11 Of Ancient Earth’s Most Unbelievable Prehistoric Animals

For thousands to millions of years, these massive creatures stalked Earth at its dawn, until climate change — or early man — hastened their demise.

Some of them, like the giant sloth or the woolly rhino, were generally gentle. Others, like the saber-toothed tiger and the dire wolves, dominated their environment with their size and fearsome fangs.

For millions of years, these ancient animals stalked through grasslands, climbed trees in the jungle, and chased prey into tar pits. Though vastly different, they all died out in similar ways due to changing climate, poaching, or disease.

Today, they exist as just a whisper of their former might — a bone here, a tooth there — but in their prime, these prehistoric animals would have struck fear and awe into early humans.

Here are 11 Of Ancient Earth’s Most Unbelievable Prehistoric Animals

1-    Glyptodon: The Prehistoric Armadillo The Size Of A Car

Between 5.3 million to 11,700 years ago, a peculiar creature called the glyptodon — meaning “grooved tooth” — walked the Earth.

Ten feet long and weighing as much as 4,000 pounds, this “giant armadillo” existed in present-day North and South America. Though the glyptodon had a powerful tail and an armored back made of 1,000 bony plates, it likely lived a fairly peaceful existence. An herbivore, it mostly ate grass and didn’t have to worry about any bloody tussles over game.

That said, the glyptodon could defend itself — even against other glyptodons — if need be. Its powerful tail could crush a human skull, and its shell-like back offered a strong defense.

Based on the damage found on glyptodon shell fossils, scientists believe that the beasts often fought each other. To settle disputes over territory or mates, they’d pummel their opponent’s shell with their strong tail.

But this ancient animal often had to contend with humans, too. Early hunters likely stalked the glyptodon for its meat and shell. To kill it, however, they had to turn it on its back — no small task — and spear its soft underbelly.

Researchers first discovered the glyptodon in 1823, when Uruguayan naturalist Dámaso Antonio Larrañaga came across a giant femur. The bone weighed about seven pounds and stretched six to eight inches long.

Most believed, however, that he’d found the bones of a giant sloth called Megatherium. Further discoveries convinced scientists that they were dealing with a different prehistoric animal, however, and biologist Richard Owen dubbed it a glyptodon because of its curved teeth.

The reign of the glyptodon came to an end shortly after the last Ice Age. Climate change, and aggressive human hunting, drove the giant armadillo into extinction.

Today, only their massive bones speak to their existence. As recently as 2020, an Argentinian farmer found several glyptodon shells in his yard.

2-    Titanoboa: The Monster Snake Of The Paleocene Epoch.

Imagine a snake. Now, imagine that it’s 45 feet long and weighs 1.25 tons. That’s what the terrifying Titanoboa cerrejonensis, or Titanoboa looked like. “The snake’s body was so wide that if it were moving down the hall and decided to come into my office to eat me, it would literally have to squeeze through the door,” explained Jason Head, a paleontologist who studied Titanoboa.

The monstrous snake lived some 60 million years ago. After the extinction of the dinosaurs, it zipped up the food chain and quickly came to dominate the tropical jungles of present-day South America. When its killer gaze latched onto five-foot giant turtles or 20-foot long crocodiles, the Titanoboa likely waited in shallow water for its prey to approach. Once the unfortunate animal got close enough, the snake would strike — and crush its meal to death.

Though this ancient animal terrorized the world for millions of years, it took a long time for modern-day humans to realize that it had even existed.

In 2002, a fossilized leaf discovered in a Colombian coal mine convinced scientists that a rainforest had once flourished at the same site. Indeed, they soon found fossils of giant turtles and crocodiles, as well as early bananas, avocados, and bean plants.

But of all the finds, one stood out: a massive vertebra. Convinced that it had once belonged to a snake, possibly one caught in a muddy landslide, researchers scoured the ground for more bones.

