updated 5/9/2012 1:30:33 PM ET 2012-05-09T17:30:33

Not far from West Palm Beach in southern Florida, people once lived alongside giant ground sloths, mammoths, tapirs, mastodons and other enormous creatures.

The discovery adds the far southeast corner of the United States to the list of places in North America where humans coexisted with massive creatures more than 10,000 years ago. The finding also adds to a growing body of evidence that modern humans spread rapidly after arriving in the Americas, though it’s still not clear when and where they first set foot on the continent.

“We found that humans came into Florida before the extinction of megafauna -- they were in Florida by 10,000 years ago,” said Bruce MacFadden, a paleontologist at the University of Florida, Gainesville. This is “clearly documenting that humans were widespread in North America.”

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In 1913, construction of a drainage canal turned up fossils in Vero Beach, Fla., about 90 miles north of West Palm Beach. When geologists followed up, they unearthed the bones of all sorts of ancient animals that lived during the last Ice Age, including jaguars, capybaras, bison, peccaries, mastodons and other creatures, large and small. Alongside the animal bones in the same layer of soil lay human skeletons.

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At first, the scientists assumed that the co-mingled bones came from animals and people that lived at the same time. Soon after, though, a famous archaeologist from the Smithsonian Institution who came to see the fossils raised doubts by proposing that people arrived long after the giants were gone and that the human bones came from more recent burials.

Despite subsequent archaeological finds in other parts of the United States showing that people coexisted with extinct megafauna during the last Ice Age, which ended about 10,000 years ago, controversy about the Vero Beach fossils has lingered. Complicating matters, the bones are too weathered to allow for radiocarbon dating, which would offer clear dates and ages.

To settle the debate, MacFadden and colleagues looked instead at levels of rare earth elements in 24 human bones and 48 animal bones from the site, now held in museum collections. Over time, fossils left underground absorb these elements at a predictable rate.

Both types of bones contained similar levels of rare earth elements, the researchers reported in the Journal of Vertebrate Paleontology. The technique couldn’t accurately date the bones, but it showed that they had all been in the ground for the same amount of time. That meant that they had lived at the same time, too. Many of the animals involved are known to have gone extinct when the last Ice Age ended.

The new findings echo what other studies have shown in Montana, New Mexico, Arizona, Ohio and elsewhere – that people lived alongside mastodons, mammoths and other massive mammals more than 10 millennia ago, said Kenneth Tankersley, an archaeological geologist at the University of Cincinnati.

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Scientists still don’t know whether people thought of the giant animals that shared their territory as friends, enemies or food. In some places, evidence suggests that ancient people hunted giant beavers, bear-sized peccaries and mastodons, though the Florida bones offer no clues. Also unanswered is why all of those enormous animals went extinct.

As scientists puzzle over those questions, they are also still trying to figure out when modern Homo sapiens arrived in North America in the first place. The oldest clear evidence comes from the Monte Verde site in Chile, where human skeletons date back to more than 14,000 years ago, Tankersley said. But genetic evidence suggests that people may have arrived in the Americas more than 20,000 years ago.

Together, ongoing research confirms oral histories of indigenous populations that have been passed down for generations.

“All along, Native Americans have been saying, ‘We’ve always been here,’” Tankersley said. “That’s what this study is showing, that that’s the case.”

© 2012 Discovery Channel


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