Tag Archives: sharks

Episode 407: Cookie Cutter Shark

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Thanks to Alyx for this week’s suggestion, the cookie cutter shark!

Further reading:

If You Give a Shark a Cookie

The business end of the cookie cutter shark:

Show transcript:

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

This week we’re going to learn about a little shark suggested by Alyx, but first let’s learn about something else that might be related to the shark.

In the 1970s, the U.S. Navy started having trouble with the navigation of their submarines. The Ohio-class submarine had what was called a sonar dome that was filled with oil, and the oil helped transmit sound. But repeatedly the subs would lose navigation abilities, and investigations turned up strange chunks removed from the electric cables, the oil lines, the sound probes, and the sonar dome itself—anywhere made of rubber that was soft enough for what looked like a hole saw to damage.

The Navy thought they were dealing with a state-of-the-art weapon. The United States and the former Soviet Union were bitter enemies, so the Navy thought the USSR had invented a technologically sophisticated underwater stealth drone of some kind that could damage the subs and leave no trace—nothing but circular chunks removed from the sonar dome and its components.

Thirty submarines were damaged before the Navy figured out the cause. It wasn’t a super-secret weapon at all. It was just a little fish called the cookie-cutter shark.

The cookie cutter shark doesn’t look very scary. It only grows 22 inches long at most, or 56 cm, and is brown in color. It has lots of very sharp evenly spaced teeth on its lower jaw, but compared to a great white shark, it’s nothing to worry about. But somehow it was able to disable 30 of the world’s most advanced submarines at the time.

That’s because of how the cookie cutter shark eats, which is also how it gets its name. It picks a target fish or some other animal, such as a whale or a seal, or possibly the sonar dome of an Ohio-class submarine, and sneaks up to it. It’s just a little fish and its coloration helps it blend in with its surroundings, so most animals barely notice it. It has lips that act like a suction cup, so quick as a wink it sticks itself to the animal, bites down, and spins around. In moments it’s cut a circular chunk out of the animal’s side like a horrible cookie, which it swallows, and by the time the animal even realizes it’s hurt, the cookie cutter shark is long gone.

The shark used to be called the cigar shark because of its shape. It wasn’t until 1971 that experts realized how the cookie cutter shark eats. Until then the circular wounds on fish and whales and other animals were thought to be from lamprey bites or from some kind of parasite.

The cookie cutter shark does have teeth in its upper jaw but they’re much smaller than the lower teeth. When it sheds its lower teeth to replace them, instead of shedding just one tooth, it sheds them all at once. Like most sharks, it swallows its old teeth so it can reuse the calcium to grow new teeth.

The shark also has photophores on the underside of its body that glow greenish, which is a common way that some fish escape predators from below. A big fish looking up toward the surface of the water high above it sees a lot of light shining down from the sun, so a fish with a glowing underside just blends in. But in the case of the cookie cutter shark, it has a strip of skin on its underside without photophores, and from below that strip shows up. It’s a sort of collar that’s actually darker brown than the rest of the fish. It looks, in fact, like a tiny fish silhouetted against the surface. The would-be predator fish approaches, expecting an easy meal. Instead, the cookie cutter shark darts around and takes a big bite out of the fish, then takes off. It’s a remarkably fast swimmer, but most of the time it hangs almost motionless in the water waiting for another animal to approach. Its eyes are large and it has good vision.

Sometimes the cookie cutter shark will travel in schools, which attracts even more predators who think they’re looking at a bunch of little bitty fish. Then all the sharks get a bite.

That leads us to the uncomfortable question: has the cookie cutter shark ever bitten a piece out of a human? The answer is yes, but no one has ever died from a cookie cutter shark attack. The shark usually stays in deep water during the day and rises closer to the surface at night, so it’s not likely to encounter humans except at night. Occasionally a swimmer has been bitten, and shipwreck survivors have reported being bitten at night while waiting for rescue, which is just insult to injury. In 2023 a swimmer was bitten by two cookie cutter sharks, but he saw them and was able to just grab them both and throw them away before he was seriously hurt. That’s not something you can do with a great white.

As for the submarines, the Navy started putting fiberglass shields over the sonar dome and other softer parts of the sub, and that solved the problem. It only cost $2 billion each to repair the subs.

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. We also have a Patreon at patreon.com/strangeanimalspodcast if you’d like to support us for as little as one dollar a month and get monthly bonus episodes.

Thanks for listening!

Episode 400: Four no wait Five Mysteries!

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To donate to help victims of Hurricane Helena:

Day One Relief – direct donation link

World Central Kitchen – direct donation link

It’s the big 400th episode! Let’s have a good old-fashioned mystery episode! Thanks to Richard from NC for suggesting two of our animal mysteries today.

Further reading:

A 150-Year-Old Weird Ancient Animal Mystery, Solved

The Enigmatic Cinnamon Bird: A Mythical Tale of Spice and Splendor

First ever photograph of rare bird species New Britain Goshawk

Scientists stumbled onto toothy deep-sea “top predator,” and named it after elite sumo wrestlers

Bryde’s whales produce Biotwang calls, which occur seasonally in long-term acoustic recordings from the central and western Pacific

A stylophoran [drawing by Haplochromis – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=10946202]:

A cinnamon flycatcher, looking adorable [photo by By https://www.flickr.com/photos/neilorlandodiazmartinez/ – https://www.flickr.com/photos/neilorlandodiazmartinez/9728856384, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=30338634]:

The rediscovered New Britain goshawk, and the first photo ever taken of it, by Tom Vieras:

The mystery fish photo:

The yokozuna slickhead fish:

The Biotwang maker, Bryde’s whale:

Show transcript:

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

We’ve made it to the big episode 400, and also to the end of September. That means monster month is coming up fast! To celebrate our 400th episode and the start of monster month, let’s have a good old-fashioned mysteries episode.

We’ll start with an ancient animal called a stylophoran, which first appears in the fossil record around 500 million years ago. It disappears from the fossil record around 300 million years ago, so it persisted for a long time before going extinct. But until recently, no one knew what the stylophoran looked like when it was alive, and what it could possibly be related to. It was just too weird.

That’s an issue with ancient fossils, especially ones from the Cambrian period. We talked about the Cambrian explosion in episode 69, which was when tiny marine life forms began to evolve into much larger, more elaborate animals as new ecological niches became available. In the fossil record it looks like it happened practically overnight, which is why it’s called the Cambrian explosion, but it took millions of years. Many of the animals that evolved 500 million years ago look very different from all animals alive today, as organisms evolved body plans and appendages that weren’t passed down to descendants.

As for stylophorans, the first fossils were discovered about 150 years ago. They’re tiny animals, only millimeters long, and over 100 species have been identified so far. The body is flattened and shaped sort of like a rectangle, but two of the rectangle’s corners actually extend up into little points, and growing from those two points are what look like two appendages. From the other side of the rectangle, the long flat side, is another appendage that looks like a tail. The tail has plates on it and blunt spikes that stick up, while the other two appendages look like they might be flexible like starfish arms.

Naturally, the first scientists to examine a stylophoran decided the tail was a tail and the flexible appendages were arm-like structures that helped it move around and find food. But half a billion years ago, there were no animals with tails. Tails developed much later, and are mainly a trait of vertebrates.

That led to some scientists questioning whether the stylophoran was an early precursor of vertebrates, or animals with some form of spinal cord. The spikes growing from the top of the tail actually look a little bit like primitive vertebrae, made of calcite plates. That led to the calcichordate hypothesis that suggested stylophorans gave rise to vertebrates.

Then, in 2014, scientists found some exceptionally well preserved stylophoran fossils in the Sahara Desert in Africa. The fossils dated to 478 million years ago and two of them actually had soft tissue preserved as the mineral pyrite. Pyrite is also called fool’s gold because it looks like gold but isn’t, so these were shiny fossils.

When the soft tissue was observed through electron microscopes in the lab, it became clear that the tails weren’t actually tails. Instead, they were more like a starfish arm, with what may be a mouth at the base. The arm was probably the front of the animal, not the back like a tail, and the stylophoran probably used it to grab food and maybe even to crawl around.

Most scientists today agree that stylophorans are related to modern echinoderms like starfish and urchins, but there is one big difference. Echinoderms show radial symmetry, but no stylophoran found so far does. It doesn’t really even show bilateral symmetry, since the two points aren’t really symmetrical to each other. We’re also not sure what the points were for and how such an unusual body plan really worked, so there are still a lot of mysteries left regarding the stylophoran.

Next let’s talk about a mythical bird, called some variation of the word cynomolgus, or just the cinnamon bird. Naturalists from the ancient world wrote about it, including Pliny the Elder and Aristotle, and it appeared in medieval bestiaries. It was said to be from Arabia and to build its nest of cinnamon sticks in the tops of very tall trees or on the sides of cliffs.

Cinnamon comes from the inner bark of cinnamon trees, various species of which are native to southern Asia and Oceania. It’s an evergreen tree that needs a tropical or subtropical climate to thrive, and it smells and tastes really good to humans. You might have seen cinnamon sticks, which are curled-up pieces of dried cinnamon bark, and that’s the same type of cinnamon people used in the olden days. Ground cinnamon is just the powdered bark. Like many other spices, it was highly prized in the olden days and cost a fortune for just a little bit of it. Ancient Egyptians used it as part of the embalming process for mummies, ancient Greeks left it as offerings to the sun god Apollo, ancient Romans burnt it during the funerals of nobility, and it was sought after by kings throughout the world.

One interesting thing is that if you live in the United States, the cinnamon in your kitchen cupboard is probably actually cassia, also called Chinese cinnamon because it’s native to southern China. Cassia is often mentioned alongside cinnamon in old writings, because they’re so similar, but true cinnamon comes from a tree native to Sri Lanka. It’s usually marketed as Ceylon cinnamon and is more expensive, but cassia is actually better for baking. True cinnamon has a more subtle flavor that’s especially good with savory dishes, but it loses a lot of its flavor if you bake with it.

Anyway, back in the olden days, no one outside of subtropical Asia and Oceania knew where cinnamon came from. The traders who bought it from locals to resell definitely weren’t going to tell anyone where it was from. They made up stories that highlighted just how hard cinnamon was to find and harvest, to discourage anyone from trying to find cinnamon on their own and to keep prices really high. As Pliny the Elder pointed out 2,000 years ago, the cinnamon bird was one of those stories.

