American Lion Right Mandible (Panthera leo atrox). Pleistocene. North America. The American Lion lived 340,000 to 11,000 years ago. The average weight for males of 256 kg (564 lb) and 351 kg (774 lb) for the largest specimen. They were 2.5 meters (8.2 ft) long and 1.2 meters (3.9 Ft) at the shoulder. Length: 25 cm.