Some 130,000 years ago, scientists say, a mysterious group of ancient people visited the coastline of what is now Southern California. This is more than 100,000 years before people were thought to have arrived in the Americas.
These unknown people used five heavy stones to break the bones of an elephant-like mastodon. They cracked open femurs to suck out the marrow and, using the rocks as hammers, scored deep notches in the bone. When finished, they abandoned the materials in the soil with one tusk planted upright in the ground like a single flag, and then, the people vanished.
A Big Setback
This is the bold claim put forward by paleontologist Thomas Deméré and his fellow researchers. The scratched-up mastodon fossils and large chipped stones were uncovered during excavation for a highway in San Diego more than 20 years ago. Researchers think they are evidence of an unknown hominin species, which are members of the great ape family that includes chimps, gorillas and humans.
If the researchers are right, it would set back the arrival date for hominins in the Americas. This suggests that modern humans might not have been the first species to arrive. But their research has raised skepticism, with many saying there is not enough evidence to prove this.
The earliest settlement of the Americas is thought to have been at the end of the ice age. Most archaeologists agree that humans crossed a land bridge from Asia into Alaska sometime after 25,000 years ago. Then, they either walked between ice sheets or took boats down the Pacific coastline to reach the wide open plains of Pleistocene America. This is thought to have happened roughly 15,000 years ago. Though scientists debated the exact timing of this journey, their estimates differed by hundreds or a few thousand years, not tens of thousands.
"It is a bold claim," Deméré said of his research findings. "This evidence begs for some explanation, and this is the explanation we've come up with."
Deep Cuts
The rocks and mastodon remains were identified in 1992 by paleontologist Richard Cerutti, a colleague of Deméré's at the San Diego Museum of Natural History. He got in touch with Deméré when he discovered the remains.
The biggest find was a partial skeleton from a single American mastodon. The largest bones were scarred and broken, but more fragile ribs and vertebrae were still together. Some of the bones seemed to have been placed alongside one another. Many had spiral fractures that are a signature of ancient people hammering on fresh bone — either to extract marrow for food or break the bone into tools.
Archaeologist Steve Holen thought the breaks on the mastodon fossils looked as though they were caused by humans, he said. But to make sure, Holen tried to recreate them using a stone hammer. After doing this, he recognized the same breakage patterns as the ones found on the fossils. There's no evidence that anyone hunted or butchered the mastodon for meat, but it seemed to him like some type of human had cracked the bones.
"Once you do the experiment then you really can understand this much better," Holen said.
Scientist James Paces studied the bone and concluded they are 130,000 years old, give or take 9,400. This date corresponds with the accepted age of the layer of rock in which the bones and cobbles were found, which far exceeds any established date for settlement of the Americas.
If the stones and bones really are evidence of people, then who were they? How did they get to this part of the world so long ago? And why haven't we found other evidence of their presence? Did they die out not long after they arrived?
"A Very Easy Claim To Dismiss"
Because there are no hominin remains at the site, and rock hammer technology was used by many hominin species, the scientists caution that discussion of the identity of these people is purely speculative.
Donald Grayson, a paleoanthropologist at the University of Washington, noted there are many examples of scientists misinterpreting strange markings on stone as evidence of human activity.
"It is one thing to show that broken bones and modified rocks could have been produced by people, which Holen and his colleagues have done," Grayson said. "It is quite another to show that people, and people alone, could have produced those modifications. This, Holen [has] most certainly not done, making this a very easy claim to dismiss."
Rick Potts, the director of the Human Origins Program at the National Museum of Natural History, pointed out a few oddities about the site. For one, it's unusual that people would use hammer stones to process bones but not any sharp-edged tools, even though that technology had been around for more than a million years. For another, as he pointed out, the mastodon's molars were also crushed, and there's no reason he can think of that humans would crack the huge teeth. If those teeth were broken by natural forces, then perhaps the rest of the bones were too.
No Other Explanation
Deméré said that he and his fellow researchers considered other explanations, but none seemed to fit.
Trampling by another large animal would not produce those breakage patterns, they concluded. And environmental forces, like a powerful flood, would have broken the smaller, more fragile bones as well as the big one.
The rock layer in which the artifacts were found is largely together and does not show disturbances like earthquakes or upheavals that would make the site more difficult to interpret.
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