1. Anomalocaris

Anomalocaris: the gigantic "abnormal shrimp" from the Cambrian, or, a weird shrimpy boy with face fangs. Plus info on trilobite cannibalism in Redlichia rex early compound eyes and biomineralisation.

5/10/202314 min read

Today on the show, we're talking about the ancient apex predator of the Cambrian, Anomalocaris. This episode we talk about pro strats for not getting eaten, the advantages of compound eyes and the first evolutionary arms race.
Hold onto your butts, it's gonna be a bumpy ride.
Pals in Palaeo presents Anomalocaris

I'd like to pay my respects to the People of the Ramindjeri, Ngarrindjeri, Kaurna and Barngalla nations, the Traditional Custodians of Karta Pintingga, and pay my respects to their Elders past, present and emerging. I extend that respect to all Aboriginal and Torres Strait Islander peoples and acknowledge their connections to land, sea and community. This episode was recorded on Koa country and fossils of Anomalocaris were found on Karta Pintingga.

This is Pals in Palaeo the show where we talk about the form, function and family groupings of your favourite fossils. I'm your host, paleontologist and PhD student Adele Pentland.

You can stay up to date with the show by following us on Instagram @palsinpalaeo

Before we get into the facts on this amazing and lowkey terrifying arthropod, you should know that today's fossil animal, Anomalocaris, almost made it into the cover art for the podcast.

By the way I didn't make the cover art for the podcast. Instead I enlisted the help of the amazing team at Crumpet Club House, Amy and Jenny. I'll put links to their social media handles in the show notes.

The questions that they asked really helped me nail down what the podcast was gonna be like, in terms of the general vibe.

So not only do I have them to thank for the podcast cover art and the social media branding for the Pals in Palaeo Instagram account, but they helped shape the tone of the podcast in a much broader sense.

Now I wanted the cover art for the podcast to have a range of different fossils, so I suggested some plants, some mammals, dinosaurs of course, plus some stuff from the age of dinosaurs like plesioaurs which aren't technically dinosaurs, and some famous fossil invertebrates.

The obvious inverts were ammonites and trilobites, but I also mentioned Anomalocaris and described it in that email as I kid you not, "a weird shrimpy boy with face fangs".

Now, in my defence, the genus name of Anomalocaris literally means "abnormal shrimp" soooo it wasn't the worst description.

I did get a couple things wrong though, because A) it's not really related to shrimp though and B) what I thought were face fangs are actually it's CLAWS.

But we'll get more into that when we discuss the Form of this animal.


But, before I serve up the main course, I want to whet your appetite with a Random Fossil Fact. Think of it as the audio equivalent to the appetiser.

This fact actually popped up when I was putting notes together for this episode, and whilst looking through papers on Google Scholar I found some articles on Trilobite cannibalism
Which came as a bit of a surprise to me... I guess for some reason, I never pictured trilobites as being predators?If you had asked me before I started look up papers for this episode, "Hey Adele, what do you think a trilobite eats? I probably would've guessed maybe detritus along the seafloor, maybe vegetation or colonial microbes.

Turns out I was wrong, they're after flesh and not so discerning when it comes to what's on the menu. Given half a chance, they'll eat one of their own kind, be it a smaller trilobite or even a member of its own species. Very on brand of an arthropod.

There's been a few papers on this topic which I'll link to in the show notes, some dating back to the 1980s, and more recent papers from 2016 and 2022.

A lot of research focuses on the Trilobites found on Kangaroo Island off South Australia. It's also worth noting that two species of Anomalocaris have been reported from this locality.

Getting back to the Trilobites though, there's been a couple papers describing healed injuries in the specimens they studied, with the most recent paper noting that most of these are on the end segment of the Trilobites.

Which to me, just conjures up this picture of a really, really slow car chase. But yeah! As it turns out, Trilobites were durophagus, you're next word to drop in Scrabble, which means they can chew through really tough material like the shell of another Trilobite.

But you know what else was eating trilobites in the Cambrian? You guessed it, Anomalocaris

Let's talk about the Form and Function of this animal, but before I get into the details I'll paint you a word picture and do my best to describe what Anomalocaris looks like.

As I mentioned up top, there are two large claw-like appendages near the front of the head that face downward that have spines. Not only are there spines coming off what's called the frontal appendages most of these spines are covered in smaller spines.

The head is wider side to side than it is long and has three hardened plates. These don't completely cover the head, and they're all near the frontal appendages, with one between the two appendages and then a left and right one near the sides.

Anomalocaris also has two relatively large eyes on stalks that are positioned along the middle portion of the head on the sides. The mouth is on what we think of as the underside of the body, so its not at the tip of its head, but I'll talk more about that later.

