Tag Archives: trilobites

Episode 214: Armored Fish and the Late Devonian Mass Extinctions

It’s the next in our short series of episodes about mass extinctions! Don’t worry, it won’t be boring, because we’re going to learn about a lot of weird ancient fish too.

Further reading:

Titanichthys: Devonian-Period Armored Fish was Suspension Feeder

Behind the Scenes: How Fungi Make Nutrients Available to the World

Dunkleosteus was a beeg feesh with sharp jaw plates that acted as teeth:

Titanichthys was also a beeg feesh, but it wouldn’t have eaten you (picture from the Sci-News article linked above):

Pteraspis: NOSE HORN FISH:

Cephalaspis had no jaws so it couldn’t chomp you:

Bothriolepis kind of looked like a fish in a mech suit:

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

Here’s the second in our small series of episodes about extinction events, this one the Late Devonian extinction. We’ll also learn about some weird and amazing fish that lived during this time, and a surprising fact about ancient trees.

The Devonian period is often called the Age of Fish because of the diversity of fish lineages that arose during that time. It lasted from roughly 420 million years ago to 359 million years ago. During the Devonian, much of the earth’s landmasses were smushed together into the supercontinent Gondwana, which was mostly in the southern hemisphere, and the smaller continents of Siberia and Laurussia in the northern hemisphere. The world was tropically warm, ocean levels were high, and almost all animal life lived in the oceans. Some animals had adapted to living on land at least part of the time, though, and plants had spread across the continents. The first insects had just evolved too.

Shallow areas of the ocean were home to animals that had survived the late Ordovician extinctions. There were lots of brachiopods, bivalves, crinoids, trilobites, and corals. Eurypterids were still thriving and ammonites lived in deeper water. But while all these animals are interesting, we’re mainly here for the fish.

The fish of the Devonian were very different from modern fish. Most had armor. Way back in episode 33 we talked about the enormous and terrifying dunkleosteus, which lived in the late Devonian. It might have grown up to 33 feet long, or 10 meters. Since we still don’t have any complete specimens, just head plates and jaws, that’s an estimate of its full size. However long it grew, it was definitely big and could have chomped a human in half without any trouble at all. It’s probably a good thing mammals hadn’t evolved yet. Instead of teeth, dunkleosteus had jaw plates with sharp edges and fanglike projections that acted as teeth.

Another huge fish from the Devonian is called titanichthys, which might have grown as long as dunkleosteus or even bigger, but which was probably not an apex predator. Its jaw plates were small and blunt instead of sharp, which suggests it wasn’t biting big things. It might not have been biting anything. Some researchers think titanichthys might have been the earliest known filter feeder, filtering small animals from the water by some mechanism we don’t know about yet. Filter feeders use all sorts of adaptations to separate tiny food from water, from gill rakers to baleen plates to teeth that fit together closely, and many others. A study published in 2020 compared the jaw mechanisms of modern giant filter feeders (baleen whales, manta rays, whale sharks, and basking sharks) to the jaw plates of titanichthys, as well as the jaw plates of other placoderms that were probably predators. Titanichthys’s jaws are much more similar to those of modern filter feeders, which it isn’t related to at all, than to fish that lived at the same time as it did and which it was related to.

Titanichthys and dunkleosteus were both placoderms, a class of armored fish. That wasn’t unusual, actually. In the Devonian, most fish ended up evolving armored plates or thick scales. What was unusual in placoderms were their jaws. Specifically, the fact that they had jaws at all. Placoderms were probably the first fish to evolve jaws.

Pteraspis, for instance, was an armored fish that wasn’t a placoderm. It had no fins at all but it was a good swimmer, streamlined and possibly a predator, although it might have been a plankton feeder at the surface of the ocean. It grew about 8 inches long, or 20 cm. It used its tail to propel itself through the water, and instead of fins it had spines growing from its armor that helped keep it stable. A spine on its back, near the rear of the body armor, acted as a dorsal fin, while spines on the sides of its armor, just over its gills, acted like pectoral fins. It also had some smaller spines along its back and a big spike on its nose. Probably not a good fish to swallow whole.

