Prehistoric Refrigerators

How do you store leftover meat from a mastodon?

If people had refrigerators eleven thousand years ago, what might they have looked like? They wouldn't have had freezer compartments or ice-cube dispensers in the door. But they would have been big enough to store an elephant.

We have no written records from that time. But clues about how prehistoric humans lived have been found at well-preserved campsites, graves, and other places. Scientists think that these people moved from place to place, hunting and gathering their food with tools made of stone, wood, bone, antler, and sinew.

Food was probably not very hard to find during the growing season. But people also needed to store food for the winter. To preserve grains, they buried them. They probably laid vegetables and berries in the sun to dry. To preserve small amounts of meat and fish, these people seem to have dried them over smoky fires or made a snack out of fat, berries, and meat.

Until recently, no one knew that some prehistoric people also had a way to store huge amounts of meat. Scientists have now found evidence that ponds and lakes were used as refrigerators.

The Mastodon
Scientists think that Native Americans of this ancient time hunted the prehistoric elephant-like animal called the mastodon. Scientists have found many fossils of this animal in North America. Both before and during the Ice Age, the mastodon lived over much of the continent. After the end of the Ice Age, about ten thousand years ago, mastodons disappeared from North America.

Some scientists think humans hunted the mastodon to extinction. Others think that as the glaciers disappeared, the climate and environment changed in ways that made it impossible for mastodons to survive.

Dr. Daniel Fisher studies mastodon fossils found in the Great Lakes area. He noticed that most mastodon skeletons have been found in layers of sediment that accumulated on the bottoms of ancient ponds. He suspected that the water at the bottom of a pond or lake might help preserve things. An early explorer once wrote that he saw some Inuit people in Labrador drop caribou meat into a lake to store it.

Odd Groups of Bones

Fisher found clues that the bones had been placed in ancient ponds by humans. He saw that the bones of each skeleton were not together, as they would be if the mastodon had died in the pond. After the animals died and before the bones were buried under pond sediment, these skeletons were separated into several groups of bones.

Rib bones, neck bones, and the skull might be in one group. Another group might have bones from the spine, a tusk, leg bones, and more rib bones.

Fisher wondered what caused these odd arrangements. By carefully examining the bones, he found that each pond held the bones of one mastodon. Near some of these fossils he found deposits of sand or gravel that were not the same color as the rest of the pond bottom. Why were the bones sorted that way, and why were the sand and gravel there?

Fisher examined the bones further under a powerful microscope. On bones that had been separated from one another, he saw scrapes that look like the marks of stone tools. These marks are different from those made when an animal gnaws on the bone or when a person or animal steps on it. Based on these fossils, Fisher concluded that the hunters cut up the mastodon, moved the many heavy pieces of meat and bone to a lake or pond, and dropped them in.

There had to be a good reason for the hunters to want to do this massive job. Fisher believes they did it to save the meat for later. The gravel deposits fit this idea. They might be the remains of weights used to sink pieces of meat.

Most sections of the mastodon probably sank to the bottom of the pond without weights. But meat with lots of fat and not much bone would have floated. To keep these pieces underwater, the people would have needed weights.

Fisher thinks the hunters used pieces of the mastodon's intestine to make anchors. A section of intestine, filled with sand or gravel and tied at each end, could have been attached to the meat before it was dropped into the water. The water would keep the meat fresh and protect it from scavengers, such as wolves and big cats.

Taste Test
To see if this storage method could work, Fisher put some fresh meat into a pond near Ann Arbor, Michigan, and checked it every few weeks. Several times during the first year, he pulled up some of the meat, cooked it, and ate it. It wasn't the best food he had ever eaten, but it could be eaten safely.

The experiment supports Fisher's idea. It seems that hunters of long ago had tried to save some meat. In so doing, they preserved a chapter from the story of their lives.