Although the words are sometimes used interchangeably, the mammoth and the mastodon were two different species. The mastodon seems to have appeared first, and a side branch may have led to the mammoth. The mastodon lived in Africa, Europe, Asia, and North and South America, appearing in the Oligocene era (38 to 25 million years ago) and surviving until less than one million years ago. It stood a maximum of 10 feet (3 meters) tall and was covered with dense, woolly hair; its tusks were straight forward and nearly parallel to each other. The mammoth evolved less than two million years ago and died out about 10,000 years ago; they lived in the cooler regions of North America, Europe, and Asia. Like the mastodon, the mammoth was covered with a long, coarse layer of outer hair to protect it from the cold. It was somewhat larger than the mastodon, standing 9 to 15 feet (2.7–4.5 meters); the mammoth’s tusks tended to spiral outward, then up.

The reasons for both creatures’ demise are still a matter of speculation. When it comes to the mammoths, the evidence is more “recent”: After finding several mammoths frozen in such places as Siberia, scientists believe that the gradual warming of the Earth’s climate—and thus a change in the animals’ environments—was the primary factor in the mammoth’s extinction. But they suggest that early humans may have killed many mammoths as well—perhaps hastening the extinction process.