Tag Archives: giant ground sloth

Episode 413: The Great American Interchange

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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. But marsupials didn’t originate in Australia and are still present in other parts of the world.

The oldest known marsupial appears in North America about 65 million years ago, which was part of the other supercontinent on Earth at the same time as Gondwana, called Laurasia. About the time marsupials were spreading out across Laurasia, from North America all the way to China, Laurasia and Gondwana were connected for a while along the northern edge of South America. Animals were able to cross from Laurasia to Gondwana before the two supercontinents split apart again. Marsupials spread from Laurasia and across Gondwana before the continent of Australia separated about 50 million years ago. Marsupials did so well in Australia that researchers think that before Australia was fully separated from Gondwana, marsupials actually started spreading back out of Australia and into Gondwana again.

While marsupials were doing extremely well in Australia, in South America, birds were the dominant vertebrate for a long time. We talked about terror birds in episode 202. Phorusrhacidae is the name for a family of flightless birds that lived from about 62 million years ago to a little under 2 million years ago. They were carnivores and various species ranged in size from about 3 feet tall to 10 feet tall, or 1 to 3 meters, and had long, strong legs that made them fast runners. The terror bird also had a long, strong neck, a sharp hooked beak, and sharp talons on its toes.

Other birds in North America were likewise huge, but could fly. Those were the teratorns, which are related to modern New World vultures. Since they had huge wingspans and could fly long distances easily, they could just fly between North and South America if they wanted to, so teratorns were found on both continents starting around 25 million years ago. They only went extinct around 10,000 years ago. The largest species known, Argentavis magnificens, lived in South America around six million years ago. It’s estimated to have a wingspan of at least 20 feet, or 6 meters, and possibly as much as 26 feet, or 8 meters. That’s the size of a small aircraft.

In addition to giant predator birds, South America had crocodilians that could grow over 30 feet long, or 9 meters, and possibly as much as 40 feet long, or 12 meters. And, of course, it had ancestral forms of animals we’re familiar with today, like sloths, anteaters, armadillos, opossums, monkeys, capybaras, and lots more. Some of these were incredibly large too, like the giant ground sloth that was as big as an African elephant and the glyptodon that was related to modern armadillos. Glyptodon had a huge bony carapace and rings of bony plates on the end of its thick tail that made it into a club-like weapon, and it was the size of a car. Both the giant ground sloths and the glyptodonts were plant-eaters, as were the notoungulates.

The notoungulates are an extinct order of hoofed animals that lived throughout South America. They were probably most closely related to rhinoceroses, horses, and other odd-toed ungulates, but they’re completely extinct with no living descendants. Some were tiny and actually looked and probably acted more like rabbits than horses, while others were massive. We talked about trigodon in episode 387, and it and many of its close relations in the family Toxodontidae were the size and build of a modern rhinoceros. Trigodon even had a small horn on its forehead. A closely related group, Litopterna, is also a completely extinct order of ungulates, which were mostly smaller and more deer-like than the notoungulates.

The Pleistocene is also called the ice age, but it’s more accurate to say that it was a series of ice ages with long periods of warmer weather in between–tens of thousands of years of warmer climate, then a colder cycle that lasted tens of thousands more years. When the glaciers were at their maximum, with ice sheets covering some parts of the world over a mile thick, or a kilometer and a half, sea levels were considerably lower because so much of the world’s water was frozen solid. That exposed more land that would ordinarily be partially or completely underwater, and it also led to a dryer climate overall. At the same time, volcanic activity in the ocean separating what is now North and South America had been building up volcanic islands for millions of years. All these factors and more combined to form the Isthmus of Panama, also called Central America, that is basically a land bridge connecting the two continents.

This started around 5 million years ago and the isthmus was fully formed by about 3 million years ago, or at least that’s the most accepted theory right now. A 2016 study suggested that the land bridge started forming far earlier than that, possibly as early as 23 million years ago, possibly 6 to 15 million years. Studies are ongoing to learn more about the timeline.

What we do know is that once the land bridge opened up, animals started migrating into this new area. Animals from North America migrated south, and animals from South America migrated north. It didn’t happen all at once, of course. It was a slow process as various animal populations expanded into Central America over generations. Some animals had trouble with the climate or couldn’t find the right foods, while others did really well and expanded rapidly.

