Tag Archives: Thalassocnus

Episode 329: Manatees and a Surprise Sloth

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Thanks to Alexandra and Pranav for their suggestions this week! Let’s learn about manatees and sloths, including a surprising extinct sloth.

Further reading:

Sloths in the Water

A West Indian manatee:

A three-toed sloth:

Show transcript:

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

This week we have a suggestion from Alexandra and Pranav, who wanted an episode about manatees. We’ll also talk about another marine mammal, a weird extinct one you may never have heard of.

The manatee is also called the sea cow, because it sort of slightly resembles a cow and it grazes on plants that grow underwater. It’s a member of the order Sirenia, which includes the dugong, and sirenians are probably most closely related to the elephant. This sounds ridiculous at first, but there are a lot of physical similarities between the manatee and the elephant. Their teeth are very similar, for instance, even if the manatee doesn’t grow tusks. The elephant has a pair of big chewing teeth on each side of its mouth that look more like the bottoms of running shoes than ordinary teeth. Every so many years, the four molars in an elephant’s mouth start to get pushed out by four new molars. The new teeth grow in at the back of the mouth and start moving forward, pushing the old molars farther forward until they fall out. The manatee has this same type of tooth replacement, although its teeth aren’t as gigantic as the elephant’s teeth. The manatee also has hard ridged pads on the roof of its mouth that help it chew its food.

Female manatees are larger than males on average, and a really big female manatee can grow over 15 feet long, or 4.6 meters. Most manatees are between 9 and 10 feet long, or a little less than 3 meters. Its body is elongated like a whale, but unlike a whale it’s slow, usually only swimming about as fast as a human can swim. Its skin is gray or brown although often it has algae growing on it that helps camouflage it. The end of the manatee’s tail looks like a rounded paddle, and it has front flippers but no rear limbs. Its face is rounded with a prehensile upper lip covered with bristly whiskers, which it uses to find and gather water plants.

Every so often a manatee will eat a little fish, apparently on purpose. Since most herbivorous animals will eat meat every so often, this isn’t unusual. Mostly, though, the manatee spends almost all of its time awake eating plants, often from the bottom of the waterway where it lives. It lives in shallow water and will use its flippers to walk itself along the bottom, and also uses its flippers to dig up plants. Its upper lip is divided in two like the upper lips of many animals, which you can see in a dog or cat as that little line connecting the bottom of the nose to the upper lip. In the manatee, though, both sides of the lips have a lot of muscles and can move independently.

There are three species of manatee alive today: the West Indian manatee that lives in the Gulf of Mexico down to the eastern coast of northern South America, the Amazonian manatee that lives exclusively in fresh water in the Amazon basin, and the West African manatee that lives in brackish and fresh water. Sometimes the West Indian manatee will also move into river systems to find food.

Back in episode 153 we talked about the Florida manatee, which is a subspecies of West Indian manatee. In the winter it mostly lives around Florida but in summer many individuals travel widely. It’s sometimes found as far north as Massachusetts along the Atlantic coast, and as far west as Texas in the Gulf of Mexico, but despite its size, the manatee doesn’t have a lot of blubber or fat to keep it warm. The farther away it travels from warm water, the more likely it is to die of cold.

In the 1970s there were only a few hundred Florida manatees alive and it nearly went extinct. It was listed as an endangered species and after a lot of effort by a lot of different conservation groups, it’s now only considered threatened, but it’s still vulnerable to habitat loss, injuries from boats, and getting tangled in fishing gear and drowning. Occasionally a crocodile will eat a young manatee, but for the most part it’s so big, and lives in such shallow water, that most predators won’t bother it. It basically only has to worry about humans, and unfortunately humans still cause a lot of manatee deaths every year with boats.

A lot of times, a manatee that’s hit by a boat is only injured. There are several rehabilitation centers in the United States, where an injured manatee can be treated by veterinarians until it’s healed and can be reintroduced into the wild.

One other detail that makes the manatee similar to the elephant is its flippers, which is probably not what you expected me to say. Most manatees have toenails on their flippers that closely resemble the nails on elephant feet. The exception is the Amazonian manatee that doesn’t have toenails at all.