The cinnamon bird was supposedly the only animal that knew where cinnamon trees grew, and it would peel pieces of the bark off with its beak, then carry them to the Arabian desert or somewhere just as remote, where it would build a nest of the bark. The birds were supposed to be enormous, sometimes so big that their open wings stretched from horizon to horizon. Their nests were equally large, but so hard to reach that no human could hope to climb up and collect the cinnamon. Instead, cinnamon hunters left dead oxen and other big animals near the area where the birds had nests. The birds would swoop down and carry the oxen back to their nests to eat, and the extra weight would cause the nests to fall. In other stories, cinnamon hunters would shoot at the nests with arrows with ropes attached. Once several arrows were lodged into a nest, the hunters would pull the ropes to dislodge the nest and cause it to fall, so they could collect the cinnamon.

Of course none of that is true. Some scholars think the cinnamon bird is probably the same mythical bird as the phoenix, but without any magical abilities. Others agree with Pliny the Elder that it was just a way for traders to raise their prices for cinnamon even more. Either way, the cinnamon bird is probably not a real animal.

There are birds with cinnamon in their name, but that’s just a reference to their coloration. Cinnamon is generally a reddish-brown in color, and in animals that color is often referred to as rufous, chestnut, or cinnamon. For example, the cinnamon flycatcher, which lives in tropical and cloud forests along the Andes Mountains in South America. It’s a tiny round bird, only about 5 inches long including its tail, or 13 cm. It’s dark brown and red-brown in color with black legs and beak, and a bright cinnamon spot on its wings. It eats insects, which you could probably guess from the name.

This is what a cinnamon flycatcher sounds like:

[tiny bird sound]

Next, we need to talk about the New Britain goshawk, which Richard from NC told me about recently. It lives in tropical forests of Papua New Guinea, and is increasingly threatened by habitat loss. In fact, it’s so rare that it was only known from four specimens, and it hadn’t been officially spotted since 1969 and never photographed—until March of 2024.

During a World Wide Fund for Nature expedition, a wildlife photographer named Tom Vierus took lots of pictures of birds. One bird he photographed was a hawk sitting in a tree. He didn’t realize it was a bird that hadn’t been seen by scientists in 55 years, until later when he and his team were going through his photographs.

The goshawk is large, and is gray and white with an orange face and legs. We know very little about the bird, naturally, but now that scientists know it’s alive and well, they can work with the local people to help keep it safe. It’s called the keango or kulingapa in the local languages.

Next, we have a bona fide mystery animal, and a deep-sea mystery animal at that—the best combination!

In 1965, the U.S. Navy teamed up with Westinghouse to build a submersible designed by the famous diver and naturalist Jacques Cousteau. The craft was called Deepstar 4000 and between 1965 and 1972 when it was retired, it conducted hundreds of dives in different parts of the world, allowing scientists to learn a lot about the ocean. It could safely dive to 4000 feet, or 1200 meters, which isn’t nearly as deep as many modern submersibles, but which is still impressive.

This was long before remotely operated vehicles, so the submersible had to have a crew inside, both scientists and pilots. One of the pilots of Deepstar 4000 was a man named Joe Thompson. In 1966 Thompson maneuvered the craft to the ocean floor off the coast of California to deploy water sensors, in an area called the San Diego Trough. They touched down on the ocean floor and Thompson looked out of the tiny porthole, only to see something looking in at him.

Thompson reported seeing a fish with mottled gray-black skin and an eye the size of a dinner plate. He estimated it was 25 feet long, or over 7 ½ meters, which was longer than the Deepstar 4000 itself. Within seconds, the fish swam away into the darkness.

But that’s not the end of the story, because the water sensors the craft had already placed sensed the animal’s movement. There was definitely something really big near the craft. Even more interesting, an oceanographer had placed some underwater cameras in the area, and soon after Thompson’s sighting, the cameras took pictures of a huge gray fish.

While Thompson was positive the fish had scales, which he described as being as big around as coffee cups, the photo shows a more shark-like skin criss-crossed with scars. The oceanographer consulted with an ichthyologist, who identified the fish as a Pacific sleeper shark. We’ve talked about other sleeper sharks in episode 74. We don’t know a lot about these sharks, but they are gray, live in deep water, and can grow over 23 feet long, or 7 meters.

But Thompson was never satisfied with the identification of his mystery fish as a big Pacific sleeper shark. He was adamant that his fish had scales, a much larger eye than sharks have, and a tail that was more reminiscent of a coelacanth’s lobed tail than a shark’s tail.

One suggestion is that Thompson saw a new species of slickhead fish. Slickheads are deep-sea fish that can grow quite large, but we don’t know much about them since they live in such deep waters. The largest known species grows at least 8 feet long, or 2.5 meters, and possibly much longer. That’s the yokozuna slickhead, which was only discovered in 2021 by a scientific team studying cusk eels off the coast of Japan.

Most slickheads are small and eat plankton. This one was purplish in color, had lots of small sharp teeth, and was a strong, fast swimmer. When it was examined later, its stomach contents consisted of other fish, so it’s definitely a predator. Its eyes are also proportionately larger than a shark’s eyes. The slickhead gets its name because it doesn’t have scales on its head, but it does have scales on the rest of its body.

The yokozuna slickhead was discovered in a bay that’s well-known to both scientists and fishers, so the team didn’t believe at first that they could possibly have found a new species of fish there, especially one that was so big. But it definitely turned out to be new to science. More individuals have since been spotted, but they live very deep in the ocean, which explains why no one had seen one before. Interestingly, when the scientists first pulled the slickhead out of the water, they thought it looked a little like a coelacanth.

This episode was going to end there, but Richard from NC sent me another article about a whale mystery I’ve been talking about for years! It’s the so-called biotwang that we covered way back in episode 27.

In 2016 and early 2017, NOAA, the U.S. Coast Guard, and Oregon State University dropped a titanium-encased ceramic hydrophone into Challenger Deep. To their surprise, it was noisy as heck down there in the deepest water on earth. The hydrophone picked up the sounds of earthquakes, a typhoon passing over, ships, and whalesong—including the call of a whale researchers couldn’t identify. This is what it sounds like:

[biotwang whale call]

Well, as of September 2024, we now know what animal produces the biotwang call. It’s a whale, and one already known to science, although we don’t know much about it. It’s Bryde’s whale, a baleen whale that can grow up to 55 feet long, or almost 17 meters. The calls have all been associated with groups of Bryde’s whales, or a mother with a calf, so the scientists think the whales might use the unusual call to communicate location with its podmates. Bryde’s whales make lots of other sounds, and the scientists also think they might be responsible for some other mystery whale calls.

If you remember episode 193, about William Beebe’s mystery fish, he reported spotting a massive dark fish from his bathysphere a few decades before the Deepstar 4000 was built. He didn’t see it well enough to identify it and never saw it again. It just goes to show that there are definitely mystery animals just waiting to be discovered, whether it’s in the deep sea or perched in a treetop.

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. We also have a Patreon at patreon.com/strangeanimalspodcast if you’d like to support us for as little as one dollar a month and get monthly bonus episodes.

Thanks for listening!

Episode 362: The Sawfish and the Sawshark

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Thanks to Murilo for suggesting this week’s episode about the sawfish and the sawshark!

Further Reading:

Sawfish or sawshark?

Two New Species of Sixgill Sawsharks Discovered

Do not step:

The underside of a largetooth sawfish [photo by J. Patrick Fischer – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=17421638]:

The sawshark has big eyes [photo by OpenCago.info – Wikimedia Commons [1], CC BY-SA 2.5, https://commons.wikimedia.org/w/index.php?curid=25240095]:

A comparison of rostrums. The sawskate is in the middle, the one with barbels is the sawshark, and the really toothy one is the sawfish [picture by Daeng Dino – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=137983599]:

Show transcript:

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

This week we’re going to learn about an amazing fish suggested by Murilo. It’s the sawfish, and while we’re at it, we’re also going to learn about a different fish called the sawshark.

There are five species of sawfish alive today in two genera, and they’re all big. The smallest species can still grow over 10 feet long, or 3 meters, while the biggest species can grow over 20 feet long, or 6 meters. The largest sawfish ever reliably measured was 24 feet long, or 7.3 meters. Since all species of sawfish are endangered due to overfishing, pollution, and habitat loss, really big individuals are much rarer these days.

The sawfish lives mostly in warm, shallow ocean waters, usually where the bottom is muddy or sandy. It can also tolerate brackish and even freshwater, and will sometimes swim into rivers and live there just fine. The largetooth sawfish is especially happy in freshwater.

Let’s talk specifically about the largetooth sawfish for a moment, since we know the most about it. Like other sawfish, the female gives birth to live young, up to 13 babies at a time, and the babies can be up to three feet long at birth, or 90 cm. When a baby is born, its saw, which we’ll talk about in a minute, is covered with a jelly-like sheath that keeps it from hurting its mother. The sheath dissolves soon after birth.

The mother usually gives birth around the mouth of a river, and instead of swimming into the ocean, the babies swim upstream into the river. They live there for the next several years, and some individuals and even some populations may live their whole lives in the river. It’s sometimes called the river sawfish or the freshwater sawfish for this reason.

One interesting thing about the largetooth sawfish is how agile it is. All sawfish are good swimmers, but the largetooth sawfish is especially good. It can swim backwards, it can jump more than twice its own length out of the water, and it can climb over rocks and other obstacles using its fins, even if the obstacle isn’t completely submerged. It’s possible that other species of sawfish can do the same, but scientists just haven’t observed this behavior yet. We actually don’t know that much about most species of sawfish because of how rare they’ve become.

The sawfish is a type of ray, and rays are most closely related to sharks. Like sharks, rays have an internal skeleton made of cartilage instead of bone, but they also have bony teeth. You can definitely see the similarity between sharks and sawfish in the body shape although the sawfish is flattened underneath, which allows it to lie on the ocean floor. There’s also another detail that helps you tell a sawfish from a shark: the rostrum, or snout. It’s surprisingly long and studded with teeth on both sides, which makes it look like a saw.

The teeth on the sawfish’s saw are actual teeth. They’re called rostral teeth and the rostrum itself is part of the skull, not a beak or a mouth. It’s covered in skin just like the rest of the body. The sawfish’s mouth is located underneath the body quite a bit back from the rostrum’s base, and the mouth contains a lot of ordinary teeth that aren’t very sharp.

