Credit: Wikimedia Commons

Most of the world’s wooly mammoths were killed around 10,500 years ago, the prime causes still up for debate — human hunting, climate change or both have been time and time again identified by scientists as prime suspects. But on a small island off the coast of Alaska, an isolated population of wooly mammoths lingered on for thousands of years. They too died around 5,600 years, and with them their entire species went extinct. Now, a group of researchers has showcased a convincing body of evidence that suggests rapid warming of the island left the massive mammals without a water supply.

The sad last chapter in the story of a megafauna species

Wooly mammoth populations survived on several small Beringian islands for thousands of years after mainland populations went extinct, isolated by rising sea levels which cut off connections with continental North America or Asia.The scientists led by Prof Russell Graham, from Pennsylvania State University, wanted to know what eventually brought the ultimate demise of a particular mammoth population — that belonging to St. Paul Island.

To this end, the team performed radiocarbon dating and DNA analysis on the remains of the youngest mammoth they could find, as well. Additionally, cylindrical sedimentary samples were drilled in the vicinity of a nearby lake, close to where the mammoth remains were found. These samples act like a sort of time capsules trapping pollen, insects, plants, offering hints of how the environment and biosphere must have looked like on St. Paul up to 10,000 years ago.

How the mammoths survived on this tiny island, which is roughly the size of Paris, France, is somewhat of a mystery. This latest investigation, however, at least tells us what made the last drop. First of all, it wasn’t humans — the first settlers arrived on the island in 1787 or almost eight thousand years after the last mammoth died. It wasn’t predators, overcrowding or volcanoes either. The likely killer was thirst, the researchers conclude, brought about by sudden climate change.

As far as freshwater goes on St. Paul, about 6,000 years ago the only sources mammoths could use were shallow lakes, and as the climate dried these became even smaller, shallower and even saltier. That was still enough for smaller mammals, like rodents, but not for a mammoth which would have required some 200 liters of water per day. To make things even worse, as the mammoths crowded about the shallow lakes, they would have trampled the vegetation around the lake. In time, this caused the underlying soil to erode and eventually collapse making the lakes even smaller, the team reported in Proceedings of the National Academy of Sciences.  This was a time bomb waiting to blow, and it did eventually — with fatal consequences for a whole mammoth population, perhaps the last of its species.

“It wouldn’t have taken long if the water hole had dried up,” Graham said. “If it had only dried up for a month, it could have been fatal.”

This extinction might seem like something from the distant past, but when you look at the timeline that’s around the first Mesopotamian cities started to flourish, or Egyptians started to mummify their dead. This was the dawn of human civilization as we know it.

“The Saint Paul mammoth story is also important in a different way, because it reminds us that the age of mammoths is also the age of modern humans,” Jacquelyn Gill from the University of Maine told The Atlantic. The last mammoths on Saint Paul and the nearby Wrangel Island were “just as modern as writing, the wheel, and celestial navigation. That’s a blink of an eye for the ecosystems that lost mammoths and other mega-beasts, and the consequence of those losses are still playing out today.”