Woolly mammoths are one of a number of large herbivores, including mastodons, elephants and other mammoth species, descended from primitive proboscideans (from the Greek proboskis, or "nose"), which split off the mammalian tree around 55 million years ago [sources: BBC; Lister and Bahn; UCMP].
The first mammoths showed up in Africa around 5-6 million years ago, but they weren't woolly [sources: Perkins; Lister and Bahn; UCMP]. By around 3 million years ago, their descendants, including the widely distributed southern mammoth (Mammuthus meridionalis), had ranged across the Sinai Peninsula into southern Eurasia. Gradually, they spread west to the British Isles and east to Siberia, but whether they crossed into the New World 1.8 million years ago remains a matter of debate. With the exception of their sloping backs, twisting tusks and overall size -- around 13 feet (4 meters) tall and weighing 8-10 tons -- southern mammoths would have much resembled modern elephants. They fed on the leaves, fruit and bark of trees and exerted a strong influence on forests, stripping bark, knocking down trees and opening up habitat for other grazers [sources: BBC; Lister and Bahn; Mueller; Poinar; UCMP].
Around 750,000 years ago, M.meridionalis was succeeded by the largest mammoth of all, the steppe mammoth (Mammuthus trogontherii), which stood 14 feet (4.3 meters) and weighed at least 10 tons. It may have originated in northeastern Eurasia around 2.0-1.5 million year ago, and was the probable ancestor of the woolly mammoth. It sported smallish ears and tail, and a bit of a shaggy coat. Primarily a grazer, it also supplemented its diet with trees and shrubs [sources: Lister and Bahn; Poinar].
The comparatively smaller woolly mammoth, established around 400,000 years ago, likely resulted from specializations suited for the chill of Siberia, and it was from this Russian icebox that botanist Mikhail Adams recovered the first woolly mammoth carcass in 1806 [sources: Lister and Bahn; Mueller]. But the species eventually spread as far as modern Ireland and, starting 125,000 years ago, crossed the Bering Strait and continued across Canada to the eastern coast [sources: Mueller; Poinar; UCMP]. Another New World species, the Columbian mammoth (Mammuthus columbi), lived at the same time, feeding on a mosaic of parklands and open woods in what is today the U.S. and Mexico. It likely evolved from steppe mammoths that arrived there 1.5 million years ago [sources: Lister and Bahn; Poinar].
The mammoth stock was highly adaptable to the fluctuations in climate that characterized the Pleistocene. Yet, within the brief period spanning 14,000-10,000 years ago, they and most other large mammal species in the Northern Hemisphere died out [source: Mueller]. Why?