In the end, they found the remains of not one but 28 enormous snakes. Thrillingly, they also found three snake skulls — which can be elusive. Snakes use the muscles in their mouths to kill, not their bones, and skulls often disintegrate over time.

As for those crocodile and turtle fossils? Likely the giant snakes’ unfortunate victims. Titanoboa, surmised the scientists, had once dominated the animal.

3-    Megatherium: The Giant (And Probably Extinct) Ground Sloth

Today’s sloths are small. But the ancient animals that preceded them, called Megatherium americanum, were veritable giants.

Standing nearly 12 feet tall and weighing upwards of four tons, Megatherium americanum once roamed the jungles of South America. Unlike today’s sloths, which live in trees, Megatherium americanum walked the earth. Fossils found in Argentina, Uruguay, and Bolivia suggest that the beast lived between 400,000 and 8,000 years ago.

Though it likely walked on four legs, Megatherium americanum could stretch up to its full height to snatch hard-to-reach leaves. The creature had fearsome claws, but chemical analyses of its teeth suggest that the Megatherium  americanum largely stuck to eating leaves and plants.

Like modern-day sloths, however, the M. americanum took its time. It moved slowly, possibly slower than anything else alive at the time. But its size offered plenty of protection, as these prehistoric animals outweighed possible predators like the saber-tooth tiger.

So if the M. americanum could find plenty to eat, and didn’t have to worry much about predators, then why did these prehistoric animals go extinct?

Scientists are unsure. It could have been a climate event, or disease, or possibly the arrival of humans, seeing as some M. americanum bones seem to bear marks consistent with hunting.

Then again, it’s possible that the M. americanum never went extinct at all. Some believe that the creature merely retreated deeper into the jungle once humans arrived on the scene.

People living in the Amazon rainforest have indeed shared stories of a beast they call mapinguari. Said to be a slow-moving, sloth-like beast that stands on its hind legs, the mapinguari does sound suspiciously like the M. americanum.

However, legend also states that the mapinguari has a giant mouth on its stomach capable of devouring anything that crosses its path. But scientists have found no evidence of such an orifice among the M. americanum — at least, not yet.

4-    Deinosuchus: The Fearsome Prehistoric Animal Called ‘Terrible Crocodile.

When it comes to prehistoric animals that seem like modern-day monsters, it’s hard to beat Deinosuchus. Stretching 33 feet long and with teeth the size of bananas, Deinosuchus terrified North America during the late Cretaceous period, some 82 to 73 million years ago. Even its name literally translates to “terrible crocodile.”

The giant crocs mostly ate sea turtles and shellfish, but sometimes tangled with T. Rex cousins like Appalachiosaurus montgomeriensis and Albertosaurus — and left the bite marks to prove it.

“Deinosuchus was a giant that must have terrorized dinosaurs that came to the water’s edge to drink,” explained Adam Cossette, a vertebrate paleontologist at the New York Institute of Technology who has studied the beasts.

These fearsome prehistoric animals lived across the present-day United States and Mexico. Fossils have been found in Utah, Montana, Wyoming, New Mexico, New Jersey, Georgia, Alabama, Mississippi, Texas, and North Carolina.

The monster does differ somewhat from modern-day crocodiles, however. In addition to its massive size, it also has a bulb-like snout with two vents. Scientists aren’t sure what Deinosuchus needed the vents for, but they possibly helped cool the animals down.

As with other prehistoric animals on this list, it took scientists a while to understand the full picture of these ancient animals. Deinosuchus fossils were originally classified under the genus Polyptychodon, another marine predator, but in 1904, the zoologist and paleontologist William Jacob Holland studied the available evidence and concluded that Deinosuchus was a monster all its own.

Specimens of Deinosuchus, Cossette noted, were few and far between. But the ones that scientists have found are “HUGE.”

