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Ghosts of Evolution

01/31/02 12:00AM By Ted Levin

Twelve thousand years ago, at the waning moments of the Ice Age--a mere blink of the geologic eye--a mythic cast of creatures traipsed around North America.

No fewer than four species of elephants and three species of horses, including a zebra, roamed the continent. There was a bison with horns that extended seven-feet from tip to tip, a one-humped camel," a giant musk ox, a beaver as big as a black bear, a forest deer, a stag moose, which looked like a monster elk, and two species of pronghorn, one with four horns.

There were also at least six species of sloth, including an eighteen-foot long ground sloth that stood on its hind legs, bending trees to its mouth. There were also several types of large armadillos lumbering around. The most abundant large Ice Age mammal was a pig-like peccary that dropped bones from Florida to California.

All these herbivores were hunted by an equally amazing group of predators. Packs of dire wolves and a fifteen hundred pound short-faced bear, chased prey across the Great Plains. The Florida spectacled bear prowled the southeast.

Two species of lions, the thousand pound American lion, and the northern cave lion (the same species that lives in Africa), patrolled opposite ends of the continent. Other North America Ice Age cats included several species of sabertooths, scimitar cats, and cheetahs, and a northern jaguar, bigger than our modern version. It was a landscape, whose pulsating megafauna was otherworldly even by modern African standards.

In addition to fossils, what other evidence to we have of the tenure of these exotic beasts? An American lion left tracks the size of dinner plates in the mud of a Missouri cave, while the dung of ground sloths litters caves in the Southwest. One sloth was itself found embalmed in bat guano. A 35,000 year old long-horned bison was found mummified in the Alaskan permafrost and innumerable mammoths and mastodons have been found frozen in glacial ice or pickled in bogs.

Some the most fascinating evidence of the passage of Ice Age giants, however, can be found right in the produce section of your local grocery or in the fruit and thorns of plants we see today.

According to recent trends in evolutionary biology, animals that no longer exist account for such mysteries as why the thorns of hawthorn are spaced so far apart since today's deer can easily browse between the thorns. Likewise, no living animal can pass an intact avocado seed through its digestive system.

Since it's hard to teach an old plant new tricks, many species, like hawthorns and avocados, still exhibit traits that originally evolved to attracted or repel now-extinct Ice Age mammals.

And the "ghosts of evolution" are not restricted to the plant kingdom either. Take the pronghorn antelope. It's the swiftest runner in North America, clocked at over 60 miles per hour, yet no current antelope predators approach such speeds. Pronghorn also herd, a sort of safety in numbers defense, yet no living North America predator is fearsome enough to warrant such a response. Not even a grizzly, which can only run half as fast.

Pronghorn behavior is a reponse to the predators with whom they shared the North American grasslands 4 million years ago -- two species of cheetahs and a hyena built for running. Although these predators have been extinct for 10,000 years, antelope behave as if they were still present, as if they were haunted by ghosts of predators past.

So, the next time you see a deer bolt across a frozen marsh, remember...the ghosts of wolves and catamounts still lurk in the alders.

This is Ted Levin from Gillette Swamp in Thetford Center, Vermont.

--Ted Levin is a writer and photographer specializing in natural history.

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