The idea of transplanting African wildlife to this continent is being greeted with gasps and groans from other scientists and conservationists who recall previous efforts to relocate foreign species halfway around the world, often with disastrous results.

But the proposal's supporters say it could help save some species from extinction in Africa, where protection is spotty and habitats are vanishing. They say the relocated animals could also restore the biodiversity in North America to a condition closer to what it was before humans overran the landscape more than 10,000 years ago.

Most modern African species never lived on the American prairie, the scientists acknowledge. But some of their biological cousins like mastodons, camels and saber-toothed cats, roamed for more than 1 million years alongside antelope and herds of bison until Ice Age glaciers retreated and humans started arriving.

The rapid extinction of dozens of large mammal species in North America — perhaps due to a combination of climate change and overhunting — triggered a landslide of changes to the environmental landscape. Relocating large animals to vast ecological parks and private reserves would begin to repair the damage, proponents say, while offering new ecotourism opportunities to a withering region.

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The scientists' discussion expanded to consider long-extinct Pleistocene species that have modern counterparts elsewhere in the world.

For example, a larger American cheetah once stalked pronghorn on these lands, with both species evolving special features that enabled them to accelerate to 60 mph. Today, pronghorns rarely are chased, except by the occasional pickup truck.

In Africa, modern cheetahs are being exterminated as vermin, with fewer than 2,000 remaining in some countries. Relocation could help both species retain important traits, the plan's proponents say.