#palaeozoic

Dimetrodon borealis walks along a dry riverbed, north-central Pangaea, 270 mya

Sigillaria – Late Devonian-Late Permian (383-254 Ma)

I know I’ve faked you out before, but today’s animal really isn’t an animal. It’s our very first venture into paleobotany, in the form of a plant named Sigillaria. For those who don’t know much about prehistoric plants (including myself before researching this), the idea of talking about a fossil plant might sound boring, but I promise, there are a lot of interesting things to know about plants, especially plants from the Paleozoic Era.

One of the most important landmarks in the Paleozoic was the invasion of land. For the first 100 million years of the Phanerozoic Eon, life was found only in the water. The land was completely devoid of life, the atmosphere barren and inhospitable. Plants were the first organisms to come ashore, and, while there’s a lot to talk about there, that’s a tangent for another genus. The main idea here is that plants got on land first, and plants are hardy sons of bitches. You can find plants almost anywhere. I work at a farm supply store, and we have torn bags of mulch with plants growing out of them. They aren’t particularly picky. This is pretty evident in the fossil record, where plants arrived on land and almost immediately diversified and conquered it all. Animals took much longer to catch up. By the time vertebrates were first starting to flop onto the shores of lakes, terrestrial plants were huge. It would be a long time before large herbivores would evolve, and in the meantime, those huge plants covered the surface of the earth, leading to the humid, global rainforests of the Carboniferous period. These rainforests looked quite different from the ones we know today. Sigillaria was one of the plants that made up this alien blanket of vegetation, and it shows up quite a lot in the fossil record.

This may look like a tree, but it’s actually a lycopod, placing it closer to club mosses and quillworts. It wasn’t woody, either, instead supported by jury-rigged leaf bases right under the surface of its trunk. Those leaf bases left imprints on the trunk and resulted in the pattern on the surface, which was different from species to species. Most Sigillaria specimens have only one branch of leaves. Forked trunks are pretty rare, but I drew one with a fork because it’s neat.

Sigillaria reproduced with spores, like ferns. Spore-bearing plants can only live in humid environments, but since the Carboniferous was pretty much a big sauna, this wasn’t much a problem. It was found mostly in floodplains or swamps As those biomes shrank, Sigillaria’s presence in the fossil record dwindled more and more, before finally disappearing during the Permian-Triassic extinction event. The more late Paleozoic animals I cover, the more the Great Dying is put into perspective. So many groups of animals and plants were lost that there’s almost no overlap in biota between Permian and Triassic rocks.

That being said, Sigillaria was a hanger-on from the Carboniferous. Big lycopods were a diverse group back then, but towards the end of the period, the earth grew colder. The earth became drier and the global rainforests started to shrink. This event is called, fittingly enough, the Carboniferous Rainforest Collapse. It wasn’t a large enough extinction event to be one of the big ones, but it caused changes that affected everything on earth. Swamps were hit the hardest, but since Sigillaria wasn’t exclusively a swamp-dweller like most of its cousins, it was able to hang on until things got really hard. That rainforest collapse was a huge part of why we have so much coal today, by the way. Places like Pennsylvania that have a whole bunch of coal also have a whole bunch of Caboniferous fossils.

You wanna know something else weird about this plant? Trees live for a long time, right? They live on a timescale that can be hard to think about, sometimes. Sigillaria, though, only lived for about 10-15 years, and might have died after reproducing. This probably means they grew really, really quickly. Imagine planting a tree after seeing Revenge of the Sith in theaters, and then having a 100ft (30m) plant in your backyard by the time The Force Awakens came out. And then it died. Such is life, I guess.

Sacabambaspis – Late Ordovician (470-453 Ma)

Today we’re talking about something really cute. It’s an ancient, primitive fish with an adorable face. It’s Sacabambaspis!

What we’re looking at is an early jawless fish. Fish in the Ordivician period were small, simple little guys. Usually tubes with eyes and sometimes armor. Most of them didn’t even have fins, so a lot of them, including Sacabambaspis, look a lot like armor-plated tadpoles. It’s hard to imagine a world where fish don’t dominate the oceans, but that’s just how it was during the Ordovician. These guys, as well as their relatives, lived in the shadow of larger invertebrates, still enjoying the twilight of their rule that began during the Cambrian period.

