An amazing find at an Ice Age site in San Diego, California may dramatically alter the accepted timeline for when early humans first reached North America. 130,000-year-old bones and teeth of a mastodon show evidence of modification by early humans.
A trove of ancient bones was found in 1992 by construction workers. It included the remains of dire wolves, horses, gophers, camels, and -the most exciting – an adult male mastodon. Ars Technica reports that It took years of testing before an interdisciplinary team of researchers could ascertain that the mastodon bones date to 130,000 years ago. But with this information in hand an even more shocking claim was waiting to be made – there are marks the researchers assert were left on the bones by early humans.
Mastodon skeleton schematic showing which bones and teeth of the animal were found at the site. (Dan Fisher and Adam Rountrey, University of Michigan)
“I realize that 130,000 years is a really old date. Of course, extraordinary claims like this require extraordinary evidence.” Thomas Deméré, principal paleontologist at the San Diego Museum of Natural History and one of the authors of the recent study, said at a press conference.
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The team waited 24 years to ascertain their facts before publishing their findings in the journal Nature – they seem positive that the dates and details add up. As they wrote in their paper:
“The earliest dispersal of humans into North America is a contentious subject, and proposed early sites are required to meet the following criteria for acceptance: (1) archaeological evidence is found in a clearly defined and undisturbed geologic context; (2) age is determined by reliable radiometric dating; (3) multiple lines of evidence from interdisciplinary studies provide consistent results; and (4) unquestionable artefacts are found in primary context. Here we describe the Cerutti Mastodon (CM) site, an archaeological site from the early late Pleistocene epoch, where in situ hammerstones and stone anvils occur in spatio-temporal association with fragmentary remains of a single mastodon (Mammut americanum).”
They go on to describe the Cerutti Mastodon site, writing that it had spiral-fractured mastodon bone and molar fragments, many of which preserve evidence of percussion. The site also had flat rocks that could have been anvils and a collection of small stones that may have been used as hammers. These artifacts were found in the same layer as the mastodon bones and show evidence of use wear and impact marks. As Ars Technica says, the site apparently looked “like a perfectly preserved tableau of an ancient tool-making workshop.”
Center for American Paleolithic Research archaeologist Steve Holen explained the modification of the bones in more detail:
“People were breaking up the limb bones of a mastodon, removing some of the big, thick pieces. They were extracting marrow for food. And they were using old technology. We have evidence of people in Africa 1.5 million years ago breaking up elephant limb bones with this same [stone] technology.”
A view of two mastodon femur balls, one face-up and one face-down. Neural spine of a vertebra exposed (lower right) and a broken rib (lower left). The fact that some bones were broken and others weren’t may be further evidence that early humans were picking and choosing which ones to crush with hammers. (San Diego Natural History Museum)
Paper co-author and University of Wollongong archaeologist Richard Fullagar, an expert on the kinds of microdamage that humans leave behind on stone tools, further asserted the evidence of humans at the site:
“The evidence at this site is remarkable. I thought… they were pounding stones. All the materials indicated that they had been used for smashing up bones. You can see fragments of hammers and anvils that can be fitted back into the stones… It’s rare that you get all that evidence at one site. It really does show humans have been there.”
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Smithsonian reports that the researchers decided to analyze and compare their findings with mastodon bones from North American sites dating from 14,000 to 33,000 years ago. The researchers also conducted experiments to see if these kinds of stone tools could damage mastodon bones in the same way they found them at Cerutti Mastodon. Their results “produced exactly the same kinds of fracture patterns that we see on the Cerutti mastodon limb bones,” said Holen, who added, “[W]e can eliminate all of the natural processes that break bones like this. These bones were not broken by carnivore-chewing, they were not broken by other animals trampling on the bone.”
As you may expect with possibly ground-breaking research, the paper is being met with shock and skepticism in much of the scientific community. According to Ars Technica, there are two main arguments that have been provided against the paper: the site was too disturbed by construction to be reliable, or the evidence provided just isn’t enough. For example, Trent University archaeologist Daniel Rafuse told Ars Technica:
“Current data suggests Homo sapiens spread out of Africa around 100,000 years ago, across Asia about 60,000 years ago, into Europe and Australia 50,000 years ago, and finally the Pacific coasts of both North and South America, and probably interior continental locations by 13,500 to 15,000 years ago. To confirm the presence of an undefined species of Homo in the Americas at 130,000 years ago requires indisputable evidence. While the Cerutti Mastodon site challenges our knowledge of the peopling of America and forces us to think beyond what is currently known, fresh fractured bone together with five large cobbles is not extraordinary evidence.”
A boulder discovered at the Cerutti Mastodon site thought to have been used by early humans as a hammerstone. (Tom Deméré, San Diego Natural History Museum)
Briana Pobiner, a paleoanthropologist with the Smithsonian Institution’s Human Origins Program, reported in the Smithsonian article about the discovery “that it is “nearly impossible” to rule out the possibility that the bones were broken by natural processes, like sediment impaction.” She says:
“I would have liked to see really easily identifiable stone tools. [The study theorizes that early humans were] bashing open bones with natural rocks. Both of those things are kind of hard to distinguish in the archaeological record book: natural rocks that were used and also the bones that were bashed open.
A concentration of fossil bone and rock. The unusual positions of the femur heads, one up and one down, broken in the same manner next to each other is unusual. Mastodon molars are located in the lower right hand corner next to a large rock comprised of andesite which is in contact with a broken vertebra. Upper left is a rib angled upwards resting on a granitic pegmatite rock fragment. Credit: Image courtesy of San Diego Natural History Museum
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However, she added:
“They have broken mammoth bones, they have broken stones, they have patterning, and damage and wear on both the bones and the stones, which look human-modified. I think that the combination of evidence is on the way to being convincing.”
But for his part University of Wisconsin, Madison paleoanthropologist John Hawks told Ars Technica he wonders:
“[…] which hominin population had the ability to establish a sustained population in Beringia? We don’t even know how many populations were in mainland Asia at the time—certainly multiple, deeply divergent populations of Denisovans and Neanderthals, maybe others with even older origins. Maybe modern humans. From the biological side, we have no reason to think that any of them were incapable of entering the New World. We’ve just been stuck with the assumption that they didn’t cross into North America—because if they did, we should see a hundred millennia of discarded tools and butchered animal bones.”
Paleontologist Don Swanson helps excavate a site near San Diego, California, that may show that early humans were present in the Americas 130,000 years ago. (San Diego Natural History Museum)
The researchers have suggested in their paper that Neanderthals or Denisovans may have been the ones who left the tools behind. Or, it’s possible that an early form of Homo sapiens who roamed Asia more than 200,000 years ago left the artifacts. With some evidence of possible boats in Indonesia 180,000 years ago and a climate that would have allowed for their passage to the Americas, there are a few contenders for who may have been the toolmakers at the California site.
Regarding the lack of artifacts, Holen has suggested that there may not have been much other evidence because the population was low. He said, “It’s possible that the early population came in and did not make it. Humans could become locally extinct if the environment wasn’t favorable for human adaptation in that area.”
Top Image: The unbroken mastodon ribs and vertebrae, including one vertebra with a large well preserved neural spine. Source: San Diego Natural History Museum