For thousands to millions of years before history, many huge creatures lurked on Earth at dawn until climate change — or early humans — hastened their demise.
Prehistoric animals once roamed and ruled the earth.
Some of them, such as giant sloths or hairy rhinos, are generally mild. Other animals, such as saber-toothed tigers and dire wolves, rule their territory with their size and fearsome fangs.
For millions of years, these ancient animals have walked the grasslands, climbed trees in the jungle, and constantly chased their prey. Despite the large differences, they are all extinct in similar ways due to climate change, poaching or disease.
Today, their existence is only a whisper of their former power—a bone, a tooth—but in their heyday, these prehistoric animals would have terrified and awed early humans.
Glyptodon: A prehistoric armadillo the size of a car
Between 5.3 million and 11,700 years ago, a strange creature called a glyptodont, which means "grooved tooth," walked the earth.
Fossils of prehistoric armadillos
This "giant armadillo" is ten feet long and weighs 4,000 pounds, and is present in present-day North and South America. Although the glypton has a powerful tail and an armored back made up of 1000 bone plates, it probably lived a fairly peaceful life. As an herbivore, it mainly eats grass and does not have to worry about any bloody fights.
That is, if needed, the glypton can protect itself – even against other glyptontodons. Its powerful tail can crush a person's skull, while its shell-like back provides a strong defense.
Based on the damage found on the fossilized carptodont shells, scientists believe the beasts often fought each other. To settle territorial or mate disputes, they will knock on the shell of their opponents with a strong tail.
But this ancient animal also often has to contend with humans. Early hunters probably tracked the glypton for its flesh and shell. However, to kill it, they must turn it over and pierce its soft belly – no easy task.
Early humans may have used the huge back of the glyptodont as a barrier
Researchers first discovered the glyptodont in 1823, when Uruguayan naturalist Dámaso Antonio Larrañaga discovered a huge femur. The bones weigh about seven pounds and are six to eight inches long.
At the time most people thought he had found the bones of a giant sloth called a giant sloth. However, further findings have led scientists to believe that they are dealing with another prehistoric animal, which biologist Richard Owen has dubbed the Glyptodont because of its crooked teeth.
Shortly after the last ice age, the reign of the glypton ended. Climate change and aggressive human hunting have brought the giant armadillo to the brink of extinction.
Today, only their huge bones speak of their existence. Just in 2020, an Argentine farmer found several glypton shells in his yard.
Titan Python: The giant serpent of the Paleocene
Imagine a giant snake 14 meters long and weighing 1.25 tons, this is what the terrifying titan python looks like.
This huge snake lived about 60 million years ago. After the extinction of the dinosaurs, it moved up the food chain and quickly dominated the tropical jungles of present-day South America.
When its ferocious gaze is locked on a giant 5-foot-long turtle or a 20-foot-long crocodile, the titan python is likely to be in shallow water waiting for its prey to approach. Once the unfortunate animal gets close enough, the snake attacks and crushes its food to death.
While this ancient animal has been threatening the world for millions of years, it took modern humans a long time to realize its existence.
In 2002, a fossil leaf found in a Colombian coal mine led scientists to believe that the rainforest once thrived in the same location. They soon found fossils of giant turtles and crocodiles, as well as fossils of early bananas, avocados and legumes.
But among all the finds, one stands out: a huge vertebrae. The researchers were convinced that it once belonged to a snake, possibly one trapped in a muddy landslide, so they searched the ground for more bones.
Titan python vertebrae (left) versus python vertebrae (right).
In the end, they found the remains of not one, but 28 giant snakes. Excitingly, they also found three snake skulls.
As for those crocodile and turtle fossils? Probably an unfortunate victim of the giant snake. Scientists speculate that the Titan Python once ruled the animal kingdom.
Behemoth of the Americas: Giant ground sloth
Sloths today are small. But the ancient animals before them, called the Behemoths of America, were veritable giants.