Sacabambaspis was a bottom-dweller. Its mouth was pretty much just a circle in structure, but the inside was lined with bony plates that aided in suction feeding as it slurped bits of nutrients off the seafloor. Its eyes were square in the front of its head, giving it an adorable face. It’s like a little submarine, I just wanna hug it! Bony plates covered its gills and the front half of its body. There’s also evidence of a feature found in most modern fish called the lateral line. This is an organ system that lets fish sense the flow of water. There isn’t really an analogue in terrestrial vertebrates, but if I had to say one, it’s kind of like our sense of hearing. Kind of.

Although Agnatha (the technical name for jawless fishes) are the oldest group of fish, Sacabambaspis likely lived at the same time as early jawed fishes (Gnathostomata). This was still the primetime for jawless fishes, though. It would be a while before their jawed counterparts became more successful. So much more successful, in fact, that there are only two groups of agnathans alive today: lampreys and hagfish. Also, a fun fact about Gnathostomata is that the technical definition includes all vertebrates with jaws. So, you and I, and your dog, and my cat, are jawed fishes.

Don’t let all this talk of fish living in the shadows of bigger animals convince you that fish were underdogs or barely eking out their existence back then. It’s easy to try and fit the history of life into a sort of poetry, where the fish struggled along until given the chance to rise up and take over. That wasn’t really the case, though. Fish were thriving in the lower niches of the food web during this time. You wouldn’t call rodents underdogs today, just because none of them are apex predators in their ecosystems. Fish were similar; they were all over the place and lived all kinds of different lives. Considering what we know about the Ordivician fish, it’s not hard to see why they jumped at the opportunity to dominate the seas once the extinction event at the end of the period wiped out everything else. We like to think fish are dumb and primitive, but they have a spectacularly well-adapted body plan for aquatic life. They’re great at being animals, and I am ready to fight anyone who disagrees.

Hallucigenia – Middle Cambrian (508 Ma)

It’s been too long since I featured something from the Burgess Shale. Last time, I featured Opabinia, along with an overview of the Cambrian Explosion and the history of our understanding of it. Today, we’re focusing on a little, inch-long invertebrate who lived alongside Opabinia, named Hallucigenia.

If you’ve ever seen a drawing or painting of a Cambrian landscape, it’s pretty likely you’ve seen Hallucigenia. It’s common as a backdrop animal in many portrayals of the Cambrian seas. Many of these tableaus are meant to evoke a feeling of unfamiliarity. They offer us a window to a much younger, alien earth. No fish swim overhead, and weird critters cover the seafloor. Hallucigenia is a perfect example of a weird critter. Then again, most of the fauna from the Cambrian period are. Most of the genera from the Cambrian have a story behind them, how we learned just how different they are from the things we know today, and this is no exception.

So, what is Hallucigenia? It’s weird, is what it is. This is normally the part where I, or any other amateur science communicator would reveal that it’s not actually as weird as it seems. The problem is, Hallucigenia really is that weird. It’s a soft-bodied worm with seven pairs of huge spikes on its back, and several tentacles underneath, perhaps used for walking. Also, it took us 50+ years to figure this out.

The Burgess Shale formation was discovered in 1909 by a man named Charles Doolittle Walcott. During his lifetime, he found and described hundreds of specimens from the Shale. However, Walcott was wrong about a lot of things. He misinterpreted several of the different fossils, including Hallucigenia. In fact, he didn’t even realize it was its own genus when he found it. For several decades, it was labeled as a specimen of an annelid worm called Canadia. It wasn’t until 1977 that paleontologist and personal idol of mine, Simon Conway Morris, recognized it as something very different. He reconstructed the animal more accurately and gave it its name, which, yeah, does come from the word ‘hallucinogen,’ because, I mean, look at this fucking thing.

Conway Morris didn’t get it quite right, though. For a while, we thought the spikes were on Hallucigenia’s underside, and that it used them to walk. In this interpretation, its tentacles would drift in the water and grab particles of food out of the air and carry them to its mouth. The accepted model has the spikes on its back, possibly as a defensive measure. We don’t know for certain that they were hard, since we haven’t found them preserved separately from the rest of the animal, like we do with other hard body parts.

This wasn’t the fault of poor fossil preservation—we have 109 specimens of Hallucigenia from the Burgess Shale, and they’re absolutely gorgeous. The problem is that this animal is so bizarre, so different from anything we have today. It’s hard to blame Walcott or Conway Morris for not being 100% correct about them right away.

