A Thunder of Hippopotamuses

Their name is Greek for “River Horse,” and though they spend most of their time in the water, hippos cannot swim or float—they merely walk along the water’s bottom. Hippopotamuses must come up for air every five minutes, which they do even when they’re sleeping. They subsist on grass, and when basking on the shoreline they secrete an oily, red substance that acts as a skin moistener and sunblock. Hippopotamuses can live to be 40 years old and are considered one of the most dangerous animals in Africa. With speeds of up to 30 mph, they can easily outrun a human. Their closest relatives are whales and porpoises.