Humans typically have two sets of teeth. The first set of smaller teeth often referred to as baby teeth, usually start falling out at or around age 6. As these teeth fall out, they are replaced with permanent teeth that we keep through adulthood.
When it comes to the animal kingdom, though, not every species’ teeth are the same. Some animals have no teeth at all, while others have teeth that just keep growing.
So, what are some animals with teeth that don’t stop growing?
Animals with teeth that never stop growing include tusked mammals like elephants, wild boars, and walruses. Toothed fish and reptiles also are constantly losing and replacing teeth. Other animals with constantly-growing teeth include manatees, kangaroos, rabbits, and rodents like squirrels and mice. These animals’ teeth keep growing because their diet wears them down.
Below, we’ll take a closer look at all these animals, their diets, and why they have teeth that don’t stop growing, as well as animals with fast-growing teeth.
Elephants
Did you know that an elephant’s tusks protrude from its mouth because they are actually teeth? Tusks are known for being made of ivory, but what they actually are is hard, bony tissue called dentine that’s covered in enamel, a substance you’re probably familiar with being on your own teeth.
While tusks are deeply rooted in the mouth and considered teeth, they don’t serve the same purpose of grinding food as the other teeth in an elephant’s mouth. Instead, tusks are often used for foraging, stripping bark from trees, lifting, and digging.
Tusks are also important for defense and protecting an elephant’s trunk, which is essential for functions like eating and breathing. Unfortunately, elephants are often poached because of the ivory in their tusks, which has contributed to all four types of elephant being on the endangered species list.
In addition to an elephant’s tusks constantly growing, their molars grow, too. Teeth are pushed toward the front of an elephant’s mouth and fall out, while new teeth come in toward the back.
Manatees
The manatee is distantly related to the elephant, so it’s no surprise that it shares a few characteristics with elephants as well. One similarity is their teeth, which move forward in their mouths to fall out while new teeth grow in the back. It’s estimated these teeth move forward at a rate of 1 cm per month.
Manatees also have a prehensile upper lip that lets them grab onto vegetation the same way that an elephant does. These hungry animals can eat anywhere from 4-9% of their body weight each day and spend about 8 hours per day eating.
Kangaroos
Like elephants and manatees, kangaroos have teeth that are constantly refreshing themselves. They grow new teeth in the back of their mouths and the older teeth are pushed forward, where they will eventually fall out.
Kangaroos are herbivores and their diet consists of rough shrubs and grass that need to be chewed a lot before being swallowed. Otherwise, kangaroos wouldn’t get as much nutritional value from their food, which is a common problem in herbivores that don’t have complex digestive tracts.
In fact, kangaroos are known to chew their food twice. They’ll chew it, spit it back out, and then chew it a second time. All this chewing wears down their teeth, which is the reason they need to be replaced over time.
Walruses
Walruses rely on their tusks for a lot, including breaking holes in the ice and giving them leverage to help them pull their bodies out of the water.
They may also use their tusks for defense, social behaviors, and even fighting with other walruses during breeding season.
Like other animals that use their tusks a lot, these tusks are constantly growing. However, researchers believe that only male walruses have tusks that grow throughout their whole lives, most walruses’ tusks stop growing after 15 years.
Wild Boars and Pigs
Tusked mammals like wild boars and even domesticated pigs (who often have their tusks removed so they don’t hurt other farm animals) have teeth as an extension of their incisors. These tusks serve a lot of different purposes.
In wild boars, their tusks are constantly growing because they use them to dig and root for food, which wears them down. They may also use them for defense.
Often, the upper teeth are referred to as “whetters” and the lower ones as “cutters”. The lower teeth protrude in a way that they rub against the upper teeth and are sharpened, like a whetstone.
Another example of this is the babirusa. These tusked hogs are known for their dental problems, as their tusks grow so far upward and back that sometimes they are known to grow into the animal’s face. It’s so common that they are often called the “wild pig with a dental problem“.
Rats and Mice
Mice and rats are some of the most well-known chewers in the animal kingdom. They are known to chew through wood, drywall, bricks, concrete, and even metal pipes.
Rats and mice have two incisors on the top of their mouths and two incisors on the bottom. Unlike teeth in humans, rodent teeth don’t have roots. This lets them keep growing and growing through the rodent’s entire life.
This is pretty important because while their teeth are strong, they still get worn down from chewing through all those hard surfaces. If mice and rats didn’t have teeth that were continuously growing, their teeth would eventually be so dull they’d be useless.
Squirrels, Groundhogs, and Beavers
Squirrels are born with milk teeth that likely help them with feeding from their mothers after being born. After about four to five months, however, squirrels lose these milk teeth and get two permanent incisors on the top and bottom of their jaws.
While squirrels also have molars in the back of their mouths to aid in chewing, their molars don’t grow. Squirrel incisors, on the other hand, grow at a rate of about six inches per year. That’s pretty incredible- almost as incredible as the fact that squirrels can fall from almost any height without dying.
Groundhogs (also called woodchucks) and beavers are closely related to squirrels and are part of the rodent family. Like other rodents, they have two incisors on the top and two incisors on the bottom without roots so they never stop growing.
Woodchucks and beavers also both have 16 flatter teeth in the back of their mouths for chewing. Groundhog teeth grow very quickly, as much as 1/16th of an inch every week. This means that they need to constantly gnaw on things to stop their teeth from getting too long.