Cephalaspis lived in the early Devonian, around 400 million years ago in fresh water. It wasn’t very big, maybe a foot long, or 30 cm. Basically, it would have fit nicely on a dinner plate, but it wouldn’t have looked much like a trout other than its size. It wasn’t a placoderm either although it did have armor. It was probably a bottom feeder and was flattened in shape with a broad, roughly triangular head covered in armor plates. Its eyes were at the top of its head and its mouth was underneath. The rest of its body was thinner and tapered to a thin tail. It probably used its head to dig around in the mud and sand to find small invertebrates, which it slurped up and swallowed whole because it had no jaws to bite with.

In comparison, the placoderm bothriolepis was about the same size as cephalaspis and was also a bottom feeder in fresh water, but that’s where the resemblance ends. It lived later, around 375 million years ago, and probably ate decomposing plant material. Like other placoderms, it had armored plates on its head and the front part of its body. The armor at the front of its head had a little opening for its eyes, which were really close together. Its tail wasn’t armored and was probably only covered in skin without scales. Bothriolepis also had long armored pectoral fins that look sort of like spikes. Its head armor was so heavy that it probably used these spike-like fins to help push itself off the bottom. The pectoral fins of some bothriolepis species had an elbow-like joint as well as a joint at the top of the fin, making them more arm-like than fin-like. Basically, bothriolepis looks like a fish wearing a mech suit that doesn’t cover its tail. It looks like an armored box with a fish tail and spikes for arms. It looks weird.

Bothriolepis was really common throughout the world with lots of species known. The largest was B. rex, which grew up to 5 1/2 feet long, or 1.7 meters, and which had thicker armor than other placoderms. Researchers think its heavy armor would have kept it from being swept to the surface by currents. Most bothriolepis species were much smaller, though.

Because it was so common, we know quite a bit about bothriolepis. In addition to the fossilized armor plates, we have some body impressions and even fossilized internal organs. This is really rare, and the reason it’s happened more than once in bothriolepis is that the internal organs were protected by the armor plates long enough for fine sediment to fill the body before the organs decomposed or were eaten by other animals. We know that the digestive system was simple compared to modern fish but the gut was spiral shaped, which allowed more time for the plant material it ate to stay in the body so more nutrients could be extracted from it. The gills were likewise primitive, and it may have also had a pair of primitive lungs. Yes, lungs! Not all palaeontologists agree that the sacs were actually lungs, but those who do think the fish would have gulped air at the surface like a lungfish. Since most, if not all, bothriolepis species seem to have lived in freshwater, it’s possible it needed lungs to breathe air if the water where it lived was low in oxygen. Some researchers think it might even have been able to use its pectoral fins to move around on land, at least enough to move to a new water source if its home dried up. Because bothriolepis remains are sometimes found in marine environments, some researchers also speculate that it may have migrated from or to the ocean to spawn, and that it used its possible land-walking ability to navigate around obstacles while migrating along rivers.

At least some bothriolepis individuals also had a pair of weird frills at the base of the tail. They might have acted as fins but they might have had something to do with mating, like a male shark’s claspers. It’s not clear if all individuals had them or only some.

Placoderms were the first fish to develop jaws, teeth, and pelvic fins. Pelvic fins were important not just because it made the fish more stable in the water, but because they correspond to hind legs in tetrapods. Here’s something to think about: if pelvic fins hadn’t evolved in fish, would land animals have eventually evolved four legs or would all land animals have just two legs and a tail? Would humans look like mermaids and mermen, or weird seals? Would birds have evolved wings even if it meant they had no feet?

Okay, so, back to the Devonian. There were lots more fish than just the placoderms, of course. Coelacanths, lungfish, and early sharks evolved at this time and are still around, as are ray-finned fish that are the most common fish today.

But maybe with all this talk of weird fish, you’ve forgotten this is an episode about an extinction event. Ocean life in the Devonian was chugging along just fine–but then something happened, something that resulted in the same loss of oxygen in the oceans that caused so many extinctions in the late Ordovician. But no one’s sure what that was.