A lot of the food the Amazonian manatee eats actually floats on the surface of the rivers where it lives, and it will also eat fruit that drops into the water. Because the Amazon basin is subject to a dry season where there’s not a lot of food, the manatee eats a lot when it can to build up fat reserves for later. During the dry season, it usually moves to the biggest lakes in the area as the rivers and shallower lakes dry up or get too shallow for the manatee to swim in. Since the manatee has a low metabolic rate, it can live off its fat reserves until the dry season is over.

One interesting thing about the manatee is that it only has six vertebrae in its neck. Almost all other mammals have seven, even giraffes. The exception is the two-toed sloth, which also has six, and the three-toed sloth, which has a varying number of neck vertebrae, up to nine in some species!

Pranav also wanted to learn about sloths, so let’s talk about them next. All sloths are native to Central and South America. The sloths living today live in forests, especially rainforests, and spend almost all their time in trees.

A sloth makes the manatee look like a speed demon. It spends most of its time hanging from its long claws beneath branches, eating leaves and other plant material, but when it does move, it does so extremely slowly. This helps it stay camouflaged from predators, because its fur contains algae that makes it look green, so a barely-moving green-furred sloth hanging from a tree just looks like a bunch of leaves. It does move from one tree to another to find fresh leaves, and once a week it climbs down from its tree to defecate and urinate on the ground. Yes, it only relieves itself once a week.

The sloth’s digestive tract is also extremely slow, which allows it to extract as much nutrition as possible from each leaf. It takes about a month for a sloth to fully digest one mouthful of food.

The three-toed sloth is about the size of a large cat while the two-toed sloth is slightly larger, maybe the size of a small to medium-sized dog. The two-toed sloth is nocturnal while the three-toed sloth is mostly diurnal. Even though they look and act very similar, the two types of sloth are not very closely related. Both have long curved claws and strong pulling muscles, although their pushing muscles are weak. This is why a sloth can’t walk like other animals; the muscles that would allow it to do so aren’t strong enough to support its own weight. And yet, it can hang from a branch and walk along it for as long as it needs to. I don’t think I could hang from a branch by my fingers for five minutes without having to let go.

Surprisingly, the sloth can also swim quite well, which allows it to find new trees even if there are streams or rivers in the way. But a few million years ago, a different type of sloth lived off the coast of western South America and did a whole lot of swimming. In fact, later species of Thalassocnus were probably fully marine mammals.

We talked about Thalassocnus briefly way back in episode 22. It was related to the giant ground sloths that were themselves related to the living three-toed sloths. 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.

Thalassocnus eventually evolved a stiff, partially fused spine, which reflects the unusual way it moved around underwater. Instead of swimming the way a whale does, or even the way a dog or person does, it moved more like a hippopotamus. Hippos sort of bounce along underwater, using their feet to push off from the bottom. Thalassocnus probably did this too and used its long tail to help it maneuver.

Thalassocnus was a lot bigger than modern sloths. Even the smallest known species were the size of a big human, and the biggest species grew up to 11 feet long, or 3.3 meters. That biggest species was the one that lived most recently, up to about 1.5 million years ago, and researchers think it was fully aquatic. Its nostrils were on the top of its snout and it had prehensile lips to help it find plants underwater. Some researchers even think it could have had a short trunk something like a tapir. It had seven neck vertebrae, as in most other mammals.

There’s still a lot we don’t know about Thalassocnus, but because we have fossils of five different species that lived at different times, scientists are able to determine a lot about how it developed from a mostly terrestrial animal to a mostly or fully marine animal. The youngest species had smaller, weaker legs than the earlier ones, which suggests it didn’t use its legs to walk on land. It probably lived a lot like modern manatees, finding sea grasses and other plants on the sea floor in shallow water, but not able to swim very fast.

One last thing about the manatee is that it spends about half of its time asleep, and it sleeps underwater. It comes up for a breath every 15 minutes or so. Modern sloths sleep a lot too, around 15 hours a day. Chill sleepy friends.

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 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 Carribbean, 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.

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. We also have a Patreon if you’d like to support us and get awesome rewards.

Thanks for listening!