Two modified osteoderms from a Pleistocene layer

Vialou et al’s Peopling South America’s centre: the late Pleistocene site of Santa Elina, should really be titled Two modified osteoderms from a Pleistocene layer. The authors claim evidence of occupation of central South America going back almost 24 000 years, which would push back settlement by at the very least 10 000 years.

There is now a well-established local tradition of claims of archaeological occupations 50 000 years or older in central and eastern South America. Boëda et al presented the case in some detail last year. Borrero provides a friendly and constructive critique, while Fiedel gives us a more spirited attack.

The story of Santa Elina is mostly familiar for those interested in the early occupation of the Americas: A well excavated, well dated site, with undisputable archaeological remains in the Holocene layers (increasingly indisputable as we near the present surface), coupled with extremely ambiguous “stone tools”, bones other than human, and a complete absence of structures or any other archaeological remains in the Pleistocene layers going back 50 000 years or more. There is the inevitable, entertainingly imaginative speculation about how such a location could have possibly been occupied by humans at such an early date. The Cerutti Mastodon find has now become the type site for this kind of claim. This particular story has a twist, however: the presence of those two apparently perforated osteoderms.

Unit I, dated to the second half of the Holocene (after 6000 years ago) no doubt has a very interesting archaeological site with well-structured hearths and very informative stone tools. Unfortunately it is not presented or analyzed at all in the paper. Unit II, which dates between about 7000 and 15 000 years ago also shows some fireplaces. The oldest date on charcoal is 12 0007 – 11 404 CalBP (95% confidence), which is not suprising, as that is already an early date for the Americas.

Units III and IV, however, which are dated to the Pleistocene, are much more problematic, and as Borrero might charitably say, ambiguous. The dates, which range from about 25 000 and 28 000 BP, are on wood, micro-charcoal, quartz and bone. The claimed stone tools in these layers are much less than encouraging, and really not that different from other eoliths that figure prominently in these kinds of claimed sites. There are no other signs of human occupation than those stone flakes.

Except for the osteoderms. Two of the thousands of Glossotherium (a ground sloth) osteoderms, apparently found in a concentration of 49 “probably deposited intentionally” show signs of modification by perforation. The paper is unclear about why they seem to be deposited intentionally. They do look drilled through. The paper presents experimentally drilled through osteoderms for comparison, although there is no account of the methods used for the experiments. The holes are small, on the order of 3mm in diameter as far as I can judge from the material provided, and the potential artefacts are interpreted as ornaments.

I must say these are the most convincing pre-15 000 artefacts from a solid context that I have seen from the Americas. It would be worth doing more robust and well reported perforation experiments on osteoderms. For example, do punched holes erode to over time to look like drill holes? More work also needs to be done on the objects themselves. We are not told whether any use-wear analysis was done on the edges of the holes, for example.

The bottom line is that we have a fairly elaborate article, built on a lot of speculation which, despite the approach the authors take, rests in the final analysis on those two objects and nothing else. But the objects are real. As far as I can tell, they have to be of the claimed age, and they are better candidates for actual, honest-to-goodness archaeological artefactual status than your average broken piece of limestone.

While this particular site is still quite flimsy as a reason to start imagining mid-glacial scenarios for the occupation of the Americas, it is certainly reason enough to keep examining those two objects, and to keep looking for more sites like Santa Elina.