The ancestors of some animals that made it to North America and are still around include the Virginia opossum, the armadillo, and the porcupine. Meanwhile, the ancestors of llamas, horses, tapirs, deer, canids, felids, coatis, and bears traveled to South America and are still there, along with many smaller animals like rodents. Many other animals migrated, survived for a while, but later went extinct. This included a type of elephant called the gomphothere and saber-toothed cats that migrated south, while ground sloths, terror birds, glyptodonts, capybaras, and even a type of notoungulate migrated north.

You may notice that more animals that migrated south survived into modern times. South America was much warmer overall than North America, and most animals that traveled north had trouble adapting to a colder climate and competing with animals that were already well-adapted to the cold. Animals traveling south encountered warmer climates early, and if they were able to tolerate hot weather they didn’t have to worry about any climactic shocks on the rest of their journey south. As a result, North American animals were able to establish themselves in larger numbers, which helped them adapt even faster since more babies were being born and surviving.

One South America to North America success story is the porcupine. Porcupines are rodents, and there are two groups, referred to as old world and new world porcupines. Those are not great terms but that’s what we have right now. The old world porcupines are found in parts of Africa, Asia, and Italy, although they were once more widespread in Europe, while new world porcupines are found in parts of North and South America. Old world porcupines live exclusively on the ground and are larger overall than new world ones, which spend a lot of time in trees. Surprisingly, the two groups are only distantly related. They evolved spines separately. They’re also only very distantly related to hedgehogs.

The one thing everyone knows about the porcupine is that it has quills, long sharp spines that make hedgehog spines look positively modest. Porcupine quills are dangerous. They’re modified hairs, and actual hair grows in between the quills, but they’re covered in strong keratin plates and are extremely sharp. They also come out easily and regrow all the time. A porcupine can hold its spines down flat so it won’t hurt another porcupine, which is what they do when they mate.

Only one species of porcupine lives in North America, called the North American porcupine. It lives throughout much of the northern and western part of the continent, from way up in the far north of Canada down to central Mexico, although it doesn’t live in most of the southeast. We don’t know if the North American porcupine developed after South American porcupines migrated north, or if it developed much earlier, around 10 million years ago. Porcupine experts have been arguing about this for years, because there aren’t very many porcupine fossils to study.

Then a nearly complete fossil porcupine was discovered in Florida. It was such a big deal that the scientific team that discovered it decided to create an entire college course for paleontology students to help study the specimen. The resulting study was published in May of 2024, and the results suggest that the North American porcupine evolved a lot longer ago than the Isthmus of Panama formed.

The North American porcupine had to change a lot to withstand the intense cold when its ancestors were tropical animals. The North American porcupine is very different from its South American cousins. It spends less time in trees and doesn’t have a prehensile tail, it eats a lot of bark instead of mostly leaves, and it has thick insulating fur between its quills. The fossilized specimen discovered in Florida still had a prehensile tail and didn’t have the strong jaw it needed to gnaw bark off trees, but it already showed a lot of adaptations that are seen in the North American porcupine but not in South American species.

Ultimately, of course, a lot of large animals went extinct around 12,000 to 10,000 years ago, the end of the Pleistocene. Animals like mammoths that were well-adapted to cold died out as the climate warmed, and so did their predators, like dire wolves and the American lion. The notoungulates and other megaherbivores in South America went extinct too.

One animal that I haven’t mentioned yet that migrated south successfully was Homo sapiens. Maybe you’ve heard of them. Until very recently, the accepted time frame for humans migrating into South America was about 16,000 years ago, although not everyone agreed. But in July of 2024, a new study pushed that date back to 21,000 years ago.

The study examined glyptodont fossils found in what is now Argentina. The fossils were found on the banks of a river and were determined to show butchering marks from stone tools. The bones were dated to almost 21,000 years ago, which means that humans probably moved into South America a lot earlier than that. It takes time to travel from Central America down to Argentina.

One detail most people don’t know about when it comes to the Great American Interchange is how marine animals were affected. It was exactly opposite for them. Instead of a new land to explore, which caused very different animals to encounter each other for the first time, the Isthmus of Panama cut populations of marine animals from each other. They’ve been evolving separately ever since. So I guess whether a land bridge is bad or good depends on your point of view.

