Climate change played a pivotal role in the extinction of mastodons in North America, new radiocarbon dating of fossils has revealed — though hunting by people may have been the last straw.
Mastodons are the relatives of modern elephants and were widespread across North America from 1,25,000 years ago, going extinct around 10,000 years ago. Their disappearance coincides with the arrival of early humans on the continent, and has led to the “overkill” hypothesis that they were hunted to extinction by our species.
The new results, which are published in Proceedings of the National Academy of Sciences , suggest a more nuanced sequence of events.
Grant Zazula, a palaeontologist with the Yukon Palaeontology Program, and his colleagues have dated the collection of 36 fossil teeth and bones, found in Alaska and Yukon. They used a technique that targets the collagen in bone, avoiding contaminants such as varnish and glue that were applied many years ago to strengthen the specimens.
All of the fossils were found to be older than previously thought, with most older than the 50,000-year limit of radiocarbon dating.
The team concluded that mastodons were probably only living in the Arctic and Subarctic for a short time around 1,25,000 years ago. This was an interglacial period in which Arctic regions of North America were covered in forests and wetlands.
“The residency of mastodons in the north did not last long,” said Mr. Zazula, “The return to cold, dry glacial conditions along with the advance of continental glaciers around 75,000 years ago effectively wiped out their habitats.” The depleted population of mastodons moved south to escape the advancing ice.
They were just one of dozens of large mammalian species that went extinct around 10,000 years ago. Together they are known as the megafauna and include sabretoothed tigers and giant sloths.
Adrian Lister, research leader in palaeobiology at the Natural History Museum, London, says, “This is a very nice finding. Radiocarbon dating is the best technique we have for this. It seems perfectly reasonable that climate change knocked these populations down in number and to different regions.” From this weakened position, the mastodons had little reserve to resist meat-hungry humans.
“We’re not saying that humans were uninvolved in the megafauna’s last stand 10,000 years ago, but by that time — whatever the mastodon population was down to — their range had shrunken mostly to the Great Lakes region,” said Ross MacPhee, a curator in the Department of Mammalogy at the American Museum of Natural History and a co-author on the paper.— © Guardian Newspapers Limited, 2014
