Stranded Mammoths
Delayed Extinction

By Doug O'Harra
Anchorage Daily News
Woolly mammoths survived on St. Paul Island in the Bering Sea for thousands of years after the species went extinct on the mainland of North America and Asia, according to new research by paleontologist Dale Guthrie.
It's the first published evidence that the 11-foot-tall, 6-ton ice age icon - Alaska's official state fossil - persisted into the present Holocene geologic epoch in the Western Hemisphere.
"That they were on St. Paul isn't any big deal at all - mammoths got to be everywhere," said Guthrie, professor emeritus at the University of Alaska-Fairbanks and one of the world's leading researchers into the fate and distribution of prehistoric mammals. "What's important is that they lasted so long and they were probably undergoing a reduction in body size."
As continental ice sheets melted away, rising sea levels gradually inundated the 1,000-mile-wide steppe that once connected Alaska and Asia from Bristol Bay north to the Arctic Ocean. That stranded a population of mammoths on what became the largest Pribilof island about 13,000 years ago, Guthrie wrote in the article published in the journal Nature.
Their isolation enabled them to escape the wave of extinctions that wiped out their continental brethren about 1,500 years later. Mammoths on what is now St. Lawrence Island died out at the same time as mainland ones, partly because that area was still connected to the mainland, with its mammoths facing the same factors.
But three different radiocarbon datings of a fossil tooth, a third molar recovered in the 1960s and held in the collection at the U.S. National Museum in Washington showed that mammoths remained on St. Paul as recently as 8,000 years ago.
The animals were simply in the right grassy upland at the right geologic moment, Guthrie explained.
"This is the first case in the New World of mammoths surviving the Pleistocene, and they did it under special circumstances because they were on an island," Guthrie said in a telephone interview from his home in Fairbanks, Alaska. "It was equivalent to putting a fence around the population."
A population of "dwarf" mammoths persisted on Wrangell Island in the Chukchi Sea even longer, until about 4,000 years ago, Russian scientists reported about 10 years ago. Another population of small mammoths on the Channel Islands off Southern California died out about 11,000 years ago, about the same time as the arrival of spear-carrying big game hunters.
The very isolation that apparently protected the Pribilof mammoths from extinction finally doomed them, Guthrie added.
As sea levels continued to rise, the island gradually shrank in area, eventually becoming too small to support a healthy breeding population of creatures with the mass and appetite of elephants.
By the time St. Paul became its present size of about 36 square miles about 5,000 years ago, the mammoths had long since died out, possibly due to inbreeding.
"We know from other populations (of elephant-like animals) that only the big old boys do the breeding," Guthrie said.
Guthrie, a retired professor from UAF's Institute of Arctic Biology, made the discovery as part of an ongoing project using advanced radiocarbon dating techniques to pinpoint the ages of hundreds of prehistoric mammoths, elk, moose, antelope and horses.
The finding of relatively recent Pribilof mammoths could complicate a theory that the first human immigrants to North America came by water about 13,000 years ago rather than by land 12,000 to 11,000 years ago, Guthrie said. It raises even more questions for paleontologists and archaeologists to pursue.
"Mammoths on that earlier island complex (about 13,000 years ago) would have been easily visible in a treeless landscape when St. Paul was separated from the mainland by a narrow channel," Guthrie wrote in Nature.
"If there were coastal watercraft colonists, and they became the continent's 'super-hunters' as per the overkill theory, we might ask why did they not find and kill off mammoths on St. Paul?"
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