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 059: The Onza and the Yemish

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This week we’re going to learn about some more big cats, especially the mysterious onza of Mexico and the yemish of Patagonia.

And you should totally check out the charming podcast Cool Facts about Animals.

A jaguar:

A jaguarundi:

A puma, not dead:

The Rodriguez onza, dead:

A giant otter:

Further reading:

The Encyclopaedia of New and Rediscovered Animals by Karl P.N. Shuker

Monsters of Patagonia by Austin Whittall

Show transcript:

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

This week we’re going to learn about a couple of mystery cats that you might not have heard of, and learn about a few non-mystery animals along the way.

There are several cats native to Mexico. We’ve talked about the puma recently, in episode 52. It’s the same cat that’s also called the cougar or mountain lion, and it lives throughout most of the Americas. It’s tawny or brownish in color with few markings beyond dark and white areas on the face, and sometimes faint tail rings and mottled spots on the legs.

The jaguar is a spotted cat related to lions, tigers, leopards, and other big cats. It lives throughout much of Central and South America, and in North America as far north as Mexico, and was once common in the southwestern United States too but was hunted to extinction there. It prefers tropical forests and swamps, likes to swim, and is relatively stocky with a shorter tail than its relatives. Its background color is tawny or brownish with a white belly, and its spots, called rosettes, are darker. But melanistic jaguars aren’t especially uncommon. They look all black at first glance, but their spots are visible up close. Oh, and a big shout-out to the charming podcast Cool Facts About Animals who did a show about jaguars recently. I definitely recommend it, especially if you’ve got younger kids who love animals.

In 2011, a hunter and his daughter in Arizona took pictures of a spotted cat treed by their dogs, and alerted wildlife officials. The officials studied the photos and said yes, that’s a jaguar. Since then, he’s been monitored by trail cam and conservationists working in the Santa Rita Mountains. Since jaguars have unique spot patterns, we know it’s the same cat, a male that local elementary school kids have named El Jefe. Officials think El Jefe moved to Arizona from a nearby jaguar sanctuary in Mexico, and for years he was the only known jaguar in the United States. In late 2017, a second male jaguar was caught on camera in southern Arizona. Researchers hope that more jaguars will move into the area, which was part of their original range.

Pumas and jaguars are the two biggest cats found in Mexico. But there is a third big cat, a mystery big cat. The onza has been reported in Mexico for centuries. It’s supposed to look like a puma but more lightly built with longer legs and possibly darker fur or dark markings, especially striping on the legs.

The first problem is the name onza. The term is applied to a lot of different big cats in Mexico and other Spanish and Portuguese-speaking countries. For instance, in Brazil the word onça means jaguar, and in fact the jaguar’s scientific name is Pathera onca. The related English word ounce was once the name of the lynx and is now sometimes used for the snow leopard, Panthera uncia. So it’s possible that old reports of onzas just refer to pumas or jaguars, or one of the many other cats that live in the area, such as the jaguarundi.

The jaguarundi sometimes lives in Mexico as far north as southern Texas, although it’s much more common in South and Central America. It’s black or brownish-grey, which is called the grey phase, or red-brown or tawny, called the red phase. In the past the two phases were thought to be separate species. Adult jaguarundis don’t usually have any markings, but cubs have spots on their bellies. That is adorable. It’s closely related to the puma but is smaller, not much bigger than a domestic cat, and unlike most cats it’s diurnal instead of nocturnal, which means it’s mostly active during the day.

The jaguarundi has a flattish head, more like an otter than a cat. A gray phase jaguarundi may be the animal referred to in the writings of Bernal Diaz del Castillo, who in the early 16th century wrote about a lion that resembled a wolf in Montezuma’s menagerie, in 1519. It also happens to be called an onza in some parts of Mexico.

Some animals labeled onzas have been killed and examined. On January 1, 1986 a big cat killed in Sinaloa State in Mexico, called the Rodriguez onza, was examined by a team of experts, including Stephen O’Brien, an expert in feline molecular genetics. They reported that the animal’s DNA was indistinguishable from that of a puma. But it definitely didn’t look like an ordinary puma. I have a picture of it in the show notes. It was long-bodied and slender with dark markings. So it’s possible that stories of onzas arose from sightings of pumas with this sort of coat color variation, or it’s possible there is a remote population of pumas with a leggier build than ordinary pumas, and every so often one wanders out where it’s seen or killed. Pumas can show considerable variance in appearance, so it wouldn’t be that unusual for an occasional individual to be born that’s longer legged than most and that also has more or darker markings than usual.