Gerbils, Hamsters, and Other Rodents
Like all the other rodents on this list, gerbils and hamsters share those same incisors that just grow and grow. In people who keep these animals as pets, it’s important that they have toys and things they can gnaw on to prevent overgrowth.
For a rodent, tooth overgrowth makes it harder to eat, chew, and swallow. When it’s left untreated, teeth that are too long cause an animal to have nutritional deficiencies from their difficulty eating.
Not being able to eat may lead to eventual starvation and death, which is one of the reasons that rodents are known chewers. While they don’t all chew through pipes and the walls of your home, rodents in the wild often use their teeth to strip bark and bite through nuts and other hard things.
Having teeth that never stop growing is important for rodents that spend their lives gnawing. Otherwise, their teeth would end up dull and ineffective after a lifetime of chewing through things like nuts and tree bark.
Rabbits
Rabbits were once classified as rodents, though they now belong to the family Lagomorpha. One of the biggest differences between rodents and rabbits is that rabbits have an additional pair of incisors behind their first set on the roof of their mouth, so they have six incisors total.
Additionally, rabbits are herbivores that eat plants like hay, grass, and even lettuce, whereas other rodents are omnivores. With the exception of rats, which will eat meat whenever the opportunity presents itself, most prefer vegetation but will eat meat foods if necessary.
Something else that sets rodent teeth apart from rabbit teeth is that all of a rabbit’s teeth are constantly growing, even their molars. Rabbit teeth keep growing because they lack enamel that makes them strong, so their fibrous diet wears down their teeth.
Alligators, Crocodiles, and Other Toothed Reptiles
Instead of having open roots like animals that have tusks or rodents so teeth constantly grow, the teeth of alligators, crocodiles, and other toothed reptiles are regularly being replaced.
Even ancestors of the crocodile (which actually ate plants) are thought to have teeth that are constantly being replaced. One hypothesis scientists have on why the teeth of animals like this grow back is because of the strength of their bite. This hypothesis could also apply to the mighty T-rex, which also had teeth that were regularly replaced.
Other toothed reptiles also grow replacement teeth when their teeth are damaged or lost. This includes critters like bearded dragons, chameleons, and iguanas.
Pacific Lingcod, Piranha, and Other Toothed Fish
Toothed fish rely on their teeth for eating in more ways than one. Unlike humans that have taste buds all over their tongues, toothed fish have taste buds on their teeth. This gives them a “taste” for certain foods in the water.
Pacific Lingcod is one of the fish most well-known for its teeth. Not only does it have a lot of teeth (more than 500 teeth, most of them arranged in a haphazard pattern in its mouth), but it’s constantly replacing them. Scientists estimate that the Pacific Lingcod may lose and replace as many as 20 teeth every single day.
The piranha is another good example of a fish that is constantly losing its teeth, likely from its powerful bite and the way that it tears into its prey. They also frequently scrape plants from rocks to supplement their diet, leaving their teeth dull. Without being able to replace its teeth, the piranha would likely lose its ability to eat.
Researchers aren’t sure why fish regrow teeth, but they believe their bodies may send out some type of signal that triggers regrowth after a tooth is lost. This is something that’s being studied closely, as scientists are trying to learn if tooth regrowth is possible in humans as well.
What Are Polyphyodonts?
When it comes to teeth, animals are classified as polyphyodonts or diphyodonts. A polyphyodont is an animal like those on the list whose teeth are continually replaced over the course of their lives.
By contrast, diphyodonts are animals that have two successive sets of teeth in their lives. Animals that are polyphyodonts include most vertebrates that are not mammals, including reptiles like geckos and crocodiles and most toothed fishes.
There are also a handful of mammals that are polyphyodonts, including tusked animals like elephants, walruses, wild boars, and members of the rodent family.
What Animals Have Fast-Growing Teeth?
Some animals with fast-growing teeth include rodents like mice, rats, squirrels, beavers, and groundhogs. Rabbits also have teeth that grow quickly, as do tusked mammals like elephants, wild boars, and walruses.
Other animals’ teeth don’t grow long, but they are constantly being replaced. This includes toothed reptiles and fish, as well as elephants, manatees, and kangaroos. These animals are known as polyphyodonts.
Why Do Some Animals Have Teeth That Never Stop Growing?
In most cases, the reason that animals have teeth that are constantly growing or being replaced is that they get worn with time. Unlike humans, animals that lose their teeth don’t have the means to go to the dentist for a replacement or change the way that they eat.
Some animals just have weaker teeth because they lack enamel, like rabbits. Even though rabbits are herbivores, chewing on fibrous foods wears down their teeth. In other cases, like with the crocodile, the strength of the animal’s bite damages the teeth over time.
The good news is that scientists believe by studying these animals, they may eventually be able to isolate a gene that allows these animals to replace their teeth. This is exciting for the field of dentistry because eventually, it might lead to a way to regenerate teeth in people who have lost them.
Final Word
In the animal world, there are all types of teeth. Animals with teeth that don’t stop growing or being replaced are known as polyphyodonts.
This includes rodents like rats, mice, hamsters, gerbils, squirrels, beavers, and woodchucks. It also includes toothed reptiles and fish, rabbits, and tusked mammals like elephants, walruses, and wild boars. Kangaroos and manatees have teeth that are constantly being replaced, too!
By learning about these animals, scientists may learn more about replacing teeth in humans (with something other than dentures!).
Hopefully, you’ve enjoyed reading about all these critters! Let me know if you think there’s any I’ve missed!
