Wikimedia Commons // Public Domain
Wikimedia Commons // Public Domain

10 Big Facts About Giant Ground Sloths

Wikimedia Commons // Public Domain
Wikimedia Commons // Public Domain

Today, the six living species of sloths are usually found dangling from tree branches, or going viral on YouTube. But sloths used to be a lot more diverse—and a lot bigger. The extinct ground sloths pursued all sorts of different lifestyles and came in just about every imaginable shape and size. Some were cow-like grazers; others might have been accomplished burrowers; and, believe it or not, a few even dined beneath the ocean waves.


Megatherium (above) means “giant beast”—a fitting name for a creature that weighed several tons, reached 20 feet in length, and—when reared up on its hind legs—stood over 12 feet tall. The biggest sloth of all time, Megatherium americanum, occupied South America between five million and eleven thousand years ago. Above the equator, its slightly-smaller cousin, the 6000-pound Eremotherium, managed to spread as far north as New Jersey.


All ground sloths were predominantly quadrupedal. While they were more than capable of standing up on two legs (more about this later), the animals preferred to get around on four—but individual species differed widely from each other in terms of limb posture.

Scientists have divided ground sloths up into four recognized families, and only one—the megalonychids—stood flat on their rear feet like humans do. Because of the shapes of their ankle and/or hind claws, sloths from the megatheriid, mylodontid, and nothrotheriid families had to trudge along by putting weight on the outer sides of their feet.


Buried in the skin of the mylodontid ground sloths—including the Harlan’s ground sloth, whose range extended from Florida to Washington state—were a series of small bony discs. Known as “osteoderms,” these little knobs (nickel-sized in Harlan’s ground sloth) were mostly clustered around the back, shoulders, and neck and would have acted like protective chainmail.

This trait isn’t all that unusual. A few modern animals, including armadillos and crocodilians, also have osteoderms of some kind—as did many dinosaurs.


For these animals, standing up on two limbs required some extra stability. Whenever a ground sloth did this, its muscular tail would act like another leg, helping to support its considerable body weight.


The Sage of Monticello’s importance to American paleontology cannot be understated. In 1796, Jefferson—a respected armchair naturalist—received some curious bones from western Virginia (modern West Virginia). This find wasn’t all that unusual—similar-looking fossils had also emerged in Kentucky and other parts of Virginia. Still, Jefferson spoke at length about the big-clawed mystery animal at a 1797 meeting of the American Philosophical Society in Philadelphia. The future president dubbed this creature Megalonyx, or “great claw.” Though we now know that it was a large, flat-footed sloth, Jefferson originally mistook the animal for an enormous lion or tiger-like carnivore.

Currently, four different species of Megalonyx are recognized; the most famous, Megalonyx jeffersonii, was named in Jefferson's honor. On March 8, 2008, West Virginia recognized the animal as its official state fossil.   


What killed off the woolly mammoth, the scimitar cat, and North America’s other ice age mega-mammals? Homo sapiens usually gets a good chunk of the blame. Scientists have long speculated that humans killed and devoured ground sloths—but, for many years, there was no physical evidence to support this idea. Then, in 2008, incriminating scars were found on the femur of an Ohio Megalonyx. The 13,000-year old fossil is riddled with 41 unusual cuts that appear to have been left by manmade tools.  

As archaeologist Haskel Greenfield points out, we’ll likely never know if early Americans killed this animal or merely scavenged its remains. “The only thing that is clear,” he said in 2012, “is that there are disarticulation marks: they were separating the limbs from each other; they were cutting the joints. And some marks show that they were filleting the meat off the bone.” 


Imagine a sloth that’s trying hard to be a marine iguana. You’ve just pictured a member of the Thalassocnus genus. These Peruvian herbivores, which lived 8 to 4 million years ago, dove into the ocean for their supper. Hooked claws helped them latch onto submerged, seaweed-covered rocks; once anchored, a Thalassocnus could consume marine algae. Over time, evolution fitted the amphibious sloths with increasingly dense ribs and limb bones. Therefore, younger species were less buoyant—and probably more aquatic—than their ancestors had been.