The extinction event actually took place in several waves millions of years apart. Researchers generally think that the same events that caused the late Ordovician extinction events may have caused the late Devonian extinction events. Toward the end of the Devonian the Earth did appear to go through several rapid temperature changes, and some researchers think the cause of these temperature changes might have been trees.

At the beginning of the Devonian, there were lots of plants on land, but they were all small. You could walk from one side of a continent to another and never encounter a plant taller than knee-high. But plants were evolving rapidly, and before long the first trees appeared. They were related to ferns, club moss, and a type of plant called horsetails, which wouldn’t have looked much like trees to us. The progymnosperms also evolved during this time, and they were ancestors of modern gymnosperms, a group which includes conifers, gingkos, and cycads. Some of these early trees didn’t even have leaves, while some had what looked like fern fronds. Some grew almost 100 feet tall, or 30 meters.

Tall trees need strong roots, and roots loosened the soil and underlying rocks to great depths. This made it more likely that heavy rains would wash soil into the water, potentially causing microbial blooms. All these trees also absorbed enormous quantities of carbon dioxide and released oxygen into the atmosphere. This sounds great, because animals need oxygen to breathe! But as trees spread across the land, growing bigger and taller, they absorbed as much as 90% of the available carbon dioxide, so much that it actually caused the earth to cool enough to cause glaciers to form.

One interesting thing about trees. Trees and other plants contain complex polymers called lignin that harden the cells. Lignin is why trees have bark and wood. Lignin is also really resistant to decay, which is why it takes so long for a fallen tree to rot down into nothing. There are specialized bacteria and fungi that can break down lignin, but most bacteria and fungi can’t affect it at all.

Plants first evolved lignin around 400 million years ago, and early trees contained a lot of it, way more than modern trees have. It took bacteria and fungi a long time to evolve ways to break that lignin down to extract nutrients from it—around 100 million years, in fact. So for 100 million years, whenever a storm knocked over a tree and it died, its trunk just…stayed there forever–or at least for a really long time, becoming more and more buried over the centuries. Lignin isn’t water soluble either, so even trees that fell into a lake didn’t rot, or at least the lignin in the trunks didn’t rot. All those tree trunks were eventually compressed by the weight of the soil above them into coal beds.

Anyway, the peak of this cycle of trees absorbing carbon dioxide and releasing oxygen actually happened in the Carboniferous period, which occurred just after the final wave of the Devonian extinctions. That’s why insects could grow so incredibly large during the Carboniferous, because the atmosphere contained so much oxygen.

But in the build-up to the late Devonian extinction events, there were periods of colder and warmer climate worldwide, possibly caused by trees, possibly by other factors, most likely by a combination of many factors. Glaciers would form and melt rapidly, possibly leading to the same issues that caused the late Ordovician extinction events.

I’ll quote a bit from episode 205 to remind you what scientists think happened in the Ordovician when a whole lot of glaciers suddenly melted:

As the glaciers melted, cold fresh water flowed into the ocean and may have caused deep ocean water to rise to the surface. The deep ocean water brought nutrients with it that then spread across the ocean’s surface, and this would have set off a massive microbial bloom.

Microbial blooms happen when algae or bacteria that feed on certain nutrients suddenly have a whole lot of food, and they reproduce as fast as possible to take advantage of it. The microbes use up oxygen, so much of it that the water can become depleted.

Rivers were also a major source of nutrients flowing into the ocean, as tree roots continued to break up rock and soil, which made its way into the water.

Whatever the cause or causes, the result was that the ocean lost most or all of its oxygen, especially in the deep sea. Oxygen, of course, is what animals breathe. Fish push water over their gills and absorb oxygen from it by a chemical process the same way we absorb oxygen from the air with our lungs. The air contains a lot of other gases in addition to oxygen, but it’s the oxygen we need.

