a bigger palaeontology stan and if I had to pick between them, I'd choose bones and rocks. Every time. 

Anyway, thanks for listening to me rant about Pokemon for five minutes, I feel a lot better now that I got that off my chest. I’m keen to hear whether anyone agrees with me or if you like these Dunkleosteous inspired Pokemon.  

If you don’t know what they look like by the way, I’m gonna make a meme with the Dunkleosteus Pokémon you deserve, in a side by side comparison with Dracovish and Arctovish. If you wanna find it, I'm starting the hashtag Justice for Dunkleosteus. Not as catchy as Justice for Barb but... actually you know what? Justice for Dunk has a really nice ring to it. Hashtag Justice for Dunk. It’ll be on the Pals in Palaeo Instagram.

- 

Considering Dunkleosteus is hyped up the the apex predator of the Devonian, it's popped up in a couple documentaries but honestly I thought there'd be more entries listed on IMDB. I guess it’s kind of overshadowed by Megalodon in that regard. 

If you’re interested, Dunkleosteus makes an appearance in ‘Sea Monsters: A Walking with Dinosaurs Trilogy’ which came out in 2003, but just bear in mind that in the 20 years since it came out, we’ve learned more about this fascinating and fierce fish.

In terms of physical objects, I feel like there’s a lot of museums these days that sell models of Dunkleosteus. In fact I have one right here, and I got it last year when I went to Lightning Ridge and visited the Australian Opal Centre on my birthday. Pretty sure I also saw the exact same one in the gift shop at the Melbourne Museum and I think Darren Naish has posted a photo of the three or four Dunk models that he owns, so yeah. There's a good chance that you can get your own Dunkleosteus at your local museum, it'll just be in amongst the dinosaur and other prehistoric animal toys. 

Of course, it would also be remis of me to not mention where you can see Dunkleosteus in person and obviously the Cleveland Museum of Natural History is one of the best places you can see fossils of Dunkleosteus, and they actually have some really exciting developments in the works. And who better to tell us than Dr Caitlin Colleary and she also wanted to let us know when you can expect to see those new exhibits open to the public.

Caitlin: I’m very excited about all of the new exhibits that we are currently developing around Dunkleosteus. We are featuring Dunkleosteus multiple times in the new galleries that we are working on right now, and it’s going to be really exciting to show Dunkleosteus as well as all the other fish from the Late Devonian period that are represented here in northeastern Ohio in a bunch of really exciting and interactive ways so I’m excited for all that to be a real thing in the end of 2024, early 2025.

We’re also working on some really exciting digital content surrounding Dunkleosteus, including an animated short.

Adele: Unfortunately Caitlin didn't tease any titles but for the moment, in my head I'm just calling it, Finding Dunk. That would also be excellent. 

Last pop culture reference to round out the show, Dunkleosteus makes an appearance in the second Dinotopia book, The World Beneath. By the way in case you’ve never heard of it, Dinotopia is a work of fiction and focuses on humans interacting with prehistoric animals. I haven’t seen any of the movies or read the books but in my husband’s childhood bedroom there’s a framed Dinotopia jigsaw puzzle, that’s kind of like, depicting a medieval fair but folks are riding dinosaurs. But yeah! There’s some submarine sea-exploration going on in the second installment of Dinotopia with Dunkleosteus making an appearance and at least one other marine creature. I know it’s been out for ages, but I’m not going to give anything else away because… spoilers.

- - -
Started out with a fish, how did it end up like this... 

I’ve been waiting the whole episode to do that. Anyway, 

I feel like I say this every episode but I had so much fun putting this together for you and I hope you enjoyed listening in to what I had to say about this super rad fossil fish. 

Thank you to one of my best mates César for editing and producing the show. He provides both technical and emotional support and I could not be happier to have him onboard with this project. His knowledge of The Simpsons has come in clutch a number of times and it’s just a good excuse for us to catch up with each other and stay connected as friends.

By the way if you hate my weird Simpson's quotes each episode, yes they’re mostly my idea but César also encourages this behavior so… If you could aim your flaming torches and pitchforks at him that’d be great. 
I think it’s worth it though, the show genuinely sounds ten times better with his his input and I’d be absolutely buggered without him. 

Our podcast theme music and all other tunes are by Hello Kelly, the teenage mutant ninja turtles of pop rock and special shout out to Francy for making that happen. You can find their latest release Sweet Nostalgia wherever you find music but if I can make a suggestion, you should check out one of their earlier releases Electricity. Especially if you love acoustic guitars and lyrics filled with metaphors. It's also just ridiculously catchy, like, one of those songs you can sing a long to halfway through listening for the first time. If you can’t find the song, Electricity, you can find Sweet Nostalgia anywhere and everywhere you get music.

The Pals in Palaeo podcast cover art is by Jenny Zhao who you can find on Instagram @jennyzdesign and we connected with her through Crumpet Club House a collective of freelance creatives in my hometown of Melbourne. Thanks Jenny and thank you Crumpet Club House.

Last thing, thanks for hanging out with me today I hope you enjoyed hearing about this fishy friend. By the way we are just over the halfway mark for season 1. If you love the show let us know, rate and review the podcast, share it on social media and tag us so we can see it, or if you know someone who's into dinosaurs and fossils, tag them in our posts. 

Pals in Palaeo will be back soon with another episode but until then, just keep digging and just keep swimming


References

I Know Dino:
https://iknowdino.com/hesperornis-episode-250/

Palaeocast:
https://www.palaeocast.com/coprolite-inclusions/

Beyond Blathers:
https://beyondblathers.com/


How Dinosaur Poop Got Its Name
https://www.smithsonianmag.com/science-nature/how-dinosaur-poop-got-its-name-32829664/#:~:text=unfortunately%2C%20not%20true.-,The%20term%20%E2%80%9Ccoprolite%E2%80%9D%20has%20its%20roots%20in%20the%20Greek%20language,and%20lithos%2C%20which%20means%20stone.

What is a coprolite?
https://www.nhm.ac.uk/discover/what-is-a-coprolite.html

Dunkleosteus Size

Ecomorphological inferences in early vertebrates: reconstructing Dunkleosteus terrelli (Arthrodira, Placodermi) caudal fin from palaeoecological data

Feeding mechanics and bite force modelling of the skull of Dunkleosteus terrelli, an ancient apex predator

Giant, swimming mouths: oral dimensions of extant sharks do not accurately predict body size in Dunkleosteus terrelli (Placodermi: Arthrodira)
https://peerj.com/articles/15131/


A Devonian Fish Tale: A New Method of Body Length Estimation Suggests Much Smaller Sizes for Dunkleosteus terrelli (Placodermi: Arthrodira)
https://www.mdpi.com/1424-2818/15/3/318