Then again, who knows? There might be a subspecies of puma or a completely different species of cat out there. If so, hopefully we’ll find out more about it soon so it can be protected and studied.

Jaguarundis make a lot of different vocalizations. Here’s one. It sounds more like a bird than a cat, but I promise you, that’s a jaguarundi.

[cat sound]

Way back in episode 22 I touched on the yemish, or Patagonian water tiger. I think it’s time to revisit it in more detail. Look, I have a fantastic book called Monsters of Patagonia so you’re going to be hearing about Patagonia on this podcast for a long, long time.

The iemisch, or hyminche, or lemisch, or some other variation, is often called a water tiger but linked not with a feline at all, but with a ground sloth. This is entirely the fault of a single man, Florentino Ameghino.

Ameghino lived in the late 19th century and died in 1911. He was from Argentina, born to Italian immigrants, and is still highly regarded as a paleontologist, anthropologist, zoologist, and naturalist, from back in the days when you could specialize in lots of disciplines and still do tons of field work. He has an actual crater on the moon named after him. You don’t get a moon crater unless you’re pretty awesome. But Ameghino had at least one bee in his bonnet, and it involved giant ground sloths like megatherium. He was convinced they were still alive in the remote areas of South America, especially Patagonia.

In an 1898 paper he wrote about the yemish in Patagonia, which he said was a “Mysterious four legged massive beast, of a terrible and invulnerable appearance, whose body cannot be penetrated by missiles or burning branches. They call it Iemisch or ‘water tiger’ and mentioning its name terrorizes them; when interrogated and asked for details, they become grim, drop their heads, turn mute or evade answering.”

I got this quote from the Monsters of Patagonia book, of course. You can find a link in the show notes if you want to order your own copy of the book. It’s a fun read, but I should point out that I do a lot of fact-checking before I include information from the book because there are some inaccuracies and fringey theories. Also, it has no index.

Ameghino said his brother Carlos, who was also a paleontologist, had sent him a piece of hide reputedly from a yemish, which he had gotten from a Tehuelche hunter. The hide had tiny bones embedded in it, called osteoderms, which are a feature of giant ground sloths. Ameghino claimed that the yemish was a giant ground sloth, which he named Neomylodon.

Mylodon, as opposed to Ameghino’s Neomylodon, was a 10 foot long, or 3 meter, ground sloth that did indeed have osteoderms embedded in its thick hide. It had long, sharp claws and ate plants, probably dug burrows, and lived throughout Patagonia and probably most of South America. The important thing here is that mylodon remains, including dung as well as dead animals, have been found in caves in Patagonia, and the remains look so fresh that the discoverers thought they were only a few years old. It turns out that they’re all about 10,000 years old, but were preserved by cold, dry conditions in the caves.

So the piece of hide was probably really from a giant ground sloth, but not one that had been alive recently. Most researchers think that the sloths of Patagonia were already extinct when the area was first settled by humans, but discoveries of what looked like recently dead animals with fearsome claws and a hide that couldn’t be pierced with arrows might very well have contributed to stories of local monsters.

But that’s beside the point, because once you get past Ameghino’s obsession with the yemish being a real live giant ground sloth, it’s clear it’s something completely un-slothlike. The exact term yemish isn’t known from any language in Patagonia, but it might be a corruption of hymché, a water monster, or yem’chen, which means water tiger in the Aonikenk language. An even closer match from the same language means sea wolf and is pronounced ee-m’cheen [iü’mchün]. Other languages in the area call the elephant seal yabich, which also sounds similar to yemish. In other words, it’s pretty clear that the yemish is a water animal of some sort.

The sea wolf is what we call a sea lion, a type of huge seal. Sea lions and elephant seals sometimes come up rivers and into freshwater lakes, which may account for some of the numerous lake monster legends in Patagonia. As for the hymché, it may have a natural explanation too that is nevertheless just as mysterious as just calling it a monster.

