The pronghorn, the only surviving member of the family Antilocapridae, order Artiodactyla, is called the "pronghorn antelope," although it is not a true antelope. It has pronged (branching) hollow horns with a permanent bony core, covered with an outer sheath, which is shed annually after the breeding season. The pronghorn grows to five feet (1.5 m) long and may weigh up to 135 pounds (60 kg). One of the fastest of the New World mammals, it can run up to 45 mph (72 km/h). Its brownish coat stays flats as an insulator in cold weather and springs erect to cool the skin in summer. Pronghorns live on grasslands and deserts from Northern Mexico to southwestern Canada.