And then there were none.

Lonesome George, known worldwide as the sole surviving Pinta Island tortoise, died Sunday at the Charles Darwin Research Station in the Galapagos. He was believed to be about 100 years old.

He may have been Earth’s rarest creature, but Lonesome George’s fate has been a common one for megafauna ever since humans came along.

The Americas were once a surreal dreamscape of giant mammals, from short-faced bears the size of Ford Explorers to monstrous dire wolves to giant sloths larger than elephants. They all suddenly disappeared around 10,000 B.C., not long after the first people are believed to have made their way down from the Bering land bridge.

Some paleobiologists blame the die-off on climate change, since it also coincided with the end of the last Ice Age. But extinctions have continued at a rapid clip throughout the ensuing Holocene Epoch, in which humans have come to dominate the globe. This has led to fears that we’re in the midst of a Sixth Great Extinction. (The fifth was 65 million years ago and involved dinosaurs.)

Megafauna are a tiny fraction of the thousands of species that vanish each year, but that’s because there weren’t that many of them to begin with. Of those that remain, many are hanging on in tiny numbers.

Lonesome George, who outlived his last relatives by decades, was an extreme example. His kin were apparently done in by feral goats, which demolished the local vegetation after humans introduced them to the island.

When Galapagos National Park officials first spotted Lonesome George in 1971, they were overjoyed — they had thought his group extinct. They tried for decades to entice him to mate with female tortoises from neighboring islands, but without success.

While conservation efforts can sometimes help endangered species rebound, Lonesome George’s case is a reminder that there are limits to what can be accomplished once a population dwindles to critical levels.