Finding of mastodon bones may rewrite story of humans in Americas
The ancient humans who came across the mastodon carcass in present-day Southern California quickly went to work on its remains. They pounded the bones open with heavy stone hammers and anvils, gathering raw material for new tools and harvesting the animal’s nutrient-rich marrow.
The remains of the mastodon show all the typical signs of scavenging by paleolithic North Americans, except for one major detail: Scientists have dated it to be 130,700 years old — or roughly 115,000 years before the generally accepted date that humans are thought to have settled the continent.
If verified and corroborated by other scientists, the discovery described in the journal Nature could radically rewrite the timeline of when humans first arrived in the Americas.
“This is the first time there’s been a demonstrated archaeological site with all the bells and whistles,” said Curtis Runnels, an archaeologist at Boston University who was not involved with the study, noting the combination of several lines of evidence at the site. “This makes it absolutely first-water importance. This is up there with one of the discoveries of the century, I would say.”
Without the benefit of actual human remains, however, the dramatic departure from the accepted timeline may not convince all scientists in the field.
“My reaction has been skeptical,” said John McNabb, a paleolithic archeologist at the University of Southampton in England who was not involved in the study. “The date that they’re quoting is so fantastically older than anything that’s quoted for the earliest occupation of the Americas, up to now. It’s a really big ask.”
The fragmented mastodon remains were first discovered in late 1992 by study co-author Richard Cerutti of the San Diego Natural History Museum during routine paleontological monitoring work at a California Department of Transportation freeway expansion project in southern San Diego. Out of the ancient stream deposits came the remains of a camel, horse and other mammals — including the bones, tusks and teeth of a mastodon, a distant and long-gone relative of elephants.
The mastodon fossils looked very different from the other bones nearby. The animal’s limb bones, molars and tusks had been smashed into many pieces. That struck the researchers as odd, because leg bones are strong and thick and should have been preserved over the eons — especially since more fragile ribs and vertebrae had survived in much better shape.
“It was a really intriguing site,” said study co-author Tom Demere, a vertebrate paleontologist at the San Diego Natural History Museum, pointing to the patterns that defied an explanation by natural causes.
The ends of some bones had been torn off — a sign that humans may have been trying to reach the bone marrow. The mastodon bones also bore the spiral fracture patterns that are typical of breaks that happen when the bone is still fresh, rather than the straight ones that tend to mark older bone broken much longer after death. (The wolf and horse bones in nearby sediment layers did not exhibit the same patterns.)
That strange, selective destruction is a sign that humans were there, targeting the thick bones and tusks that could be shaped into new tools, the study authors said.
On top of that, the bones were not arranged in the way that usually happens when an animal dies from natural causes. Instead, the bones had been grouped into two clusters — and near each bunch of bones lay two or three large stone cobbles.