For a long time, Deinosuchus was considered the largest crocodile ever discovered. It’s since been dethroned by Sarcosuchus imperator who, at 40 feet long and 17,600 pounds, could have taken Deinosuchus in a fight.

5-    Ursus Spelaeus: The Ice Age Cave Bears

Standing 11 feet tall and weighing up to 2,200 pounds, the Ice Age cave bear, or Ursus spelaeus, must have struck fear into the hearts of early humans.

But the bear probably wouldn’t have killed — at least not to eat. Scientists think that these prehistoric animals were primarily herbivores and munched on plants, not people.

During the Late Pleistocene era, these bears lived across Europe. Tens of thousands of their fossils have been found in caves across the continent, suggesting that they spent more time in caves than modern-day bears (who often use caves solely for hibernation).

They did, however, seem to venture out enough to cross paths with people. Scientists aren’t sure exactly how early humans interacted with the bears, but they have come across some puzzling clues.

In Drachenloch, Switzerland, for example, researchers found seven cave bear skulls seemingly arranged to face the front of the caves, and six more skulls stuck into cave alcoves.

That head-scratching discovery, however, pales in comparison to the nearly intact cave bear found by reindeer hunters in 2020.

The hunters came across the bear in the melting permafrost of Bolshoy Lyakhovsky Island in Siberia. Likely between 39,500 and 22,000 years old, the frozen tundra kept it in remarkably good shape. The cold preserved even its internal organs.

So, what happened to these Ice Age cave bears? Although their cousins walk the earth today, Ursus spelaeus slowly went extinct starting around 24,000 years ago.

It’s unclear what exactly did them in. Scientists have noticed high rates of disease in cave bear fossils, which could have been a contributing factor. However, changing climate could also have contributed to the extinction of the Ice Age bears.

6-    Megalania Prisca: The World’s Largest Lizard

Today’s Komodo Dragons can weigh up to 150 pounds, but their ancestor, Megalania prisca — also called Varanus priscus or Giant Monitor Lizard — could grow to between 500 and 4,000 pounds. It’s the largest known lizard to have ever walked the Earth.

Between two million and 40,000 years ago, these intimidating creatures easily reigned over present-day eastern Australia. Up to 25 feet long, they likely feasted on a wide variety of animals, including kangaroos, pygmy elephants, and tortoises.

Though they could certainly use their size to subdue and kill prey, the M. prisca also had another tool at their disposal: toxic saliva. Scientists believe that they used venom from glands in their lower jaw to kill.

That said, it’s possible that M. prisca occasionally faced predators of its own. During its life, it shared an environment with The Marsupial Lion (called Thylacoleo) and a 500-pound crocodile (known as the Quinkana). It’s hard to predict if the Giant Monitor Lizard could win a bout with these dangerous prehistoric animals.

English naturalist Richard Owen first described M. prisca in 1859. He’s the one who gave it its name (which means giant roamer) but contemporary scientists believe he mislabeled it, which is why it also goes by the name Varanus priscus.

Since Owen’s discovery, however, scientists have found very few fossilized remains of the Giant Monitor Lizard. That means that there’s still a lot to learn about this prehistoric animal.

There are some theories out there about why the M. prisca died out, however. Although humans didn’t seem to hunt it directly, they did hunt animals that the M. prisca relied on as prey. As such, people may have played an indirect role in its extinction.

Then again, as with the giant sloth, some believe that the Great Monitor Lizard never went extinct at all. Rumor has it that the beast simply crept into the Australian wilderness and lives there to this day.

7-    Entelodont: The Prehistorical Animals With Teeth As Thick As A Human Wrist

The next prehistoric animal looks like it waltzed straight out of hell. Indeed, the entelodont goes by the nickname “hell pigs.”

These beasts had teeth the size of a human wrist, nubby bones in their face for fights with each other or other animals, and cloven hooves. The largest of their genus, called Daeodon — Greek for “hostile teeth” — could weigh up to 2,000 pounds.