So, now that we’ve studied these animals for so long, where does Hallucigenia fall on the tree of life? Good question. It’s a worm, but “worm” doesn’t really mean anything. All kinds of animals are worms, so what kind is this one? Scientists are torn, but two of the most popular hypotheses are that it’s either an early ancestor of velvet worms, or a distant cousin of what eventually became arthropods.

I could write an entire book about Hallucigenia and its cohorts in the Burgess Shale (in fact, one day, I want to), but I’m running late for some plans I have, so I’ll wrap it up here. Join me in a couple of days for… I don’t know. You ought to know I’m winging this by now.

Eophrynus – Late Carboniferous (318-299 Ma)

Today, we’re going back to the Carboniferous period! If you’ve been following this blog for a while, you might remember Westlothiana, a little amphibian and/or reptile* that looked a little like a lizard. As I said back then, vertebrates were only just getting started on land. They were mostly small, skittering animals. Arthropods, though, were a different case. They first arrived on land in the Silurian period, almost 60 million years before fish took their first soggy, awkward steps onto land. Arthropods were the first animals in earth’s history to fly, and had set up shop pretty firmly by the Carboniferous period.

The earth was wetter and covered in rainforests back then. There was also a lot more oxygen in the air. Insects and other arthropods have very simple respiratory systems. Air flows into their bodies through openings in their exoskeletons called spiracles, then makes its way into the air sacs and distributed accordingly. This is all I know about arthropod breathing. But, this system is much less efficient than the one seen in vertebrates. It puts a size cap on terrestrial arthropods. If they get too big, the air can’t flow through their bodies, and they can’t breathe. But, in the Carboniferous, arthropods were able to get HUGE, thanks to the increased oxygen content of the air. And Eophrynus is… not one of them.

No,Eophrynus is around an inch long (2.5cm, for you non-yanks). It’s a little arachnid from the late Carboniferous. It’s is a Trigonotarbid, an order of arachnids that lived from the late Silurian until the early Permian. They were closely-related to spiders, but slightly more archaic. They were shaped similarly, but didn’t make silk, and their front pair of limbs—called pedipalps—weren’t modified into claws or pincers. Also, there’s no evidence they used them to deliver sperm into females, which is apparently something spiders have been doing for a while.

 It’s a little hard to say exactly how closely or distantly they were related. Arachnids are hard to sort phylogenetically, partially because they all share a very similar body plan. We can usually say if they’re closer to spiders or scorpions, but we haven’t quite figured out much beyond that. We have theories, sure, but it’s not quite set in stone. Well, it’s the fossil record, so, it’s… You know what I mean.

Anyway, like most arachnids, Eophrynus was a predator. It lived on the forest floor, and used its long legs to chase down other, smaller arthropods. But, of course, being a tiny arthropod, it was probably eaten by small amphibians and reptiles. Its abdomen was lined with protective spikes in an attempt to keep this from happening, but let’s be real, if something wants to eat you badly enough, it will. Look at Koalas and Eucalyptus, or Mongooses and venomous snakes. Animals are buckwild.

That’s our animal for today! I’ve talked about invertebrates a few times on this blog, but they’ve always been marine. Marine invertebrates are my favorite group of animals, and I think my bias has been a little clear here.

And, I’ll talk about giant Carboniferous insects soon, I promise. I like them, too. I just want to give the lesser-known, more mundane animals their time to shine, too.

*Mspaleoart drinking game: take a shot every time I mention how wack taxonomy is

Diplocaulus- Early-Late Permian (~270-245 ma*)

Our second Permian animal, and our first definite-absolute amphibian, is Diplocaulus, a 3-foot long predator from Texas, and maybe Morocco. It’s… super weird and I feel very strongly about it.

For the most part, Diplocauluslooked and acted pretty much like a Giant Salamander. It had a sprawling, four-legged gait. It spent most of its time in the water hunting fish. It lived and reproduced in burrows near lakes or other bodies of fresh water. It weighed about 5-10 pounds, as much as a cat.

Anyway, let’s talk about that head. It’s shaped like a boomerang because… It just happened like that? The problem with extinct animals is that the farther back in the fossil record you go, the less information we have on them. But no, everything under natural selection happens for a reason, even things as ridiculous as this. Maybe it served as a hydrofoil, letting it swim faster. Another theory is that it was shaped so awkwardly so nothing could swallow it. I like that one. It was definitely hard to lug around on land, though. They can’t all be winners.

