Image: Graeme Shannon

The hippopotamus, literally meaning “river horse,” is the second heaviest land mammal on earth, and the most dangerous mammal in Africa. They’re highly aggressive and unpredictable, so keep your distance.

Hippos are some of the most interesting (and strange) animals on the planet. Here are some facts that you probably don’t know about them:

They leave the water every night.

These colossal herbivores spend the majority of their time escaping the heat in the pools of sub-Saharan Africa. While they spend the majority of their time in the water (up to 16 hours every day!), hippos leave the pools at dusk and travel inland to graze on short grasses. Sometimes, they’ll travel up to 6 miles in search of food!

They can easily outrun humans.

Don’t think these tanks aren’t speedy on land; Despite their stocky shape and gigantic size, hippos can run up to 19 mph for short distances out of the water. The average human sprinting speed is only 15 mph.

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They make their own sunscreen.

While on land and exposed to the African sun, hippos have the ability to secrete a natural moisturizer and sunscreen. The liquid is a reddish color and has an oily texture, which people used to mistake for blood.

They can weigh up to 4 tons.

Hippos weigh roughly 100 pounds at birth and reach 5,000 to 8,000 pounds in adulthood.

Their closest living relatives live in the ocean.

Hippos may resemble pigs in appearance, but their closest living relatives are actually the cetaceans (whales, dolphins and porpoises). Notice how their nostrils have migrated to the surface to allow them to easily breathe while submerged? This is similar to the evolution of the blowhole in whales!

They eat more than 50lbs of food per day.

The hungry, hungry hippo is not just a saying — the average hippo eats about 80lbs of grass each night and will sometimes travel more than 5 miles per day in order to satisfy their appetites. Hippos will occasionally feed on fruit and even meat. 

Image: belgianchocolate, Flickr

They have similar gestation periods to humans.

Hippos carry their calves around for about eight months before giving birth, just one month short of a typical nine month human gestation period. And, like humans, hippos usually only carry one calf at a time. The big difference? Calves weigh between 50 and 100 pounds at birth!

They can stay underwater longer than the average human.

Whereas people can generally only hold their breath for a minute or two, hippos can stay underwater for up to five minutes. Even while they’re asleep in the water their bodies naturally float to the surface for a breath when needed and then return to their position at the bottom. How is this possible? Their nostrils are actually on top of their head.

They are incredible noisy.

Hippos are capable of wheezing, grumbling, snorting, and on occasion expelling sounds similar to roaring. Zookeepers are very cognizant of this fact and have measured their noise at above 110 decibels.

Image: William Warby, Flickr

They can go three weeks without food.

In rare circumstances when food is scarce, hippos are capable of storing enough plant matter in their stomachs that allows them to survive up to three weeks without food — although at the end of which they will be a very hungry, hungry hippo.

Their jaws can open 150 degrees.

In addition to their aggressive nature, hippos have extremely sharp incisors, massive tusks, and are capable of opening their jaws up to 150 degrees. Their teeth are even self-sharpening and rub against one another while they graze.

Watch as researchers go INSIDE the hippo: