Prehistoric humans — perhaps Neanderthals or another lost species — occupied what is now California some 130,000 years ago, a team of scientists reported on Wednesday.

The bold and fiercely disputed claim, published in the journal Nature, is based on a study of mastodon bones discovered near San Diego. If the scientists are right, they would significantly alter our understanding of how humans spread around the planet.

The earliest widely accepted evidence of people in the Americas is less than 15,000 years old. Genetic studies strongly support the idea that those people were the ancestors of living Native Americans, arriving in North America from Asia.

If humans actually were in North America over 100,000 years earlier, they may not be related to any living group of people. Modern humans probably did not expand out of Africa until 50,000 to 80,000 years ago, recent genetic studies have shown.

If California’s first settlers weren’t modern, then they would have to have been Neanderthals or perhaps members of another extinct human lineage.

“They present evidence that the broken stones and bones could have been broken by humans,” said Vance T. Holliday, an archaeologist at the University of Arizona. “But they don’t demonstrate that they could only be broken by humans.”

San Diego Natural History Museum paleontologist Don Swanson points at a rock fragment near a large mastodon tusk fragment. Photograph by San Diego Natural History Museum

For years, Dr. Deméré and his colleagues struggled to figure out how long ago the mastodon died. The scientists finally contacted James B. Paces, a research geologist at the United States Geological Survey, who determined how much uranium in the bones had broken down into another element, thorium.

That test revealed, to their surprise, that the bones were 130,000 years old. Yet the fractures suggested the bones were still fresh when they were broken with the rocks.

Two mastodon femur balls, one face up and one face down, are among the remains found at the Cerutti site in San Diego.

If early humans really did smash those mastodon bones 130,000 years ago, scientists will have to rethink how humans came to the Americas.

The oldest fossils of anatomically modern humans, found in Africa, date back about 200,000 years. The ancestors of Europeans, Asians, and Australians did not expand out of Africa until somewhere between 50,000 and 80,000 years ago, according to recent studies.
 Source National Geo

 A close-up view of a spirally fractured mastodon femur bone from the site.

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