Hell pigs charged onto the scene during the Eocene era. From Mongolia, they rapidly spread to Europe and even to North America. Archeologists have found fossils of the entelodont in places like Nebraska, Wyoming, and South Dakota.

However, the entelodont didn’t spend its days preying on other prehistoric animals. Instead, it seems that it used its enormous jaws to dig for roots and chew plants.

That said, the hell pigs were likely omnivores. Even if they didn’t kill first-hand, they may have just waited for other animals to kill before scaring them off and eating their prey.

The hell pigs probably scared most animals in their environment, even if they didn’t outright kill them to eat. Bite marks left by Daeodon have been found on a number of animals including prehistoric rhinos.

In the end, it took a combination of factors to finally take down the entelodont. As the climate changed, the hell pigs’ beloved forests turned into grassy fields. Forced to travel long distances for food, the pigs likely lost out to animals that moved faster.

Plus, a number of new predators appeared on the horizon during the entelodont’s existence. They soon faced formidable foes like the saber-toothed cat as well as bear dogs.

The last of the entelodont went extinct between 19 and 16 million years ago. Since then, these fearsome ancient animals exist only as fossils in museums — or perhaps as hellish pigs, running through your nightmares.

8-    Smilodon: Sharp-Fanged Saber-Toothed Tigers

Perhaps the most famous prehistoric animal on this list is the Smilodon, or saber-toothed cat. Its striking canine teeth give it an especially fearsome appearance.

The Smilodon lived between 2.5 million to 11,700 years ago, and populated the forests of North and South America. The cat varied in size depending on the species. Smilodon gracilis grew to about 150 pounds, Smilodon fatalis at 200 pounds, and Smilodon populator tipped the scales at around 500 pounds.

One recently discovered Smilodon populator fossil, however, suggests that the cat could have been much bigger. Based on the size of its head, scientists think that it could have grown to weigh 1,000 pounds.

Regardless of size, these big cats shared one defining characteristic: their canine teeth. Set on the side of their jaw, these sharp fangs hung menacingly on either side of the cat’s face. To stab their prey, the saber-toothed cats had to open their mouths more than 90 degrees.

Surprisingly, however, the big cats’ teeth were fragile. They sometimes lost them entirely while fighting to subdue their prey. As such, the cats often hunted from the trees. Using the element of surprise, they leaped from the branches and sunk their teeth into unsuspecting animals below.

They were nonetheless effective killers. The saber-toothed cats likely preyed on bison, sloths, mammoths, horses, pigs, and llamas. In other words, they killed whatever they could.

Sometimes, the pursuit of prey proved fatal for the Smilodon. Thousands of saber-toothed cat bones have been extracted from the La Brea Tar Pits in California. There, many Smilodon met a literal sticky end while chasing prey into the pits.

A changing climate — and the ensuing lack of prey — likely spelled the end for these terrifyingly majestic ancient animals.

9-    Dire Wolves: The Prehistoric Animals Depicted In ‘Game Of Thrones’

In the TV series Game Of Thrones, a number of characters have a dire wolf companion. On the show, these wolves are depicted as large, fierce, and loyal. Game of Thrones may have taken some liberties, but dire wolves were actual ancient animals.

Real dire wolves — called Canis dirus, or “fearsome dogs” — existed from about 125,000 to 10,000 years ago in present-day North and South America. Though similar to gray wolves, dire wolves are genetically different.

Slightly bigger than gray wolves and with reddish fur, dire wolves weighed around 130 pounds and measured about six feet long. Like the dire wolves of fiction, Canis dirus also had formidable jaws that helped them kill.

The dire wolves went after a variety of prey. They killed horses, bison, and even young mammoths when they could get it. By springing on their prey and latching on with their jaws, dire wolves dragged animals down so that they could kill them. As such, their fossils are often found with neck injuries.

Sometimes, they actually competed with saber-toothed cats to make the kill.

