The sediment beneath an Indiana lake is providing clues. One thing is clear: A meteor didn't kill off the mammoths, mastodons and other large plant-eaters, as previously theorized.
By John Johnson Jr.
Because the fungus is commonly found in the dung of large plant-eaters, its prevalence in the fossil record should be a direct measure of population density, Gill said. The research team found that the decline of the large mammals started about 14,800 years ago--and was virtually complete a thousand years later.
The first is habitat loss due to a changing climate. Around this time, tree species such as black ash, elm and ironwood began spreading across the landscape of North America. According to Gill, the die-off of the big mammals predated this change. In fact, the loss of the big herbivores may have helped precipitate it. Without the large plant-eaters around to keep them in check, the tree species were free to colonize the countryside.
Another theory suggested that a comet or meteor impact that occurred about 12,900 years ago could have wiped out the big mammals in the same way that a similar but larger impact is believed to have killed off the dinosaurs. The new timeline shows the extinction event was already over when that impact took place, Gill said.
A third theory held that the animals were wiped out by a so-called "blitzkrieg" of hunting by Clovis culture humans. The Clovis culture is distinguished by the fluted spear points used by hunters to bring down large animals. But according to Gill, the die-off was already underway before the Clovis hunters arrived. "This was already happening before humans adopted the Clovis tool kit," Gill said.
The precise timeline doesn't necessarily rule out any of the theories. A previous era of climate change or comet or meteor strikes could've wiped out the megafauna. Even a previous wave of Paleo-Indian immigrants could've done the job.
I'm still betting on some variation of climate change. Several Ice Ages occurred over the previous millennia, so this was an epoch of cataclysmic climate shifts. Each cooling and warming period must've been a huge shock to ecosystems.
For more on the subject, see Dennis Prager and The Ecological Indian.
Below: "Researchers found that the decline of large mammals started about 14,800 years ago--and was virtually complete a thousand years later." (Ethan Miller, Getty Images/September 30, 2009)
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