So, you may be asking, if the sawfish has plenty of teeth in its mouth, how and why does it also have those extra teeth on both sides of its saw? It’s because the rostral teeth evolved from dermal denticles. We’ve talked about dermal denticles a few times before, but a few months ago we had a Patreon bonus episode that went into more detail. In that episode, I talked about an article about a type of catfish, so let me just quote the whole section of that episode. It’s not long and I think it’s really interesting. Heck, I’ll just drop the audio in directly from that Patreon episode:

Our next article is from October 2017 and is intriguingly titled “When teeth grow on the body.” It sounds horrific, but it’s actually a study of certain catfish that grow bony plates with tiny teeth on their bodies as defense.

Catfish don’t have scales, but some species of denticulate catfish that live in South America grow bony plates that act like armor. Many of these plates are covered in thin little teeth–actual teeth, including enamel and dentin, with pulp inside. They’re called extra-oral teeth, dermal denticles, or odontodes, and the study determined that they appeared about 120 million years ago in ancient catfish that hadn’t yet evolved the bony plates. The teeth regrow when they’re lost, and in some species, males grow larger teeth than females and use them to fight other males. Imagine biting someone without needing to open your mouth.

Anyway, dermal denticles aren’t all that rare in fish. Sharks and rays are both covered with them. They’re also called placoid scales but they’re literally teeth, they’re just not used for eating. In the case of the sawfish, the rostral teeth grow much larger than an ordinary dermal denticle, and stick out sideways like the teeth of a saw. Different species have differently shaped rostral teeth. The teeth grow throughout the sawfish’s life, but unlike the teeth in the mouth, if the sawfish loses a rostral tooth, it doesn’t grow back. If it chips the top off a rostral tooth, though, that part will grow back.

The sawfish uses its rostrum to find the fish, crustaceans, and mollusks it eats. Both the rostrum and the head are packed with electroreceptors that allow the sawfish to sense tiny electrical charges that animals emit as they move. This might mean a school of fish swimming through muddy water, or it might mean a crustacean hiding in the sand. The sawfish sometimes uses its rostrum to dig prey out of the sand, but it also uses it to slash at fish or other animals. Then the sawfish can either grab the injured or dead animal with its mouth or pin it to the sea floor with its rostrum to maneuver it into its mouth. Its mouth is relatively small and it prefers to swallow its food whole, head-first, so it can only eat fish that are smaller than its mouth.

This means the sawfish leaves humans alone, because we’re way too big to fit into its mouth. It doesn’t want anything to do with us. Unfortunately, people keep bothering the sawfish, either by catching it illegally, leaving fishing nets and other trash in the ocean that sawfish and lots of other animals get tangled in, or by destroying its habitat with destructive dredging or trawling. The largetooth sawfish used to live around southern North America, but it relied on mangrove swamps to act as a nursery for baby sawfish. So many of the mangrove swamps have been destroyed so that people can build fancy hotels and shopping centers that the largetooth sawfish hasn’t been seen around North America in over 50 years, although the smalltooth sawfish is still hanging on.

Sawfish do well in captivity but require gigantic tanks, and even when given the best of care, they almost never breed in captivity. They live a long time, though, sometimes for decades.

Luckily for the sawfish, the female can reproduce without a male if she can’t find a mate. Instead of her eggs being fertilized by the male’s sperm, sometimes a female’s eggs will just develop into her genetic clones. Conservationists are working to make sure the sawfish and its habitat are protected so the babies can grow up safe and healthy.

We can’t talk about the sawfish without mentioning the sawshark. It’s a shark, not a ray, but it looks a whole lot like a sawfish–so much so that in places where both animals live, such as around Australia, people have a hard time telling them apart.

The sawshark mostly lives in much deeper water than the sawfish and is much smaller on average, about five feet long, or 1.5 meters. It has a pair of barbels about halfway down its saw that help it find food when there’s not much light to see by. Another major difference is that its gill slits are on the sides of its neck instead of under its body. It eats fish, squid, and crustaceans.

The sawshark’s rostrum also contains electroreceptors, although we don’t know for sure that it uses its saw the same way as the sawfish does. We actually don’t know very much about the sawshark, not even how many species are alive today. A new species was described in 2013 and two new species were described in 2020. There are probably more that are completely unknown to science, and maybe completely unknown to people in general.

Finally, there’s another fish that looks like a sawfish or sawshark, the sawskate, but its entire suborder, Sclerorhynchoidei, is completely extinct. It disappears from the fossil record 66 million years ago. I feel like I need a sound effect to play every time I mention that an animal went extinct 66 million years ago, to remind listeners that that’s the date of the extinction event that killed off the non-avian dinosaurs and many other animals. Maybe something like this. What do you think?

[comet sound]

Anyway, scientists are pretty sure the sawskate wasn’t very closely related to sawfish or sawsharks, but was more closely related to modern skates. Skates look a lot like rays but belong to a different family. Modern skates don’t have much of a rostrum at all, but the sawskate had a long tapering rostrum and some species had rostral teeth. Most species of sawskate were fairly small, but at least one grew an estimated 6 feet long, or about 2 meters.

If you’ve been thinking that a rostrum with teeth on both sides sounds like the kind of sword that old-timey warriors would use, you’re actually right. Traditionally, people in parts of the world where sawfish are common would sometimes use a big dried rostrum as a weapon.

These days, of course, sawfish are protected species. That means you can’t have a sawfish rostrum sword, sorry. Let the sawfish keep its sword.

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. We also have a Patreon at patreon.com/strangeanimalspodcast if you’d like to support us for as little as one dollar a month and get monthly bonus episodes.

Thanks for listening!

Episode 353: Warm-Blooded Fish

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This week we’re going to learn about some fish that feature warm-bloodedness! Thanks to Eilee for suggesting the moonfish, or opah.

Further reading:

Are all fish cold-blooded?

The Opah Fish Is Warm-Blooded!

Basking Sharks Are Partially Warm-Blooded, New Research Suggests

Megalodon Was Partially Warm-Blooded, New Research Shows

The opah, or moonfish, looks like a pancake with fins but is an active swimmer [picture from first article linked above]:

An opah not having a good day [photo by USA NOAA Fisheries Southwest Fisheries Science Center – https://swfsc.noaa.gov/ImageGallery/Default.aspx?moid=4724, Public Domain]:

Show transcript:

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

Months ago now, Eilee suggested we talk about the sunfish. We’re actually not going to talk about the sunfish this week, although it is on the list to cover eventually. Instead, we’re going to talk about something else in Eilee’s email. Eilee asked if there was a moonfish too, and not only is there a moonfish, it’s basically the most unique fish alive today in one particular way. It’s warm-blooded!

The moonfish is also called the opah. It’s golden-orange in color with little white spots, and it’s very round and flattened side-to-side, like a pancake with orange fins. It has big golden eyes and a tiny mouth. It’s also quite large, with the biggest species growing up to 6 and a half feet long, or 2 meters. That’s a really big pancake. It lives in the ocean, sometimes diving deeply, and despite looking like a pancake, it can swim very quickly to catch squid and small fish. It also eats krill. The reason it can swim so quickly is because it has huge muscles that power its fins, and the muscles also generate a lot of heat, enough to keep its entire body at least several degrees warmer than the surrounding water. This is a warm-blooded trait, but fish are supposed to be cold-blooded.

The scientific term for warm-bloodedness is endothermy. Mammals and birds are endothermic, meaning our internal body temperature stays roughly the same no matter what temperature it is outside. Cold-bloodedness, called ectothermy, means an animal’s internal body temperature fluctuates depending on the temperature outside its body. Reptiles, amphibians, fish, and invertebrates are all cold-blooded.

To us as mammals, it feels like warm-bloodedness is a really good idea, but it comes at a high cost. Mammals and birds have to eat a lot more and a lot more often than cold-blooded animals do, because keeping our body temperature steady takes a whole lot of energy. An endothermic animal generates heat mainly by metabolizing food, although muscle movements like shivering and running also generate heat. An endothermic animal can be as active at night as it is during the day, and can be as active in winter as it is in summer.

Some otherwise cold-blooded animals can generate enough heat with muscle movements to warm parts of the body, called regional endothermy, or can generate heat with muscle movements in certain situations, called facultative endothermy. The female of some species of snake, especially some pythons, will wrap her body around her eggs and shiver, which generates enough heat to keep the eggs warm. Bumblebees can also shiver to warm their bodies enough to allow them to fly in cold weather. At least some species of sea turtle, including the green sea turtle and the leatherback, generates enough heat in its muscles while swimming that it’s able to migrate long distances in very cold water. Some scientists think all marine reptiles may be regional endotherms to some degree.

Some fish demonstrate regional endothermy too. So far, 35 species of fish are known to be partially warm-blooded, including some species of tunas, sharks, and billfish. Scientists originally thought that only predatory fish needed the extra boost of speed and endurance that endothermy provides, but then they discovered the basking shark is regionally endothermic, and the basking shark is a filter feeder that doesn’t need to chase after fast-moving fish. Also, almost nothing eats it, so it’s not running from anything either.

The basking shark is also huge, one the largest sharks alive today. It can grow over 40 feet long, or more than 12 meters, and possibly longer, although most individuals are closer to 25 feet long, or around 7 1/2 meters. It mostly lives in cold waters, sometimes diving quite deeply but sometimes feeding at the surface of the ocean. It just goes where it can find lots of tiny food that it filters out of the water with structures called gill rakers. The basking shark just swims forward with its gigantic mouth open, water flows through its gills, and the gill rakers catch any tiny particles of food. The gill rakers funnel the food toward the throat so the shark can swallow it. It mostly swims slowly and isn’t a threat to anything in the ocean except the tiniest of tiny animals. So why does it need parts of its body to be warmer than the water it’s in?

Scientists think it may have something to do with how far the basking shark travels in a year, since endothermy provides more energy for endurance swimming. The basking shark migrates thousands of miles, presumably following the best conditions to find plenty of food, although we don’t know for sure. It could be that it prefers a specific type of environment to breed or have babies. In the summer basking sharks do congregate in groups even though the rest of the year they’re solitary. The female retains fertilized eggs in her body, where the eggs hatch and the babies continue developing until they’re born a few months later. Scientists think the unborn babies eat unfertilized eggs after the food in their yolk sacs runs out.

The basking shark is critically endangered and is protected in many countries, but because it migrates such long distances it doesn’t always stay where it’s safe. Learning more about it helps conservationists know how best to protect it, and that’s how scientists discovered it was regionally endothermic. It generates heat from muscles deep inside its body as it swims, which helps keep its organs warmer than the surrounding water.

