Yellowstone is the only place in the U.S. where bison have lived continuously since prehistoric times. By 1902, poachers had cut its herd to about two dozen animals.

Yellowstone is the only place in the United States where bison have lived continuously since prehistoric times, the National Park Service says.

Bison are the largest land-dwelling mammals in North America. Males weigh up to 2,000 pounds and females up to 1,000 pounds.

In the 1800s, market hunting and the U.S. Army nearly caused the extinction of bison. By 1902, poachers had reduced Yellowstone's herd to about two dozen animals. The Army, which then administered the park, protected them from further poaching, and bison from private herds were later used to help rebuild the population.