|Photo by author|
And that's odd, if you think about it. Why do pronghorn need to be that fast--far faster than any predator on the plains? Nature doesn't usually give its creatures abilities beyond their needs, so the pronghorn's excessive speed is a puzzle.
The poet Robinson Jeffers offers a hint of an answer:
What but the wolf’s tooth whittled so fineWolves were certainly important predators of pronghorn, but they probably aren't the whole story. Pronghorn can run 20 miles per hour faster than wolves, which means they may be built to outrun an even faster predator. And just such a predator once existed: the American cheetah, or false cheetah. Until about 12,000 years ago, there was a big cat in North America that fit into the same "turbocharged grassland predator" niche that modern African cheetahs occupy. As the name "false cheetah" suggests, it wasn't closely related to African cheetahs. It's an example of convergent evolution--it resembled a cheetah because it evolved to fill a similar ecological niche. It's also an example of what the science writer Connie Barlowe called a "ghost of evolution": a species that's now gone, whose legacy we can still see reflected in other species.
The fleet limbs of the antelope?
|Photo by Greg Hume, |
Some of the other ghosts in the landscape come from much farther back in time. If you look closely at certain rocks at the edge of the Rocky Mountains, near the Mile High City of Denver, you may get lucky and find a shark tooth. Of course, actual sharks are rare these days in the Rockies. The fossilized teeth are actually older than the mountains. They're reminders that Colorado was once covered by a sea, where sharks patrolled alongside giant aquatic reptiles that went extinct along with the dinosaurs.
|Cretaceous Shark Tooth from Colorado. Photo by Author|
|Glacial Cliffs near Chicago Lakes, Colorado. Photo by Author|
|Table Mountain, Golden, Colorado. Photo by Ross Mays, ancient landscape drawing based on Drewes, 2008|
More details on giant sloths, locust trees, and the mesa above:
How a Valley Became a Mesa, and Why a River Runs Through It
Table Mountain Shoshonite Porphyry Lava Flows and Their Vents,Golden, Colorado / Harald Drewes, 2008