We also have fossil evidence that Dimetrodonwas a frequent predator of this soggy boy. One set of remains looks like a crime scene, where a Dimetrodondug up a burrow and ate some young Diplocaulus. This maybe says that Diplocaulustook care of its young beyond squeezing them out and walking away, but maybe it’s best not to read too much into it. Maybe they all just holed up in the ground together during the dry season.

Diplocaulusis unique within its group, the Lepospondyls. Lepospondyls were one of the oldest groups of amphibians, and were characterized by simple backbones, which were basically just the primitive notochord wrapped in bone. Diplocaulusis one of the largest in that class, as well as the youngest, living well into the late Permian. It’s also the only one we know of that looked like a banana. The placing of Lepospondyli is a little up in the air. We’re not sure if they’re the early ancestors of modern amphibians, or if they’re directly descended from the earliest land vertebrates, or what.

For some reason, it’s been the subject of a number of hoaxes claiming it’s still alive. Seriously, google ‘diplocaulus real’ and you’ll find so many pictures and videos of people trying to say they saw one. I don’t know why this keeps happening to Diplocaulus, of all animals, but it does. Maybe because it’s small and easy to fake? It’s also appeared in pop culture a few times, which is kinda strange for something of this sort. It’s in ARK: Survival Evolved (Basically in name only. It’s REALLY big and REALLY angry-looking), as well as a few Jurassic Park games (again in name only). It also shows up briefly in the anime Neon Genesis Evangelion, which I only mention because I like NGE. It’s only there for like, a second in the last episode. I can’t offer any further context, because it’s the last episode of Neon Genesis Evangelion.

Diplocaulushas always had a special place in my heart. When I was a kid, my grandparents gave me a bunch of books about Dinosaurs that belonged to my dad when he was young. One of them was titled Prehistoric Monsters did the Strangest Things. It’s from 1974, and the cover literally has a bunch of sauropods standing in a lake munching on seaweed, so that should tell you everything you need to know about the accuracy of the book. I still ate that shit up. Diplocaulusis the animal they use to talk about the transition from sea to land (on this spread right here). I stole the color scheme, because in my head it’s always been yellow.

*There are no exact dates for Diplocaulus’ span of existence, so I snowballed it from the beginning of the Permian to a bit before the Great Dying. If I’m wrong, and there are dates for it, please let me know!

Lystrosaurus – Late Permian-Early Triassic (255-250 Ma)

I’m back! I was sort of at a loss of what animal to talk about when I came back from my hiatus in earnest, but during the spotty downtime I had last week, I read When Life Nearly Died by Michael Benton, and that pointed me in the direction of this chubby little gentleman, whose name is Lystrosaurus.Lystrosaurus is one of the (very very VERY) few animals to survive the Permian-Triassic Extinction event, and we’re gonna take a look at why exactly that is.

Lystrosaurus is yet another synapsid, or proto-mammal. This guy was a member of the second wave of Paleozoic synapsid radiation, a member of the order Therapsida, which were characterized by being more similar to true mammals than the first group, the pelycosaurs. EdaphosaurusandCotylorhynchuswere both pelycosaurs, and were a bit more basal. Lystrosaurus shows a few of those therapsid traits, most importantly the shape of its skull and its semi-sprawling gait. On the less mammalian side of things, it probably had a beak made of horn for shearing vegetation. It had the characteristic deep body cavity for digesting all the tough plants it ate. It also had no teeth except for a pair of enlarged canines, which it probably used to uproot its food. The most common species was about the size of a schnauzer, although a much rarer species grew a bit larger. All-in-all, it wasn’t really anything special compared to its contemporaries.

Despite being tiny and rather typical of an animal from its time period, Lystrosaurus is an important animal for a few reasons. Even though plate tectonics are common knowledge and accepted as fact now, it took a long time for it to gain any serious traction. Alfred Wegener was pretty much laughed off when he first suggested the continents move in 1915. As a part of this theory, Wegener also suggested the continents had been united at some point into a supercontinent he called Pangea. His contemporaries heard the idea and basically said, “Okay but continents don’t move, obviously. Have you ever seen a continent move?” To their credit, the evidence at the time was, more or less, Africa and South America fitting together and other such things. Which, yeah, we know were right now, but back then it wasn’t so obvious. The next several decades were a slow march to acceptance of the theory of continental drift. Lystrosaurus figures into this by having been found in Asia, Africa, Europe, and even Antarctica by the 70s. At that point, even the most hardened skeptics shrugged and said, “Okay, yeah, fine.”