French naturalist André Tournouer explored Patagonia in 1900, and at one point while following a stream, he and his expedition saw what their guide called a hymché. It was the size of a large puma but with dark fur, rounded head, no visible ears, and pale hair around the eyes. It sank under the water when Tournouer shot at it, and later they found some catlike tracks in the sand along the bank.

From the description, it’s possible that the hymché was a spectacled bear. We learned about it in episode 42. It lives in the Andes Mountains of South America but was formerly much more widespread, and is usually black with lighter markings around the eyes that give it its name. Its ears are small and its head is more rounded than other bears. While it spends most of its time in the treetops, it actually does swim quite well. But as far as we know, spectacled bears don’t live in Patagonia.

So, back to the yemish. According to Ameghino’s 1898 paper, he said the Tehuelche referred to it as the water tiger. Since there is no local word for tiger in South America, since tigers live in Asia, this is probably a translation of the local word for puma. The jaguar did formerly live in Patagonia but was hunted to extinction there over a century ago. The yemish supposedly spent much of its time in the river and dragged horses and other animals into the water when they came down to drink. Its feet were flat, its ears tiny, it had big claws and fangs, and its toes were webbed for swimming. It had shorter legs than a puma but was bigger than one.

This sounds like one specific animal that does live in Patagonia, and it’s not a tiger or any kind of feline at all. It may be an otter. Flat feet with claws and webbed toes? Check. Tiny ears and scary teeth? Check. Longer than a puma but with much shorter legs? Check. Otters don’t kill animals as big as horses, of course, but this could be an exaggeration. Otters will scavenge on freshly dead animals, so the story of a mule that fell off a precipice onto a river bank, and was discovered dead and half-eaten the next morning with strange paw prints all around it, fits with an otter family having an unexpected feast delivered to their doorstep.

Not only that, but some tribes do call otters “river tigers.” Stories of monstrous otter-like animals are common throughout much of South America, not just Patagonia, and are frequently translated as “river tiger.” In Monsters of Patagonia, Whittall wonders why some tribes have two names for the otter in that case, an ordinary name and a name denoting a monster. It’s possible the monster version of the otter either refers to a folkloric beast, an animal like a sea lion that was once seen far from its ordinary home, or two kinds of otter in the area, one bigger and more ferocious than the other.

The southern river otter lives in Patagonia, both in rivers and along the seashore. It’s not especially big, maybe four feet long including the tail, or 1.2 meters. But the rare marine otter also lives along the western and southern coasts of Patagonia. Its scientific name, Lontra felina, means “otter cat, and in Spanish it’s often called gato marino, or sea cat. But the marine otter is small, typically smaller than the river otter and at the very most, around five feet long or 1.5 meters.

But if you remember episode 37, about the dobhar-chu, you may remember the giant otter. It lives in South America north of Patagonia and is now endangered, with only around 5,000 animals left in the wild after being hunted extensively for its fur for decades. It’s protected now, although loss of habitat and poaching are still big problems. It grows to around 6 feet long now, or 1.8 meters, but when it was more common some big males could grow over eight feet long, or 2.5 meters. If in the past an occasional giant otter—twice the length of an ordinary otter—strayed into the rivers of Patagonia, it would definitely be seen as a monster.

Whittall rejects the idea that the yemish is an otter, although he doesn’t mention the giant otter. He also rejects the jaguarondi as the yemish since it’s much too small, although it does like to swim and fish and, as mentioned earlier, it does look remarkably like an otter in many ways. He suggests the yemish might be an unknown giant aquatic rodent, citing as proof the existence of a cow-sized rodent that once lived in Patagonia during the ice age. I’m not convinced. Nothing about the yemish sounds like a rodent. It does sound like an otter, possibly a known otter, possibly a now extinct otter—or, maybe, a giant version of the jaguarondi, also now extinct. But maybe not.

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

Thanks for listening!

Episode 022: Megatherium

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Episode 22 is all about megatherium, the giant extinct ground sloth–and a little bit about glyptodon, the giant extinct…thing.

Megatherium vs trees was basically no contest. Giant ground sloth FTW!

Giant sloth big, yeah yeah yeah, it’s not small, no no no

Glyptodon. Like a giant armadillo that can’t roll up and doesn’t need to.