To date, thousands of dire wolf skeletons have been found at the La Brea Tar Pits in California. Like the Smilodon, dire wolves often chased their prey with a bit too much enthusiasm and got caught in the tar.

But it wasn’t the La Brea Tar Pits alone that killed off the last of the dire wolves. It seems likely that these wolves died off because their prey did. Lacking slow-moving animals to kill — and unable to catch up with faster ones — the dire wolves went extinct.

They live on in the world of fiction, however. Dire wolves have enjoyed a renaissance thanks to George R.R. Martin’s book series and the Game Of Thrones TV show.

10-                      Gigantopithecus: The Largest Ape That Ever Lived

Maybe Bigfoot doesn’t exist — or maybe he does. But in any case, a similarly gigantic beast did once walk the earth. Gigantopithecus blacki, a prehistoric giant ape, could give Bigfoot a run for his money.

Like Bigfoot, however, G.blacki is elusive. Scientists have few fossils of them, and the ones they do have are mostly of teeth and pieces of the great ape’s jaw. Even from that, researchers have drawn some stunning conclusions, however.

G.blacki, they believe, stood around 10 feet tall and could weigh almost 600 pounds. A likely ancestor of today’s orangutans, the ape lived in Southeast Asia for about six to nine million years before going extinct some 100,000 years ago.

Based on its teeth — nearly 2,000 large molars, canines, and other teeth have been found — researchers suspect that G.blacki ate a vegetarian diet. These ancient animals likely consumed plants, fruits, seeds, and maybe even bamboo.

 

However, G.blacki‘s diet may have doomed it to extinction. While most prehistoric animals of its time foraged in both the forest and grasslands, the apes stuck to the forests.

As the forests shrank, so did their food supply. Seemingly unable to adapt — and unwilling to leave the safety of the woods — the giant apes died out.

In fact, it wasn’t until 1935 that modern-day humans got a whiff of G.blacki‘s existence. Then, a German paleontologist named Gustav von Koenigswald came across some of the ape’s teeth in China. Sold as “dragon teeth,” they suggested to many scientists that humans had had a giant ancestor.

Instead, they came across the giant ape — and a giant mystery. Hopefully more fossils of G.blacki will be uncovered in the future.

11-                      Wooly Rhinoceros: The Furry Prehistoric Animals That Wandered Eurasia

Everyone has heard of woolly mammoths. But what about woolly rhinoceroses?

In some ways, woolly rhinos (Coelodonta antiquitatis) looked a lot like today’s rhinos. Like contemporary rhinoceroses, they stood about six feet tall and weighed around three tons. They also had a set of two horns, one large anterior horn and one smaller one between their eyes.

But woolly rhinos differed in a couple of significant ways. For one, they had longer heads and bodies and shorter legs. Woolly rhinos also had a large hump behind the shoulder, likely to help support their horns. And, of course, they had fur — plenty of it.

Before going extinct some 14,000 years ago, the woolly rhino wandered far and wide. Its fossils have been found in Spain, Siberia, and South Korea. As such, the woolly rhino sometimes appears — though not as frequently as woolly mammoths or bison — in ancient cave paintings.

Humans and woolly rhinos likely had limited interactions, although evidence does suggest that humans sometimes hunted the prehistoric beasts. That said, scientists think that changing climate — and not overhunting — led to the woolly rhino’s extinction.

But if climate change thousands of years ago killed off the woolly rhino, then today’s climate change might revive it — in a way. Melting permafrost in Serbia has revealed a number of well-preserved Ice Age creatures, including the woolly rhino.

In 2020, locals in eastern Siberia stumbled across the frozen body of a young woolly rhino in the melting ice. The frozen earth had preserved the ancient animal’s intestines, fur, and even its horn.

So far, however, there’s no talk about trying to reproduce the woolly rhino as some want to do with the woolly mammoth. For now, we’ll have to revere these ancient animals from fossils.