You might dread going to the dentist, but at least human teeth are fairly straightforward.
They line up in rows, stay inside your mouth, and have standard toothy shapes.
We have these all-purpose teeth because we have a pretty all-purpose diet.
Humans can survive on a wide range of foods,
so we don't have to have any super-specialized teeth.
That's not the case for a lot of other animals, though.
If an animal has a set of teeth that seems really weird to us,
there's generally a reason.
Those teeth must help it survive in some way.
But for these seven animals, that doesn't really make their teeth less unsettling.
The most abundant species of seal in the world, the crabeater seal,
lives on the Antarctic ice shelf.
From the outside these guys just look like another cute seal,
but if you peek in one's mouth, you'll get a different perspective.
Crabeater seals have bizarre-looking, serrated teeth
that kind of look like they're full of little hooks.
That's because about 90% of a crabeater seal's diet
is made up of tiny shrimp-like crustaceans called krill.
The most famous krill-eaters are whales, which have baleen instead of teeth
to strain these itty bitty animals out of the seawater.
In the case of crabeater seals, though, evolution arrived
at a different solution to the same problem: their teeth have interlocking lobes
that act as sieves to filter krill out of mouthfuls of seawater.
They even have a ridge of bone that fills the gap between the last teeth
and the back of their jaw, keeping the krill from escaping their fate.
Naked mole rats would be weird even if it weren't for their teeth.
They're mostly hairless, live in underground colonies with the same social structure as beehives,
and are apparently immune to cancer.
But their teeth are pretty weird, too.
They have two pairs of huge, protruding incisors, one on the top and one on the bottom.
They need them to dig their burrows and to gnaw tough roots, and their lips actually
close behind these teeth to keep dirt from getting into their mouths as they tunnel.
They'll also use their teeth to move their babies around and to carry food.
But what makes these teeth especially strange is that the naked mole rats
can move each bottom tooth independently, like a tiny pair of chopsticks,
because their lower jaws are flexible.
Their teeth are so important that a naked mole rat
devotes a lot of its body's resources to them.
About a quarter of each rat's musculature is devoted to their jaws,
and in their brains, things get even more extreme.
The part of the brain that's responsible for receiving sensory input from the body
is called the primary somatosensory cortex.
Every spot on the surface of your body maps
to a specific spot on the primary somatosensory cortex.
But it isn't necessarily proportional.
For example, in humans, a lot of real estate in the cortex is devoted to our hands, because
they're such a big part of how we interact with the world through touch.
Naked mole rats don't have hands, but they do have weird giant incisors that they use
to carry stuff around, and it turns out that one third of a naked mole rat's primary
somatosensory cortex is dedicated to its enormous teeth.
Since naked mole rats are almost blind, their big teeth are the main thing they use to interact
with the world, and it shows in the way their brains are organized.
The cookiecutter shark is a small, cigar-shaped shark, about a half a meter long,
that lives in deep water.
But unlike other sharks, this one's not a deadly predator,
it's a parasite, because it leaves the animal it feeds on alive.
Tiny light-producing organs on the shark's pale underside glow to attract prey.
When a potential victim swims within range, the cookiecutter shark attaches itself to
it with its sucking lips and pointy upper teeth.
Then it spins to remove a plug of flesh with its larger, serrated bottom teeth, leaving
a characteristic cookie-sized wound, hence the name.
The shark's teeth are interconnected at the base, which allows the whole row to operate
as a unit when it's slicing out a disk of muscle.
Eventually, the whole row of teeth is replaced at once as a single unit, and the shark actually
swallows the old, discarded teeth to reabsorb their calcium.
Cookiecutter sharks usually go after marine mammals and large fish, but the telltale scars
have also been found on giant squid, and they've been known to try attacking
the sonar domes on nuclear submarines.
Marine biologists didn't actually figure out the cause of the weird scars until the
1960s, when they started to connect them with cookiecutter sharks' unique teeth and find
small plugs of flesh in the sharks' stomachs.
Thanks to their small size and preference for deep water,
cookiecutter sharks are generally harmless to humans.
But there have been a few reports of shipwreck survivors and long-distance swimmers being
attacked in the open ocean by what were probably cookiecutter sharks.
The moray eel is a finless fish that grows to be over three meters long.
It's a predator that eats other fish whole,
lying in wait in coral crevices to strike at passing prey.
Until recently, though, we didn't actually know very much
about moray eels' feeding behavior.
Scientists knew they were part of a group of fish that feed using structures
called pharyngeal jaws and teeth.
These fish expand their mouth cavity suddenly to suck in prey, and then use this secondary
set of jaws, complete with its own teeth, to get the food down their throat.
