Can you believe that an animal that looked like this actually existed?

Wellll, it didn't.

But for a while, experts thought that, hundreds of millions of years ago, fish that looked like this once swam the seas around the supercontinent of Pangea.

It turns out that paleontology is just ... tricky sometimes.

Some fossils are easy to identify right from the start.

Everyone knows what a trilobite looks like, or a theropod track.

But, just like our old friend the Tully Monster, there are many fossils that challenge our ability to form even the most basic idea of how a living thing looked, or lived, or functioned.

And one of the longest-running of these mysteries involved a 270-million-year-old sea creature called Helicoprion.

It all started with a swirl.

Back in 1899, Russian geologist Alexander Karpinsky was studying a strange, circular fossil found in the Ural Mountains that dated back to the Permian Period.

At first, he thought it was an ammonite -- one of the ancient relatives of today's nautilus.

But it turned out the spiral was actually made of ... teeth.

Shark-like teeth.

So Karpinsky determined that the fossil belonged to an extinct shark, and named it Helicoprion, or "spiral saw" -- because, let's face it, looks like you could cut lumber with this thing.

But where did this weird feature -- known as a tooth-whorl -- actually go?

It was hard to tell, because at the time, no other known sharks had teeth like this.

So, one of the main challenges posed by Helicoprion was its life reconstruction -- that is, what it looked like when alive, based on its fossil.

The result of a life reconstruction is usually a drawing or a model.

But it's more than paleo-art.

It requires a lot of study -- of the specimen itself, but also of other fossils from its environment, and even the anatomy of related animals.

Together, all this information can be used to "re-build" an extinct creature.

To reconstruct Helicoprion, step one was figuring out where this tooth whorl belonged.

And that was a lot harder than it sounds!

Some experts thought the wheel of teeth was in the upper jaw.

Others put it under the lower jaw.

Karpinsky's best guess?

The snout.

He originally imagined that it had a swirl of teeth that curled up over its nose, like something out of a Dr. Seuss nightmare.

But then he changed his mind.

Because some extinct sharks were known to have spines and other tooth-like features on their fins, so he thought the blade of teeth might have belonged on its back!

The true picture of Helicoprion only started to come into focus when more fossils were discovered.

Specimens found in Nevada and China, and fossils of related species, like Ornithoprion, began to bolster the idea that the tooth whorl was part of the lower jaw.

But still, there was no way to show exactly where it fit, or if there were upper teeth to match, or what was going on with this thing.

Part of the problem was that sharks' skeletons are made of cartilage, not bone.

So, by and large, the only parts of these creatures that fossilize are its teeth.

The fossil record left paleontologists without much to work with -- until they used new technology to look at a long-forgotten fossil.

One of the best places in the world to find Helicoprion fossils is Idaho.

And there, in 1950, workers at a phosphate mine cracked open a concretion of rock and found a perfectly-preserved Helicoprion whorl.

And as a bonus, there even seemed to be some fossilized tissue around it, possibly part of the jaw and the cranium.

It was the most complete fossil of its kind, and it was beautiful.

A paper was written about it, and then the specimen was kept for 50 years in the Idaho Museum of Natural History Until, researchers decided to take it out again, and give it another, closer look, using new technology.

In 2013, museum researchers conducted a CT scan of the specimen -- basically a really high-resolution x-ray.

And this allowed them to finally reconstruct this strange fish.

The scan revealed impressions of cartilage that formed both the upper and lower jaw.

And it turned out the lower jaw consisted of that saw-blade of teeth.

The whorl stood vertically in the mouth like where your tongue is, supported on both sides by cartilage.

And there were no upper teeth at all, or any other equipment to chew with.

Sooo how did Helicoprion eat?

Well, I could tell you, but I'd need a time machine and some scuba gear.

In other words, no one knows for sure.

But some experts think it used its wheel of teeth to slice through its prey.

Or it could have used them to grip hard-bodied creatures like ammonites and basically shuck them out of their shells.

Oh, and one more thing: Based on the structure of the upper jaw, the researchers found out that Helicoprion wasn't a shark at all - it was a ratfish!

These are distant, cartilaginous cousins of sharks that live in the deep sea today.

None of them have crazy saw-blades in their mouths, but they're the closest living relatives of this ancient predator.

So, it took more than a century, and specimens from three continents, to finally piece together the fossil puzzle that is Helicoprion.

Like I said, paleontology can be tricky But to know that a creature like this actually existed?

Totally worth it.