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  • Episode 414: Two Marvelous Frogs

    Episode 414: Two Marvelous Frogs
    2025/01/06
    Thanks to Eilee and Alexis for their suggestions this week, two amazing frogs! Further reading: Paradoxical frog: The giant tadpole that turns into a little frog Fungus is wiping out frogs. These tiny saunas could save them. How to build a frog sauna The paradoxical frog [photo by Mauricio Rivera Correa - http://calphotos.berkeley.edu, CC BY-SA 2.5, https://commons.wikimedia.org/w/index.php?curid=6703905]: The Vietnamese mossy frog [photo by H. Zell - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=81804225]: Show transcript: Welcome to Strange Animals Podcast. I’m your host, Kate Shaw. Let’s start 2025 off right with an episode about frogs! Thanks to Alexis and Eilee for their suggestions. Let’s start with Eilee’s suggestion, the paradoxical frog. The paradoxical frog is a type of tree frog that lives in South America. Like other frogs, it likes ponds and shallow lakes. Some individuals are green and some are brown, and a frog may have darker stripes or splotches, or might just be plain. The tadpoles eat algae and other tiny food, while the adults eat insects. As with most frogs, the paradoxical frog hatches into a larval stage called a tadpole or pollywog, which is fully aquatic. It later metamorphoses into its adult form as a frog. Most tadpoles start out very small and grow larger, then metamorphose into a juvenile frog which then grows to fully adult size. But while the paradoxical frog’s tadpole starts out small, it can grow to as much as 11 inches long, or 28 centimeters! It’s the largest tadpole in the world as far as we know. So how big is the adult frog if the tadpole is so enormous? About 3 inches long, or 7.5 cm, from snout to vent. That’s why it’s called the paradoxical frog, because a paradox is something that seems contradictory to expectations. Instead of the ordinary way of things, where a small tadpole grows into a bigger frog, in this case a big tadpole grows into a smaller frog. It’s sometimes called the shrinking frog. One interesting detail is that not all of the tadpoles are that big. If a female lays her eggs in a small body of water that’s likely to dry up, or that doesn’t have a lot of food available, or if there are a lot of predators in the water, the tadpole metamorphoses quickly and doesn’t grow very big. But if the tadpole is in a better location it matures much more slowly, which allows it to reach much larger size before metamorphosing. I should also mention that the 11-inch-long tadpole that is the largest ever measured was actually raised in captivity. In the wild, the largest paradoxical frog tadpole ever measured was 6 ½ inches long, or almost 17 cm. That’s still really big, but not that ridiculously big. But the confusing thing is that the tadpole is big and bulky, up to four times the size of the adult frog. Where does all that mass go after it transforms? Early scientists who learned about the paradoxical frog wondered the same thing. They were so confused that they suggested that the frog actually came first and later metamorphosed into the tadpole, which then metamorphosed into a fish. But the main reason the tadpole is so long is its tail. When it metamorphoses into a frog, it absorbs the tail and therefore appears to shrink. The bulkiness of the tadpole’s body matches the bulkiness of the frog’s body. And unlike most frogs, which metamorphose into juvenile frogs that still have some growing to do, the paradoxical frog metamorphoses into a completely adult frog. It’s as big as it will ever get and fully mature, ready to mate and lay eggs. Next, Alexis wanted to learn about the Vietnamese mossy frog. It lives in parts of Vietnam, Laos, and other nearby areas. It prefers mountainous rainforests and the female often chooses to lay her eggs in a tree hollow or even a rock cavity where water has collected. Instead of laying her eggs in the actual water, though, she lays them on rocks or branches above the water.