But moray eels don't use suction like their relatives do, and in 2007, researchers figured
out why: the eels don't have the muscles and skull bones they'd need to to create
powerful suction, so they have to rely on their bite to catch their prey.
But they have a secret weapon.
Their pharyngeal jaws and teeth are much more complex and vicious than the simple blocky
version that other related fishes have, so those secondary jaws
can deliver a powerful bite of their own.
When moray eels lunge at their prey, they first grab it with their front set of jaws.
Then, muscles contract to launch their pharyngeal jaws forward into their mouth, where the second
set of teeth clamps down on the prey and drags it to its doom.
This actually lets them catch bigger prey that the suction method wouldn't work on.
If this sounds familiar, that might be because
it's basically the anatomy of the monster from Alien.
But the moray eel's ability to fire an extra set of jaws and teeth out of its throat wasn't
discovered until well after the movie came out.
The writers might have thought they were coming up with something too extreme to be real,
but it turns out that nature is just as horrifying all on its own.
There's a wild pig that's native to Indonesia,
where it lives along rivers in thick jungle habitat.
Its name, "babirusa," is Malay for "pig-deer", probably because these pigs have some really
intense tusks that could almost be mistaken for antlers.
If the male pigs' extremely long, curving tusks aren't broken off or worn down, say,
during a fight, they can eventually grow long enough to pierce the babirusa's skull.
That wouldn't be great news for the babirusa, but it doesn't actually happen too often.
The only known skull with ingrown tusks is in a natural history museum in Sweden.
The giant tusks aren't used for foraging, since they eat mostly fruit, leaves, and berries.
And they aren't weapons, either.
Instead, they act as shields, protecting the pig's eyes during fights
while they use their shorter, sharp lower tusks to attack.
These ridiculously long tusks probably developed when the babirusa's ancestors arrived on
the Indonesian archipelago and found themselves
in a predator-free environment for the first time.
Suddenly, they didn't need their tusks to defend themselves from being eaten -- instead,
the greatest threat males faced was competition from other males for resources and females.
So scientists think that over time, evolution co-opted their tusks
into the outlandish facial armor we see today.
In 1899, a Russian geologist discovered a bizarre, buzzsaw-shaped spiral whorl
of fossilized teeth from a fish.
He named the mysterious animal the "helicoprion," which means "spiral saw."
For a long time, no one knew exactly how and where the weird structure would have fit into
the fish's mouth when it was alive, though there were lots of guesses.
Some even suggested it protruded along the fish's back
or from its tail as a defensive display.
Over time, a few better, though still partial and crushed, skulls turned up.
And by the 1950s, paleontologists were at least sure that the weird structure had been
a part of the fish's jaw, though that still left a lot of possibilities.
Finally, in 2013, researchers used a high-resolution CT scanner on a fossil found in the 1950s
to create a new 3-D model of the fish's skull.
They were able to confirm that the structure grew inside the fish's lower jaw
rather than extending out from it.
Basically, where your tongue sits in your mouth, picture a spiral of teeth protruding
from the floor of your mouth instead.
Scientists think that even though the spiral of teeth is kinda scary-looking, the helicoprion
ate soft-bodied prey like octopuses, which it broke down by slicing them over and over
again with its single row of teeth.
When it closed its mouth, the spiral of teeth was pushed backwards, producing an efficient
slicing motion and forcing the food back toward the throat.
Okay, this one isn't technically about teeth, they're really cartilage.
But they act like teeth, and they're so weird that we just have to share.
Leatherback sea turtles are the largest of all living turtles,
named for their rubbery shells.
And if you ever happen to see a leatherback sea turtle yawn,
be sure to take a peek down its throat, if you dare.
Their throats are lined with prongs of cartilage called esophageal papillae.
They grip onto whatever the turtle is eating, usually jellyfish, to make sure it doesn't
slip back out as the turtle expels seawater from its mouth.
They also help protect the turtle's throat from jellyfish stingers.
And they're just super creepy.
It's like the Sarlacc pit from The Return of the Jedi.
Of course, what seems weird and creepy to us probably just seems totally ordinary to
these animals, since we're biased towards thinking that "normal" means "human."
It's pretty hard to picture what it would be like to use your front teeth like chopsticks,
or have a buzzsaw spiral of teeth where your tongue should be.
But then again, you probably don't need to dig tunnels with no hands
or efficiently slice up octopuses.
To keep up with all the different ways animals find food, reproduce, and survive,
nature includes an amazing array of diversity for pretty much every body part,
and the pearly whites are clearly no exception.
Thanks for watching this episode of SciShow!
If you want to learn more about super strange adaptations,
check out this video about animals that live in only one place.
If you want to help us keep making videos like this, go to patreon.com/scishow,
and don't forget to go to youtube.com/scishow and subscribe!
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