Lystrosaurus is known from an absolutely stupid number of fossils. The Great Karoo Basin in South Africa has an unreasonable amount of Lystrosaurus remains. They make up 95% of the animals found there, and they’re so abundant that paleontologists pull their hair out trying to find literally anything else. The most studied parts of the Karoo Basin span the late Permian and Early Triassic, and once you get into the Triassic rocks, it’s pretty much Lystrosaurus all the way down. Why is that?

Because nothing else survived the Permian Extinction.

There are five major mass extinctions in the Phanerozoic Eon. I’ve talked about two of them on this blog so far. I talked about the End-Ordovician extinction event when I covered Endoceras, and the End-Triassic extinction with Effigia. And I’m here to say that those events were fucking peanuts compared to this one. This was the single greatest crisis for life on earth, to the point that it’s often called The Great Dying. This was the destruction of about 90% of all species on earth at the time, and for a while we weren’t even really sure what was causing everything to fucking die. The most accepted theory nowadays is the series of eruptions of the Siberian Traps at the end of the Permian period. Basically, most of what we now call Siberia turned into a volcanic wasteland and exploded every so often, anywhere from every few thousand years to every few months.

These were more than volcanic eruptions. This was fire and brimstone, magma punching massive holes in the earth and launching toxic gasses and solid ejecta into the atmosphere. Anything remotely nearby suffocated or was struck by fiery debris. This wasn’t the most severe killing agent, though, not at all. The Great Dying earned its name because of the secondary effects. The gasses spewing into the atmosphere blocked out the sun and caused flash-freezing, followed by periods of global warming. Glaciers melted and released even more toxic gasses trapped beneath them, poisoning the seas and killing anything unadapted to anoxic conditions. It’s pretty telling that the majority of the marine animals that survived into the early Triassic were clearly adapted to life without plentiful oxygen. Plants on land were suffocated or frozen to death, and the ecosystems collapsed from there. The earth was a frigid, barren landscape. The seas and land alike would be littered with corpses of animals and plants. The earth has mechanisms to balance these influxes of toxic chemicals, but the problem was that by the time those mechanisms could get started, Siberia would erupt again and start the process all over again. If you were to walk around Pangea during the peak of this crisis, 1) It would fucking suck, and 2) You’d probably come across a very distressed Lystrosaurus before finding any other animal.

Why in the goddamn hell did Lystrosaurus survive when so many other animals didn’t? It’s a complicated question, because it’s important to ask another question first: What animals are vulnerable to extinction events? There are a couple of broad categories of vulnerable animals during mass extinctions:

Large animals: Large animals are especially vulnerable because they need more energy to keep themselves going, and almost always have small populations and slow reproductive cycles. This goes for predator and prey alike. When plants start dying, herbivores can’t feed themselves, and the large carnivores that prey on them don’t have anything substantial to eat. This is the reason animals like elephants and rhinos have such a hard time bouncing back after we nearly hunted them all to extinction.

Specialized animals:Specialized animals are almost always doomed in big extinctions. If an animal is really, really good at functioning in a specific environment, it’s going to bite it as soon as that environment gets thrown off-kilter. Animals that specialize in eating a specific plant or hunting in a specific environment don’t usually survive when everything gets hit.

So, the animals who are most likely to survive a mass extinction are the small generalists, who can thrive pretty much anywhere. Lystrosaurus fits this description, but forget all of that for the purpose of this conversation, because the Great Dying decimated life of all sorts. Generalists were more or less just as likely to die off as the specialized animals or the big guys. So, we ask again, why did Lystrosaurus survive when so many other animals, even those similar to it, didn’t?