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    8 分
  • Episode 413: The Great American Interchange

    Episode 413: The Great American Interchange
    2024/12/30
    Thanks to Pranav for suggesting this week's massive topic! Further reading: When did the Isthmus of Panama form between North and South America? Florida fossil porcupine solves a prickly dilemma 10-million years in the making Evidence for butchery of giant armadillo-like mammals in Argentina 21,000 years ago Glyptodonts were big armored mammals: The porcupine, our big pointy friend: Show transcript: Welcome to Strange Animals Podcast. I’m your host, Kate Shaw. This week, at long last, we’re going to learn about the great American interchange, also called the great American biotic interchange. Pranav suggested this topic ages ago, and I’ve been wanting to cover it ever since but never have gotten around to it until now. While this episode finishes off 2024 for us, it’s the start of a new series I have planned for 2025, where every so often we’ll learn about the animals of a particular place, either a modern country or a particular time in history for a whole continent. These days, North and South America are linked by a narrow landmass generally referred to as Central America. At its narrowest point, Central America is only about 51 miles wide, or 82 km. That’s where the Panama Canal was built so that ships could get from the Atlantic Ocean to the Pacific and vice versa without having to go all around South America. It wasn’t all that long ago, geologically speaking, that North and South America were completely separated, and they had been separated for millions of years. South America was part of the supercontinent Gondwana, while North America was part of the supercontinent Laurasia. We’ve talked about continental drift before, which basically means that the land we know and love on the earth today moves very, very slowly over the years. The earth’s crust, whether it’s underwater or above water, is separated into what are called continental plates, or tectonic plates. You can think of them as gigantic pieces of a broken slab of rock, all of the pieces resting on a big pile of really dense jelly. The jelly in this case is molten rock that’s moving because of its own heat and the rotation of the earth and lots of other forces. Sometimes two pieces of the slab meet and crunch together, which forms mountains as the land is forced upward, while sometimes two pieces tear apart, which forms deep rift lakes and eventually oceans. All this movement happens incredibly slowly from a human’s point of view--like, your fingernails grow faster than most continental plates move. But even if a plate only moves 5 millimeters a year, after a million years it’s traveled 5 kilometers. Anyway, the supercontinent Gondwana was made up of plates that are now South America, Africa, Australia, Antarctica, and a few others. You can see how the east coast of South America fits up against the west coast of Africa like two puzzle pieces. Gondwana actually formed around 800 million years ago, then became part of the even bigger supercontinent Pangaea, and when Pangaea broke apart around 200 million years ago, Gondwana and Laurasia were completely separate. North America was part of Laurasia. But Gondwana continued to break apart. Africa and Australia traveled far away from South America as molten lava filled the rift areas and helped push the plates apart, forming the South Atlantic Ocean. Antarctica settled onto the south pole and India traveled past Africa until it crashed into Eurasia. By about 30 million years ago, South America was a gigantic island. It’s easy to think that all this happened just like taking puzzle pieces apart, but it was an incredibly long, complicated process that we don’t fully understand. To explain just how complicated it is, let’s talk for a moment about marsupials. Marsupials are mammals that are born very early and finish developing outside of the mother’s womb, usually in a special pouch. Kangaroos, wallabies, koalas, wombats, and Tasmanian devils are all marsupials, and all from Australia.