Show transcript:

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

For this week’s episode, let’s learn about some Ice Age megafauna! But first, a quick note about my schedule. I’ll talk more about this in a few weeks, but in August I’m going to be in Helsinki, Finland for WorldCon 75. I don’t have the final schedule yet, but I am going to be on a panel about podcasting. If you’re going to WorldCon too, or if you’ll be in Helsinki the week of the convention or the week after, let me know so we can meet up! I’ll also be in Oslo, Norway for part of the day on August 7. I got a cheap flight to Helsinki because it has an 11-hour layover in Oslo, but to me that’s a bonus. Oslo has birds! Birds I’ve never seen before! So if you’re going to be in Oslo on August 7 and you’d like to meet me for a birding trip and/or lunch, definitely let me know! And don’t worry, I’ll schedule episodes ahead of time so you can continue to learn about strange animals even while I’m gone.

Now, on to the megafauna. Until about five million years ago, South America was a big island continent the way Australia is today. As a result, many of the animals that evolved there at the time don’t look anything like animals in other parts of the world.

The various species of giant ground sloth, such as Megatherium and Eremotherium, were South American mammals that lived from around 30 million years ago until only about 10,000 years ago—but we’ll come back to that in a minute. Those two species were huge—as big as African elephants. It was 20 feet long and stood more than 12 feet high on its hind legs. They liked woodlands and grasslands and ate plants.

Megatherium had huge curved claws on its forefeet just like modern sloths, four claws that were a foot long each, and we know it walked on the sides of its paws as a result because we have some fossilized tracks. A ground sloth could walk on its hind legs, at least for short distances, and when feeding it spent a lot of its time reared up on its hind legs, helped to balance by its thick tail. It could reach branches some 20 feet off the ground that way. It hooked the branches down with its claws to eat the leaves.

Around 5 million years ago, South America became connected to North America by the Central American Isthmus, which is volcanic in origin. Over the millennia, peaking around 3 million years ago, North American animals migrated south, and South American animals migrated north, called the Great American interchange. A lot of South American megafauna went extinct with the increased competition for resources, but nothing bothered the giant ground sloths. One medium-sized species, named Megalonyx by Thomas Jefferson, spread throughout North America as far north as Alaska. It was “only” about 10 feet long and weighed some 800 pounds, with three claws on its forefeet.

The North American sloths died out first, around 11,000 years ago. It didn’t take long for most of the South American sloths to go extinct too, a little over 10,000 years ago. And yes, that was the same time that humans were spreading deeper into the Americas. It’s not a coincidence, although climate change after the last big ice age probably played a part too. Ground sloths had thick skin reinforced with osteoderms, knobs of bone tissue that grow in the skin like armor, so killing one would have been a lot of work for our ancestors, and was undoubtedly dangerous too.

But a whole lot of islands make up the Carribean, and giant sloths lived on some of those islands. Many had developed in isolation long enough that they’re now considered separate species from the mainland sloths. And many of the island sloths persisted for thousands of years after their gigantic mainland cousins were long dead.

The island sloths were much smaller than Megatherium. Megalocnus only weighed about 200 pounds—a big sloth, but nothing like the five tons that Megatherium could weigh. But Megalocnus survived until some 6,000 years ago in Cuba and maybe much more recently. Another Cuban sloth lived another thousand years after that. A small ground sloth called Neocnus survived on Hispanolia until only about 4,500 years ago.

You may have heard recently about a lot of huge tunnels in Brazil. Until recently, people assumed they were natural caves. It wasn’t until the 2000s that geologists started investigating the tunnels and immediately saw that they weren’t natural at all. They were burrows, many with claw marks on the walls as though just dug, thousands of them scattered across Brazil and a few other parts of South America. Some are tall enough to stand up inside comfortably. One paleoburrow in the Amazon is a network that adds up to around 2,000 feet of tunnels, six feet tall and almost that wide. It was probably used by generations of animals, enlarged and extended as new adults dug their own burrows.

The burrows were probably dug by giant sloths. No one is sure why. Giant sloths had no predators until humans moved into the area. But it’s also possible that some or most of the burrows were dug by the extinct ancestors of armadillos, glyptodon.

