Mammoth bones have some rethinking when humans came to America

KENOSHA, Wis. -- Scientists have dated man-made marks on bones of two woolly mammoths, excavated about 10 years ago from farms in Kenosha, at 15,000 years old.

That casts doubt on a decades-old theory that suggests humans came to America 14,000 years ago after crossing a land bridge from Siberia.

Since archaeologists David Overstreet of Marquette University and Dan Joyce of the Kenosha Public Museum revealed the findings to a skeptical scientific community, the evidence -- and agreement from other researchers -- has grown.

Called the Schaefer and Hebior mammoths after the farms where they were discovered, each skeleton has about 10 marks that, under scrutiny of a scanning electron microscope, were found to be cuts from man-made tools.

The bones were found scattered and not in connected skeletons of mammoths that died undisturbed. Geological analysis suggests the bones hadn't moved since they settled to the bottom of an ice age pond.

A few rough stone tools were found touching the bones, and experts who have reviewed the site agree they are the same age as the mammoths.

Tom Stafford, who has radiocarbon bone-dating labs in Colorado, has dated the bones at about 15,000 years old.

"All of these lines of evidence point in the same direction -- that somebody in southeastern Wisconsin was mucking about with mammoths 15,000 years ago," Overstreet said.

A major find

Archaeologist Ronald Mason of Lawrence University in Appleton, Wis., was originally suspicious, but now he calls the mammoths a major archaeological find.

"I'm convinced Overstreet's really got something remarkable there," Mason said. "Now we just want to find some distinctive or diagnostic artifacts with those mammoths, and he hasn't done that yet."

Scientists also worry that the Kenosha mammoth find is not repeated elsewhere.

"When you have one site that is unique, it's a problem, but when you see a pattern -- similar tools, similar age, in different places -- then the evidence becomes stronger," said University of Wisconsin-Madison archaeologist James Stoltman. "So the problem with the Kenosha find is that, at that age, it's virtually one of a kind in North America -- and you can't just parachute into Wisconsin from outer space."