Friday, November 20, 2009

Megafauna, Fungus, and the First North Americans

Very interesting study published today in Science by Jacquelyn Gill et al. They studied lake bottom sediments from Indiana and New York, looking for spores of the fungus Sporormiella. Sporormiella grows in animal dung, especially big piles, so its presence is a marker of the presence of large herbivores like elephants. They were trying to find out when the "megafauna" of North America went extinct, that is, mammoths, mastodons, giant ground sloths, giant beavers (the size of black bears) and the like.

Their conclusion is that those animals began to decline in numbers around 14,800 years ago, more than a thousand years before the appearance of the Clovis hunters who are the first certain human occupants of North America. The final extinction of the megafauna happened around 13,300 to 12,900 years ago, during the Clovis culture. These dates rule out the supposed comet impact of 12,900 years ago as the cause of the extinction, as well as the rapid climate fluctuations of the centuries around that time.

The interpretation offered is that humans were present in the Americas by 14,800 years ago, and that the Clovis big game hunters with their huge spear points represent an adaptation to the decline of large animals, that is, once the animals became rare, it was necessary to develop more sophisticated technology and a more focused adaptation to hunt them.

This is a fascinating piece of data, but it seems a lot to hang on one well-studied Indiana lake and a few other samples. Their argument only holds if the pattern is the same across diverse North American environments. But we already have data on Sporormiella frequencies in several western lakes, and they show a different pattern, with a dramatic decline around 12, 900 years ago. From what I can tell, that western data is not as precisely dated as the new material, but it certainly suggests that the picture for North America as a whole is different from the picture in Angel Lake. So I will file this under "important if confirmed."

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