Bears of the Pleistocene

[brotherbear]

In the Shadow of the Sabertooth by Doug Peacock.

Short-faced bears belong to the tremarctine, or "running bears," group of New World bears. Having spent much of a lifetime living close to wild grizzly bears, I don't buy into a demystified edition of A. simus as a peaceful grazing omnivore. With big bruins, behavior is what defines what a bear wants to eat and how he gets it.
Grizzlies are true omnivores and prodigious diggers with long claws. Adults can't climb trees. Brown bears hibernate; they dig dens on high mountain slopes.
With its great body mass, the short-faced bear couldn't make it up a tree and likely didn't dig much either. Many paleontologists doubt A. simus hibernated. If they could find sufficient protein during the winter by scavenging or predation, they didn't have to. Smaller specimens of the short-faced bear have been found in caves in the contiguous states. These caves are probably not normal lairs but rather, in a species with pronounced sexual dimorphism ( male bears are larger than females ), the winter homes of pregnant females or mothers with young.

In solving the argument about what the big bears ate, a key observation is that the grizzly survived the Late Pleistocene and the gigantic short-faced bear did not. The obvious reason, I think, is that the brown bear is a true omnivore, more flexible and adaptable than the meat-eating A. simus. Once the great megafauna declined, the serving portions for scavengers and predators certainly shrunk. If the short-faced bear had been a successful non-selective grazer and browser of shrubs for fruit, it might still be around. Bears can't live by non-selective grazing. If the short-faced bear's broad muzzle, as argued by some of the paleontologists, precluded selecting green grass and sedges from more cellulose-laden forage, then A. simus would have had trouble plucking berries from the bushes they grew on. That makes for a lousy vegetarian. Also, A. simusdidn't den, as far as we know, and would have had trouble finding den sites with caves rare and their claws poorly designed to dig dens. The big bears died off because they couldn't live off plant life when their real food, the great megafauna, dwindled down toward extinction 13,000 years ago.

In the Far North, the short-faced bear diet, confirmed by isotope studies ( the nitrogen-15 signature is that of a carnivore ) on fossils, is meat by predation or scavenging. Any sizable carcass in bear country means competition by violent defense and fierce aggression. Reply