Other sharks are known to share this trait, and in June of 2023, a new study about megalodon indicated that it was probably regionally endothermic too. Megalodon went extinct almost 4 million years ago and was so big that it makes even the largest great white shark look like a teeny little baby shark. I may be exaggerating a little bit. The great white’s teeth grow around 2 and a half inches long, or a little over 6 cm. Megalodon’s teeth were 7 inches long, or 18 cm. We don’t know how big Megalodon’s body was, but it could probably grow at least 34 feet long, or 10.5 meters, and possibly grew as much as 67 feet long, or 20 meters. It ate whales. Like the basking shark and some other living sharks, including the great white, the heat generated by its muscles as it swam would have kept its internal organs, eyes, and brain warmer than the water around it.

But the opah takes this a step farther. Instead of keeping parts of its body warm, it’s just full-on endothermic. It’s warm-blooded. It mainly generates heat by moving its muscles, and it retains heat with a layer of special fatty tissue around its gills, organs, and some muscles. It also has a heat exchange system in its blood vessels that’s incredibly efficient. Cold water flowing through the gills chills the blood, but as the chilled blood flows deeper into the body, it’s warmed up by passing closely alongside heated blood flowing out from the heart. As a result, the opah can maintain its body temperature even when spending lots of time in cold water.

We actually don’t know that much about the opah, even though it’s a fish people like to catch and eat. It was described scientifically in 1799, which means it took well over 200 years for scientists to figure out that it was a warm-blooded fish. That means it’s very likely that it’s not the only endothermic fish alive today, it’s just the only one we’ve found so far.

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. We also have a Patreon at patreon.com/strangeanimalspodcast if you’d like to support us for as little as one dollar a month and get monthly bonus episodes.

Thanks for listening!

Episode 314: Animals Discovered in 2022

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Let’s learn about some of the animals discovered in 2022! There are lots, so let’s go!

Further Reading:

In Japanese waters, a newly described anemone lives on the back of a hermit crab

Rare ‘fossil’ clam discovered alive

Marine Biologists Discover New Giant Isopod

Mysterious ‘blue goo’ at the bottom of the sea stumps scientists

New Species of Mossy Frog Discovered in Vietnam

A Wildlife YouTuber Discovered This New Species of Tarantula in Thailand

Meet Nepenthes pudica, Carnivorous Plant that Produces Underground Traps

Scientists discover shark graveyard at the bottom of the ocean

Further Watching:

JoCho Sippawat’s YouTube channel

A newly discovered sea anemone (photo by Akihiro Yoshikawa):

A mysterious blue blob seen by a deep-sea rover:

A newly discovered frog:

A newly discovered tarantula (photo by JoCho Sippawat):

Show transcript:

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

It’s the 2022 discoveries episode, where we learn about some of the animals discovered in 2022! Most of the time these animals were actually discovered by scientists before 2022, but the description was published in that year so that’s when we first learned about them. And, of course, a lot of these animals were already known to the local people but had never been studied by scientists before. There are lots of animals in the world but not that many scientists.

The great thing is, so many animals get discovered in any given year that I have to pick and choose the ones I think listeners will find most interesting, which in a stunning coincidence turns out to be the ones that I personally find most interesting. Funny how that works out.

We’ll start in the ocean, which is full of weird animals that no human has ever seen before. It’s about a hermit crab who carries a friend around. The hermit crab was already known to science, but until a team of scientists observed it in its natural habitat, the deep sea off the Pacific coast of Japan, no one realized it had an anemone friend.

The sea anemone is related to jellyfish and is a common animal throughout the world’s oceans. Some species float around, some anchor themselves to a hard surface. Many species have developed a symbiotic relationship with other animals, such as the clownfish, which is sometimes called the anemonefish because it relies on the anemone to survive. Anemones sting the way jellyfish do, but it doesn’t sting the clownfish. Researchers aren’t sure why not, but it may have something to do with the clownfish’s mucus coating. Specifically, the mucus may have a particular taste that the anemone recognizes as belonging to a friend. If the anemone does accidentally sting the clownfish, it’s still okay because the fish is generally immune to the anemone’s toxins.

The clownfish lives among the anemone’s tentacles, which protects it from predators, and in return its movements bring more oxygen to the anemone by circulating water through its tentacles, its droppings provide minerals to the anemone, and because the clownfish is small and brightly colored, it might even attract predators that the anemone can catch and eat.

Anemones also develop mutualistic relationships with other organisms, including a single-celled algae that lives in its body and photosynthesizes light into energy. The algae has a safe place to live while the anemone receives some of the energy from the algae’s photosynthesis. But some species of anemone have a relationship with crabs, including this newly discovered anemone.

The anemone anchors itself to the shell that the hermit crab lives in. The crab gains protection from predators, who would have to go through the stinging tentacles and the shell to get to the crab, while the anemone gets carried to new places where it can find more food. It also gathers up pieces of food that the crab scatters while eating, because crabs are messy eaters.

The problem is that hermit crabs have to move into bigger shells as they grow. Anemones can move, but incredibly slowly. Like, snails look like racecar drivers compared to anemones. The anemone moves so slowly that the human eye can’t detect the movement.

What the team of scientists witnessed was a hermit crab spending several days carefully pushing and pinching the anemone to make it move onto its new shell. If it wasn’t important, the crab wouldn’t bother. The sea anemone hasn’t yet been officially described since it’s still being studied, but it appears to be closely related to four other species of anemone that also attach themselves to the shells of other hermit crab species.

In other marine invertebrate news, a researcher named Jeff Goddard was turning rocks over at low tide at Naples Point, California a few years ago. He was looking for sea slugs, but he noticed some tiny clams. They were only about 10 mm long, but they extended a white-striped foot longer than their shells. Goddard had never seen anything quite like these clams even though he was familiar with the beach and everything that lived there, so he took pictures and sent them to a clam expert. The expert hadn’t seen these clams before either and came to look for the clams in person. But they couldn’t find the clams again. It took ten trips to the beach and an entire year before they found another of the clams.

They thought the clam might be a new species, but part of describing a new species is examining the literature to make sure the organism wasn’t already described a long time ago. Eventually the clam research team did find a paper with illustrations of a clam that matched, published in 1937, but that paper was about a fossilized clam.

They examined the 1937 fossil shell and compared it to their modern clam shell. It was a match! But why hadn’t someone else noticed these clams before? Even Goddard hadn’t seen them, and he’s a researcher that spends a lot of time along the coast looking specifically for things like little rare clams. Goddard thinks the clam has only recently started extending its range northward, especially during some marine heatwaves in 2014 through 2016. He suspects the clam’s typical range is farther south in Baja California, so hopefully a future expedition to that part of the Pacific can find lots more of the clams and we can learn more about it.

We talked about deep-sea isopods just a few weeks ago, in episode 311. They’re crustaceans related to crabs and lobsters, but also related to roly-polies that live on land. The deep-sea species often show deep-sea gigantism and are referred to as giant isopods, and that’s what this newly discovered species is. It was first found in 2017 in the Gulf of Mexico and is more slender than other giant isopods. The largest individual measured so far is just over 10 inches long, or 26 cm, which is almost exactly half the length of the longest giant isopod ever measured. It’s still pretty big, especially if you compare it to its roly-poly cousins, also called pillbugs, sow bugs, or woodlice, who typically grow around 15 mm at most.

Before we get out of the water, let’s talk about one more marine animal. This one’s a mystery that I covered in the October 2022 Patreon episode. It was suggested by my brother Richard, so thank you again, Richard!

On August 30, 2022, a research team was off the coast of Puerto Rico, collecting data about the sea floor. Since the Caribbean is an area of the ocean with high biodiversity but also high rates of fishing and trawling, the more we can learn about the animals and plants that live on the sea floor, the more we can do to help protect them.

When a remotely operated vehicle dives, it sends video to a team of scientists who can watch in real time and control where the rover goes. On this particular day, the rover descended to a little over 1,300 feet deep, or around 407 meters, when the sea floor came in view. Since this area is the site of an underwater ridge, the sea floor varies by a lot, and the rover swam along filming things and taking samples of the water, sometimes as deep as about 2,000 feet, or 611 meters.

The rover saw lots of interesting animals, including fish and corals of various types, even a fossilized coral reef. Then it filmed something the scientists had never seen before. It was a little blue blob sitting on the sea floor.

The blue blob wasn’t moving and wasn’t very big. It was shaped roughly like a ball but with little points or pimples all over it and a wider base like a skirt where it met the ground, and it was definitely pale blue in color.

Then the rover saw more of the little blue blobs, quite a few of them in various places. The scientists think it may be a species of soft coral or a type of sponge, possibly even a tunicate, which is also called a sea squirt. All these animals are invertebrates that don’t move, which matches what little we know about the blue blob.

The rover wasn’t able to take a sample from one of the blue blobs, so for now we don’t have anything to study except the video. But we know where the little blue blobs are, so researchers hope to visit them again soon and learn more about them.

It wouldn’t be a newly discovered species list without at least one new frog. Quite a few frogs were discovered in 2022, including a tree frog from Vietnam called Khoi’s mossy frog. It lives in higher elevations and is pretty big for a tree frog, with a big female growing over 2 inches long, or almost 6 cm, from snout to vent. Males are smaller. It’s mostly brown and green with little points and bumps all over that help it blend into the moss-covered branches where it lives. That’s just about all we know about it so far.

Our next discovery is an invertebrate, a spider that lives in bamboo. Specifically it lives in a particular species of Asian bamboo in Thailand, and when I say it lives in the bamboo, I mean it really does live inside the bamboo stalks. Also, when I say it’s a spider, specifically it’s a small tarantula.

It was first discovered by a YouTuber named JoCho Sippawat, who travels around his home in Thailand and films the animals he sees. I watched a couple of his videos and they’re really well done and fun, and he’s adorable even when he’s eating gross things he finds, so I recommend his videos even if you don’t speak the language he speaks. I’m not sure if it’s Mandarin or another language, and I’m not sure if I’m pronouncing his name right either, so apologies to everyone from Thailand for my ignorance.

Anyway, Sippawat found a tarantula where no tarantula should be, inside a bamboo stalk, and sent pictures to an arachnologist. That led to a team of scientists coming to look for more of the spiders, and to their excitement, they found them and determined right away that they’re new to science. It was pretty easy to determine in this case because even though there are more than 1,000 species of tarantula in many parts of the world, none of them live in bamboo stalks. The new spider was placed in a genus all to itself since it’s so different from all other known tarantulas.

