The bison has become the official national mammal of the United States under legislation signed into law by President Barack Obama.

Policy-makers spearheading the effort said the once nearly extinct animal deserves the elevated stature because of its economic and cultural significance in the nation's history.

Millions of bison once roamed the Great Plains. About 500,000 now live in the US but most have been cross-bred with cattle, and are semi-domesticated. About 30,000 wild bison roam the country, with the largest population in Yellowstone National Park.

Supporters of the legislation said the recognition will elevate the stature of the bison to that of the bald eagle, long the national emblem, and bring greater attention to recovery efforts for the species.

"I hope that in my lifetime, thanks to a broad coalition of ranchers, wildlife advocates and tribal nations, we will see bison return to the prominent place they once occupied in our nation's shortgrass prairies," said Democratic senator Martin Heinrich of New Mexico, who worked with Republican John Hoeven of North Dakota to pass the Senate version of the legislation.