rose was reading about the early giant mammals. she learned that several types of giant mammals thrived during the paleogene and neogene periods. for what reason might these giant mammals have flourished at the time? a. at this time, forests thinned and grass and ground plants grew in place of trees. b. at this time, the climate warmed and changed the kinds of food available. c. giant mammals had multiple predators and moved slowly due to their size. d. giant mammals had little need for large amounts of food.