It’s mostly black and dark brown with narrow white stripes on its legs, and its body is only about an inch and a half long, or 3 1/2 cm. It can’t make holes into the bamboo plants itself, so it has to find a hole made by another animal or a natural crack in the bamboo. It lines its bamboo stalk with silk to make a little home, and while there’s a lot we don’t know yet about how it lives, it probably comes out of its home to hunt insects and other small animals since tarantulas don’t build webs.

Finally, let’s wrap around to the sea anemone again, at least sort of. If you remember episode 129, we talked about the Venus flytrap sea anemone, which is an animal that looks kind of like a carnivorous plant called the Venus flytrap. We then also talked about a lot of other carnivorous plants, including the pitcher plant. Well, in 2022 a new species of pitcher plant was discovered that has underground traps.

The pitcher plant has a type of modified leaf that forms a slippery-sided pitcher filled with a nectar-like liquid. When an insect crawls down to drink the liquid, it falls in and can’t get out. It drowns and is dissolved and digested by the plant. Almost all known carnivorous plants are pretty small, but the largest are pitcher plants. The biggest pitcher plant known is from a couple of mountains in Malaysian Borneo, and its pitchers can hold over 2 ½ liters of digestive fluid. The plant itself is a messy sort of vine that can grow nearly 20 feet long, or 6 meters. Mostly pitcher plants just attract insects, especially ants, but these giant ones can also trap frogs, lizards, rats and other small mammals, and even birds.

The newly discovered pitcher plant grows in the mountainous rainforests of Indonesian Borneo and is relatively small. Unlike every other pitcher plant known, its pitchers develop underground and can grow a little over 4 inches long, or 11 cm. Sometimes they grow just under the surface, with leaf litter or moss as their only covering, but sometimes they grow deeper underground. Either way, they’re very different from other pitcher plants in other ways too. For one thing, scientists found a lot of organisms actually living in the pitchers and not getting eaten by the plant, including a new species of worm. Scientists aren’t sure why some animals are safe in the plant but some animals get eaten.

The new pitcher plant is found in parts of Indonesian Borneo that’s being turned into palm oil plantations at a devastating rate, leading to the extinction or threatened extinction of thousands of animal and plant species. The local people are also treated very badly. Every new discovery brings more attention to the plight of the area and makes it even more urgent that its ecosystems are protected from further development. The fastest way to do this would be for companies to stop using so much palm oil. Seriously, it’s in everything, just look at the ingredients list for just about anything. I try to avoid it when I’m grocery shopping but it’s just about impossible. I didn’t mean to rant, but the whole palm oil thing really infuriates me.

You know what? Let’s have one more discovery so we don’t end on a sour note.

A biodiversity survey of two of Australia’s marine parks made some really interesting discoveries in 2022. This included a new species of hornshark that hasn’t even been described yet. It’s probably related to the Port Jackson shark, which grows to around five and a half feet long, or 1.65 meters, and is a slow-moving shark that lives in shallow water off the coast of most of Australia. Instead of a big scary mouth full of sharp teeth, the Port Jackson shark has a small mouth and flattened teeth that allow it to crush mollusks and crabs. The newly discovered shark lives in much deeper water than other hornsharks, though, around 500 feet deep, or 150 meters.

Another thing they found during the survey wasn’t a new species of anything, but it’s really cool so I’ll share it anyway. It was a so-called shark graveyard over three miles below the ocean’s surface, or 5400 meters. The scientists were trawling the bottom and when they brought the net up to see what they’d found, it was full of shark teeth–over 750 shark teeth! They were fossilized but some were from modern species while some were from various extinct species of shark, including a close relative of Megalodon that grew around 39 feet long, or 12 meters. No one has any idea why so many shark teeth are gathered in that particular area of the sea floor.

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 Podchaser, or just tell a friend. We also have a Patreon at patreon.com/strangeanimalspodcast if you’d like to support us for as little as one dollar a month and get monthly bonus episodes.

Thanks for listening!

Episode 261: Walking Fish

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Thanks to my brother Richard for suggesting one of the fish we talk about this week–fish that can walk! (Sort of.)

Further watching:

Video of a gurnard walking

Further reading:

Walking shark moves with ping-pong paddle fins

Walking sharks discovered in the tropics

The Hawaiian seamoth (the yellowy one is a larval seamoth, the brighter one with the snoot the same fish as a juvenile, both pictures by Frank Baensch from this site):

 

The slender seamoth (an adult, photo from this site):

A flying gurnard with its “wings” extended:

A flying gurnard with its “wings” folded, standing on its walking rays:

An eastern spiny gurnard standing on its walking rays:

A mudskipper’s frog-like face:

Mudskippers on land:

Walking sharks:

Show transcript:

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

This week we’re going to look at some weird fish, specifically fish that use their fins to walk. Well, sort of walk. Thanks to my brother Richard for suggesting one of these fish.

Before we get started, let’s learn the terms for a fish’s two main pairs of fins. Different types of fish have different numbers and locations of fins, of course, but in this episode we’re focusing on the pectoral fins and the pelvic fins. Pectoral fins are the main fins in most fish, the ones near the front on each side. If a fish had arms, that’s roughly where its arms would be. The pelvic fins are near the tail on either side, roughly where its legs would be if fish had legs. If you remember that people lift weights with their arms to develop their pectoral muscles in the chest, you can remember where pectoral fins are, and if you remember that Elvis Presley was sometimes called Elvis the Pelvis because he danced by shaking his hips, you can remember where the pelvic fins are.

So, let’s start with the seamoth, which lives in shallow tropical waters of the Indo-Pacific Ocean and the Red Sea, including around Australia. We don’t know enough about it to know if it’s endangered or not, but since it’s considered a medicine in some parts of Asia, it’s caught to sell as an aquarium fish, and its habitat is increasingly impacted by bottom trawling and coastal development, it probably isn’t doing great. It’s never been especially common and doesn’t reproduce very quickly. Researchers think it may even be a social fish that forms a pair bond with its mate, since pairs are often found together.

The seamoth doesn’t even look that much like a fish at first glance. It’s covered with bony plates that act as armor, including bony rings around its tail. It even has to shed its skin as it grows larger.

The seamoth has a long, pointed snout with a tiny mouth underneath, but it can protrude its mouth out of its…mouth–okay that doesn’t make sense. Basically it’s able to extend its mouth into a tube that it uses like a straw to slurp up worms and other small animals from the sea floor.

It can change colors to match its surroundings too. If all this makes you think of seahorses and pipefish, the seamoth is related to both, but it looks very different because of its fins.

The seamoth’s pectoral fins are so large they resemble wings, and its modified pelvic fins are stiff and more fingerlike than fin-like so that it can walk across the sea floor with them. It spends most of its time walking on the sea floor, only swimming when it feels threatened and has to move faster. Sometimes a seamoth will cover itself with sand to hide from a predator. During breeding season, males develop brightly colored patterns on their pectoral fins.

The seamoth is a small fish, with the largest species growing about five inches long, or 13 cm. One species of seamoth, the little dragonfish, sheds its armor in one big piece—not just once or twice a year, but as often as every five days or so when it needs to rid itself of parasites. Its body is flattened but broad, which makes it look kind of like a piece of shell from above.

The flying gurnard is similar in some ways. It lives in warm coastal waters where it spends most of its time on the sea floor, looking for small animals to eat. We’ve talked about it before, in episode 101, but let’s go over it again in case like me you haven’t listened to episode 101 since it came out over three years ago.

The flying gurnard is a bulky fish that grows more than a foot and a half long, or 50 cm. It has a face sort of like a frog’s and can be reddish, brown, or greenish, with spots and patches of other colors. But most importantly, its pectoral fins are extremely large, looking more like fan-like wings than fins. The so-called wings are shimmery, semi-transparent, and lined with bright blue. They sort of look like butterfly wings and can be more than 8 inches long, or 20 cm. The fins actually have two parts, a smaller section in front and the larger wing-like section behind. The front section is stiff and makes the fish able to walk along the sea floor. It’s possible the flying gurnard can also use its wing-like fins to glide above the water for short distances like a flying fish, but at the moment we don’t know for sure.

The flying gurnard hasn’t traditionally been recognized as being related to the seamoth despite their similarities, but DNA studies suggest that they might actually be related after all. The flying gurnard may be related to the true gurnards, too. Both the flying gurnard and the true gurnard have a special muscle that beats against the swim bladder to make a drumming sound, and they look and act alike in many other ways too.

The gurnard is the fish my brother Richard recommended. There are actually a lot of different gurnards and they’re all kind of weird. Gurnards in the family Triglidae are bottom dwellers that grow around 16 inches long, or 40 cm. Some species have armor plates that make their heads so strong that a gurnard will occasionally ram snorkelers with its forehead if they get too close. Like the flying gurnard, the gurnard has pectoral fins that are divided into a front section and a rear section, with the rear section being larger and the front section highly modified, called walking rays, used by the fish to walk across the sea floor.

Walking rays look more like long, thin, stiff fingers than a fish’s fins, although they’re also bendy. The gurnard has three walking rays on each side of the body, and they have special muscles that allow the fish to actually use them as little legs. It’s really disturbing to watch an otherwise pretty ordinary fish crawl forward on what look like invertebrate legs.

The mudskipper is another fish that uses its fins to walk, but not like the fish we just talked about. Instead of having walking rays, its pectoral fins are muscular and allow it to climb out of the water and onto land. In fact, it can climb into low branches and can even jump.

It’s so good at living on land the mudskipper is actually considered semi-aquatic. It lives in mudflats, mangrove swamps, the mouths of rivers where they empty into the ocean, and along the coast, although it prefers water that’s less salty than the ocean but more salty than ordinary freshwater. It only lives in tropical and subtropical areas because it needs high humidity to absorb oxygen through its skin and the lining of its mouth and throat.

The mudskipper is a fish, but it looks an awful lot like a frog in some ways, due to convergent evolution. It has a wide mouth and froglike eyes at the top of its head and will often float just under the water with its eyes above water, looking for insects it can catch. The largest species grows about a foot long, or 30 cm, and while it has some scales, its body is coated with a layer of mucus to help it retain moisture. It spends most of the day on land, hunting for insects and other small animals. Not only can it absorb oxygen through its skin, it keeps water in its gill chambers to keep the gills wet too. It even has a little dimple under its eye that holds water, that helps keep its eyes moist.