The first wave of extinctions in the Devonian is called the Taghanic Event. A lot of brachiopods and corals went extinct then, among many other animals. About the time life started to rebound from that wave, the Kellwasser Event killed off more brachiopods and corals, a lot of trilobites, and jawless fish. Finally, the biggest and worst wave of all was the Hangenberg Event.

The Hangenberg Event was really bad. Really, really bad. In the late Ordovician extinction event, some researchers think it took three million years for the oceans to recover from their lack of oxygen. In the late Devonian extinction event, it may have taken 15 million years for the oceans to fully recover. Some researchers think that in addition to everything else going on in the world, a nearby star may have gone supernova and damaged the ozone layer that protects the earth, which would have damaged plants and animals that lived on land.

The end result of the late Devonian extinction event was that 97% of all vertebrate species went extinct, especially those that lived in shallow water, and 75% of all animal species. All placoderms went extinct and almost all corals went extinct.

Most people think that oil—you know, the stuff we use to make gasoline and plastic—came from dead dinosaurs, but that’s not the case. A lot of oil actually formed from the animals that died in the Devonian extinction events. Fish and other animals suffocated as the water lost oxygen, and the lack of oxygen at the bottom of the ocean meant that all those bodies that sank into the depths didn’t rot. They were buried by sediment and as the years and then centuries and millennia passed, more and more sediment piled up, causing pressure and heat that transformed the organic remains into a substance called kerogen. Kerogen is still an organic material and if it’s exposed to oxygen it will oxidize and decay, but if it remains deep underground for millions of years the heat and pressure will eventually transform it chemically into hydrocarbons that make up oil. Don’t ask me to explain this in any more detail than that. My mind is still blown about tree trunks not decomposing for 100 million years; there’s really no room left in my brain to wonder about how oil forms.

Anyway, luckily for us, by the time of the late Devonian extinction events, the first land vertebrates had already evolved and they survived. They spread throughout the world and thrived for 110 million years until the next major extinction event, which was so profound it’s called “the great dying” by palaeontologists. We’ll learn about that one in a few months. Next week I promise we’ll have a light, happy episode where nothing goes extinct!

You can find Strange Animals Podcast at strangeanimalspodcast.blubrry.net. That’s blueberry without any E’s. If you have questions, comments, or suggestions for future episodes, email us at strangeanimalspodcast@gmail.com. If you like the podcast and want to help us out, leave us a rating and review on Apple Podcasts or just tell a friend. We also have a Patreon at patreon.com/strangeanimalspodcast if you’d like to support us that way.

Thanks for listening!

Episode 057: Horseshoe Crabs and Cone Snails

Let’s learn about horseshoe crabs and cone snails! The former is harmless, the latter is deadly. Both are interesting!

This episode’s animals are inspired by the podcast Animals to the Max and by the book Strange Survivors by Dr. Oné R. Pagán. Check both out because they are awesome!

A horseshoe crab will never hurt you and just wants to be left alone to be a horseshoe crab:

A trilobite fossil:

A cone snail just wants to be left alone to be a cone snail but it will kill you if it has to:

Above: the stripey tube thing is the snail’s siphon, the pink tube thing is the snail’s proboscis, or VENOM DUCT.

The Glory of the Sea has a pretty shell:

More cone snail shells:

The rarest seashell in the world:

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

This week we’re going to look at animals inspired by a book I recently read and a podcast I recently discovered.

The podcast is called Animals to the Max, and it’s one of several new animal podcasts that I’ve been enjoying lately. In most episodes, the host Corbin Maxey interviews someone who works with animals. Recently I was listening to episode 15, and the subject of horseshoe crabs came up briefly. Those things are awesome and well deserving of the term living fossil, so let’s start there.

First of all, horseshoe crabs are not actually crabs. They’re not even crustaceans. In fact, they’re more closely related to spiders and scorpions than to crustaceans. There are four species of horseshoe crabs alive today, three from Asia and one from the Gulf of Mexico and American Atlantic coast. Females are larger than males and depending on the species, may be about a foot long including the tail, or 30 cm, or twice that length.

