Thread by @BiIndia

A new study reveals how the last woolly mammoths died out 4,000 years ago. That's after the Egyptians had built the pyramids.

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About 4,000 years ago on a remote island in the Arctic, the last woolly mammoth died out. Elephantine in shape and size, mammoths dominated northern hemisphere during Earth's last ice age for nearly 90,000 years,before changing climates and human hunting drove them to extinction

Scientists have uncovered mammoth skeletons and frozen carcasses everywhere from Spain to Siberia, and the understanding was that these creatures had wholly disappeared by about 11,000 years ago.

But a handful of mammoth populations survived on two tiny, isolated islands nestled between Russia and Alaska that were cut-off from the mainland by rising seas.

Researchers think one of these refuges, name Wrangel Island, became the last mammoth hold-out; these tusked giants outlived their North American and European counterparts by some 7,000 years before going abruptly extinct.

That means mammoths as a species lasted far longer than scientists previously thought. When the last woolly mammoth kicked the bucket, the Great Pyramid of Giza had already been built in Egypt.

According to a new study, published in the journal Quaternary Science Reviews, the Wrangel Island inhabitants didn't die of the same causes as other mammoths. Rather, the study authors argue, the isolated animals started to inbreed, which weakened their genetic diversity.

The weakened population was then unable to adapt to extreme weather events, which likely caused their sudden, untimely demise.

A mysterious, 'fairly abrupt' extinction

Wrangel Island is about 86 miles northeast of Chukotka, Siberia, a 3,000 square-mile chunk of land in the Chuckchi Sea that broke off from Asia about 10,000 years ago.

The population of mammoths that went along for the ride were seemingly spared the global extinction of their species, until about 4,000 years ago when they all disappeared.

Radiocarbon dating of skeletons from Wrangel Island showed that the mammoth population's extinction was "fairly abrupt" without any warning signs, according to the study authors. But the reason behind this sudden die-off wasn't clear.

Looking for clues inside mammoth bones

So the researchers behind the new study decided to look for the same telltale clues in the Wrangel mammoth bones to discern whether their island population had met the same fate.

They analyzed the collagen in 4,000-year-old mammoth bones and teeth from the island, and compared those results to bones from mammoths that had died in other parts of the world like Alaska and Siberia as old as 40,000 years ago.

The scientists were looking for drops in the levels of carbon, nitrogen, and sulfur isotopes in the bones - which would indicate changes in the mammoths' diets due to environmental changes.

Their results showed that the compositions of the Wrangel Island fossils, unlike those of their mainland counterparts, had not changed as the climate warmed 10,000 years ago when the ice age ended and almost all the other mammoths worldwide went extinct.

So if a changing environment didn't kill them, what did?

Given that it seemed unlikely the Wrangel Island mammoths died of thirst or climate change, the researchers sussed out other possible reasons behind the extinction.

It was unlikely that human hunting contributed to the sudden die-off, the authors wrote, because there's only a single site of human occupation on Wrangel Island, and archaeological evidence show the campsite was used for hunting marine mammals and geese.

A previous genetic analysis of some of the Wrangel Island mammoths revealed that the creatures were interbreeding, which caused a severe loss in genetic diversity.

Another 2017 study revealed that the island population had shrunk 43-fold compared to previous mainland mammoth population sizes by the time it went extinct.

The researcher also showed the mammoths had accumulated "detrimental" genetic mutations that diminished the population's ability to survive disease outbreaks, famines, or natural disasters that could cull large numbers at once.