Rivaling a black bear in size, Nothrotheriops would have been dwarfed by behemoths like Megatherium. Still, we know more about it than any other ground sloth thanks to one amazing find. Eleven thousand years ago, a New Mexican Nothrotheriops stumbled into a volcanic gas vent and died. Then, in either 1927 or 1928 (sources differ), a group of explorers happened upon the incredibly well preserved body. Not only were almost all of its ligaments and bones intact, but this Nothrotheriops also came with a few muscle fibers. Even more interestingly, the specimen retained some original skin—covered by rough, yellowish hair. The cherry on top was an accompanying dung ball, which helped confirm that Nothrotheriops ate a diverse array of plants—including cacti fruit, yuccas, and saltbushes. 

In 1928, Yale’s Peabody Museum of Natural History acquired the mummy, and today, visitors can find the creature on display in Mammal Hall.


Your average ground sloth was—in all likelihood—a browsing herbivore, pulling down tree branches with its strong forelimbs. However, the mylodontids may have also gathered food by digging for it. Experts argue that their wide, flattened claws look like ideal tools for excavating roots and tubers [PDF].

Believe it or not, mylodontids might have even been burrowers. Several huge, prehistoric tunnels have been found in Argentina [PDF]. Made sometime during the Pleistocene epoch (between 2.6 million and 11,700 years ago), these were natural marvels, with the longest stretching 130 feet from end to end. What could have possibly dug them? Two top suspects are Scelidotherium and Glossotherium: a pair of mylodonts with claws that match scratch marks found inside the burrows. 


The Caribbean islands seem like an unlikely place for ground sloths to have made their last stand—but that’s exactly where it happened [PDF]. Mainland North America lost all of its indigenous species around 11,000 years ago, and half a millennium later, South America, too, became a ground sloth-free continent.

But despite these extinctions, some ground sloths didn't die out until much later. Hispaniola and Cuba were home to assorted dwarf species. Descended from their full-sized counterparts on the mainlands, these mammals were resilient. Ultimately, Megaloncus rodens was the last ground sloth standing: Radiocarbon dating indicates that this 200-pound vegetarian waddled across Cuba as recently as 4200 years ago

Why Tiny 'Hedgehog Highways' Are Popping Up Around London

Hedgehogs as pets have gained popularity in recent years, but in many parts of the world, they're still wild animals. That includes London, where close to a million of the creatures roam streets, parks, and gardens, seeking out wood and vegetation to take refuge in. Now, Atlas Obscura reports that animal activists are transforming the city into a more hospitable environment for hedgehogs.

Barnes Hedgehogs, a group founded by Michel Birkenwald in the London neighborhood of Barnes four years ago, is responsible for drilling tiny "hedgehog highways" through walls around London. The passages are just wide enough for the animals to climb through, making it easier for them to travel from one green space to the next.

London's wild hedgehog population has seen a sharp decline in recent decades. Though it's hard to pin down accurate numbers for the elusive animals, surveys have shown that the British population has dwindled by tens of millions since the 1950s. This is due to factors like human development and habitat destruction by farmers who aren't fond of the unattractive shrubs, hedges, and dead wood that hedgehogs use as their homes.

When such environments are left to grow, they can still be hard for hedgehogs to access. Carving hedgehog highways through the stone partitions and wooden fences bordering parks and gardens is one way Barnes Hedgehogs is making life in the big city a little easier for its most prickly residents.

[h/t Atlas Obscura]

Penn Vet Working Dog Center
Stones, Bones, and Wrecks
New Program Trains Dogs to Sniff Out Art Smugglers
Penn Vet Working Dog Center
Penn Vet Working Dog Center

Soon, the dogs you see sniffing out contraband at airports may not be searching for drugs or smuggled Spanish ham. They might be looking for stolen treasures.