Anomalocaris is an arthropod so it has a segmented body made of lots of chunks that look the same. Basically once you draw past the head, you can just hit copy paste.

On the sides of each chunk there are petal like structures or flaps that help it swim around and the tail ends in a fan shape. Because Anomalocaris has a segmented body, it moves through the water like a dolphin.

OK so, I've mentioned a couple times now, that Anomalocaris was a hunter. Not only that, but it's widely considered to be the apex predator of its time.

Meaning that nothing at the time preyed on it, even though there were other predators in the Cambrian, they didn't and couldn't hunt Anomalocaris.
One of the biggest reasons why, is its size. There are some incredibly cool things going on with its body, but first let's talk about how big they are.

Keep in mind, there's not just one, Anomalocaris, it's a genus with a few different species, but they range from half a metre to 1 metres in length.

Which is the same as 20 inches long and 3 feet and 3 inches long. By comparison, another predator from this time period, Opabinia ranges in size from 4 to 7 cm, or 1.5 inches to 2.75 inches.
Opabinia... looks like an alien by the way. Like Anomalocaris it has a shrimpy body but it has 5 eyes, a trunk on the end of its face and on the end of the trunk is a claw bear trap looking doohicky. I'll probably do an episode on it at some point.

But yeah, there's no size comparison between the two. While there were some larger trilobites getting as big as 45 cm or 18 inches long, most were itty bitty and centimetres long or a couple inches.


So Anomalocaris is hands down the biggest predator in the ancient oceans during its time. It lived during the Cambrian, so about 510 - 500 million years ago, and when you're one of the biggest animals in the ocean, nothing can take you down.

I couldn't find any scholarly articles discussing cannibalism in Anomalocaris, but it's worth noting that some arthropods will eat juveniles of their own species, when there's sexual dimorphism, others demonstrate parental care like some species of scorpion where the mother carries the babies around on her back.

Until we find, idk, an Anomalocaris with eggs preserved tucked under its tail, or, an Anomalocaris with a large bite mark that could have only been made by another Anomalocaris, we won't know if this extinct arthropod was a cannibal.

What we do know, is that its size meant it could've eaten basically anything it wanted.

Another really cool feature of the form of this animal, are what I thought were face fangs or claws, but are actually appendages.

Lots of arthropods have appendages near their mouth including spiders, as well as insects like the praying mantis. It's incredibly helpful to hold what you're about to eat and say, eat the best stuff first, avoid any tough bits you want to leave behind and, oh yeah, STOP IT FROM RUNNING AWAY.

Because predators don't necessarily kill their prey before they start eating it. I myself enjoy a little bit of fast food every now and then.

The appendages of Anomalocaris can curl up because it's made of multiple segments. It probably wasn't punching it's prey like the peacock mantis shrimp, but would have helped it hold onto whatever it was eating.

These appendages are were among some of the earliest fossils known from Anomalocaris. The reason why they were finding the appendages on their own, without anything else, is because these were tough and hard, compared some of the other parts of its body.

This process, known as Biomineralisation, is not unique to Anomalocarisbut something the Cambrian is famous for.

During this time animals are eating other animals and in response to this, we see the evolution of hardened body parts as a defence mechanism. This back and forth between predators and prey is sometimes called an evolutionary arms race.
If you're a Simpsons fan, think Springfield and Shelbyville:

Getting back to biomineralisation though, biomineralisation is when life creates its own minerals. It'd be like, if you created your own armour just by breathing.

This isn't something the animal is doing intentionally, but it's able to grab trace elements in the water and combine them together to make something new, in this case a tough outer shell to protect its body.

Biomineralisation is weird in that, it can actually form minerals that don't naturally occur in the environment. I don't want to get into the specifics of this, but think of Activation Energy, the energy taken to start a chemical reaction as pushing a ball up a hill.

It can be something as simple as striking a match. Anyway all this to say, that a living organism, can push a ball up a bigger hill, and reap the rewards. In this case, cool weapons and armour.

Now, some animals like trilobites incorporated biomineralisation into basically their entire outer shell. Anomalocaris only part of assignment.

The appendages and mouth, as well as those hardened plates on the head are more common as fossils, compared to the rest of this animal's body.

So much so that it used to really confuse palaeontologists trying to study the hardened appendages of Anomalocaris, without the rest of the animal.

When fossils of Anomalocaris were first found by Western scientists in Canada in the 1880s, they were mistakenly identified as abdomens, so the bodies of crustaceans.

