Mastodon teeth from the University of Alaska Museum of the North and a group of current and former UAF paleontological personnel have helped solve a question that's been puzzling scientists.
Carbon dating had previously suggested that the extinct member of the elephant clan tromped around Alaska during the height of the last Ice Age, between 10,000 and 75,000 years ago. During that period Alaska was widely covered with glaciers, but also had grassy steppes or prairies. What it didn't have much of was forest, not even the dwarf alder and willow that thrive here now.
Mammoths, a different species, were grass-munchers, as scientists deduce from their flat molars made for grinding. Mastodons, however, had pointy, cupped teeth suitable for masticating wood. So what did they live on during the peak of the Ice Age?
Nothing, as it turns out. They weren't here.
A team led by Grant Zazula of the Yukon Palaeontology Program set out to determine how to square the teeth with the carbon dating and what was known about the botanical environment of the Ice Age. The team included UAF faculty members Patrick Druckenmiller, Pam Groves and Dan Mann, former UAF graduate student Paul Matheus and BLM archaeologist Mike Kunz. They suspected that previous testing of mastodon remains had been contaminated by plants or bacteria that infiltrated the fossils long after the animals were dead, perhaps tens of thousands of years later.
The problem was how to get samples that had not been infiltrated. Tooth enamel turned out to be particularly resistant, so they went for those. Some 36 teeth were used, 15 from the UA Museum collection. They cut out pieces out with a Dremel tool, ran them through the test and found more or less what they were expecting: Mastodons passed through Alaska around 120,000 years ago, during a period between two glacial surges when woody sustenance could be found north and south of the Brooks Range.
Mastodons continued to roam the Lower 48 up until about 10,000 years ago, when 70 percent of North American mammal species abruptly disappeared. But by that point they were well quit of Alaska, where the grass-grazing mammoths continued to live.
The mastodons weren't here for long, said Druckenmiller. "Mastodons were only temporary inhabitants of what became Alaska and the Yukon during warm spells of the last ice age," he said.
It was the climate, not human hunters, that made the Arctic inhospitable for them. Mastodons would have died out in Alaska long before the first people entered North America via the Bering land bridge.
The study was published in the Dec. 1, 2014, online edition of the Proceedings of the National Academy of Sciences.