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Broken Bones Could Rewrite Story of the First Americans

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Broken Bones Could Rewrite Story of the First Americans

In the fall of 1992, a construction crew made an unusual discovery during a freeway expansion in a coastal area of San Diego County. Buried deep within the silty soil were the bones, tusks, and molars of a mastodon, an elephant-like mammal that once lived in North America. When archaeologists took a closer look, they found signs that humans had battered the animal shortly after its death with the large stones buried alongside it.

But the real surprise came when geologists determined the age of the bones. Radiometric dates showed the mastodon had been buried for about 130,000 years. If correct, this means that ancient humans were in coastal California many tens of thousands of years before they were thought to be in the Americas. The details of the finding, which took 25 years to unravel, were published in Nature today, raising questions about when humans first migrated to North America.

“It’s a huge claim,” says John McNabb, a Paleolithic archaeologist at the University of Southampton in the United Kingdom, who was not part of the study. “It’s 115,000 years older than most people would accept as the earliest occupation of the Americas.”

Most archaeologists generally agree that humans traveled into North America about 14,500 years ago and then spread across the continent. The Clovis people, once thought to be the first humans to enter the Americas, lived about 11,000 years ago, but the recent discoveries of ancient feces in Oregon, the remains of a large campsite in southern Chile, and bones and stone tools at the bottom of a Florida river have bumped the timeline at least 2,000 years earlier. Other studies have heated the debate, placing humans in the Calico Hills in California 50,000 to 80,000 years ago, in Brazil 20,000 to 40,000 years ago, and in Canada’s Yukon Territory as early as 24,000 years ago.

Perhaps it’s not surprising then that many are skeptical about the new claims. “If you are going to push human antiquity in the New World back more than 100,000 years in one fell swoop, you’ll have to do so with a far better archaeological case than this one,” says David Meltzer, who studies the origins of the first Americans at Southern Methodist University in Dallas, Texas.

Mastodon bones human migration - The breaks in mastodon bones found at a research site in California matched the breakage patterns observed by the researchers when they used stones to hammer elephant and cow bones in experiments.

The breaks in mastodon bones found at a research site in California matched the breakage patterns that the researchers observed when they used stones to hammer elephant and cow bones in experiments. Kate Johnson/San Diego Natural History Museum

According to the analysis in Nature, the position of the bones, the clusters of stones nearby, and the fracture patterns on the bones all point to someone bludgeoning the mastodon—perhaps for food or to use the bones as tools. The radiating spiral fractures, the cone-shaped bone flakes, and the notches in the bones could only have been made by humans, says Steven Holen, an expert in early human archaeology and bone technology at the Center for American Paleolithic Research, who worked on the study. As part of the investigation, the team broke elephant and cow bones using stone or wood anvils and heavy stone hammers to compare the breakage patterns.

What’s more, the authors claim, the fossils were found in fine-grained sediments, making it unlikely that a storm or landslide had deposited the rocks next to the mastodon. Finally, geologists used a technique called uranium-thorium radioisotope dating to put the age of the bones at 121,000 to 140,000 years old.

Despite the detailed study and the authors’ attempts to exclude all natural explanations for the patterns they found, many experts remain unconvinced. Meltzer and others say it doesn’t show that people were the only force that could have fractured the bones and modified the stones. McNabb points to the lack of corroborating tools, such as well-made stone tools like flakes or scrapers, which are typically found at butchery sites of the same age or older. Luis Borrero, an archaeologist in Argentina who studies first peopling sites, wants to know about any information that “does not fit within their interpretation.”

For its part, the team has invited other researchers to take a look at the artifacts. They also intend to reconsider broken limb bones in collections across Southern California and re-examine the material collected from other sites. In the past, paleontologists and archaeologists may not have been looking for the right clues in the right places, says Holen. “A lot of the evidence may have fallen between the academic cracks of archaeology and paleontology.”

