 During this period new stone tools were created to process and prepare plants for meals.Gilmore submits that bison antiquus, the primary source of food for the Paleo-Indian, became extinct due to increasingly warm and arid climate changes of the Holocene Altithermal period [a warm period about 9,000 to 5,000 years ago].To survive people adapted by hunting smaller game and gathering plants, seeds, and nuts.