Really similar things happened with the mouths of Anomalocaris , which are shaped in a ring: they were mistaken for jellyfish when in fact, they were studying a piece of an animal, not the whole thing.

Speaking of its mouth, let's talk more about the controversies surrounding the oral cone, or as I like to think of it, The Circle of Doom.

Anomalocaris differs from most other animals we see today, in that it has a disk-like or circular mouth facing downwards and the mouth or oral cone opens and closes using a bunch of plates. And in case that wasn't enough to give nightmares, the plates have scale-like bumps closer to the centre where it opens and closes.

Now the controversy is in the arrangement of the plates, and how that impacts feeding behaviour. Anomalocaris has 3 main plates, with smaller plates of different sizes in between.

Research published by Allison Daley and Jan Bergström in 2012 argued that because the oral cone has 3 plates, Anomalocaris isn't a predator specialising in trilobites and other hard shelled organisms, but that they were suction feeders.

More recent research has suggested that Anomalocaris might have used its frontal appendages to snap its prey in half before sucking up the insides, which would then explain why Trilobites curl up into a ball to protect themselves.

Or, Anomalocaris might have snaffled up trilobites in between moult stages. Much like crustaceans today, Trilobites needed to shed their skin to keep growing, but at that time, they're at their most vulnerable.

It's been noted that the plates that make up the oral cone in Anomalocaris don't appear worn down, hinting that they're not eating a lot of tough shelled animals. So maybe they were in fact picky eaters coasting around in search of soft, squishy trilobites in the middle of moulting.

I'm just spitballing here, and hopefully more research will shed more light on what exactly Anomalocaris ate, but it definitely has the hallmarks of a predator. Which brings me to my next point, it's excellent eyesight.

The eyes of Anomalocaris were just as good as those we see in some modern arthropods, based on the number of hexagonal lenses packed in there. This is based on research by John Paterson and colleagues from 2011, describing a fossil from Kangaroo Island South Australia.

The eyes were about 2-3cm, so both about an inch, and each eye had at least 16 THOUSAND lenses.

What's cool about this is that it tells us that complex eyes were present in the early Cambrian arthropods, in this case, 515 million years ago AND that eyes like this had evolved in arthropods before the exoskeleton.

So not only were they big, with spiny appendages at the front of its head, which it used to hold and manipulate prey into its circular mouth, but these were highly visual predators.

It's no coincidence that appendages at the front and excellent Eyesight are traits we see today in modern arthropods, as this is the Phylum Anomalocaris belongs to. Now that we're comfortable with what Anomalocaris is and what it does, let's talk more about its taxonomy.


Anomalocaris is a type of arthropod, which is a big group that includes things like insects, crustaceans, arachnids, millipedes and a bunch of other animals. That being said, Anomalocaris isn't closely related to any of the arthropods I just mentioned because, and in fact, Anomalocaris has no modern day descendants.

It took a long time for palaeontologists to work out what Anomalocaris was closely related to, partly because the hard biomineralised parts of its body would fossilise without the soft squishy parts in the middle to hold it all together.

As you can only imagine, the family grouping of this species couldn't be determined until they fully understood how its body was laid out.

Our current understanding of the taxonomy of Anomalocaris, is that it belongs to a group called the Radiodonta. Now, like Max Fischer from Rushmore written by Wes Anderson, I too believe Latin is not a dead language.

And I'm not just saying that to impress the person I've got a major crush on. No! Knowing even a little bit of Latin helps us work out what the defining feature is for a particular group of animals.

In this case, the Radiodonta, are defined by their weird circular mouths, because radio means circular, like how sea urchins have radial symmetry, and "dont"? "Dont" means tooth.

Other animals in Radiodonta are, other weird shrimpy looking animals, including one I've already mentioned in this episode, Opabinia!

Like I said before, everything belonging to this group is extinct and there are no descendants of this group. When you think about it, that makes sense, since there aren't any arthropods with circular mouths today.

The Radiodonta disappeared from the face of the Earth 485 million years ago, at the end of the Cambrian. While this isn't considered one of the 5 mass extinction events, the end of one geologic period and start of another is defined by a shift in the composition of ecosystems globally.

As with many other extinction events, the end Cambrian has been linked to a depletion of dissolved oxygen in marine waters, glaciation and volcanism, specifically the Kalkarindji Large Igneous Province in the northern Territory of Australia.

Those three things are all bad news for marine creatures and can severely impact the biomineralisation process. The Radiodonta were an incredibly successful group spanning roughly 56 million years, with a diverse range of hunting strategies and body sizes.

We've heard about the Form, Function and family of Anomalocaris, but what else do we know?