Fossils of huge American behemoths
Nearly 4 meters tall and weighing more than 4 tons, the American Behemoth once roamed the jungles of South America. Unlike the sloths that live in trees today, American sloths walk the earth. Fossils found in Argentina, Uruguay and Bolivia suggest that the beast lived between 400,000 and 8,000 years ago.
Although it may walk on four legs, the American behemoth can stretch to maximum height to grab hard-to-reach leaves. This creature has fearsome claws, but chemical analysis of its teeth suggests that the American largemouth fish mainly eats leaves and plants.
However, like modern sloths, American sloths take their breath in stride. It moved slowly, probably slower than anything alive at the time. But its size provides ample protection, as these prehistoric animals weighed more than possible predators such as saber-toothed tigers.
Restoration diagram of the American Behemoth
So, if the American behemoths could find a lot of food and didn't have to worry too much about predators, why did these prehistoric animals go extinct?
Scientists aren't sure the answer to that question. It could be due to climatic events, or disease, or it could be the arrival of humans, as the bones of some American behemoths appear to bear traces consistent with hunting.
There is also an idea that the American behemoths may not have gone extinct at all. Those who hold this view believe that once humans arrive at the scene, the creature retreats deep into the jungle.
People living in the Amazon rainforest do share stories of a beast they call mapinguari. Mapinguari is said to be a slow-moving, sloth-like beast that stands on its hind legs.
Dire crocodile: A prehistoric animal known as the "scary crocodile"
The skull of the terrible dire crocodile
When it comes to prehistoric animals that look like modern monsters, I'm afraid it's hard to get around the dinosaurs. In the late Cretaceous period, about 82 to 73 million years ago, the dinosaur crocodile was more than 10 meters long, with teeth the size of bananas, and even its name literally translated as "terrible crocodile".
Dire crocodiles eat mainly turtles and shellfish, but sometimes entangle with Tyrannosaurus rex cousins such as Montgomery Appalachian and Albertasaurus, as evidenced by bite marks left on fossils.
"The dinosaur is a giant, and it must have scared the dinosaurs who came to the water's edge to drink," explains Adam Cossett, a vertebrate paleontologist at the New York Institute of Technology who studies the beast.
These fearsome prehistoric animals lived in present-day America and Mexico. Their fossils have been found in Utah, Montana, Wyoming, New Mexico, New Jersey, Georgia, Alabama, Mississippi, Texas, and North Carolina.
However, this monster does differ somewhat from modern crocodiles. In addition to its huge size, it has a bulb-shaped muzzle with two ventilation holes. Scientists aren't sure what dinosaurs need vents for, perhaps to help them cool down.
Like the other prehistoric animals on this list, it took scientists a while to understand the full picture of these ancient animals. Dire crocodile fossils were originally classified as another marine predator, Polyptychodon, but in 1904, zoologist and paleontologist William Jacob Holland studied the available evidence and concluded that the dire crocodile was a monster in its own right.
Cave Bear: Ice Age cave bear
At 3.4 meters tall and weighing 2,200 pounds, the Ice Age cave bear (also known as Ursus spelaeus) must have terrified early humans.
But bears probably won't kill — at least not cannibalize. Scientists believe that these prehistoric animals were mainly herbivores, feeding on plants rather than humans.
During the late Pleistocene, these bears lived all over Europe. Tens of thousands of their fossils have been found in caves across the continent, suggesting that they spent longer in caves than modern bears, which typically only hibernate in caves.
However, they do seem to dare to take risks and socialize with people. Scientists aren't sure how early humans interacted with bears, but they've found some puzzling clues.
In Drachenloch, Switzerland, for example, researchers found seven cave bear skulls that appeared to be arranged to face the front of the cave, and six skulls stuck in cave niches.
However, the above finding pales in comparison to the nearly intact cave bear found by reindeer hunters in 2020.
Hunters met the bear in the melted permafrost of the Siberian island of Bolshoy Lyakhovsky. Probably between 39,500 and 22,000 years ago, the frozen tundra kept it in very good condition, and even its internal organs were well preserved.