The mudskipper also takes a big mouthful of water with it when it climbs on land, but not to breathe. It uses the water to hunt with. When it encounters an insect or other small animal on land, it carefully rotates its mouth–you heard me right, it can rotate its mouth–so that it’s just above the animal. Then it spits out the mouthful of water onto the insect and immediately sucks the water back into its mouth, carrying the insect with it. When it catches an animal underwater, it opens its big mouth quickly, causing suction that sucks the animal right into its mouth that way. It also has sharp teeth, so when an animal is in its mouth, it’s not getting out again.

The mudskipper’s pectoral fins look like little arms, complete with an elbow. The elbow is actually a joint between the radial bones, which in most fish are hidden within the body but which stick out of the mudskipper’s sides a short distance, and the actual fins. This helps it move around on land more easily. Its pelvic fins are also shaped in such a way that they act as little suction cups on land.

Another bottom-dwelling fish that uses its fins to walk on the sea floor is the walking shark. There are several species known but they’re not very big, only around four feet long at most, or 107 cm. It lives in shallow coastal waters, often around reefs, and spends most of the time swimming just above the sea floor or using its pectoral and pelvic fins to walk on the sea floor while it searches for small animals to eat. It doesn’t walk like gurnards do, and it doesn’t skip or climb the way mudskippers do. Instead, it wriggles like a salamander as it uses its fins to push itself along.

At least one species of walking shark can also walk on land. That’s right: land shark. Don’t worry, it’s harmless to humans. (Still: land shark.) Because the walking shark often lives in really shallow water, including in tidal pools that sometimes dry up completely between high tides, it has to be able to reach water by walking on land. The walking shark can also survive in water with low oxygen content for short periods of time. Four newly identified species of walking shark were announced in January 2020, all from around New Guinea and northern Australia.

The really interesting thing is that the walking shark’s pectoral and pelvic fins are different from other shark fins. Not only are they strongly muscled, they can rotate to make it easier for the shark to use them as legs. Researchers think that this type of locomotion may have given rise to land animals in our far, far-distant ancestors. In other words, we’re all land sharks if you think about it.

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 Podchaser, or just tell a friend. We also have a Patreon at patreon.com/strangeanimalspodcast if you’d like to support us for as little as one dollar a month and get monthly bonus episodes.

Thanks for listening!

Episode 229: Blue Ghosts and Vanishing Sharks

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I got to meet some listeners this week to see the synchronous fireflies, so thanks to Shannon, Diana, Derek, and Autumn for hanging out with me! This week we’ll learn about a different kind of lightning bug as well as a shark mystery!

Derek’s photography, Enchanting Ectotherms

Further reading:

A shark mystery millions of years in the making

I suspect this is a doctored image but it’s gorgeous so here it is anyway, supposedly some blue ghost fireflies:

This is a real photo, no photoshop, taken by Derek Wheaton during our trip. The long line of light in the middle is a blue ghost moving with its light on during a long exposure:

A synchronous firefly on Derek’s hand (photo by Derek Wheaton):

A tiny blue ghost firefly on Derek’s hand (photo by Derek Wheaton):

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw. It’s been an amazing week for me because I got to take some people to see our local synchronous fireflies! The fireflies put on a brilliant show for us and the weather was perfect, and it was so much fun to meet Shannon and Diana! Then, two nights later, I also took Derek and Autumn out to see the fireflies. In between, I started research on the blue ghost firefly, since I had originally thought it was just another name for the synchronous firefly, but it’s not. So this week we’re going to learn about the blue ghost firefly, along with some interesting breaking news about a shark mystery.

The blue ghost firefly only lives in parts of the eastern and central United States. In most places it’s rare, but like the synchronous fireflies that all flash together, the blue ghost fireflies are actually pretty common in the southern Appalachian Mountains. The reason why people don’t see them more often is that these days, most people don’t spend much time in the woods at night.

Like other fireflies, the blue ghost lives in forests with deep leaf litter where there’s a lot of moisture in the ground. The female lays her eggs in the leaf litter and when the eggs hatch, the larval fireflies eat tiny insects and other invertebrates like snails.

The blue ghost firefly is different from other firefly species in several ways. First, it doesn’t flash. The male stays lighted up for around a minute at a time while he flies low over the ground watching for a female to light up too. Its glow also appears bluish-white to human eyes, at least in the distance and when it’s really dark out. Up close, it looks yellow-green like other firefly lights. Researchers think it only looks blue because of the way human eyes perceive color in low light.

In the daytime, blue ghost fireflies don’t look like much. They’re small, around 7 mm long, and males are all brown. The females don’t have wings, and in fact they never metamorphose into the adult form and still look like larvae as adults. The female crawls to the end of a twig or blade of grass and glows to attract a mate.

When I was doing my research to learn about blue ghost fireflies, I kept seeing articles comparing its size to a grain of rice. I looked up the average size of a grain of rice, and that’s where I got 7 mm. I didn’t think too much about it.

When Shannon, Diana, and I were watching the synchronous fireflies, we noticed some fireflies that didn’t flash, just stayed glowing while they drifted along low over the forest floor. After I started researching blue ghost fireflies, I realized that was what had seen! So I was especially excited to go back out with Derek and Autumn and confirm it.

Derek works for a nonprofit that breeds endangered fish for conservation projects, which is awesome, but he’s also a photographer, so he brought his camera to try and get pictures and video of the fireflies. His photographs are amazing so if you want to see them I’ve linked to his Facebook page, EnchantingEctotherms, in the show notes. He does a lot of snorkeling so a lot of the animals he photographs are fish or other water animals like turtles and snakes, and he gives information about them in his posts.

Anyway, he wanted to get close-up pictures of a synchronous firefly and a blue ghost firefly, so we all spent some time trying to catch one of each—gently, of course, and without leaving the trail. We didn’t want to hurt ourselves in the dark or disturb the fireflies’ habitat. Derek caught a synchronous firefly first, and it looks like an ordinary firefly that I’m used to, the common eastern firefly, which grows to about 14 mm long. That’s half an inch long. Then, eventually, he also caught a blue ghost. It was so small that at first we thought he might have caught some other beetle by accident, until we looked more closely and saw the telltale head shape of a lightning bug. I took a photo myself and put it in the show notes so you can see just how small it is.

From my own observation, the blue ghosts are much dimmer than other fireflies, which makes sense since they’re so much smaller. The light does look faintly blue-white in the distance, but when it’s closer to you it looks like an ordinary firefly’s light. They do indeed fly very low to the ground while lit up, but they’re also cautious. We had trouble catching one because when we got too close, the firefly would fly down to the ground and put his light out.

Naturally, after photographing our lightning bugs we let them go again. I’m happy to report that the synchronous fireflies have expanded their range a lot since I first stumbled across them about ten years ago, and the blue ghosts seem reasonably common too. They live in a protected area of our local watershed so they’ll be safe and sound forever, hopefully.

This is good, because blue ghosts in particular are vulnerable to habitat loss. Since the female can’t fly, she can’t travel far to lay her eggs. During mating season, some state and national parks in the southern Appalachians close some trails to protect the blue ghost and other fireflies, especially from light pollution from flashlights.

The synchronous fireflies and blue ghosts are only active for a few weeks in June, which is their mating season. We’ll probably be just about at the end of this year’s display by the time you hear this, but if you’re going to be in East Tennessee and want to go out and see them with me next summer, just let me know. As we talked about in episode 180, they only live a few minutes’ walk away from a small parking lot but no one but me seems to know about them.

Next, let’s learn about a shark mystery that’s 19 million years old but that scientists only learned about recently. This month, June of 2021, a team of researchers published results of a shark study in the journal Science. The team had decided to graph the number and diversity of shark species known from the fossil record so they’d have a baseline to compare modern shark diversity to. But they discovered something really surprising.

Nineteen million years ago, there were over ten times as many sharks in the oceans as there are today. They were an important part of the ocean’s ecosystems, especially in the open ocean. And then…they disappear from the fossil record. Over 90% of the world’s sharks died, with shark diversity decreasing by more than 70%. Not only that, sharks never fully recovered from whatever happened.

So what did happen? We don’t know yet. There was a small extinction event called the Middle Miocene extinction peak five million years after the sharks vanished, which researchers think was due to global cooling leading to climate change. The cooling period was caused by a lot of factors, but a big cause was changes in ocean currents and air currents as the continents moved into new positions. Before that, though, the world was comfortably warm for millions of years and the shark population was overall quite stable. Researchers have found no reason why sharks suddenly started dying in such huge numbers, especially in the open ocean instead of in coastal waters.

The leader of the study, Elizabeth Sibert, says that there might have been a climate event of some kind that was disastrous to sharks but that was over relatively quickly, leaving very little evidence behind except for the fossil remains of way more sharks than usual and a lack of sharks afterwards.

Other scientific teams have already started studying the open ocean ecosystem from 19 million years ago and earlier for clues as to what happened, whether other animals were affected, and why sharks never regained their supremacy in the world’s oceans afterwards. That’s how science works: someone makes a discovery and that inspires lots of new studies, which lead to more discoveries. When we do learn more about the great shark die-off of the Miocene, I will keep you posted.

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 Podchaser, or just tell a friend. We also have a Patreon at patreon.com/strangeanimalspodcast if you’d like to support us that way, and don’t forget to join our mailing list. There’s a link in the show notes.

Thanks for listening!

 

Episode 227: The Great Dying

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It’s another extinction event episode! This one’s about the end-Permian AKA the Permian-Triassic AKA the GREAT DYING.

Further Reading:

Ancient mini-sharks lived longer than thought

Lystrosaurus’s fossilized skeleton:

Lystrosaurus may have looked something like this but I hope not:

This artist’s rendition of lystrosaurus looks a little less horrific but it might not be any more accurate:

Show transcript:

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

It’s time for our next extinction event episode, and this week it’s the big one. Not the extinction event that killed the dinosaurs, but one you may not have heard of, one that almost destroyed all life on earth. I mean, obviously it didn’t and things are fine now, but it was touch and go there for a while. It’s the Permian-Triassic extinction event, or end-Permian, which took place just over 250 million years ago. It was so bad that scientists who aren’t given to hyperbole refer to it as the Great Dying.

Don’t worry, we won’t talk about extinction the whole time. We’ll also learn about some interesting animals that survived the extinction event and did just fine afterwards.

We have a better idea of what happened at the end of the Permian than we have about the earlier extinction events we talked about in episodes 205 and 214. Right about 252 million years ago, something caused a massive volcanic eruptive event in what is now Siberia. Some researchers speculate that the cause of the volcanic eruptions may have been a huge asteroid impact on the other side of the Earth, which was so powerful that it caused magma to move away from the impact like water sloshing in a jostled glass. The magma rose up toward the earth’s crust and eventually through it onto the surface.