The horseshoe crab gets its name from its rounded, slightly domed carapace that’s kinda sorta the shape of a horse’s hoof, with a long spike of a tail sticking out from its rear. It has a ridiculous number of eyes—seriously, it has nine eyes plus some photoreceptors on its tail. But it doesn’t see very well. Mostly it just senses light, although it can also see into the ultraviolet range.

It also has five pairs of legs tipped with little claws, and its mouth is in the middle of the base of its legs. Its legs act as shredders to cut up its food into tiny pieces. It eats worms and other invertebrates, and will eat fish if it can get it. Most of the time it swims upside-down. It can breathe air on land for short periods of time as long as its gills stay damp. Oh, and it can regenerate legs if one is injured.

Horseshoe crab blood is blue because instead of hemoglobin, its blood contains hemocyanin to transport oxygen throughout the body. Hemoglobin contains iron, which is red, while hemocyanin contains copper, which is blue. Its blood also contains amebocytes instead of white blood cells, and amebocytes have medical applications for humans, specifically as a way to detect bacteria in medical equipment. That means horseshoe crab blood is valuable. Half a million horseshoe crabs are caught every year, up to 30% of their blood is harvested, and the crabs released back into the wild none the worse for wear. At least, that’s how it’s supposed to go. In fact, almost 30% of the horseshoe crabs released just up and die due to stress, and some companies don’t even release them. They just quietly sell them as bait. Horseshoe crabs have been used as commercial fishing bait and ground up as fertilizer for years. Because of all these pressures, along with pollution and the development of beaches where they lay their eggs, the horseshoe crab has gone from being one of the most numerous animals in the ocean to threatened in a matter of decades. Fortunately, many places have put protections and harvesting limits in place to help the population rebound.

Horseshoe crabs first appear in the fossil record 450 million years ago, near the end of the Ordovician Period, back when most life lived in the oceans and fish with jaws were only just evolving. This was well before dinosaurs. This was well before any animals were living on land at all, although probably some marine animals had discovered that if they laid their eggs on the beach, nothing much would eat them, and some other marine animals had discovered that if they could haul themselves out onto the beach for short periods of time, they might find some eggs to eat. The horseshoe crabs alive today are basically identical to the horseshoe crabs found throughout the fossil record. They hit on a successful body plan hundreds of millions of years ago and have stuck with it ever since.

Trilobites were also everywhere during the Ordovician as well as before and after, until they died out 252 million years ago. Trilobite fossils are really common so you’ve probably seen them, but they looked sort of like big roly-polies, or pill bugs, or sow bugs, depending on what you call them. Horseshoe crabs are actually related to trilobites, and one of the big questions is why trilobites died out after being so incredibly successful for so long—270 million years—while horseshoe crabs didn’t. It was probably just luck. The Great Permian Extinction event wiped out almost 90% of all life on earth, and even before then trilobites were already in decline, while the horseshoe crab was chugging along just fine.

If you’re on the beach and see a horseshoe crab on its back, trying to get right side up, help it by flipping it onto its feet. It won’t hurt you, and you might very well save its life.

The other animal I want to look at today is the cone snail, inspired by a brand new book called Strange Survivors by Oné Pagán. Dr. Pagán kindly sent me an advance copy and it is definitely a book a lot of you would find interesting. It’s about evolutionary forces and how things like venom developed in various animals. I’ll put a link in the show notes if you want to order a copy for yourself. One of the animals Dr. Pagán talks about in the book is the cone snail. I’d never heard of it before but it’s fascinating.

There are something like 800 species of cone snail, in fact. They live in tropical oceans and their shells often have beautiful geometric patterns, the kind collectors spend big bucks for. But all cone snails are venomous and some can be fatal. Cone snails are snails and therefore not exactly known for their speed, but the larger ones hunt and kill fish. How do snails hunt fish? Usually it’s the other way round.

Well, let me just tell you. You are not even going to believe this, but you should, because it is a real thing that actually happens. I’ll use the geographic cone snail as an example, because it’s been well studied. It’s about 6 inches long, or 15 cm, and is common throughout shallow reefs in the Indian Ocean and the Red Sea. It’s also the most toxic of cone snails, and there is no antidote to its venom.

