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Drawing from Oliver P. Hay, 'The Pleistocene Mammals of Iowa' in 'Iowa Geological Survey Annual Report,' 1912  
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Mammoth: Witness to Change

The close of the great Ice Age brought many changes to the upper Midwest. It was an ending time and a beginning time. The mighty surges of ice sheets and glaciers from the north had ended. Great rivers, vegetation, animals, and the landscape itself changed as the climate warmed. With these changes came human habitation.

The great beasts that had lived during the Pleistocene epoch watched as their world and their dominance disappeared. Among these huge beasts were the largest of them all—the mammoths.

Once monarchs of their realm, mammoths now relinquished dominance to humans. Once protected in their long, woolly coats, they now faced warming temperatures and a changing environment.

Two particular mammoths, separated by a few hundred miles and a few hundred years, witnessed their world changing. Their deaths, in what are now Iowa and Wisconsin, preserved those particular moments in time.

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The Hebior Mammoth

The Hebior mammoth died about 15,000 years ago in a small depression or pond not far from Lake Michigan in southeastern Wisconsin. Over time its body decomposed. Wetland sediment settled over it.

In 1994, farmer John Hebior discovered bones when he was digging a drainage ditch across the old pond. A team of archeologists led by David Overstreet excavated the site.

What they found startled many archeologists. Here was the most complete mammoth skeleton found to date in the Upper Midwest. Ninety percent of the bones were still there. Even more astounding was the discovery of stone tools and butchering marks on some of the bones, making this one of the earliest known butchering sites in North America.

Here was a rare glimpse of the time when mammoths and humans crossed paths. On path led to extinction. The other, to dominance.

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The Allied Mammoth

In preparation for building the new Allied Insurance and Farmland Insurance parking ramp in downtown Des Moines, a large number of support pillars were formed by drilling down to bedrock and pouring reinforced columns of concrete.

On August 14, 2001, an enormous auger, with a bit 6.5 feet wide, bore down through old building rubble, then through yards and yards of sand and gravel. At 10:30 in the morning, 55 feet below the surface, the auger struck bedrock—and bone. The auger had cut through the skeleton of a mammoth lying on the very floor of the Raccoon River valley.

The construction workers recognized the significance of this find and notified the executives of Allied Insurance. They, in turn, contacted the State Historical Society of Iowa for assistance and later donated the bones to the museum.

A small sample of the bone was sent to Stafford Research Laboratories, Inc., in Colorado, for radiocarbon dating. The bones were dated at 16,500 BP (before present).

When the auger cut through a part of the skeleton, it broke the bones into pieces. Not all the pieces were brought to the surface in the slurry. Some of the fragments form a portion of the right shoulder region. They include vertebrae, a scapula, and parts of the front leg.

The dig at Allied Insurance and Farmland Insurance parking ramp

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The American Mastodon

The American mastodon, Mammut americanum, first appears in the fossil record about 3.5 million years ago throughout North America. Although the mastodon was similar to the mammoth in form and size, they were only distant relatives. The mastodon was shorter, about ten feet tall, and its head lacked the characteristic high dome of the mammoths. The greatest difference, however, was in their teeth. This meant that mastodons and mammoths did not compete for exactly the same foods. both lived in Iowa about the same time.

Each mastodon tooth had several heavy, rounded cones covered with enamel. These were will suited for crushing and eating a variety of plant material including grasses, twigs and leaves, the kinds of plants found in conifer forests, woodlands , and on the edges of grasslands. (The flat planes of mammoth teeth were best suited for eating grasses.)

A tooth from an American Mastodon

Both mastodons and mammoths became became extinct about 10,000 years ago.

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Mammoth History

The woolly mammoth has come to symbolize the last Ice Age and the arrival of humans in the Western Hemisphere. Here in Iowa, mammoth bones have been unearthed in the daily activities of Iowans tilling the land, excavating for buildings and bridges, or merely walking along creeks and streams. Finding mammoth bones reminds us that change is ever present.

A little woollyRemains of both woolly mammoths and Columbian mammoths have been found in Iowa, but sometimes it's difficult to tell which is which. Bones and teeth of the two species are similar, and of course there are individual variations within each species.

Learn more about mammoths and how they lived. »»

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