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    18 分
  • Episode 412: Whales and Dolphins

    Episode 412: Whales and Dolphins
    2024/12/23
    Thanks to Elizabeth, Alexandra, Kimberly, Ezra, Eilee, Leon, and Simon for their suggestions this week! Further reading: New population of blue whales discovered in the western Indian Ocean An Endangered Dolphin Finds an Unlikely Savior--Fisherfolk The humpback whale: The gigantic blue whale: The tiny vaquita: The Indus river dolphin: The false killer whale: Show transcript: Welcome to Strange Animals Podcast. I’m your host, Kate Shaw. This week we’re going to have a big episode about various dolphins and whales! We’ve had lots of requests for these animals lately, so let’s talk about a bunch of them. Thanks to Elizabeth, Alexandra, Kimberly, Ezra, Eilee, Leon, and Simon for their suggestions. We’ll start with a quick overview about dolphins, porpoises, and whales, which are called cetaceans. All cetaceans alive today are carnivorous, meaning they eat other animals instead of plants. This includes the big baleen whales that filter feed, even though the animals they eat are tiny. Cetaceans are mammals that are fully aquatic, meaning they spend their entire lives in the water, and they have adaptations to life in the water that are simply astounding. All cetaceans alive today belong to either the baleen whale group, which filter feed, or the toothed whale group, which includes dolphins and porpoises. The two groups started evolving separately about 34 million years ago and are actually very different. Toothed whales are the ones that echolocate, while baleen whales are the ones that have extremely loud, often beautiful songs that they use to communicate with each other over long distances. It’s possible that baleen whales also use a limited type of echolocation to navigate, but we don’t know for sure. There’s still a lot we don’t know about cetaceans. Now let’s talk about some specific whales. Ezra wanted to learn more about humpback and blue whales, so we’ll start with those. Both are baleen whales, specifically rorquals. Rorquals are long, slender whales with throat pleats that allow them to expand their mouths when they gulp water in. After the whale fills its mouth with water, it closes its jaws, pushing its enormous tongue up, and forces all that water out through the baleen. Any tiny animals like krill, copepods, small squid, small fish, and so on, get trapped in the baleen. It can then swallow all that food and open its mouth to do it again. The humpback mostly eats tiny crustaceans called krill, and little fish. The humpback grows up to 56 feet long, or 17 meters, with females being a little larger than males on average. It’s mostly black in color, with mottled white or gray markings underneath and on its flippers. Its flippers are long and narrow, which allows it to make sharp turns. The humpback is closely related to the blue whale, which is the largest animal ever known to have lived. It can grow up to 98 feet long, or 30 meters, and it’s probable that individuals can grow even longer. It can weigh around 200 tons, and by comparison a really big male African elephant can weigh as much as 7 tons. Estimates of the weight of various of the largest sauropod dinosaurs, the largest land animal ever known to have lived, is only about 80 tons. So the blue whale is extremely large. The blue whale only eats krill and lots of it. To give you an example of how much water it can engulf in its enormous mouth in order to get enough krill to keep its massive body going, this is how the blue whale feeds. When it finds an area with a lot of krill floating around, it swims fast toward the krill and opens its giant mouth extremely wide. When its mouth is completely full, its weight—body and water together—has more than doubled. Its mouth can hold up to 220 tons of water. Since the whale is in the water, it doesn’t feel the weight of the water in its mouth. Blue whales live throughout the world’s oceans, but a few years ago scientists analyzing recordings of whale song from the we...
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    13 分
  • Episode 411: Lionfish and Sea Squirrel

    Episode 411: Lionfish and Sea Squirrel
    2024/12/16
    Thanks to David and Jayson for their suggestions this week! Further reading: Unveiling the lionfish invasion in the Mediterranean Sea DeepCCZ: The Weird and Wonderful Megafauna of the Abyssal CCZ The red lionfish is beautiful but does not look like a lion [photo by Alexander Vasenin - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=25523559]: The sea squirrel is yellow above and red underneath (pictures from article linked above): Under side of a gummy squirrel photographed on shipboard showing its bright red feeding palps (flower-like structure) and underbelly. Gummy squirrel (“Psychropotes longicauda”) at 5100 m depth on abyssal sediments in the western CCZ. This animal is ~60 cm long (including tail), with red feeding palps (or “lips”) visibly extended from its anterior end (right). Show transcript: Welcome to Strange Animals Podcast. I’m your host, Kate Shaw. This week we’re going to learn about two interesting marine animals suggested by Jayson and David. Let’s start with David’s suggestion, the lionfish. The lionfish doesn’t actually look like a lion although it is a fish. It lives in shallow tropical water in the Indian Ocean and western