How Woolly Mammoths Worked

We often picture woolly mammoths lumbering across snow-swept Arctic tundra or snuffling their way through some boggy Russian steppe. In actuality, these mammals roamed landscapes unlike any that exist today. During many parts of the Pleistocene -- an epoch lasting from 1.7 million to 11,500 years ago and ending with the most recent ice age -- a rich and varied mixture of grasses, herbs and sedges spread from Ireland to Siberia, across the Bering land bridge to much of modern Canada. This mammoth steppe was supported by a different climate. As growing glaciers locked up water, sea levels dropped, exposing great swaths of land dominated by dry, clear and breezy blue skies [sources: Lister and Bahn; Mueller; Saey; Willerslev et al.].

Grazing across this landscape in a 20-hour-a-day pursuit of food were vast numbers of Mammuthus primigenius, creatures about the size of modern elephants. These woolly mammoths occurred as lone males, each standing around 9-11 feet (3-4 meters) tall and weighing about 6 tons, or in matriarchal family groups of 2-20 smaller females and calves. They withstood the chill of their northern climes through a number of adaptations, including a 3-4-inch (8-10-centimeter) layer of fat, inch-thick oily skin and a wooly undercoat. The latter was covered with coarser guard hairs ranging from a few inches to up to 3 feet (1 meter) long, with the longest hanging in a musk-ox-like skirt along the mammoth's flanks and belly [sources: BBC; Lister and Bahn; Mueller; National Geographic]. Even their hemoglobin had heat-retaining properties, a trait echoed in many modern, cold-adapted mammals [sources: Campbell; Rummer].

Woolly mammoths shared these lands with other massive mammals, including grazers like woolly rhinoceroses and long-horned bison and predators such as saber-tooth cats and cave hyenas. Given their bulk and massive tusks, healthy adult mammoths could take all comers in a standup fight, especially if gathered in a protective group, so predators likely preyed on sick or injured adults, or picked off the occasional straggling calf [sources: Lister and Bahn; Mueller].

Mammoth calves were mostly born in spring, when fresh growth could support lactating mothers. A 22-month gestation period meant that conception occurred in late summer. Detecting a female in estrus, competing males would demonstrate their fitness via tusk displays, ritualistic sparring or out-and-out fights. Like modern elephants, male woolly mammoths had a musth gland, which secreted a fluid that helped establish reproductive hierarchy during their aggressive, unpredictable musth phase [source: Lister and Bahn].

If, as experts suspect, mammoths resembled today's elephants, then they were likely highly social, educating their calves and perhaps even guarding and burying their dead. They may have periodically come together in great migratory herds and could probably swim to islands a few miles offshore [sources: BBC; Lister and Bahn; Poinar]. In short, they were animals that had evolved to become well adapted to their environment.

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?

Paleontologists have advanced several theories to explain mammoths' rapid disappearance at the end of the last ice age, including meteors, diseases, climate change and human hunting. Evidence for meteor strikes has failed to materialize. As for human- or dog-borne diseases, experts say that it's hard to imagine a bug that could kill such a wide range of animals and only affect the large ones [sources: Lister and Bahn; UCMP]. That leaves climate and hunting.

As far as we know, mammoths could not live in areas akin to today's steppes, deserts, savannas or tropical forests, but were confined to the mix of plants peculiar to the mammoth steppe and parkland biomes. According to the climate hypothesis, that specialization may have doomed them to isolation and starvation. As the climate shift melted glaciers and raised sea levels, continents shrank and wetter conditions prevailed. Ill-adapted to such conditions, mammoth food sources dwindled, and mammoth populations declined with them [sources: Lister and Bahn; Mueller; Saey; Willerslev et al.].

Like the disease hypothesis, the overkill hypothesis emphasizes the fact that mammoths' shockingly fast decline coincides with the generally accepted arrival of humans in North America 13,300-12,800 years ago. It argues that big-game hunters, wielding spears with fluted, hafted Clovis points, hunted mammoths to extinction. Clovis points have been found with mammoth bones, and we know that humans used mammoth furs, meat and ivory. Moreover, we have found that both Neanderthals and Stone Age humans constructed buildings from mammoth bone [sources: Bower; Demay, Péan and Patou-Mathis].

But many questions remain. Given that many humans could have survived on a single mammoth, especially aided by natural refrigeration, and that early humans venerated the beasts in cave art, it's possible they treated mammoths with the reverence and restraint that Native Americans used toward buffalo [source: MGP]. Either way, hunter-gatherers likely had a varied diet and relied on small to medium game for meat, so how often they actually hunted mammoths (versus scavenging their remains) is unclear [sources: AMNH; Guthrie; Lister and Bahn].

Ultimately, the limitations of large mammals like mammoths, with their low birth rates and vast need for sustenance, might well have hastened their end, worsening the effects of isolation, habitat loss and predation, leaving only their dwarf descendants, cut off from the mainland on scattered islands, to carry on for another 6,000 years [sources: AMNH; Bower; Lister and Bahn; Nikolskiy and Pitulko].