Overview:North America - 13,000 years ago While the world was still in the grip of the last ice age, humans first crossed Siberia and entered the New World. They encountered creatures familiar to them from their travels, such as the woolly mammoth and the steppe bison, but also a whole host of new marvels. The Americas was the only continent where humans ever came face to face with sabre-toothed cats, giant ground sloths or the massive short-faced bears. As the climate warmed and the ice melted, all these megafaunal marvels vanished. What or who was responsible for their demise?