Pacific, especially around coral reefs. There are twelve species of lionfish known, but they’re mostly fairly similar. The lionfish is brown or dark red in color with white stripes, fan-like fins, and lots of long spines, all of which are striped black and white or red and white to make them more visible. When a fish or other animal has markings that make it stand out against the background, you can be pretty sure that it’s dangerous, and that’s the case for the lionfish. The lionfish’s spines are venomous, especially the spines on the dorsal fin. If it feels threatened, it will point the dorsal fin at the predator and keep it pointed at it no matter which direction the predator moves. If the predator swims below the lionfish, the lionfish will turn upside-down in the water to keep the dorsal fin pointed at it. Most predators back off at that point, and I don’t blame them because that sounds really scary. People have died from lionfish venom, but it’s rare. Mostly it’s just extremely painful and makes the person feel really sick for a day or two. Divers have to be careful when they’re around lionfish, because lionfish can be aggressive and will point that dorsal fin at the diver as a warning. You don’t want a lionfish to point at you. The lionfish eats smaller fish, including smaller lionfish, invertebrates, and other small animals. It confuses other fish by blowing water at them. The little fish turns to face into what it thinks is a weird water current, and suddenly, there’s a lionfish that just gulps it down. As David points out, even though the lionfish is dangerous, it’s definitely beautiful. Some people keep lionfish in saltwater aquariums, although they’re hard to care for in captivity, and unfortunately sometimes the fish escape into the wild or are released. The red lionfish is especially invasive in the Caribbean Sea, the Gulf Coast, and off the southeastern coast of the United States. Lionfish have also been introduced to parts of the Mediterranean Sea, where they’re becoming more and more invasive. Because invasive lionfish eat so many native fish, and because it’s spreading rapidly and becoming extremely common, people have been trying to find ways to reduce the invasive population. It turns out that lionfish are good to eat if you’re careful when handling the spines during cleaning, so people in areas where it’s invasive are encouraged to catch lionfish to eat. Invasive lionfish are even served in fancy restaurants. Since the red lionfish can grow around 18 inches long, or 47 cm, there’s lot a of meat on one. No one’s sure why it’s called a lionfish. It doesn’t look remotely like a lion. It’s also called the zebrafish because of its stripes. Next,
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    7 分
  • Episode 410: Electric Catfish

    Episode 410: Electric Catfish
    2024/12/09
    Thanks to Cosmo for suggesting this week's animal, the electric catfish! Further reading: The shocking truth about electric fish Efficient high-voltage protection in the electric catfish Gimme kiss [electric catfish photo from this site]: Show transcript: Welcome to Strange Animals Podcast. I’m your host, Kate Shaw. This week we’re finally going to talk about a fish Cosmo wanted us to learn about, the electric catfish! Catfish are really common fish that live throughout the world, except for Antarctica. We’ve talked about various types of catfish in lots of different episodes, since there are well over 3,000 known species and they’re incredibly diverse. The electric catfish lives in freshwater in tropical areas in western and central Africa, as far north as the Nile River. All animals generate electric fields in their nerves and the contracting of muscles. Animals that can sense these fields are called electroreceptive. An electroreceptive animal can find hidden prey without using its other senses. Many electroreceptive animals can also generate weak electrical fields, usually less than a single volt—small electrical pulses or a sort of wave, depending on the species, that can give them information about their environment. Like a dolphin using echolocation, a fish using electro-location can sense where potential prey is, where predators, plants, and rocks are, and can even communicate with other fish of its same species. Of course, those same electric pulses can also attract electroreceptive predators. Some fish can generate an electric shock so strong it can stun or kill other animals. The most famous is the electric eel, which we talked about way back in episode 10, but the electric catfish falls in this category too. The electric catfish isn’t a single species but several in the family Malapteruridae. Some are very small, but one grows as much as four feet long, or 1.2 meters, and can weigh over 50 lbs, or 23 kg. That’s Malapterurus electricus, THE electric catfish. The electric catfish is grayish-brown mottled with black spots. Like a lot of catfish, it’s a cylinder-shaped chonk, and has three pairs of barbels around its broad mouth. Barbels are the feelers that give the catfish its name, because they look sort of like a cat’s whiskers. Sort of. Not actually very much like a cat’s whiskers. The electric catfish also has what look like surprisingly kissy lips, which are often pale in color so they stand out, especially when the mouth is open, which is frankly hilarious. It doesn’t have a dorsal fin and it’s not a fast swimmer. It spends