Did Your Ancestor Eat the Last Woolly Rhino?

Which species will adapt to climate change—and which ones won’t.
Feb. 28 2013 5:13 PM

Did We Doom the Mammoths?

The end times of saber-toothed cats, giant wombats, and carnivorous koalas.

An artist's rendering of an Ice Age mammoth skeleton on display at the Page Museum at the La Brea Tar Pits in Los Angeles
An artist's rendering of an Ice Age mammoth skeleton on display at the Page Museum at the La Brea Tar Pits in Los Angeles

Courtesy of the Page Museum/La Brea Tar Pits/Reuters

Climate change killed the last mammoths. Hunkered down on their final holdout, Siberia’s Wrangel Island, the shaggy herbivores died out as rising seas shrank their refuge and warm weather baked their cool grasslands. By 3,700 years ago, within the span of written human history, mammoths disappeared.

But the real reason there are no more mammoths—and cloning projects aside, the reason we’ll never get to hug an adorable baby mammoth at a petting zoo—is a hotly contested topic. Mammoths wound up hopelessly marooned on a Siberian island in the first place because they were wiped across the rest of their range—an impressively disheartening fact when you realize that the behemoths once trod the widespread “mammoth steppe” grasslands from western Spain through northern Asia to the interior of North America. Explanations for their disappearance have historically involved climate change, “hyperdisease,” comet impact, and hungry humans. Figuring out what happened to mammoths and other lost species is not just an exercise for academic keepers of the dead. If we can understand the mechanics of extinction and how life responds to fluxes like climate change, we might be able to use the dead to look to the future.

Just as non-avian dinosaurs were only part of a major mass extinction 66 million years ago, mammoths are but one icon of a deeper loss of biodiversity. The Pleistocene extinction saw the death of much of the world’s most spectacular megafauna (creatures that weighed more than 44 kilograms, or 97 pounds) from Australia, Asia, Europe, and the Americas. Mammoths, giant ground sloths, sabercats, and terror birds were among the losses. Some species that survived the die-off were swept from parts of their ranges; there are no more spotted hyenas in Europe, for example.

This global disaster did not occur all at once. There is a pattern in the geological record of extinction, one that seems to follow the path of wandering humans.

Mass extinctions are murder mysteries. In the case of the Pleistocene extinction, two culprits are likely intertwined: humans and climate change. Other suspects don’t hold up. The kind of indiscriminate hyperdisease that would kill smilodons (in the cat family), dire wolves (dog family), woolly mammoths (elephant family), and all the other lost forms wildlife is totally unknown. The proposal that North America’s extinction pulse was caused by a falling comet lacks solid support.  

From Australia to North America, large mammals and assorted other creatures often disappeared shortly after the arrival of humans on their continent, whether it was 50,000 years ago or 10,000 years ago. We know that humans hunted at least some of the lost mammals. Butchered bones found at archaeological sites include the remains of mammoths and mastodons. At the same time, the world was going through its last oscillation from an Ice Age world to the one we know today. The cool, dry global climate gave way to a warmer, wetter one. Pleistocene creatures had to move with their favored environments, adapt to their new surroundings, or go extinct. What paleontologists continue to tussle over is how important humans and climate change were to the Pleistocene crisis.

From the perspective of Deep Time, the Pleistocene extinctions happened extremely rapidly. If we were able to travel 66 million years into the future and look back at the Pleistocene fossil record, the event might appear to be instantaneous. Since we’re so close to the massive bleed of species, though, we can pick through the evidence with more resolution.

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?

Brian Switek is the author of My Beloved Brontosaurus and Written in Stone. He blogs at Laelaps on National Geographic's Phenomena.