In late 2017, news stories announced a discovery that could rewrite the orthodox history of the settling of the Americas by humans: mastodon fossils found during a road excavation project that were in a layer that was 130,000 years old…but appeared to have been manipulated by human hands.
The problem: humans aren’t supposed to have populated the Americas until more than 100,000 years later.
At the core of the discovery were – among the mastodon ribs, vertebrae and molars – multiple cobble stones that might have been used as tools, and femur bones including two femur heads, “detached from their shafts and nearly touching, one hemisphere facing up, the other facing down”.
The team wondered how this could be. Mastodon femurs — those pier pilings — are almost 3 feet long and up to 8 inches in diameter. What could have detached these heads from their shafts and positioned them side by side? Next to them was a large boulder that somehow seemed implicated.
They tried not to speculate but kept returning to the possibility that humans might have been here, might have broken these bones and walked away. That meant the evidence they left behind — all this debris — was almost the same age as the sediments that eventually buried the site.
Analysis of the broken femur bones appeared to show spiral fractures, which only occur when the bone is young and not dried out, leading researchers to hypothesize that the bones were fractured by human hands using the stones as tools.
But what of the anomalous dating of the site? “If you claim something is that old, you get blasted,” one of the researchers said, “which is why some archaeologists stopped working on sites like this. They didn’t want to get blasted.”
However, a newly-released paper is now suggesting that the construction work on the freeway being built at the time of the discovery “was responsible for the damage” to the bones and the accumulation of cobblestones:
[A]t the time of discovery, paleontological site monitors observed the excavator raking up bone and tooth fragments at the east end of the CM site. Such action, unobserved, may have drawn cobbles into the CM site prior to its discovery. The track of the dump trucks over the CM site has been calculated, and it crosses the two concentrations of broken femur bones, each centered on a large cobble. The cobbles seem to have concentrated pressure from the heavy trucks onto the bones, crushing them into more than 300 fragments. This is far more damage than is necessary either to harvest marrow, or to obtain material for tool manufacture.
That is not to say that this is the definitive explanation. The author of the paper notes that there are ‘outliers’ in the discovery that go against their hypothesis (although they do also offer possible explanations), and that their own reconstruction of the possible causes are “in some sense circumstantial”. Nevertheless, they do feel that their investigation, “based on construction plans, common construction practices, contemporary photographs, and direct observations…offers a viable alternative explanation for the damage found.”
It’s worth noting also though that when news of the discovery first broke, reports explicitly mentioned that paleontologists, concerned by the dating, had “tried to find an alternative theory” – including the construction equipment theory – but felt they were lacking.
Could these bones have been broken by construction equipment or by other animals? Perhaps another mastodon? If so, then why were more fragile bones, like ribs, still intact?
Could a mudflow have swept in the large cobblestones? Maybe, but wouldn’t a mudflow have also swept away, even destroyed the smaller skeletons of birds and lizards they’d also found at the site?
And what about the cobblestones? There were five of them, ranging from 9 to 30 pounds, caught in this sedimentary layer of fine-grained sand. Why weren’t there more?
For that matter, why hadn’t they found more of the mastodon’s skeleton, especially the large pieces like the skull, the pelvis, the scapulas?
So it will be interesting to see where the discussion and debate over this find goes from here – I’m sure there will be plenty!