A mammoth is any of a number of an extinct genus of elephant, often with long curved tusks and, in northern species, a covering of long hair. They lived during the Pleistocene epoch from 1.6 million years ago to around 3,500 years ago. The woollies were a spectacularly successful species; they ranged from Spain to North America and are thought to have existed in huge numbers. Researchers have estimated that during the last Ice Age, parts of Siberia may have had an average population density of sixty animals per hundred square kilometres - equivalent to African elephants today. Most mammoths died out at the end of the last Ice Age.