There isn’t really an answer to that question. Scientists have puzzled over the remains of Lystrosaurus and asked over and over again, “Why this little bastard?” and they’ve come up with nothing substantial. It was luck that a little beaked herbivore was one of the lucky few. There’s no adaptation that made it particularly hardy in the face of total metazoan annihilation. There’s no reason it survived the act break between the Paleozoic and Mesozoic eras. It just did because it happened to survive. This isn’t a parable of survival as much as it is one of dumb luck. One of the characteristics of a mass extinction is that it is essentially indiscriminate. Lystrosaurus had every reason to perish like its relatives, but it just didn’t. Being the generalist that it was, it wasn’t hard for it to recover when the Siberian Traps died down and life finally gained a foothold. It multiplied at an absurd rate and covered the earth. The early Triassic was unequivocally dominated by waddling herds of Lystrosaurus. An argument could be made that it’s the single most successful genus of synapsid in history, although MusandRattus would probably argue that point.

Whew. That was a lot. I hope it serves as a fitting return! Lystrosaurus was an animal I’d been meaning to cover for a long time, but only now felt like I was able to do it any justice. There’s so much to say about Lystrosaurus, to the point I could write a book about it. The cover would probably look something like this:

I’ll see you next time!

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Cotylorhynchus – Early Permian (279-272 Ma)

Before the Mesozoic Era, millions of years before dinosaurs even thought about showing up, was a 50 million year-long period called the Permian. You probably know that already. The Permian was the first real boom in vertebrate diversity on land. Terrestrial vertebrates had come a long way during the Carboniferous, and made several important adaptations that helped them conquer the earth during the following period. Among them was the evolution of waterproof, hard shelled, or, “amniote,’ eggs. The ability to reproduce on land let vertebrates spread all over the continent of Pangea. This is especially helpful, because the Permian was drier than the Carboniferous.

Despite popular belief, the Permian wasn’t an age of reptiles. There were big reptiles, for sure, but they weren’t the majority. The majority was the other branch of amniotes, the synapsids. They were in charge, and had free rein to turn into all sorts of weird shapes. That’s how something like Cotylorhynchushappens.

This was the biggest guy around in the early Permian, which wasn’t as big as you might think. Think a cow that’s closer to the ground, and you have Cotylorhynchus. Oh, and shrink its head a bunch, too. Do you want to know why its head was so tiny? So do I.

Yeah, its head was just kind of like that. Its body was massive for a reason, though. Well, a few reasons. Like I mentioned a minute ago, Cotylorhynchus was a built motherfucker. It was significantly bigger than anything around it, even Dimetrodon, which was only about half its size without the sail. Cow-sized was enough to be absolutely massive back then, and its sheer bulk kept it safe. It also housed a powerful digestive system to break down plant matter. It was one of nature’s first examples of the walking glacier archetype, and it even reminds me of the Pokémon Avalugg, which is a literal walking glacier. And would you believe that the best way to beat both is to not even bother challenging their defense? Just set them on fire and they’ll both go down.

But really, Cotylorhynchus was essentially indestructible in the eyes of your average early Permian predator. It’s also worth mentioning that it had a cousin called Casea, which basically looked the same but was the size of an iguana. This begs the question, which came first, the big one, or the small one? Were they all tiny with tiny heads, or did they just shrink down to that size after a while? CotylorhynchusandCasea lived at the same time, so it’s hard to say. We do know that there were members of their family who had reasonably-sized heads, on top of that.

Some other features worth mentioning: It had really broad shoulders and dexterous hands. It probably dug up roots and such as part of its diet. The shape of its skull implies it was really good at smelling, which is a good thing to be when you’re hungry all the time and constantly looking for food to nourish your colossal body. It also had long fingers and broad, paddle-like hands. Yes, I’m going there. From what we can tell about its range of motion and everything listed above, it was probably semi-aquatic. Yeah, it’s not really streamlined in any way whatsoever, but did it need to be? Manatees can get away with it. Cotylorhynchus probably swam more like a turtle, by drifting and propelling itself with its limbs. It wasn’t much more graceful underwater than it was on land, but it really didn’t have to be, if you ask me.

Perspicaris – Middle Cambrian (508 Ma)

Today is a special day for a couple of reasons! 1) I get to talk about the Burgess Shale again, and, 2) Today’s animal is MSPTD’s very first requested animal! So, before I get into the writeup, I want to thank @futureimagineer843 for requesting this animal! This writeup was a lot of fun and I hadn’t actually heard of this one before xe mentioned it. Also, if you ever want me to talk about a specific animal, requests are something I am absolutely open to.