The result was probably the largest volcanic event in the last half-billion years and it continued for an estimated two million years. Most of the eruptions were probably pretty low-key, just runny lava pouring out of vents in the ground, but there was just so much of it. Lava covered almost a million square miles of land, or 2.6 million square km. Ash and toxic gases from some eruptions also ended up high in the atmosphere, but one big problem was that the lava poured through sediments full of organic material in the process of turning into coal. Lava, of course, is molten rock and it’s incredibly hot. It’s certainly hot enough to burn a bunch of young coal beds, which added more ash and toxic gases to the air—so much ash that shallow water throughout the entire world became choked with ash.

The carbon dioxide released by all that burning coal caused severe ocean acidification and ocean anoxia—a lack of oxygen in the water. But it gets worse! A lot of lava erupted into the ocean right at the continental shelf, where the shallow coastal water becomes much deeper. This is exactly the place where you find methane deposits in the sediments on the ocean floor. When those deposits were suddenly disturbed by lava flowing into them, all the methane in the formerly tranquil depths was released and bubbled to the surface. Methane is a powerful greenhouse gas, meaning that if a whole lot of it ends up in the atmosphere in a short amount of time, it can cause rapid global warming—much faster than that caused by carbon dioxide. This global warming would have happened after a period of global cooling due to reduced sunlight reaching the earth through ash clouds, which lasted long enough and was severe enough that sea levels dropped as glaciers formed. Then everything heated way, way up. The ice caps melted, which may have led to a stagnation of ocean currents. This in turn would have contributed to the water’s anoxicity and toxicity. The average temperature of the ocean would have increased by almost 15 degrees Fahrenheit, or 8 degrees Celsius. Atmospheric warming may have been as much as 68 degrees Fahrenheit in places, or 20 degrees Celsius. That’s not the average temperature of the world, that’s the temperature increase.

So, basically, everything was terrible and it happened very quickly in geologic terms. A 2018 study found that everything looked pretty much fine for the 30,000 years leading up to the great dying. Some researchers even think the initial extinction event might have taken place over just a few centuries.

Marine animals were affected the most, especially marine invertebrates. Trilobites and placoderms went extinct, eurypterids went extinct, and corals went extinct until about 14 million years later when modern corals developed. Some researchers estimate that 95% of all marine species went extinct.

Things were better on land, but not that much better. At the end of the Permian, life was good on land and it was especially good for insects because of the high percentage of oxygen in the air and the variety of plant life in huge swamps around the supercontinent Pangaea. The largest insects that ever lived were buzzing around in the Permian. This included an order of insects called Meganisoptera, or griffinflies. Griffinflies looked like dragonflies and may be related to them. Some species had a wingspan 28 inches across, or 71 cm. The arthropod Anthopleura, sometimes called the giant millipede, lived in the Permian too. Some species grew six feet long, or 2.5 meters, and were about 18 inches wide, or 45 cm. It looked like a millipede but had even more legs. It probably looked scary, but it only ate plants as far as we know.

Instead of actively breathing the way most vertebrates do, most invertebrates use a passive system to absorb oxygen from the air. This is great when there’s a lot of oxygen. When the level of oxygen drops, though, the largest species can’t absorb enough oxygen to function and die out rapidly. That’s one reason why you don’t have to worry about spiders the size of bears. So all the large invertebrates and a lot of the smaller ones went extinct as oxygen was replaced with carbon dioxide, methane, and other toxic gases in the atmosphere.

The acid rain caused by toxic gases and the reduced sunlight caused by ash in the atmosphere also killed off plants. Forests died, so that the fossil record during and after the extinction event contains massive amounts of fungal spores from fungi that decompose trees. Some researchers think all of the world’s trees died. Forests disappeared for some four million years. Since trees absorb carbon dioxide from the atmosphere and release oxygen, the lack of trees made oxygen levels drop even more.

Animals that depended on forests to survive also went extinct, including about two-thirds of all amphibians, reptiles, and therapsids. Therapsids were proto-mammals and it’s a good thing they didn’t all die out because they eventually gave rise to mammals.

Everything I’ve described sounds so incredibly bad, you may be wondering how anything survived. One stroke of luck was probably the size of Pangaea. That was the supercontinent made up of most of the world’s landmasses all smushed together. Before the extinction event, the middle of Pangaea was probably pretty dry with swampier climates around the edges. After the extinction event, the interior of the supercontinent was the safest place to be.

One of the most common land animals after the extinction event was a herbivore called Lystrosaurus. Lystrosaurus was a therapsid, and it was nothing exciting to look at unless you were also a lystrosaurus. Some species were the size of a cat while some were much larger, up to 8 feet long, or 2.5 m. It had a short snout, a short tail, and a semi-sprawling gait. A lizard walks with its legs stuck out to the sides, while a dog or cat or pig walks with its legs underneath its body. Lystrosaurus was somewhere between the two.

It probably lived in burrows that it dug with its strong front legs. While it had a pair of tusks that grew down from the upper jaw, those were its only teeth. Instead it probably had a turtle-like beak that helped it bite off pieces of vegetation.

Lystrosaurus lived in the central part of Pangaea, in what is now Asia, Antarctica, South Africa, and eastern Europe back when all those areas were all scrunched up close together. It survived the extinction event and expanded its range, and for millions of years it was almost the only big land animal in the world. It had almost no predators because they’d all gone extinct, and it had very few competitors for food because they’d all gone extinct. Lystrosaurus made up 90% of all land vertebrates for millions of years.

How did it survive when so many other animals died out? There are several theories, but the most important factor was probably its lack of specialization. It could survive on any kind of plant instead of needing to feed on specific species of plant. There’s also evidence that it could enter a torpor similar to hibernation where its metabolism slowed way down. This would have been a literal lifesaver during the time when the air and water were toxic and very little plant life survived. Lystrosaurus could hunker down in its burrow for long stretches of time, then come out and find enough food and water to keep it going for another stretch of torpor.

Just imagine the world back then, after the initial extinction event but before the world had recovered—say, a million years after the volcanic activity stopped. Picture a series of gentle rolling hills dotted with grazing animals. It’s peaceful and very open because there are no trees. Grass hasn’t evolved yet so the ground is covered in fern-like plants from the genus Dicroidium, which lives in dry conditions. As you look closer with your mind’s eye, you realize that every single one of those grazing animals—thousands of them visible in every direction—are the same kind of animal that looks sort of like a fuzzy pig with a stumpy lizard tail, clawed feet, and a turtle’s beak. Lystrosaurus, living the good life.

In the ocean, the situation was similar. The shallows were toxic waste dumps of ash where the water had so little oxygen that nothing could survive. But the deeper ocean was still livable for some animals.

For a long time, scientists thought a group of early sharks called cladodontomorphs had gone extinct during the great dying. Their distinctive teeth had been common in the fossil record, but after the extinction event they disappeared. Cladodontomorphs only grew about a foot long at most, or 30 cm, and may have had a weird-shaped dorsal fin that pointed forward. They lived in shallow coastal waters. You know, the worst possible place to be 252 million years ago.

Then palaeontologists found some of those teeth in rocks that were in much deeper water 135 million years ago. It turns out the little sharks had survived the extinction event by moving into the open ocean where conditions were better. And they didn’t just survive, they lasted for another 120 million years.

So let’s break it down. It was probably four million years before trees developed again from different plants. It was some 14 million years before coral reefs could rebuild as modern corals developed after their cousins went extinct. It took 30 million years for terrestrial vertebrates to recover from the great dying and 50 million years for all the ocean’s ecosystems to fully recover. That’s a colossally long time. But it did recover.

So what animals arose once the recovery was well underway? Icthyosaurs. Archosaurs, which eventually evolved into pterosaurs, crocodilians, dinosaurs, and birds. And therapsids that eventually gave rise to modern mammals.

I don’t usually tease the following week’s show, but next week we’re going to learn about some weird and interesting animals that developed in the early to mid Triassic, after the extinction event was over and life started evolving in new directions. As I’ve said in the previous extinction event episodes: no matter how bad things get, there’s always going to be some little animal stumping along out of the carnage to get on with the business of surviving and thriving.

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 Podchaser, 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 216: Gentle Giant Sharks

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Let’s learn about some of the biggest sharks in the sea–but not sharks that want to eat you!

Further reading:

‘Winged’ eagle shark soared through oceans 93 million years ago

Manta-like planktivorous sharks in Late Cretaceous oceans

Before giant plankton-eating sharks, there were giant plankton-eating sharks

An artist’s impression of the eagle shark (Aquilolamna milarcae):

Manta rays:

A manta ray with its mouth closed and cephalic fins rolled up:

Pseudomegachasma’s tooth sitting on someone’s thumbnail (left, photo by E.V. Popov) and a Megachasma (megamouth) tooth on someone’s fingers (right):

The megamouth shark. I wonder where its name came from?

The basking shark, also with a mega mouth:

The whale shark:

Leedsichthys problematicus (not a shark):

Show transcript:

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

This week we’re going to look at some huge, weird sharks, but they’re not what you may expect when you hear the word shark. Welcome to the strange world of giant filter feeders!

This episode is inspired by an article in the brand new issue of Science, which you may have heard about online. A new species of shark is described in that issue, called the eagle shark because of the shape of its pectoral fins. They’re long and slender like wings.

The fossil was discovered in 2012 in northeastern Mexico, but not by paleontologists. It came to light in a limestone quarry, where apparently a quarry worker found it. What happened to it at that point isn’t clear, but it was put up for sale. The problem is that Mexico naturally wants fossils found in Mexico to stay in Mexico, and the authors of the study are not Mexican. One of the authors has a history of shady dealings with fossil smugglers too. On the other hand, the fossil has made its way back to Mexico at last and will soon be on display at a new museum in Nuevo León.

Fossils from this quarry are often extremely well preserved, and the eagle shark is no exception. Sharks don’t fossilize well since a shark’s skeleton is made of cartilage except for its teeth, but not only is the eagle shark’s skeleton well preserved, we even have an impression of its soft tissue.

The eagle shark was just slightly shorter than 5 ½ feet long, or 1.65 meters. Its tail looks like an ordinary shark tail but that’s the only ordinary thing about it. The head is short and wide, without the long snout that most sharks have, it doesn’t appear to have dorsal or pelvic fins, and its pectoral fins, as I mentioned a minute ago, are really long. How long? From the tip of one pectoral fin to the other measures 6.2 feet, or 1.9 meters. That’s longer than the whole body.

