Mammuthus (Woolly mammoth, partial tusk) — The Shane Bodimer Collection

The Woolly Mammoth

Mammuthus primigenius is the best-known mammoth because its remains include frozen carcasses recovered from permafrost in Siberia and North America, with skin, hair and stomach contents intact. Its closest living relative is the Asian elephant, Elephas maximus; DNA studies place the split at roughly 6 to 8 million years ago. The mastodon, Mammut, is only a distant relative.

Adult male woolly mammoths stood roughly 2.8 to 3.15 meters (9 to 10 feet) at the shoulder and weighed an estimated 4.5 to 6 metric tons. Adult males commonly carried tusks of 2.4 to 2.7 meters measured along the curve. The animal was built for cold: a coat of guard hairs up to 90 centimeters long lay over a dense underwool, with a layer of fat up to 10 centimeters thick beneath the skin. Mammoths ate mainly forbs and grasses, and many tusks show flat, polished areas and scratches consistent with sweeping snow aside to reach the plants beneath.

Fig. 1 Life-size model of a woolly mammoth, Royal BC Museum, VictoriaPhoto by Thomas Quine via Wikimedia Commons · CC BY 2.0

The Tusk

This specimen is a partial tusk of a woolly mammoth, Mammuthus primigenius. Mammoth tusks are the animal's upper incisors, as they are in living elephants. They grow throughout life from an open base set in the skull, and the dentine is laid down in layers around the pulp cavity, the oldest layers outermost.

Nearly all of a tusk is dentine, the material called ivory when it is carved. A layer of cementum covers the outside. Enamel is present only as a cap on the tip of a young animal's tusk. It wears off early and is not replaced, so the shaft is dentine under cementum, not enamel.

Cut across and polished, elephant and mammoth ivory shows Schreger lines, a pattern of crossing arcs named for the German anatomist Bernhard Schreger, who described it in 1800. Mammoth angles between the outer lines are typically below 90 degrees and elephant angles above 115 degrees. Because the ranges overlap between 90 and 115 degrees, the method relies on the average of several angles.

The same cross-section shows growth lines. In a mammoth tusk each major line represents a year, and the dark bands form in summer, so a tusk can record the season of death. The earliest years are held in the tip, which is usually worn away, so a count of the lines gives a minimum age.

Fig. 2 Polished cross sections of African elephant (a, b) and woolly mammoth (c, d) tusks showing annual growth rings and the Schreger patternPhotographs by S. Döring (Senckenberg), figure by Sebastian J. Pfeifer, Wolfram L. Hartramph, Ralf-Dietrich Kahlke and Frank A. Müller via Wikimedia Commons · CC BY-SA 4.0

The Pleistocene Epoch

The Pleistocene Epoch lasted from about 2.58 million to 11,700 years ago, a span defined by repeated glaciations. At the Last Glacial Maximum, between roughly 26,500 and 20,000 years ago, global sea level stood about 120 to 125 meters lower than today. Beringia, the region spanning northeastern Siberia, Alaska and the Yukon, was exposed as a land bridge up to 1,000 kilometers wide between Asia and North America. Mammoths lived on the cold, dry mammoth steppe that stretched across it.

Mammoth numbers fell as the climate warmed and peatlands, wet tundra and forest replaced open steppe. The last mammoths on the Siberian mainland died about 10,000 years ago, and the youngest radiocarbon-dated mammoth from mainland Alaska died about 11,600 years ago. Mammoths on St. Paul Island survived until 5,600 years ago, give or take 100 years. Those on Wrangel Island, off northeastern Siberia, survived until about 4,000 years ago, the last known population.

Fig. 3 Beringia during the Last Glacial Maximum, about 21,000 years agoMap by U.S. National Park Service via Wikimedia Commons

Alaska: A Mammoth Graveyard

Alaska has yielded a large number of mammoth fossils. During the last ice age much of the state lay in Beringia, a largely unglaciated region. Permafrost froze bones, tusks and teeth soon after burial, which kept them intact for tens of thousands of years.

Many Alaskan mammoth fossils have come to light through gold mining. Gold was found in the creeks around Fairbanks in 1902, and placer miners there removed the frozen silt of the valley bottoms, exposing the remains of Ice Age animals. A 1975 U.S. Geological Survey study called the Goldstream Formation, a frozen silt deposit near Fairbanks, the greatest repository of Pleistocene vertebrate remains in Alaska, if not in North America. The University of Alaska Museum of the North in Fairbanks holds about 1,500 mammoth fossils, many collected by gold miners. The woolly mammoth was named Alaska's state fossil in 1986.

Fig. 4 A mammoth tusk exposed in permafrost, Espenberg Beach area, Chukchi-Imuruk, Alaska, 1976Photo by David Cohen, National Park Service (August 1976) via Wikimedia Commons

Provenance

This specimen was acquired in March 2024 from The Stones & Bones Collection, a fossil dealer. The record for the piece gives Alaska as its origin and an estimated age. The age is the dealer's estimate and has not been independently verified. No find site, collection date or stratigraphic horizon is recorded here, so it cannot be tied to a particular deposit or mining district.

Image forthcoming

Fig. 5 The specimen