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

Mark Ralston, AFP/Getty Images
How a Hairdresser Found a Way to Fight Oil Spills With Hair Clippings
Mark Ralston, AFP/Getty Images
Mark Ralston, AFP/Getty Images

The Exxon Valdez oil tanker made global news in 1989 when it dumped millions of gallons of crude oil into the waters off Alaska's coast. As experts were figuring out the best ways to handle the ecological disaster, a hairdresser from Alabama named Phil McCroy was tinkering with ideas of his own. His solution, a stocking stuffed with hair clippings, was an early version of a clean-up method that's used at real oil spill sites today, according to Vox.

Hair booms are sock-like tubes stuffed with recycled hair, fur, and wool clippings. Hair naturally soaks up oil; most of the time it's sebum, an oil secreted from our sebaceous glands, but it will attract crude oil as well. When hair booms are dragged through waters slicked with oil, they sop up all of that pollution in a way that's gentle on the environment.

The same properties that make hair a great clean-up tool at spills are also what make animals vulnerable. Marine life that depends on clean fur to stay warm can die if their coats are stained with oil that's hard to wash off. Footage of an otter covered in oil was actually what inspired Phil McCroy to come up with his hair-based invention.

Check out the full story from Vox in the video below.

[h/t Vox]

A New Chew Toy Will Help Your Dog Brush Its Own Teeth

Few pet owners are willing to sit down and brush their pet's teeth on a regular basis. (Most of us can barely convince ourselves to floss our own teeth, after all.) Even fewer pets are willing to sit calmly and let it happen. But pet dental care matters: I’ve personally spent more than $1000 in the last few years dealing with the fact that my cat’s teeth are rotting out of her head.

For dog owners struggling to brush poor Fido’s teeth, there’s a slightly better option. Bristly, a product currently being funded on Kickstarter, is a chew toy that acts as a toothbrush. The rubber stick, which can be slathered with doggie toothpaste, is outfitted with bristles that brush your dog’s teeth as it plays.

A French bulldog chews on a Bristly toy.

Designed so your dog can use it without you lifting a finger, it’s shaped like a little pogo stick, with a flattened base that allows dogs to stabilize it with their paws as they hack at the bristled stick with their teeth. The bristles are coated in a meat flavoring to encourage dogs to chew.

An estimated 80 percent of dogs over the age of 3 have some kind of dental disease, so the chances that your dog could use some extra dental attention is very high. In addition to staving off expensive vet bills, brushing your dog's teeth can improve their smelly breath.

Bristly comes in three sizes as well as in a heavy-duty version made for dogs who are prone to ripping through anything they can get their jaws around. A Bristly stick costs $29 and is scheduled to start shipping in October. Get it here.


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