Mammals' lucky space impact By Paul Rincon BBC science A comet collision with Earth around 55 million years ago may have kick-started a crucial early phase of mammal evolution. Did a comet strike deliver carbon to heat up the Earth The impact could have triggered the greenhouse warming thought to have encouraged primitive mammals to disperse across the world and diversify into three important groups still with us today. These groups were the Artiodactyla, the Perissodactyla and the Primates - the mammalian order that includes humans. Modern Artiodactyls include sheep, pigs, camels and giraffes. Today's Perissodactyls include horses, tapirs, rhinos...