most of its time lurking in rocky areas in muddy, slow-moving water. It’s also nocturnal. The electric catfish eats other fish, although it will also eat pretty much anything it can swallow. It likes muddy water because it doesn’t want potential prey to see it, and of course it doesn’t want any potential predators to see it either. That includes humans, who consider it a delicacy. Humans also sometimes keep electric catfish as aquarium fish, which is sort of the opposite of being killed and eaten. Contracting a muscle causes a tiny, tiny electrical impulse, as I mentioned earlier, but in electric fish certain muscles have developed the ability to generate much stronger electrical impulses. Instead of muscles, they’re called electric organs. The interesting thing is that this is only found in fish, but that the ability evolved separately at least six times in different lineages of fish. The electric catfish uses its ability to generate electric shocks as a defense when it needs to, but mainly it uses it to stun or outright kill other fish, which it then gulps down. It can discharge up to 300 volts of electricity in pulses that last only a few milliseconds, but since it can generate up to 500 pulses in waves, that’s a lot of electricity. That’s not enough to kill a person, but you’d definitely feel it and try to get away. But,
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    7 分
  • Episode 409: Guinea Pigs and Capybaras

    Episode 409: Guinea Pigs and Capybaras
    2024/12/02
    Thanks to Mary, Mila, and Riley for their suggestions this week! Further reading: Comfortable and dermatological effects of hot spring bathing provide demonstrative insight into improvement in the rough skin of Capybaras Comfort of capybaras determined by SCIENCE: An especially attractive guinea pig: Guinea pigs come in lots of colors, patterns, and fur types [picture taken from this excellent site]: Show transcript: Welcome to Strange Animals Podcast. I’m your host, Kate Shaw. This week we’re going to learn about two rodents, one small and one big. Thanks to Mary and Mila who both suggested the guinea pig, and thanks to Riley who suggested the capybara. This episode is a bit unusual because part of it comes from a Patreon episode from 2023. Like, literally a big chunk of this episode is the original audio from that one, and you’ll be able to tell the difference in audio and know just how lazy I was this week. The episode actually came together in an unusual way too. Riley’s parent emailed me last week with some new suggestions, including capybaras, but wasn’t sure if we had already covered the topic. I thought we had, but of course there’s always more to learn about an animal. Well, since this is the beginning of a new month I was on the Patreon page to upload the December episode, and while I was there I did a quick search for capybaras and discovered the episode I was thinking of. I decided to add some more information about guinea pigs to it since I already mention guinea pigs a lot in that episode, and here is the result! The capybara is a rodent, and a very big one. It is, in fact, the biggest rodent alive today. To figure out just how big the capybara is, picture a guinea pig. The guinea pig is also a rodent, native to the Andes Mountains in South America. No one’s sure why the guinea pig is called that in English, since it doesn’t come from Guinea and doesn’t have anything to do with anything else called guinea, but as someone who had two pet guinea pigs when I was a kid, I know exactly why they’re called guinea pigs. This is what an actual pig sounds like: [pig squealing] And this is what a guinea pig sounds like: [guinea pig squealing] Also, it’s sort of shaped like a pig. The guinea pig is a chonky little animal with short legs, only a little stub of a tail, and little round ears. Its face is sort of blocky in shape and it has a big rounded rump, similar to that of a capybara. The guinea pig is actually closely related to the capybara, and is a pretty good-sized rodent in its own right. It grows about 10 inches long, or 25 cm, on average, and roughly half that size tall. The guinea pig has been domesticated for at least 7000 years, but it wasn’t domesticated for people to keep it as a pet. In South America and many other places now, it’s a very small farm animal raised for its meat. Guinea pig has been an important source of protein for all that time, so important that it was considered sacred in many cultures. In the early 16th century when Europeans started arriving in South America, sailors took guinea pigs with them on ships so they’d have fresh meat on the voyage. But when the cute little animals arrived in Europe, people started buying them as pets. Guinea pigs eat plants, mostly grass, and are social animals. If you want a pet guinea pig, make sure to get at least two. Like rabbits and some other animals, including the capybara, the guinea pig excretes special pellets that aren’t poop, but are semi-digested pellets of food. The guinea pig eats the pellets so they can pass through the digestive system again and the body can extract as many nutrients as possible from it. What’s left is then excreted as a regular poop pellet. Even in places where the guinea pig is routinely kept as livestock and eaten, people breed guinea pigs as pets too. The pet variety is smaller than the meat variety and has different markings and different colors.