So, imagine a cone snail on the bottom of a shallow, warm ocean. Small fish are swimming around. The cone snail has a mottled brown and white shell, quite pretty, and the snail itself is somewhat similar in color with a siphon sticking out of the bottom of its shell. It’s not bothering anything and some little fish ignore it because hey, they’re fast fish and it’s just a slow snail.

But when the little fish get close to the snail, something odd happens. They just sort of slow down. They stop moving and sink to the bottom, but they don’t act panicked. That’s because the snail has released venom into the water, venom containing insulin that mimics the insulin found in fish. When a fish absorbs the venom through its gills, it goes into hypoglycemic shock, which stuns it. The snail then fires a modified hollow tooth called a harpoon into the fish, injecting more venom and killing the fish. The harpoon is attached to the snail’s body by a proboscis, or venom duct, which the snail uses to winch the fish into its mouth to digest.

So far researchers have found two snails that stun fish with venom released into the water, the geographic and the tulip cone snails, but all cone snails have the harpoon contraption to shoot fish with. And the harpoon is fast. It travels at about 400 miles per hour, or 644 km per hour, and special muscles at the base of the venom duct can pump venom into the fish just as fast. Sometimes a snail will hide in the mud or sand and wiggle its proboscis like a worm, and when a fish comes to investigate, the snail harpoons it. It takes the snail a week or two to digest a fish, and during that time it also grows a new harpoon.

Cone snails also use their harpoons defensively, and they can penetrate right through clothes and even divers’ wetsuits. And the venom can kill a human in a matter of hours. The problem is that many cone snail shells are really pretty, so people pick them up to look at. The snail thinks it’s about to be eaten, defends itself, and the person thinks, “Ow, that felt funny. And my hand is going numb. Hmm. Now my whole body is going numb, how strange.” And then they die. Well, it takes longer than that, but you get the idea. Of course, only 36 people have actually died from cone shell stings in the last 90 years, but just a reminder that if you don’t get in the water you are probably safe from venomous marine snails.

On the other hand, researchers are very interested in the cone snail’s toxins. They could lead to painkillers that don’t cause dependency, better treatments for diabetes, and even treatments for nervous system disorders like Parkinson’s disease and Alzheimer’s. At least one painkiller developed from peptides in a cone snail toxin is already on the market.

One cone snail, the Glory of the Sea, was at one time thought to be the rarest shell in the world. In 1970 its habitat was discovered by divers, in various places throughout the Indo-Pacific but mostly near the Solomon Islands. Before then, though, collectors would spend thousands of U.S. dollars on a specimen. These days they can still go for around one or two hundred bucks just because they’re really pretty and still not terribly common. I’ll put a picture of one in the show notes.

This episode is a little short so let’s just plunge down this rare shell rabbit hole. The rarest shell in the world is arguably that of Sphaerocypraea incomparabilis, and its story is pretty awesome. In 1963 a trawler dredged up a dark brown cowrie type shell that made its way to a Russian shell collector. Rumors of the shell leaked out and in the 1990s, a collector named Donald Dan flew to Moscow and managed to buy the shell. It turned out to be the shell of a snail that had been thought extinct for 20 million years. It’s still extremely rare, though. Only six of the shells are known to be in collections and the living snail still hasn’t been examined by scientists or formally described.

I don’t want to get in the water more than about ankle deep, but I do enjoy beachcombing. Apparently there’s some money to be made in shell collecting, too, but don’t pick up any cone snail shells unless you’re 100% certain the shell is empty.

You can find Strange Animals Podcast online at strangeanimalspodcast.com. We’re on Twitter at strangebeasties and have a facebook page at facebook.com/strangeanimalspodcast. If you have questions, comments, or suggestions for future episodes, email us at strangeanimalspodcast@gmail.com. If you like the podcast and want to help us out, leave us a rating and review on Apple Podcasts or whatever platform you listen on. We also have a Patreon if you’d like to support us that way.

Thanks for listening!