K-9 Artifact Finders, a new collaboration between New Hampshire-based cultural heritage law firm Red Arch and the University of Pennsylvania, is training dogs to root out stolen antiquities looted from archaeological sites and museums. The dogs would be stopping them at borders before the items can be sold elsewhere on the black market.

The illegal antiquities trade nets more than $3 billion per year around the world, and trafficking hits countries dealing with ongoing conflict, like Syria and Iraq today, particularly hard. By one estimate, around half a million artifacts were stolen from museums and archaeological sites throughout Iraq between 2003 and 2005 alone. (Famously, the craft-supply chain Hobby Lobby was fined $3 million in 2017 for buying thousands of ancient artifacts looted from Iraq.) In Syria, the Islamic State has been known to loot and sell ancient artifacts including statues, jewelry, and art to fund its operations.

But the problem spans across the world. Between 2007 and 2016, U.S. Customs and Border Control discovered more than 7800 cultural artifacts in the U.S. looted from 30 different countries.

A yellow Lab sniffs a metal cage designed to train dogs on scent detection.
Penn Vet Working Dog Center

K-9 Artifact Finders is the brainchild of Rick St. Hilaire, the executive director of Red Arch. His non-profit firm researches cultural heritage property law and preservation policy, including studying archaeological site looting and antiquities trafficking. Back in 2015, St. Hilaire was reading an article about a working dog trained to sniff out electronics that was able to find USB drives, SD cards, and other data storage devices. He wondered, if dogs could be trained to identify the scents of inorganic materials that make up electronics, could they be trained to sniff out ancient pottery?

To find out, St. Hilaire tells Mental Floss, he contacted the Penn Vet Working Dog Center, a research and training center for detection dogs. In December 2017, Red Arch, the Working Dog Center, and the Penn Museum (which is providing the artifacts to train the dogs) launched K-9 Artifact Finders, and in late January 2018, the five dogs selected for the project began their training, starting with learning the distinct smell of ancient pottery.

“Our theory is, it is a porous material that’s going to have a lot more odor than, say, a metal,” says Cindy Otto, the executive director of the Penn Vet Working Dog Center and the project’s principal investigator.

As you might imagine, museum curators may not be keen on exposing fragile ancient materials to four Labrador retrievers and a German shepherd, and the Working Dog Center didn’t want to take any risks with the Penn Museum’s priceless artifacts. So instead of letting the dogs have free rein to sniff the materials themselves, the project is using cotton balls. The researchers seal the artifacts (broken shards of Syrian pottery) in airtight bags with a cotton ball for 72 hours, then ask the dogs to find the cotton balls in the lab. They’re being trained to disregard the smell of the cotton ball itself, the smell of the bag it was stored in, and ideally, the smell of modern-day pottery, eventually being able to zero in on the smell that distinguishes ancient pottery specifically.

A dog looks out over the metal "pinhweel" training mechanism.
Penn Vet Working Dog Center

“The dogs are responding well,” Otto tells Mental Floss, explaining that the training program is at the stage of "exposing them to the odor and having them recognize it.”

The dogs involved in the project were chosen for their calm-but-curious demeanors and sensitive noses (one also works as a drug-detection dog when she’s not training on pottery). They had to be motivated enough to want to hunt down the cotton balls, but not aggressive or easily distracted.

Right now, the dogs train three days a week, and will continue to work on their pottery-detection skills for the first stage of the project, which the researchers expect will last for the next nine months. Depending on how the first phase of the training goes, the researchers hope to be able to then take the dogs out into the field to see if they can find the odor of ancient pottery in real-life situations, like in suitcases, rather than in a laboratory setting. Eventually, they also hope to train the dogs on other types of objects, and perhaps even pinpoint the chemical signatures that make artifacts smell distinct.

Pottery-sniffing dogs won’t be showing up at airport customs or on shipping docks soon, but one day, they could be as common as drug-sniffing canines. If dogs can detect low blood sugar or find a tiny USB drive hidden in a house, surely they can figure out if you’re smuggling a sculpture made thousands of years ago in your suitcase.


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