Friday, Aug 29, 2008
Ecological historian Tim Flannery describes the days of megafauna, when 13-ton elephants and shoulder-height armadillos clomped around among humans.
Mar 7, 2002 | They were the monster trucks of mammals, homely Ice Age giants who weighed as much as 13 tons. While dinosaurs get all the flashy movie deals these days, the megafauna -- shaggy herbivores like the mastodon and mammoth and giant sloth -- have their own gentle-antihero star power.
These giant animals shared the planet with humans less than 20,000 years ago. And it's humans with their mammoth-steak barbecues that likely wiped them out, according to Tim Flannery, a mammalogist and paleontologist who is the director of the South Australian Museum. He is the author, most recently, of "The Eternal Frontier: An Ecological History of North America and Its Peoples," as well as the discoverer of 29 new kangaroo species. Flannery challenges the romantic notion that indigenous peoples once lived in symbiotic harmony with their prey. It seems our human ancestors did to megafauna roughly what we do now at buffets around the world: decimate it and move on.
Flannery argues that it's human hunting, or "overkill," not climate change, that killed off these mammal monsters. He spoke with Salon from his office in Adelaide, Australia, about what the megafauna's lives were like.
How did the megafauna come about?
Until the dinosaurs were wiped out, the mammals were all rat-sized things. There were a few that were cat-sized, but very, very few. At the time that the dinosaurs get wiped out, most of the mammals get wiped out as well by the asteroid impact, 65 million years ago. After that, just a few species are left.
The slate is sort of wiped clean. Animals start diversifying very rapidly because there are lots of open ecological niches. So the mammals start getting larger pretty quickly, and within half a million years you've got mammals the size of calves. And by 55 million years ago, you've got mammals as big as anything living on earth today, for example the uintatheres. They're these enormous mammals whose fossils were first found in the Unita Mountains in Utah. Four or 5 tons in body weight, they have three sets of horns on their head, with these long, dagger-like canines, even though they're herbivores.
But were they really megafauna?
Well, what we normally talk about as megafauna is really the big animals that existed in North America between about 2 million and 13,000 years ago.
There's a real global crisis in climate about 5 million years ago when things seem to get very hot and dry. The rich grasslands start shrinking. And soon after that, the earth seems to go into this paroxysm of climate change. It's warm and dry, and then temperatures start plummeting.
By the time of the Ice Age, North America has more ice on it than Antarctica has. North America above 40 degrees north, somewhere between Boston and New York, by and large was covered by this enormous ice cap, 2 miles deep at its center.
The ice sheet itself was composed of several subsheets. The biggest of them was called the Laurentide ice sheet, that covered the bulk of North America. There was enough water frozen in that ice to lower the world's sea level by 74 meters. Those conditions really only ended 15,000 years ago, and they will certainly return.
Those subtropical grasslands have disappeared at this point, and instead you've got tundralike grasslands, much less productive. Cold conditions with less productive pasture really tend to select for very large animals, because the larger an animal is, the more poor-quality food -- tundra grass, sedge or spruce -- it can ingest and survive.
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