Mastodons long gone from the north
They differ from woolly mammoths which hung around much longer
George Rinaldino Teichmann graphic
A mastodon, compared beneath to a woolly mammoth.
A long, long time ago, a hairy elephant stomped the northland, wrecking trees and shrubs as it fed of twigs, leaves and bark. These mastodons left a few scattered teeth and bones in Alaska and the Yukon, reminders of an animal that lived as far south as Honduras. A recent look at those far-north mastodons shows the creatures vanished from the Arctic thousands of years before earlier than researchers had thought.
A re-try at carbon dating northern mastodon fossils proved that they were much older than initial tests suggested. This confirmed the doubts of Grant Zazula and others who study vanished landscapes of the north. Zazula is with the Yukon Palaeontology Program in Whitehorse. Co-authors on the paper are Alaskans Patrick Druckenmiller, Pam Groves, Dan Mann and Michael Kunz.
Zazula got excited about digging in about what he thought were way-too-recent dates on mastodon bones when Earl Bennett of Whitehorse in 2008 donated a partial mastodon skeleton. Miners had found it in the early 1970s when a gold dredge ran into it on a Yukon creek.
Zazula doubted earlier reported dates on mastodon teeth found in a northern Alaska river and in northern Yukon that suggested the creatures must have been roaming when no forest existed in the far north. That did not mesh with what researchers think the mastodon was. Mastodons had pointy teeth that belonged in a wood chipper. Skeletons of mastodons found farther south showed twigs, cones, and leaves in stomachs and manure.
Because they believe mastodons were forest creatures, researchers re-dated the mastodon fossils using newer techniques of radiocarbon dating and found they were all more than 50,000 years old. That means mastodons probably lived in northern Alaska and Yukon during a brief time when temperatures were as warm as they are today. Mastodons endured farther south until about 10,000 years ago. Researchers know this from bones found in the Midwest and near Puget Sound.
Mastodons differ from woolly mammoths - which hung around much longer in Alaska and Yukon - in their appearance and what they ate. Mastodons looked like elephants with fur coats. Their tusks were straighter than mammoths and their ears were smaller. Mastodons had conical teeth used to strip and crush twigs, leaves and stems of shrubs and trees. Mammoths had flat teeth. Mammoths grazed on grasses and forbs that were a feature of northern Alaska and Yukon during the colder parts of the ice ages.
Researchers think mastodons crossed the land bridge from Asia millions of years ago, while wooly mammoths showed up in North America after about 150,000 years ago. Mammoth bones and tusks are much more common on the Alaska landscape today.
At the return of the last ice age, when glaciers began covering North America around 75,000 years ago, colder temperatures pushed the boreal forest and muskeg southward. Mastodons moved south with the forest and ended up south of the ice sheets. According to the fossils left behind, Jefferson's ground sloths and giant beavers went with them.
Photo courtesy Dan Mann
Pam Groves holds a mastodon tooth in her right hand, a mammoth tooth in her left. Both were in a river on Alaska's North Slope.
Researchers at the University of Oxford and the University of California radiocarbon dated 36 fossil teeth and bones for the new mastodon study. They tested the protein collagen within the samples, avoiding varnish and glues applied by museum workers that may have contaminated the results before.
A mystery regarding mastodons: After the last ice age, the boreal forest reestablished itself in a corridor through Canada and back to the far north. Mastodons could have followed the food pathway back up to Alaska and the Yukon. But for some reason, they never did. For millions of years the hulking beasts followed their sweet trees and shrubs across North America as ice sheets grew and melted. What was different about the last big melt that killed off the mastodons for good?
(Since the late 1970s, the director of the Geophysical Institute at the University of Alaska Fairbanks has supported the writing and free distribution of this column to news media outlets. This is Ned Rozell's 20th year as a science writer for the Geophysical Institute.)