Researchers think the eagle shark was a filter feeder. Its mouth would have been wide to engulf more water, which it then filtered through gill rakers or some other structure that separated tiny animals from the water. It expelled the water through its gills and swallowed the food.

The eagle shark would have been a relatively slow swimmer. It glided through the water, possibly flapping its long fins slowly in a method called suspension feeding, sometimes called underwater flight. If this makes you think of manta rays, you are exactly correct. The eagle shark occupied the same ecological niche that manta rays do today, and the similarities in body form are due to convergent evolution. Rays and sharks are closely related, but the eagle shark and the manta ray evolved suspension feeding separately. In fact, the eagle shark lived 93 million years ago, 30 million years before the first manta remains appear in the fossil record.

The eagle shark lived in the Western Interior Seaway, a shallow sea that stretched from what is now the Gulf of Mexico straight up through the middle of North America. Because it’s the only specimen found so far, we don’t know when it went extinct, but researchers suspect it died out 65 million years ago at the same time as the non-avian dinosaurs. We also don’t have any preserved teeth, which makes it hard to determine what sharks it was most closely related to. Hopefully more specimens will turn up soon.

Now that we’ve mentioned the manta ray, let’s talk about it briefly even though it’s not a shark. It is big, though, and it’s a filter feeder. If you’ve never seen one before, they’re hard to describe. If it had gone extinct before humans started looking at fossils scientifically, we’d be as astounded by it as we are about the eagle shark—maybe even moreso because it’s so much bigger. Its body is sort of diamond-shaped, with a blunt head and short tail, but elongated fins that are broad at the base but end in drawn-out points.

Manta rays are measured in width, sometimes called a wingspan since their long fins resemble wings that allow it to fly underwater. There are two species of manta ray, and even the smaller one has a wingspan of 18 feet, or 5.5 meters. The larger species can grow 23 feet across, or 7 meters. Some other rays are filter feeders too, all of them closely related to the manta.

The manta ray lives in warm oceans, where it eats zooplankton. Its mouth is wide and when it’s feeding it moves forward with its mouth open, letting water flow into the mouth and through the gills. Gill rakers collect tiny food, which the manta ray swallows. It has a pair of fins on either side of the mouth that are sometimes called horns, but which are properly called cephalic fins. Cephalic just means “on the head.” These fins help direct water into the mouth. When a manta ray isn’t feeding, it closes its mouth just like any other shark, folding its shallow jaw shut. For years I thought it closed its mouth by folding the cephalic fins over it, but that’s not the case, although it does roll the fins up into little points. The manta ray is mostly black with a white belly, but some individuals have white markings on the back and black speckles and splotches underneath. We talked about some mysteries associated with its coloring in episode 96.

The eagle shark isn’t the only filter feeding shark. The earliest known is Pseudomegachasma, the false megamouth, which lived around 100 million years ago. It was only described in 2015 after some tiny shark teeth were found in Russia. The teeth looked like those of the modern megamouth shark, although they’re probably not related. The teeth are only a few millimeters long but that’s the same size as teeth from the megamouth shark, and the megamouth grows 18 feet long, or 5.5 m.

Despite its size, the megamouth shark wasn’t discovered until 1976, and it was only found by complete chance. On November 15 of that year, a U.S. Navy research ship off the coast of Hawaii pulled up its sea anchors. Sea anchors aren’t like the anchors you may be thinking of, the big metal ones that drop to the ocean’s bottom to keep a ship stationary. A sea anchor is more like an underwater parachute for ships. It’s attached to the ship with a long rope on one end, and opens up just like a parachute underwater. The tip of the parachute has another rope attached with a float on top. When the navy ship brought up its sea anchors, an unlucky shark was tangled up in one of them. The shark was over 14 ½ feet long, or 4 ½ m, and didn’t look like any shark anyone had ever seen.

The shark was hauled on board and the navy consulted marine biologists around the country. No one knew what the shark was. It wasn’t just new to science, it was radically different from all other sharks known. Since then, only about 100 megamouth sharks have ever been sighted, so very little is known about it even now.

The megamouth is dark brown in color with a white belly, a wide head and body, and a large, wide mouth. The inside of its lower lip is a pale silvery color that reflects light, although researchers aren’t sure if it acts as a lure for the tiny plankton it eats, or if it’s a way for megamouths to identify each other. It’s sluggish and spends most of its time in deep water, although it comes closer to the surface at night.

The basking shark is even bigger than the megamouth. It can grow up to 36 feet long, or 11 meters. It’s so big it’s sometimes mistaken for the great white shark, but it has a humongous wide mouth and unusually long gill slits, and, of course, its teeth are teensy. It’s usually dark brown or black, white underneath, and while it spends a lot of its time feeding at the surface of the ocean, in cold weather it spends most of its time in deep water. In summer, basking sharks gather in small groups to breed, and sometimes will engage in slow, ponderous courtship dances that involve swimming in circles nose to tail.

But the biggest filter feeder shark alive today, and possibly alive ever, is the whale shark. It gets its name because it is literally as large as some whales. It can grow up to 62 feet long, or 18.8 meters, and potentially longer.

The whale shark is remarkably pretty. It’s dark gray with a white belly, and its body is covered with little white or pale gray spots that look like stars on a night sky. Its mouth is extremely large and wide, and its small eyes are low on the head and point downward. Not only can it retract its eyeballs into their sockets, the eyeballs actually have little armored denticles to protect them from damage. The body also has denticles, plus the whale shark’s skin is six inches thick, or 15 cm.

The whale shark lives in warm water and migrates long distances. It mostly feeds near the surface although it sometimes dives deeply to find plankton. It filters water differently from the megamouth and basking sharks, which use gill rakers. The whale shark has sieve-like filter pads instead. The whale shark doesn’t need to move to feed, either. It can gulp water into its mouth by opening and closing its jaws, unlike the other living filter feeders we’ve talked about so far.

We talked about the whale shark a lot in episode 87, if you want to know more about it.

All these sharks are completely harmless to humans, but unfortunately humans are dangerous to the sharks. Even though they’re all protected, they’re vulnerable to getting tangled in nets, killed by ships running over them, and killed by poachers.

One interesting thing about these three massive filter feeding sharks is their teeth. They all have tiny teeth, but the mystery is why they have teeth at all. Their teeth aren’t just tiny, they have a LOT of teeth, more than ordinary sharks do. It’s the same for the filter feeding rays. They have hundreds of teensy teeth that the animals don’t use for anything, as far as researchers can tell. One theory is that the babies may use their teeth before they’re born. All of the living filter feeders we’ve talked about, including manta rays, give birth to live pups instead of laying eggs. The eggs are retained in the mother’s body while they grow, and she can have numerous babies growing at different stages of development at the same time. The babies have to eat something while they’re developing, once the yolk in the egg is depleted, and unlike mammals, fish don’t nourish their babies through umbilical cords. Some researchers think the growing sharks eat the mother’s unfertilized eggs, and to do that they need teeth to grab hold of slippery eggs. That still doesn’t explain why adults retain the teeth and even replace them throughout their lives just like other sharks. Since all of the filter feeders have teeth although they’re not related, the teeth must confer some benefit.

So, why are these filter feeders so enormous? Many baleen whales are enormous too, and baleen whales are also filter feeders. Naturally, filter feeders need large mouths so they can take in more water and filter more food out of it. As a species evolves a larger mouth, it also evolves a larger body, and this has some useful side effects. A large animal retains heat even if it’s not actually warm-blooded. A giant fish can live comfortably in cold water as a result. Filter feeding also requires much less effort than chasing other animals, so a giant filter feeder has plenty of energy for a relatively low intake of food. And, of course, the larger an animal is, the fewer predators it has because there aren’t all that many giant predators. At a certain point, an adult giant animal literally has no predators. Nothing attacks an adult blue whale, not even the biggest shark living today. Even a really big great white shark isn’t going to bite a blue whale. The blue whale would just bump the shark out of the way and probably go, “HEY, STOP IT, THAT TICKLES.” The exception, of course, is humans, who used to kill blue whales, but you know what I mean.

Let’s finish with a filter feeder that isn’t a shark. It’s not even closely related to sharks. It’s a ray-finned fish that lived around 165 million years ago, Leedsichthys problematicus. Despite not being related to sharks and being a member of what are called bony fish, its skeleton is partially made of cartilage, so fossilized specimens are incomplete, which is why it was named problematicus. Because the fragmented fossils are a problem. I’m genuinely not making this up to crack a dad joke, that’s exactly why it got its name. One specimen is made up of 1,133 pieces, disarticulated. That means the pieces are all jumbled up. Worst puzzle ever. Remains of Leedsichthys have been found in Europe and South America.

As a result, we’re not completely sure how big Leedsichthys was. The most widely accepted length is 50 feet long, or 16 meters. If that’s anywhere near correct, it would make it the largest ray-finned fish that ever lived, as far as we know. It might have been much larger than that, though, possibly as long as 65 feet, or 20 meters.

Leedsichthys had a big head with a mouth that could open extremely wide, which shouldn’t surprise you. Its gills had gill rakers that it used to filter plankton from the water. And we’re coming back around to where we started, because like the eagle shark, Leedsichthys had long, narrow pectoral fins. Some palaeontologists think it had a pair of smaller pelvic fins right behind the pectoral fins instead of near the tail, but other palaeontologists think it had no pelvic fins at all. Because we don’t have a complete specimen, there’s still a lot we don’t know about Leedsichthys.

The first Leedsichthys specimen was found in 1886 in a loam pit in England, by a man whose last name was Leeds, if you’re wondering where that part of the name came from. A geologist examined the remains and concluded that they were part of (wait for it) a type of stegosaur called Omosaurus. Two years later the famous early palaeontologist Othniel Marsh examined the fossils, probably rolled his eyes, and identified them as parts of a really big fish skull.

In 1899, more fossils turned up in the same loam pits and were bought by the University of Cambridge. IA palaeontologist examined them and determined that they were (wait for it) the tail spikes of Omosaurus. Leeds pointed out that nope, they were dorsal fin rays of a giant fish, which by that time had been named Leedsichthys problematicus.

In 1982, some amateur palaeontologists excavated some fossils in Germany, but they were also initially identified as a type of stegosaur—not Omosaurus this time, though. Lexovisaurus. I guess this particular giant fish really has been a giant problem.

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