Nothing had a smile like Smilodon.

This fearsome Ice Age cat, the size of a modern-day tiger, had a pair of fangs nearly 18 centimeters long.

And you know what?

Those giant teeth just might make a comeback.

As famous as Smilodon is, it was only the last and largest of the great sabertooths.

Ridiculously long canines had already been a trend for millions of years by the time Smilodon was prowling around, and scientists have only just begun to understand how sabertoothed carnivores used their dental weapons.

First things first, though - what does sabertooth actually mean?

Technically speaking, a sabertooth is simply any animal with extremely elongated canine teeth.

That's it!

And there have been all kinds of sabertoothed critters over the past quarter-billion years.

The very first one we know of is Tiarajudens, a goofy-looking protomammal from Brazil that dates back to the Permian Period, about 265 million years ago.

And over the eons, saberteeth have also shown up in herbivores like the strange, horned Uintatherium, primates like lemurs and baboons, and about 4 million years ago in the Pacific Northwest, there was even a species of sabertooth salmon.

But when we say "sabertooth", usually we're talking about the mammals who used their teeth not just to show off, but to slice and dice their prey.

And for that, we need to get acquainted with some rather pointy beasts.

Let's rewind back to the Eocene, about 45 million years ago.

Between then and now, there were basically three different kinds of terrifying, cat-like predators, each of which had evolved their own saberteeth.

The first were nimravids.

They looked a lot like cats, but they actually belonged on a totally different branch of the carnivore family tree.

And they were prickly customers.

Fossils show that these carnivores fought a lot, often biting each other on the face and around the eyes.

Now, fast forward to the Miocene Epoch, about 20 million years ago and you'll find barbourofelids another group of not-quite-cats Many of them, like Barbourofelis in North America, had long pockets in their jaws that their teeth could slot into when they closed their mouths.

Then came the true sabercats.

In the Pliocene Epoch there was the leggy, sprinting Homotherium, and more recently, in the Pleistocene, we find the famous Smilodon.

So from their own, separate starting points, the nimravids, the barbourofelids, and the true cats each wound up with its own type of sabertooth species.

This is a great example of convergent evolution, when different organisms develop the same trait independently of each other, because that's just what works The marine reptiles known as ichthyosaurs, for example, look a lot like sharks because that streamlined shape is just great for slicing through water.

And the same goes for flight -- both bats and pterosaurs developed wings made of leathery skin stretched out on long fingers.

But when it comes to saberteeth, the question is... why?

What made these teeth so ... cutting edge?

Well, there's been no shortage of theories about how sabertooths used their fangs.

One of the earliest ideas was that cats used them to penetrate the armor of Ice Age animals like giant armadillos and ground sloths.

It's like they were cats who were also their own can openers!

Other experts thought they used their fangs to stab, jumping on the back of a mammoth, say, and slamming their teeth into their prey.

There was even a suggestion that these cats were bloodsuckers!

One expert looked at the palate of Smilodon and thought its mouth may have been suited for drinking blood.

None of these ideas held up, though -- mostly because saber-shaped teeth were, in fact, incredibly fragile.

They were long, flat, and not very good at twisting or bending, as you can see in the many painful-looking broken sabers that have been found in the fossil record.

So the latest thinking is that, because their teeth were so fragile, sabercats were probably very picky eaters, and they had to time their bites very carefully.

This means that they didn't hunt like the cats we know today.

Lions and tigers don't slash or rip at their prey.

Instead they rely on what's called a throttling bite, which keeps the victim's mouth or windpipe closed until it suffocates.

Sabercats couldn't use a throttling bite.

So, paleontologists think these cats used their powerful arms to grapple their prey to the ground, and then unleashed a devastating shear bite to cut through the windpipe and blood vessels of the neck, or maybe open the belly of their prey.

If the initial bite didn't kill it, the prey would soon die of blood loss.

So, Smilodon probably hunted less like your house cat, and more like a great white shark, ambushing its prey in a powerful strike to cause massive damage.

Now, this might seem like a high-risk way to hunt, but it obviously worked!

Because, like we've already seen, saberteeth are one of evolution's greatest hits.

But if they're so great, what happened to them?

Well, paleontologists think that hunting in such a specialized way required large prey, like the camels and horses that used to be common in North America.

And when many of the megafauna died off at the end of the last Ice Age, the sabercats might have run out of food to eat.

But no one really knows.

The fact remains, by the time the last of the sabercats disappeared -- only about 8,000 years ago -- there had been some kind of sabertoothed predator on the planet somewhere for 40 million years!

So it only makes sense to consider the possibility that evolution will converge yet again on this winning design.

After all, if natural history has shown us anything it's that good body plans tend to show up over and over.

Today, there are over 40 species of cat, large and small, on the planet.

So, given a few million years and the right evolutionary nudge, we might still see a smile like Smilodon's again.