The bear is well preserved, with its nose, fur and teeth intact
So, what happened to these ice age cave bears? While their cousins walk the Earth today, burrowing bears slowly became extinct from about 24,000 years ago. Scientists note high incidence in cave bear fossils, which may be a contributing factor; Climate change could also lead to the extinction of ice age bears.
Monitor lizard: The largest lizard in the world
Today's Komodo dragons can weigh up to 150 pounds, but their ancestor, Megalania prisca (also known as Varanus priscus or giant monitor lizard), can weigh between 500 and 4,000 pounds. It is the largest known lizard on Earth.
Skeleton of a monitor lizard
Between 2 million and 40,000 years ago, these formidable creatures easily ruled what is now eastern Australia. They are up to 25 feet long and may feed on a wide variety of animals, including kangaroos, pygmy elephants, and turtles.
While they can use their size to subdue and kill prey, monitor lizards also use another tool: poisonous saliva. Scientists believe they use venom from jaw glands to kill prey.
British naturalist Richard Owen first described the monitor lizard in 1859. He named it the Giant Rover.
However, since Irving's discovery, scientists have found very few fossil remains of giant monitor lizards. This means that there is still a lot to learn about this prehistoric animal.
The skull of a monitor lizard
However, there are some theories about why monitor lizards went extinct. Although humans don't seem to hunt it directly, they do hunt their food. Thus, humans may have played an indirect role in its extinction.
Then again, just like giant sloths, some people believe that the great monitor lizard never went extinct at all. Rumor has it that the beast just sneaked into the Australian wilderness and has lived to this day.
Megalodon: A prehistoric animal with teeth as thick as a human wrist
The moniker of the megalodon is "Hellpig".
These beasts have teeth the size of human wrists, flesh-like bones on their faces, can fight with each other or other animals, and split hooves.
During the Eocene period, the hell pig spread rapidly from Mongolia to Europe and even to North America. Archaeologists have found fossils of megalodons in places like Nebraska, Wyoming and South Dakota.
However, Megalodon did not use its megalodon to hunt other prehistoric animals all day. Instead, it seems to use its huge jaw to dig for roots and chew plants.
That said, hellhogs are most likely omnivores. Even if they don't kill with their own hands, they may wait for other animals to kill them and then scare them away and eat their prey.
Hellhogs may scare most animals in their surroundings, even if they don't kill them directly to eat. The bite marks they leave behind have been found in many animals, including prehistoric rhinos.
As the climate changes, the forest beloved by the hell pigs turns into meadows. Being forced to travel long distances in search of food, it is likely to lose out to animals that move faster.
In addition, during the existence of megalodon, many new predators appeared on the horizon. They soon encountered fearsome enemies such as saber-toothed cats and bear dogs.
The last megalodons went extinct between 19 and 16 million years ago. Since then, these terrifying ancient animals have only existed in museums in the form of fossils – or perhaps in the form of hellish pigs, running through your nightmares.
Saber-toothed tiger: Sharp saber-toothed tiger
Perhaps the most famous prehistoric animal on this list is the saber-toothed tiger, or saber-toothed cat. Its striking canine teeth make it look particularly scary.
Saber-toothed tigers lived between 2.5 million and 11,700 years ago and inhabited forests in North and South America. Their size varies from species to species. Some can grow to about 150 pounds, some can grow to 200 pounds, and some can weigh about 500 pounds.
However, a recently discovered fossil of a saber-toothed tiger population suggests that the saber-toothed tiger may have been much larger. Depending on the size of its head, scientists believe it could grow up to 1,000 pounds.
Regardless of size, these big cats have one thing in common: canine teeth. These sharp fangs are located on one side of the chin and hang menacingly on either side of the cat's face. In order to stab its prey, the saber-toothed tiger's mouth must be open more than 90 degrees.
Surprisingly, big cats have fragile teeth. They sometimes lose their teeth in battle. Therefore, saber-toothed tigers often prey from trees. They jumped down from the branches and made a surprise attack, biting the unsuspecting animals below with their teeth.
Still, they are terrible killers. Saber-toothed tigers may prey on bison, sloths, mammoths, horses, pigs, and llamas. In other words, they kill everything they can.
