During the last ice age -- some 100,000 to 15,000 years ago -- mammoths were widespread in the northern hemisphere from Spain to Alaska. As the climate warmed, their habitat in Northern Siberia and Alaska shrank. On Wrangel Island, some mammoths were cut off from the mainland by rising sea levels. The Wrangle Island population survived until 4,000 years ago.
The team of researchers from Finland, Germany and Russia examined mammoth bones and teeth from Northern Siberia, Alaska, the Yukon, and Wrangel Island, ranging from 40,000 to 4,000 years in age. They documented changes in the diet of the mammoths and disturbances in their environment. The results showed that Wrangel Island mammoths' bone isotopic compositions remained unchanged until the mammoths disappeared, seemingly from the midst of stable, favorable living conditions.
This result contrasts with the findings on woolly mammoths from the Ukrainian-Russian plains, which died out 15,000 years ago, and on the mammoths of St. Paul Island in Alaska, who disappeared 5,600 years ago. In both cases, the last representatives of these populations showed significant changes in their bone's isotopic compositions, indicating changes in their environment shortly before they became locally extinct.
The researchers found an intriguing difference between the Wrangel Island mammoths and their ice age Siberian predecessors: a difference in the fats and carbohydrates in the populations' diets. "We think this reflects the tendency of Siberian mammoths to rely on their reserves of fat to survive through the extremely harsh ice age winters, while Wrangel mammoths, living in milder conditions, simply didn't need to," says Dr. Laura Arppe from the Finnish Museum of Natural History Luomus, University of Helsinki. The bones also contained levels of sulfur and strontium that suggested the weathering of bedrock intensified toward the end of the mammoth population's existence. This may have affected the quality of the mammoths' drinking water.
Why did the last woolly mammoths disappear so suddenly? The researchers suspect that they died out due to short-term events. Extreme weather such as a rain-on-snow, i.e. an icing event could have covered the ground in a thick layer of ice, preventing the animals from finding enough food. That could have led to a dramatic population decline and eventually to extinction. The population, perhaps already weakened by genetic deterioration and drinking water quality issues could have succumbed after something like an extreme weather event.
Another possible factor could have been the spread of humans. The earliest archaeological evidence of humans on Wrangel Island dates to just a few hundred years after the most recent mammoth bone. The chance of finding evidence that humans hunted Wrangel Island mammoths is very small. Yet a human contribution to the extinction cannot be ruled out.