American Buffalo by Steven Rinella Read Free Book Online Page B

Beringia was dominated by rolling hills, grasslands, and broad valleys. It did not get much snow and was free from glaciers. The dire wolf fed on horses where king crabs now feed on clams.
    Several times during the Pleistocene, the dryland corridor of Beringia was open long enough to allow a nearly complete homogenization of wildlife between Siberia and Alaska. That is, animals were able to move freely back and forth between the continents. Of course, these migrating animals would probably have had no idea that they were “going” anywhere. They were just moving along, heading where there was food and a more suitable climate. Individual animals would have been born and would have died on land that is now underwater, and it may have taken several generations for a population of animals to actually “cross” the land bridge.
    While there was some interchange going from North America to Siberia, such as the horse, the predominance of faunal exchanges went in the other direction, from Siberia to North America. It seems that the first of several bison migrations happened during the second-to-last glacial episode, about 140,000 years ago. Scientists often refer to these early arrivals as Eurasian steppe bison (
Bison priscus
). In the cave art of Paleolithic European hunters, the steppe bison is often portrayed with curvaceous horns, a large shoulder hump, and a mane so thick that it almost appears to be a second hump. The steppe bison shared the North American landscape with a host of bizarre and fascinating animals that I wish were still around: flat-headed peccaries and beavers that were the size of modern pigs; an armadillo the size of a black bear; the ox-sized Jefferson’s ground sloth, which had lips capable of gripping things; the twenty-foot-long, elephant-sized Rusconi’s ground sloth, which dragged itself along on its knuckles and used its tail as a support when it stood up to feed on leaves; the one-ton giant short-faced bear, which had catlike teeth and a skull that was almost as wide as it was long; as many as six different camels, including one that was seven feet tall at the shoulder; two horses, including one that may have been striped like a zebra; several elephants, including the five-ton Columbian mammoth, the ten-ton woolly mammoth, and the forest-dwelling American mastodon; and also an impressive array of large cats, including the 275-pound dirk-toothed cat, the 400-pound Ice Age jaguar, the 600-pound scimitar cat, the 700-pound saber-toothed cat, the 850-pound American lion, and two American cheetahs of indeterminate size.
    The steppe bison thrived alongside many of these mammals on the semi-arid grasslands of eastern Beringia, where it was confined by the same factors that had allowed for its arrival. That is, the glaciers that caused the ocean levels to drop also served to block the animal’s southward migration into what is now the Lower 48 of the United States, or the mid-continent.
    Eventually, during the interglacial period that separated the last two glacial periods, a north-south corridor opened through western Canada. Bison passed through the corridor maybe a hundred thousand years ago, emerging on the Great Plains near the location of Edmonton, Alberta. During the next and final glacial period, the Wisconsinan, that corridor was closed again by advancing glaciers. The bison in the south would never again interbreed with those in the north, and they would each follow their own evolutionary paths: the northern path led to extinction, the southern to the American buffalo.
    Populations of animals that are colonizing new territory sometimes undergo sudden and dramatic evolutionary changes. There are a couple of reasons for this. First, the colonizing population is likely to be numerically small and may contain only a fraction of the original population’s genetic diversity. Thus, the new founder population can turn out to be slightly different from the parent population, and there’s less genetic