The glyptodonts are related to both the giant ground sloths and modern-day armadillos. Glyptodon and its two related species, Panochthus and Doedicurus, lived in the same areas where the giant burrows have been discovered. And modern armadillos are good burrowers. But Glyptodon had even less reason to need burrows than giant ground sloths did. It was an enormous animal, 11 feet long and five feet high, weighing over two tons, with a massive domed carapace like a tortoise shell, made of rows of osteoderms. It also had osteoderms that protected its head like a cap, and rings of bony plates on the end of its thick tail that made it into a club-like weapon. Even its jaws contained osteoderm ridges, which helped grind up the plants it ate, although it also had huge grooved teeth.

In other words, glyptodon was a walking tank. Nothing much ate them until humans showed up. A full-grown glyptodon was a bonanza for humans if they could kill it. Not only did it provide a whole lot of meat, its shell could be used as shelter. Clean it out good first. At least one human burial has been found in a glyptodon shell.

Considering how amazing glyptodonts are, you’d think they’d be more well known and better studied. There’s still a whole lot we don’t know about them, including how many species there actually were and how recently they died out. There aren’t even very many reported sightings of living ones, which tends to happen with just about any extinct animal.

Giant ground sloths, on the other hand, do get reported every so often, and there are hints that giant ground sloths might have lived until much more recently than ten or eleven thousand years ago. Megatherium remains found in caves sometimes seem suspiciously fresh, although so far radiocarbon dating hasn’t given us any surprises. In 1740 the Portuguese historian Lozano mentioned an animal that sounds a little like a ground sloth, which was supposedly called the su by locals.

Some cryptozoologists believe that a legendary South American monster, the mapinguari, may have been inspired by megatherium. The mapinguari is supposed to be nine feet tall and smelly, with feet that face backwards, an extra mouth in its belly, skin that deflects arrows, and sometimes it’s said to have only one eye in the middle of its forehead. It also eats meat. That sounds a little on the far-fetched side to me, and a lot of cryptozoologists group the mapinguari with bigfoot type monsters.

There is another monster story from Patagonia that sounds a lot more sloth-like on the surface. The yemisch is supposed to be a cow-sized animal that sleeps in burrows it digs with its huge claws. It can’t be killed because arrows bounce off its hide. In fact, yemisch is supposed to mean “the one covered in little stones.”

That sounds promising, but the story comes exclusively from a man called Florentino Ameghino, who was convinced that a smaller giant ground sloth named mylodon still lived in Patagonia. The first mention anywhere of the Yemisch comes from Ameghino’s 1898 paper about mylodon, where he said the Tehuelche of Patagonia referred to it as the water tiger. It was semi-aquatic, spending much of its time in the river. It was said to drag horses into the water with its huge claws. Its feet were flat, its ears tiny, it had huge claws and fangs, and its toes were webbed for swimming. It was bigger than a puma but with shorter legs.

This doesn’t sound like a ground sloth, which were not carnivores despite their big claws. In 1900 a French naturalist, Andrew Tournouer, spotted an animal in a stream that looked a lot like Ameghino’s description of the Yemisch. Tournouer said it was definitely not a ground sloth; his guide said it was called a Hymche.

The water tiger Ameghino describes is well known in Patagonian native lore, but not under the name Yemisch. It’s possible Ameghino mangled the word Hymche. Whatever the water tiger is, though, it’s definitely not a giant ground sloth and I’m going to save it for a future episode if I can dig up more about it.

There was an aquatic giant ground sloth once, though, Thalassocnus. It grew to around five or six feet long and lived off the Pacific coast of South America, where it ate seaweed and other marine plants. Fossils document how it adapted to marine life over the generations. The earliest Thalassocnus fossils are of semi-aquatic animals that grazed in shallow water. Fossils from more recent species show increasing adaptations to deeper water, including increased weight of the skeleton to help it stay underwater instead of bobbing up to the surface. It died out around two and a half million years ago, after the Isthmus of Panama formed, probably because the new land mass caused the water temperature to cool and many of the ocean plants in its habitat went extinct.

Whether or not any giant ground sloths are still alive in the remote parts of South America, I think we can all agree that they’re not going to eat anyone. So if you see one, don’t shoot it unless it’s with a camera.

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