Unicorns are among the most enduring and beloved of mythical beasts. However, now the real creature behind the myth may have been found – and it’s probably not what you would expect.

Millions of children all over the world have grown up with tales of unicorns, their young imaginations fed by the depictions of pretty creatures in movies like Legend and the Harry Potter series – not to mention the My Little Pony franchise. However, the real animals behind the unicorn myths are more likely to give kids nightmares than sweet dreams.

Stories about unicorns were around a long time before Hasbro churned out its first rainbow-colored plastic toy, of course. The fantastical creatures are actually associated with Greek myths; and yet to the ancient Greeks, they were not considered mythical, at all, but rather real live animals from India.

These early unicorns were not the graceful creatures we think of today, either. Greek historian Ctesias in fact gave us the first account in the 5th century B.C., portraying them as wild asses with long horns. We then hear of them from Pliny the Elder, who was writing in the 1st century A.D.; Pliny describes them as having “the head of the stag, the feet of the elephant and the tail of the boar, while the rest of the body is like that of the horse.”

The single horned magical beast is not only a European myth, mind you; China and Japan both have their own versions of unicorns, the qilin and kirin respectively. The qilin was said to appear before the birth or death of someone important. It wasn’t particularly horse-like, though, what with a curled horn, a scaly-green deer’s body and a lion’s head.

Some people believe the Bible contains references to unicorns, too. However, most scholars say this is actually a mistranslation of the Hebrew word re’em. These creatures are actually mentioned nine times in the sacred text, where they are symbols of strength – but the word most likely refers to an ancient variety of ox.

Strength furthermore continued to be one of the attributes assigned to unicorns into the Middle Ages. For instance, an Alexandrian merchant and traveler from the 6th century named Cosmas Indicopleustes passed on Ethiopian accounts of the unicorn as being a “ferocious beast,” with its power originating in its horn.

Saint Isidore of Seville, who lived in the 7th century, also described the unicorn as a strong animal. Indeed, according to that scholar, the creature was able to kill elephants by stabbing them in the stomach. During this time, unicorns weren’t yet all mystical horses, though; instead, they were sometimes still defined as more like wild asses or goats.

In medieval times, many also thought that unicorn horns were composed of a substance called “alicorn.” The growths were believed to have magical properties, too, capable of neutralizing poison and curing mental and physical diseases. And one group to profit especially from this belief were the Vikings, who ran a thriving trade in narwhal horns from the Arctic Ocean. Yes, the seafarers sold the whales’ tusks as unicorn horns.

Other real animals that may have inspired the unicorn myth are the oryx, eland and auroch; and two-horned animals that lost one horn through mutation or fighting perhaps did the same. Another possibility is the Indian rhinoceros – and as we shall see, something like a rhinoceros might actually be the origin of the unicorn myth.

In 1808 a newly discovered genus called the Elasmotherium was named by Gotthelf Fischer von Waldheim, director of the Natural History Museum at Moscow State University. Previously, the Elasmotherium had only been identified by fossils and was believed to have been extinct for 350,000 years.

Nineteenth-century scientists speculated that the Elasmotherium must have had a single horn. “The whole analogy with the rhinoceros points with the greatest certainty to the previous existence of a horn,” wrote Russian zoologist Alexander Brandt. “Which, to judge from the size of the blood vessels once encircling the base, must have possessed enormous dimensions.”

Brandt suspected the Siberian Elasmotherium (Elasmotherium sibiricum) of being the basis of a Tatar myth about a unicorn with a gigantic horn. However, since the Elasmotherium was thought to have disappeared about 350,000 years ago, no humans would have been around to see them back then.

Then, in March 2016, the skull of an Elasmotherium was unearthed in Kazakhstan. Moreover, this put the date of extinction much later – at only 29,000 years ago – and that changed things. Now there was at least a chance that the Elasmotherium would have been around long enough to be seen by humans – and inspire the unicorn legend.

Unfortunately for those who like to think of unicorns as the graceful white-haired horses that feature on posters – often with a rainbow in the background – the Elasmotherium was not quite so dainty. Rather than being an ethereal pony, it was closer in form to a terrifying monster rhinoceros.

Yes, Elasmotherium sibiricum would have been an intimidating sight. Standing around six or seven feet tall, measuring 15 feet long and most likely covered in fur like a mammoth, each of these mighty animals weighed four and a half tons. And while no definite size has yet been given for the horn, it may have been up to six feet long.

As its name partially suggests, Elasmotherium sibiricum roamed what is now Western Siberia. They were also to be found in modern-day southwestern Russia and further south in today’s Eastern Europe. Despite the creature’s fearsome appearance, though, it was a herbivore, like the contemporary rhinoceros, grazing over large areas.

“Most likely, the south of Western Siberia was a refugium, where this rhino persevered the longest in comparison with the rest of its range,” paleontologist Andrey Shpanski told Phys.org. “There is another possibility that it could migrate and dwell for a while in the more southern areas.”

Yet although it’s possible that humans encountered the Elasmotherium, it’s not entirely certain that they did. Some, like cryptologist Willy Ley, suspect that stories about the species have survived from the prehistoric era. However, certain accounts, like that of 10th-century traveler Ibn Fadlan, seem to describe the giant rhinoceros too accurately to be merely retelling a myth.

Meanwhile, depictions of unicorns that appear somewhat more like Elasmotherium than the Western version does are found in stories from those regions where the animal once lived. For example, an Old Turkic book contains a description of the Chinese qilin as a “quadruped with the body of a deer, the tail of a cow, the head of a sheep, the limbs of a horse, the hooves of a cow and a big horn.”

So when did unicorns really die out? Well, nobody knows yet, as new evidence is still being discovered. However, one theory, based on a fossilized Siberian Elasmotherium skull, is that they died off because of a meteoroid impact. Alternatively, they may have been victims of environmental change. Researchers are still working on an answer.