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  • kso721

    Mastodon/Mamoth mosh pits? 😉

  • Robert Kelly

    In the article’s abstract the authors claim that the Cerutti Mammoth “substantially revises the timing of arrival of Homo into the Americas.” The probability that conclusion is correct is minuscule. If humans arrived in the Americas >130,000 years ago then, although 130,000 year old sites might be hard to find, population growth would have produced a human population large enough to leave a quite visible archaeological record by, let’s say 50,000 years ago, if not much earlier. Sites dating to 50,000 years should be fairly common and uncontroversial. But they are not common; in fact, there are none. The alternative is that the 130,000 year old human population went extinct (or went back to Asia). In that case, the likelihood of finding evidence of a failed colonization (a) at a distant time period and (b) of nomadic peoples who leave few material traces, approaches zero. So the likelihood of this site being what the excavators claim it is, is close to 0. One cannot claim that North American archaeologists have simply missed the evidence of sites >14,000-14,500 years old because the U.S. has a greater density of archaeologists and a greater density of field projects than, say, Australia or far eastern Russia, both places where, decades ago, investigators pushed their respective prehistories back considerably earlier than that of North America. In other words, we’ve looked hard and ~14,500 is the best we can do using, as we should, stringent criteria. Genetic data are quite clear that the ancestors of Native Americans came from Asia, and for people to arrive in the New World from Asia, they first have to be in far eastern Russia. Nothing in that area speaks to a human presence at >130,000. In addition, stone artifacts that are ~130,000 years old elsewhere in the world are unequivocal (e.g., those of Africa’s Middle Stone Age). The “tools” at Cerutti are completely equivocal. The investigators must account for these inconsistencies. I will leave aside commenting on the site’s geologic context; suffice to say that a fluvial deposit is less than ideal for easy interpretation of shattered bone and stone. The site, however, is significant: since it dates to a time when we can be certain there were no members of Homo in the New World it demonstrates what criteria cannot be used to establish a human presence for sites that, in terms of age (e.g., 15,000-20,000 years old), might be considered viable candidates for pushing human colonization of North America back a little farther.

  • Robert Schott

    From 200,000 to 140,000 years ago there was an ice age. The sea level was hundreds of feet lower than today. A land bridge between Alaska and Siberia was there and just as easy to have been traversed as in the last ice age that lasted between 20-27K years ago at it’s peak. I can easily see how either Homo erectus or Denisovans could have migrated over to North America during that long ice age. Both Homo erectus and Denisovans lived in Siberia and northern China at that time. It’s unlikely Homo sapiens where there and in a position to migrate using that land bridge during that time but recent finds in China have reported Homo sapiens there 120,000 years ago. Maybe they were in that part of the world even earlier and migrated into North America at that time during the tail end of the ice age.

    Given the nature of hominins to spread out everywhere I can easily accept them migrating to the Americas 200 to 140K years ago.

  • Jim O’Donnell

    This is fascinating and highly controversial. I’d love to see some regular updates on where the researchers go with this. Thanks for a great article!

  • tad_daley

    I am confused not just by the finding, but by the article.
    Because the article makes NO MENTION of what I thought was widely agreed — that NO humans left Africa at all until something like 50k-70k years ago.
    Am I wrong?
    tad daley
    @TheTadDaley

    • Robert Schott

      It is widely accepted that the first “Out of Africa” migration of Homo sapiens occurred in the 120 to 140K range. The second and larger Out of Africa wave occurred 70-60K range. Homo erectus migrated out of Africa some 1.6 million years ago and evolved into Homo heidelbergensis some 1.2 million years ago. Heidelberg man evolved into the Neanderthals and Denisovans 700 to 500K years ago (based on DNA). Denisovans lived in Siberia and the rest of Asia. In fact a lot of Asians have 4 to 6% Denisovan DNA in them while everyone (except for sub shariah Africans) have 1 to 3% Neanderthal DNA.

      The point being that there were ‘humans’ all over the old world for a long time.