Our third trip to the Burgess Shale, the famous Cambrian fossil bed from British Columbia, examines a lesser-known and lesser-understood animal named Perspicaris. Using Perspicaris, we can really put into perspective how much of a treasure trove the Burgess Shale really is. This is one of the more rare animals from the Burgess Shale, and it’s known from only 202 specimens. For comparison, we have around 50 specimens of Tyrannosaurus rex, an animal found in significantly younger rocks and one of the better-known theropod dinosaurs. It might sound ridiculous to call it rare, but those 202 fossils of Perspicaris make up only 0.38% of the Greater Phyllopod Bed, where most of the Burgess Shale fossils have been found.

We don’t know much about Perspicaris. It’s a really weird animal. It’s really similar to a common Burgess Shale animal called Canadaspis (known from 4,525 specimens and making up about 9% of the organisms found), and we can extrapolate a bit about its appearance and how it might have acted from looking at it.

Perspicaris is a tiny arthropod. It was less than an inch in length (2-3cm), and bears more than a passing resemblance to shrimp and other modern crustaceans. We’re unsure of whether or not it was an early crustacean, a basal Euarthropod (the modern groups of arthropods), or from a family outside of that group that left no descendants. It’s definitely some kind of arthropod, but getting more specific is pretty hard. That’s the problem with the Cambrian fauna, and one of the reasons it’s so fascinating. This is when just about every modern phylum evolved, so when can we say they split for sure?

It’s also hard to say what the hell it was doing with that body plan. It had big eyes on the end of stalks and limbs that could have aided swimming. But, it didn’t have any claws or enlarged biramous limbs (limbs that branch into two different segments that are usually adapted to some special purpose), so if it was swimming, how did it eat? We know Canadaspis was a bottom-feeder, but don’t have any evidence for that in Canadaspis.

This brings up the question: How do we know all these things about prehistoric animals? We use a lot of methods to figure out all this. Since the Cambrian Explosion, most animals fill different roles in a given modern ecosystem. A lot of those ecosystems have parallels between each other. Let’s use the Great Barrier Reef and an African savannah as an example. I’ll simplify it, because food webs can be really complex and can make it hard to get what I’m getting at.

At the base of both ecosystems are vegetation. In the Reef, it’s algae and kelp. In the savannah, it’s grass. Then you have the herbivores who eat those things. So, dugongs/krill, and gazelles/wildebeests. Then you have the carnivores, which eat other animals, like tiger sharks and lions. A lot of animals have a parallel animal in other ecosystems, and we can apply that same logic to prehistoric ecosystems, too. We can figure out roughly where animals fall in prehistoric food webs based on the features they share with modern animals. Canadaspis has a lot in common with modern benthic (bottom-feeding) animals, so we can say pretty confidently that it was a bottom-feeder. But what do you do when you have an animal like Perspicaris, which has a mix of traits but nothing pointing definitively in any direction? You speculate. Throw stuff at your peers and see what sticks.

Perspicaris looks a bit like tadpole shrimp. They have plenty of differences, but in broad strokes they look alike. Now, tadpole shrimp are bottom-feeders, too, but doesn’t have eyestalks like Perspicaris. Our friend here shares that with internet celebrity called the mantis shrimp, which actively hunts larger prey. But it doesn’t have claws like the mantis shrimp, so…

You see the problem. That’s why paleontologists debate a lot. A lot of media likes to sensationalize these disagreements like they’re rap beefs or something, but no they’re usually just discussions about stuff where people don’t agree. You know, like, how science works.  

Also, the media tends to latch onto the more outlandish stuff. There are plenty of folks around who still correct people by saying stuff like, “Actually, they found out that T. rex was a scavenger,” even though it was a theory that people only really looked at because Jack Horner liked it, and Jack Horner is, putting it lightly, a big fucking deal. That being said, there’s a truckload of evidence against that, and most scientists brush it off because Tyrannosaurus was built like a predator. Maybe I’ll talk about that someday.

So, what’s the deal with Perspicaris? In short: ¯\_(ツ)_/¯. It’s a weird little arthropod with a really vague body shape, and it’s really hard to figure it out because it doesn’t really look much like anything around now. And the thing it does look like has specializations it lacks. They’re little mysteries in a field full of little mysteries.

P.S. I have to talk about this whenever the Burgess Shale comes up, but Perspicaris has really pretty fossils.