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    11 分
  • Episode 408: Dog-Like African Doggos

    Episode 408: Dog-Like African Doggos
    2024/11/25
    Thanks to Lydia and "warblrwatchr" for this week's suggestions! Further reading: Sweet tooth: Ethiopian wolves seen feeding on nectar The African wild dog is not actually a dog and eats lots of things: The aardwolf is not a dog at all and eats insects: The Ethiopian wolf is not a dog (or a wolf or a fox) and eats rodents and nectar [photo by Adrien Lesaffre and taken from this page]: Show transcript: Welcome to Strange Animals Podcast. I’m your host, Kate Shaw. This week we’re going to talk about three dog-like animals from Africa, suggested by Lydia and “warblrwatchr,” even though none of the three animals are dogs. We’ll start with one of Lydia’s suggestions, the African wild dog, also called the painted dog or painted wolf. Despite those names, it’s not very closely related to dogs and wolves. It’s the only species in its own genus, although it is a member of the family Canidae. Colonizers from Europe thought the animal was just a feral dog, not anything special that should be protected, and they also brought domestic dogs with them to Africa. Domestic dogs mean diseases that other canids can catch. Between introduced diseases, farmers killing the animals to keep them away from livestock, and habitat loss, the African wild dog is endangered. Luckily, these days conservation groups have been working to protect the animal, and its numbers are increasing slowly in Kenya’s national parks in particular. The African wild dog is a tall, strong canid with great big ears and no dewclaws. It has a yellowish coat with black blotches and some white spots, including a white tail tip, although some subspecies have darker coats. Unlike most canids, its fur is bristly and doesn’t have a soft undercoat, and as the dog ages, it loses its fur until old dogs are nearly bald. It’s very social, as canids almost always are, and its varied coat pattern helps individuals recognize friends and pack-mates at a distance. The African wild dog prefers savannas and other open areas. It hunts in packs and mostly preys on antelopes, although it will also kill zebras and other large animals, and individual dogs will sometimes catch small animals like hares and rodents. The African wild dog pack isn’t especially hierarchical. The males of the pack are mainly led by the dominant male, while the females are mainly led by the oldest female, who is usually the most dominant. The dominant pair is usually the only pair that has babies. A mother dog has up to 16 pups at a time but only one litter a year. In a lot of animals, as the babies grow up, the males are usually the ones who are driven out of the pack or leave on their own to find a new pack. In the African wild dog, females are the ones who leave as they grow up. Sometimes the females join a different pack and sometimes they start their own. Either way, it stops a pack from becoming inbred. The African wild dog is extremely vocal, making lots of different sounds to communicate with its pack-mates. It sounds a lot more like a bird than a dog. This is what African wild dogs sound like: [doggo sounds] Next, Lydia and warblrwatchr wanted to learn about the aardwolf, which lives in eastern and southern Africa. Unlike the African wild dog, which is mostly active during the day, the aardwolf is nocturnal. It spends most of the day in a burrow, sometimes one it digs itself, but more often one that another animal dug and abandoned at some point. The aardwolf has black stripes on a yellowish or reddish coat, a mane of long hair down its neck and back, large ears, and a bushy tail. It’s about the size of a big dog, about 20 inches tall at the shoulders, or 50 cm, but it looks like a small, slender hyena. That’s because it is actually a type of hyena, although it’s not closely related to other hyenas. Hyenas look dog-like but they aren’t canids at all. In fact, they’re more closely related to cats than to dogs,
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    10 分
  • Episode 407: Cookie Cutter Shark

    Episode 407: Cookie Cutter Shark
    2024/11/18
    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.
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    6 分