As I mentioned before there isn't just one OG Anomalocaris, it's a genus that actually multiple species within it.


This genus is fairly widespread, with fossils found in South Australia, southwest China, southern California and Utah in the US, the Burgess Shale a very famous fossil site in British Columbia, Canada.

Mind you, in the Cambrian, the world looked very different back then. The continents you and I are familiar with were in different positions, with most of the continental landmass in the southern hemisphere and indeed, extending from the equator to the south pole.

The southern supercontinent is of course, Gondwana, made up of Australia, Antarctica, New Zealand, India, Madagascar, the Arabian Peninsula, Africa and South America. The other continents at this time are Laurentia (made up of what is now North America and Greenland), and the other two major Cambrian continents were Siberia and Baltica.

When I looked online to see what the world looked like during the Cambrian, I was not expecting south China to be an island off the coast of Gondwana and nearest to Australia. In fact I wasn't expecting the continents to be named, Gondwana and Laurentia.

The Cambrian is about 510 to 500 million years ago and I mostly work on Cretaceous fossils that are about 100 million years old... idk for some reason I thought the continents would have different names, but I guess I was thinking of Pangaea when everything was all gummed up together in a single supercontinent.

Before we wrap up for this episode I wanted to quickly mention my favourite pop culture references inspired by Anomalocaris.

Personally, my earliest introduction to Anomalocariswas through the Pokémon Anorith, which isn't something you encounter in game.

If you haven't played Pokémon before, in a few of the games you can find fossils which are initially items, keep them in your inventory and later resurrect those fossils into living breathing Pokémon. a la Jurassic Park.

For more on fossil Pokémon and the science behind their form and function, highly recommend you check out an episode of the Common Descent Podcast dedicated entirely to fossil Pokémon. Just search for Common Descent Pokémon Palaeontology and it'll come up.

There's also an Anomalocaris yowie, which by the way, if you don't know, yowie is something we have here in Australia kind of like an Easter egg, or more like a kinder surprise. On the inside of the chocolate is small, plastic container containing parts for a toy you have to assemble. So not only was it a treat, but you got a little animal toy, and a little stat sheet telling you about where this animal is found and for extant species or living animals, info on their conservation status.

And to round out our Anomalocaris pop culture facts, and the show, on IMDB, there are 7 titles linked to Anomalocaris, and it features in a couple documentaries and a few TV episodes. I did not know that species could get listed on IMDB, I thought it was just for you know, actors and directors but it turns out you can list species as a keyword.

So if it want to learn more about Anomalocaris and watch some cool documentaries I'll also link to them in the show notes.

If you didn't know anything about Anomalocaris before listening to this episode I hope you enjoyed hearing about this complete and utter weirdo. Don't forget you can check out what Anomalocaris looks like on the Pals in Palaeo Instagram and I'll also post a photo of Anorith, its Pokémon doppelganger.

Thanks so much for listening to the show, I hope you enjoyed listening to it, and I hope you'll be back for more.

Big thanks to my friend César for editing and producing the show.

Since the show has just launched, if you could take just a couple minutes to leave us a review or rating in your podcast app, that would literally mean the world to me.

Our theme music is by Canadian pop rock band Hello Kelly, you can find their music on their website, on instagram @hellokellymusic and their Spotify where you can find their latest drop Sweet Nostalgia. The title track is a banger by the way. Definitely, if liked jamming out to the theme music, check out Sweet Nostalgia.

Thank you to Francy, the singer of Hello Kelly for our other tunes, and final thank yous to Crumpet Club House and Jenny Zhao for the podcast cover art.

Pals in Palaeo will be back soon with another episode but yeah, feel free to send your suggestions through for potential episode topics through on social media.

Ok, bye!


Random Fossil Fact
Healed injuries in Early Cambrian trilobites from South Australia

World's oldest known case of cannibalism revealed in trilobite fossils

Trilobite Fossils Suggest Cannibalism Is More Ancient Than Once Thought

The sharp eyes of Anomalocaris, a top predator that lived half a billion years ago

New anatomical information on Anomalocaris from the Cambrian Emu Bay Shale of South Australia and a reassessment of its inferred predatory habits

Acute vision in the giant Cambrian predator Anomalocaris and the origin of compound eyes

The oral cone of Anomalocaris is not a classic ‘‘peytoia’’

The Pals in Palaeo Cover Art

Jenny Zhao Design @jennyzdesign

Crumpet Club House@crumpetclubhouse

The Pals in Palaeo Theme Music

Hello Kelly @hellokellymusic

Podcast Editing

Jean-César Peuchmarin @cesar_on_safari