Each continent suffered a unique extinction that fit the global pattern. Australia lost more than 60 species: wombats the size of compact cars; hyper-carnivorous koala cousins; huge, flightless duck-like birds called mihirungs; and other oddities. But as paleontologists and archaeologists have reviewed the evidence, the timing has slipped. By the time humans arrived in Australia more than 40,000 years ago, only 13 species of megafauna may have still existed, and they persisted alongside humans for at least 15,000 years. Their extinction was not instantaneous but prolonged. Humans may have hunted the animals and used fire to alter the landscape, and humans and climate change are still the top contenders for extinction triggers in Australia (and elsewhere). But paleontologists face persistent problems connecting events we know must have happened with mechanisms that killed populations, species, and genera.
The extinction peaked a little later in Eurasia and the Americas. Many of the most charismatic megafauna were gone by about 10,000 years ago. (Africa lost some lineages of large mammals during the 2-million-year span of the Pleistocene, but in general, the continent is as a haven for large mammals.) Still, as the Wrangel Island mammoths demonstrate, some species persisted in small numbers for a few thousand years more.
Unlocking the secrets of the extinction requires reliable dates. We need to know when humans first arrived and when a species made its last appearance. The quirks of the fossil record are unlikely to record the very first steps of a person in virgin habitat, nor is the record so complete that we can ever be sure that we have the very last member of a species, but bones and archaeological sites at least narrow down the timeline. South America is a prime example of this ongoing quest.
South America lost more genera during the Pleistocene extinction than any other continent: 52 genera in total, or 83 percent of its animals that weighed more than 44 kilograms, including horses, sabercats, giant ground sloths, armored glyptodonts, mastodons, and more. After reviewing the existing reliable radiocarbon dates, paleontologists Anthony Barnosky and Emily Lindsey found that some extinct animals survived for more than 6,000 years after humans arrived at South America and 1,000 years after climate fluctuations. The pattern doesn’t fit a scenario of blitzkrieg carnage or an inability to adapt to the quick switch between a last cold snap and rapid warming.
The controversy about what killed off so many species will undoubtedly continue, especially since the reason giant wombats disappeared is probably not the same reason there are no more flightless terror birds or woolly rhinos. And widespread species might have faced different threats on different continents. There are more sites with butchered mammoths in North America than in Eurasia, for example. Could it be that humans hankering for mammoth steak were more responsible for the demise of the shaggy elephant in North America, but the loss of mammoth steppe habitats helped eliminate the species from Eurasia? Understanding how the two major pressures interacted may explain the biodiversity crisis that now looms.
Our species still hunts elephants, rhinos, tigers, and other large animals. Now these animals are gunned down for body parts sold on the black market rather than for food. People still kill these Pleistocene remnants, even as others among us try to protect the animals (a kind of inter-species benevolence never seen before in the history of life on Earth). But even with our best intentions, we are altering the planet on a scale and with a speed that stretch the imagination. Climate change at the end of the Pleistocene was a natural process that had been cycling back and forth for the previous 2 million years. Now we, not natural geological cycles, drive the climate, and the planet is abruptly on its way to a greenhouse world that hasn’t been seen in 55 million years. We have already seen what happens when hunting and climate change create a deadly synergy. The question is, how long are we going to ignore this lesson, passed down to us in bone by long-lost mammoths and other vanished species?