Beavers once lived all over Europe and North America.
But because they have beautiful fur, people hunted them to make warm coats.
As beavers started to disappear, scientists became worried and decided to learn more about them.
The first thing scientists studied was a beaver's body.
Beavers are part of the rodent family, which means squirrels and rats are their cousins.
Their front teeth are very long, and beavers use them to cut wood and pull off bark.
Like a hamster or rat, a beaver's teeth grow and grow and grow for its whole life!
However, beavers are bigger than all of their cousins.
Most beavers weigh fifteen to thirty-one kilograms, and are almost 117 centimeters long!
Even though beavers have fur, they like to be in water instead of on land.
Beavers are very beautiful swimmers, but they look silly when they try to walk.
Their heavy tails make walking very difficult.
A beaver tail is the size of a computer keyboard, and it helps a beaver stand, balance heavy logs, and steer in the water.
And, if an enemy comes too close, one beaver will warn other beavers by slapping its tail on the water.
When a beaver dives into the water, two important changes happen.
First, it closes its eyes, nose, and mouth.
Beavers have two kinds of eyelids:
the inside one is clear—like goggles—and the outside one is black.
When a beaver is underwater, it protects its eyes by using the goggle-like eyelids to see where it's swimming.
The beaver's nose also has special skin inside which closes to keep out water.
However, its mouth is even more amazing.
A beaver needs its front teeth to grab logs underwater, but it doesn't want a mouthful of water and logs.
Amazingly, its lips are behind its front teeth so that it can keep water out and still grab whatever it needs.
The second underwater change is when the beaver goes from a walker to a swimmer.
On land, a beaver's back feet look like its cousin's.
But when it dives into water, the toes pull apart to show a web in between.
This webbing helps it swim through water quickly.
Most beavers stay underwater for three to five minutes.
But some can stay down for as long as fifteen minutes.
That's a long time for only one breath—especially since most humans stay underwater for less than sixty seconds.
Scientists were very impressed with the beaver's body.
Few animals can live in water and on land as well as the beaver.
But scientists are still worried.
The more that people wear fur coats, the fewer beavers there are in the wild.
And the fewer beavers there are in the wild, the more problems scientists see in nature.
Now that scientists have learned about a beaver's body, they know more about how a beaver lives.
But scientists are still looking for ways to help beavers and humans live together.