Horses are ungulates — mammals with hooves. They also have long tails, short hair, muscular torsos, long thick necks and elongated heads. Due to domestication, they are found all over the world.
Horses have lived on Earth for more than 50 million years, according the American Museum of Natural History. According to Scientific American, the first horses originated in North America and then spread to Asia and Europe. The horses left in North America became extinct about 10,000 years ago and were re-introduced by colonizing Europeans.
It is believed that horses were first domesticated in Asia between 3000 and 4000 B.C., according to Oklahoma State University. Back then, horses were used mostly for milk and meat. Eventually, horses joined oxen as a form of animal transportation.
There are more than 400 different breeds of horses. Horses can be as big as 69 inches (175 centimeters) from hoof to shoulder and weigh as much as 2,200 lbs. (998 kilograms). Tiny horses exist, too. The smallest breeds of horses can be as small as 30 inches (76 centimeters) from hoof to shoulder and weigh only 120 lbs. (54 kg), according to National Geographic.