An analysis of the bones of a boy who died in what is now Montana 12,800 years ago shows that nearly half of his diet came from mammoth meat.
鈥淭o have it turn out to be 40 per cent, it鈥檚 just like, wow!鈥� says at McMaster University in Canada. In fact, when compared with other animals alive at this time, the boy鈥檚 diet was more similar to that of the carnivorous scimitar-toothed cat than that of the omnivorous short-faced bear, he says.
Artefacts such as stone tools show that around 15,000 years ago, as the ice retreated after the last glacial maximum, people from Asia crossed the land bridge that existed across the Bering Strait and moved into North America. These people, known as the Clovis culture, developed distinctive stone tools characterised by large, finely made stone points.
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While Clovis tools have been discovered at many sites, only one set of human bones has been found alongside them. These bones, now reburied, are of an 18-month-old boy known as Anzick-1. His genome shows that the Clovis people are probably the .
It has been long been clear that the Clovis hunted mammoths and other megafauna, but there is an ongoing debate about how much they relied on them. Some think the Clovis people were generalist hunter-gatherers who only occasionally hunted large animals. Others think they specialised in killing megafauna and that is what their stone tools were designed for.
To try to answer this question, Chatters and his colleagues looked at the ratios of certain oxygen and nitrogen isotopes听in the bone collagen of Anzick-1, then compared them with those of various other听animals from the same time.
Different types of plants have different ratios of these isotopes. This, along with their differing digestive systems, affects the ratios in the tissues of the herbivores that eat them. The result is that each herbivore has a distinctive isotopic 鈥渇ingerprint鈥�.
The isotopic fingerprints of predators, in turn, reflect those of the herbivores they eat. Anzick-1鈥檚 isotopic fingerprint is between that of mammoths, bison and elk, the team found, with a statistical analysis providing the 40 per cent mammoth estimate.
Because Anzick-1 was so young, this mostly reflects his mother鈥檚 diet. The team鈥檚 calculations assume that two-thirds of his diet up to his death was milk from his mother, based on weaning ages in modern hunter-gatherers, says Chatters.
鈥淚f he had been eating more solid food, the mammoth signal would be even stronger,鈥� he says. 鈥淲hat we can say definitively is that this one group was living heavily on mammoth.鈥�
鈥淚t definitely supports the specialist hypothesis, but it is only one individual from one part of North America,鈥� says at the University of Wyoming.
But if one individual is randomly picked from a population, they are more likely to reflect the norm than the extremes, says Chatters. 鈥淚t鈥檚 simple probability.鈥� When put together with all the other evidence pointing to the Clovis being specialist hunters, he thinks the case is very strong.
鈥淭his study provides strong evidence of large animals being a major part of the diet,鈥� says at Ohio University. 鈥淲ith this being said, I think the debate may still continue.鈥� Some may question the isotopic evidence, he says, and the poor preservation of most Clovis sites also leaves room for argument.
Chatters says the findings also support the case that hunting by the Clovis led to the extinction of many large animals. 鈥淲e鈥檙e the ultimate invasive species,鈥� he says. 鈥淢any tens of species went extinct, almost all of them megafauna.鈥�
Many of these species, including types of horses, camels and giant ground sloths, had survived ice sheets advancing and retreating across the continent on several occasions before, says Chatters, meaning climate change alone is unlikely to have wiped them out.
鈥淚 think the evidence they present is consistent with Clovis contributing to the end-Pleistocene extinction of mammoths, but does not answer the question as to the cause of the larger extinction event that included over 35 genera of animals,鈥� says at the University of South Carolina.
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