Ancient, fingernail-size rodent skulls plucked from the dirt with tweezers are forcing scientists to rethink their assumptions about the arrival of much larger mammals in North America.
In recent years, bones from the world's oldest mountain goat, coyote and black-footed ferret—and several teeth from one of the oldest cheetahs ever found—have been pulled from Porcupine Cave in Colorado, said Russ Graham, chief curator at the Denver Museum of Nature and Science.
Subtle evolutionary changes in the tiny prehistoric rodents allowed scientists to date the larger animals. Those studies suggest that some Ice Age beasts were here hundreds of thousand of years earlier than scientists had thought, Graham said. It's even possible that some evolved here, then spread to the rest of the world.
The conventional view is that many Ice Age mammals came to North America from Eurasia and elsewhere relatively recently—tens of thousands of years ago, not hundreds of thousands or a million.
But at Porcupine Cave, researchers have found a mountain goat, a black-footed ferret, a coyote and a cheetah that date to 780,000 years ago, 1 million years ago, 1.5 million years ago, and 1 million years ago, respectively, Graham said.