Sometimes, the chase of prey is fatal to saber-toothed tigers. Thousands of saber-toothed cat bones were extracted from the La Brea tar pit in California.
The changing climate, and the consequent scarcity of prey, may have brought an end to these fearsome and majestic ancient animals.
Dire Wolf: A prehistoric animal depicted in Game of Thrones
In the TV series Game of Thrones, many characters have a fearsome wolf companion. These wolves tend to be large, fierce and loyal. Game of Thrones may have some imaginary elements, but dire wolves are truly ancient animals.
True dire wolves — known as Canis dirus, or "scary dogs" — existed in present-day North and South America about 125,000 to 10,000 years ago. Although similar to gray wolves, dire wolves are genetically different.
Dire wolves are slightly larger than gray wolves, have a red fur, weigh about 130 pounds, and are about 6 feet long. Just like the dire wolves in the novel, dire wolves have powerful jaws that help them kill.
Dire wolves chase all kinds of prey. They hunt horses, bison, and even young mammoths. By pounced on its prey and biting it with its jaw, dire wolves drag animals to the ground in order to kill them. As a result, their fossils are often found with neck injuries.
Sometimes, they actually compete with saber-toothed tigers for prey.
Great Ape: The largest great ape ever created
Maybe Bigfoot doesn't exist, but there were once equally massive beasts on Earth – prehistoric great apes that could compete with Bigfoot.
However, like Bigfoot, prehistoric great apes are elusive. Scientists have hardly found fossils of them, and most of the fossils they have are fragments of teeth and gorilla jaws. Even so, however, the researchers came to some startling conclusions.
They believe that the prehistoric great ape was about 10 feet tall and weighed nearly 600 pounds. Prehistoric great apes may be the ancestors of today's orangutans, which lived in Southeast Asia for about 6 to 9 million years before going extinct about 100,000 years ago.
Based on its teeth — nearly 2,000 large, canine and other teeth have been found — researchers suspect that the prehistoric great ape was vegetarian. These ancient animals probably ate plants, fruits, seeds, and maybe even bamboo.
Although scientists have found few fossils, they have found many ape jaws and teeth
However, the diet of the prehistoric great ape may have doomed it to extinction. While most prehistoric animals foraged in forests and grasslands at the time, apes stayed in the forests.
As the forest shrank, so did their food supply, and the great apes went extinct.
In fact, it was not until 1935 that modern humans felt the existence of prehistoric great apes: a German paleontologist named Gustav von Koenigswald stumbled upon the teeth of some apes in China. They are sold in the form of "dragon's teeth," suggesting to many scientists that humans once had a huge ancestor.
Long-haired rhinoceros: A furry prehistoric animal that roams Eurasia
Everyone has heard of mammoths. But what about the hairy rhinoceros?
In some ways, the woolly rhinoceros (Coelodonta antiquitatis) looked a lot like today's rhinos. Just like their contemporaries, they stand about 6 feet tall and weigh about 3 tons. They also have a set of two horns, a large anterior horn and a small one between the eyes.
But long-haired rhinos differ in several important ways. On the one hand, they have longer heads and bodies and shorter legs. Long-haired rhinos also have a large hump behind their shoulders, which may help support their horns. They have fur - and a lot.
Before it went extinct about 14,000 years ago, long-haired rhinos roamed around. Its fossils have been found in Spain, Siberia and Korea. As a result, woolly rhinos sometimes appear in ancient cave paintings – though not as frequently as woolly mammoths or bison.
Interaction between humans and woolly rhinos may be limited, although there is evidence that humans sometimes hunted the prehistoric beast. That said, scientists believe climate change is the main cause of the extinction of the woolly rhinoceros.
But if climate change thousands of years ago killed the woolly rhinoceros, climate change today could bring it back to life. Serbia's melting permafrost reveals many well-preserved ice age creatures, including the woolly rhinoceros, which reappeared in another form.
In 2020, locals in eastern Siberia stumbled upon the frozen body of a juvenile woolly rhinoceros in the melting ice. The frozen land preserved the intestines, fur, and even its horns of this ancient animal.