Previous age estimates of the fossils of American mastodons, a distant relative of elephants that inhabited North and Central America, suggest that they lived in the Arctic and Subarctic when the area was covered by ice caps.
Scientists have puzzled over this chronology as mastodons, which looked similar to modern-day Asian elephants, are known to have had a preference for forests and wetlands filled with heaps of leafy goods. In a paper published today in the Proceedings of the National Academy of Sciences, an international team suggests that the Arctic and Subarctic were just temporary “holiday homes” for mastodons when the local climate was warm around 125,000 years ago.
When the cold weather returned, their populations moved much further to the south, where the paper suggests they ultimately died out about 10,000 years ago. The findings debunk theories about over hunting by early humans being the reason for their disappearance from this region as these new dates show they were wiped out locally before human colonisation.
Researchers from the University of Oxford and the University of California radiocarbon dated collagen from 36 fossil teeth and bones of American mastodons from Alaska and Yukon. The dates for all of the fossils were older than previously thought. Alaska and Yukon were part of an ancient region known as eastern Beringia which is thought to have connected Asia with North America at various times. When taking mastodon habitat preferences and other ecological and geological information into account, the results show that mastodons probably only lived in eastern Beringia for a relatively short time when temperatures were as warm as they are today.
Dr Fiona Brock, a researcher from the Oxford Radiocarbon Accelerator Unit at the University of Oxford, said: ‘We applied dating techniques to target the collagen, avoiding contaminants such as varnish and glues, applied several years ago to strengthen the specimens, which otherwise may make the dates “younger” than they should be. Our state of the art techniques developed at Oxford to isolate and date individual amino acids from the bones have resulted in new dating evidence that provides a big shift in our thinking. The American mastodons weren’t suddenly wiped out by the humans but moved south where their population dwindled away.’
Lead author Grant Zazula, a palaeontologist from the Yukon Government, said: ‘The residency of mastodons in the north did not last long. The return to cold, dry glacial conditions along with the advance of continental glaciers around 75,000 years ago effectively wiped out their habitats. This new evidence suggests that mastodons disappeared from Beringia, and their populations became displaced to areas much further to the south, where they ultimately suffered complete extinction about 10,000 years ago.’
Over the course of the late Pleistocene (between about 10,000 and 125,000 years ago), the American mastodon (Mammut americanum) species was widespread. They lived in many parts of continental North America, as well as the tropics of Honduras and the Arctic coast of Alaska. Scholars had presumed that the mass extinction of mastodons was the result of rapid climate change in North America or that they were over hunted. However, the new findings show they died out several tens of millennia before the onset of climate changes at the end of the Ice Age 10,000 years ago. Researchers know that giant ground sloths, American camels, and giant beavers made the migration south as well, but they are still investigating what other groups of animals might have done this.