The final days of an isolated population of Alaskan woolly mammoths have been lonely and thirsty.
As the dawn of human civilization began to rise some 5,500 years ago, these island-dwelling woolly mammoths were surviving on a remote piece of land that was once part of the Bering Strait.
The isolated woolly mammoths had been the second-to-the-last known population in the world, living on a tiny Alaskan island thousands of years after their cousins and relatives have gone extinct.
However, they also did not survive.
Now, a new study reveals what might have pushed the prehistoric animals to extinction. Researchers point to rising sea levels and lack of access to freshwater as the culprit.
The Perils That Woolly Mammoths Faced
To begin investigations, a team of scientists analyzed layers of a dated sediment core unearthed from a lake on St. Paul Island. This helped them estimate that the woolly mammoths went extinct approximately 5,600 years ago.
The Bering Sea Island, where the mammoths once lived, had a phase of dry conditions and declining water quality at about the same time the prehistoric animals vanished, researchers said.
According to Matthew Wooller, the study's co-author and a director of the Alaska Stable Isotope Facility, the woolly mammoths had been trapped on the island when sea levels began to rise and flooded the Bering Sea land bridge.
The isolated woolly mammoths on the island survived 5,000 years longer than mainland populations, but it was the lack of freshwater on the island that doomed them.
In 2013, a group of experts gathered a sediment core from the bed of a freshwater lake on St. Paul Island.
Wooller and colleagues then measured the stable oxygen isotope ratios of the remains of aquatic insects that were preserved in the sediment. The preservation had happened before, during and after the mammoths' extinction.
Because the fossils of aquatic insects still retain water isotope signatures in their bodies, researchers studied the organisms' exoskeletons and found that the lake levels had decreased.
Scientists also discovered that the remains of the aquatic insects from the core changed over time. This suggests that lake levels and water quality were diminishing up to the extinction of the woolly mammoths.
Furthermore, a nitrogen isotope analyses of mammoth teeth and bones revealed significantly drier conditions up until the extinction event.
Authors of the study said these lines of evidence of plummeting lake levels offer a strong case for what truly pushed the animals to extinction.
"It paints a dire picture of the situation for these mammoths," said Wooller.
Why The Findings Are Important
The new report not only revealed how Alaskan woolly mammoths went extinct, but it also exhibited the vulnerability of small island populations to climate change.
In fact, St. Paul Island slowly shrank to 110 square kilometers (42.47 square miles) as sea levels began to rise, reducing the chances that mammoths could transfer to a new area with freshwater.
Conditions on the island also changed for 2,000 years before the mammoth extinction. Wooller said that modern climate change could progress more rapidly, making the story of the St. Paul Island relevant today.
Details of the new study are published in the journal Proceedings of the National Academy of Sciences.