University of Alberta researchers are part of an international team that has used DNA samples from frozen dirt, not fossilized bones, to revise the history of North America's woolly mammoths and ancient horses.
The work of U of A Earth and Atmospheric Sciences professor Duane Froese and his colleagues counters an important extinction theory, based on radiocarbon dating of bones and teeth. That analysis concluded that more than half of the large mammals in North America (the 'megafauna') disappeared about 13,000 years ago.
In the new research, DNA samples recovered from Alaskan permafrost showed that woolly mammoths and ancient horses were still roaming through central Alaska about 10,000 years ago, and possibly as recently as 7600 years ago. That predates the established record from fossil bones and teeth by at least 3,000 years.
The DNA samples were recovered from permafrost near the central Alaskan community of Stevens Village, on the banks of the Yukon River. Analysis of the samples from soils that formed between 10,000 and 7600 years ago showed the presence of mammoth and horse DNA together with animals typically found in the region today, such as moose and arctic hare.
The challenge of dating extinction events is finding fossilized remains from the last animal left standing of any given species. The chances of finding those exact bones are remote. But animals are constantly leaving behind tell-tale samples of DNA in the form of skin cells and feces in the environment. That's what Froese and the other researchers found in the permafrost, at a depth and time line that radically changes the extinction date for two members of North America's megafauna in the late Pleistocene.
Froese, and U of A graduate students Simon Robinson and Alberto Reyes, are co-authors of research that will be published Dec. 14 in Proceedings of the National Academy of Sciences.
Journal
Proceedings of the National Academy of Sciences