Being confronted with a pack of wolves is bad enough, but if you happened to be in Alaska some 12,000 years ago, things would be much, much worse. Back then, the icy forests were patrolled by a sort of super-wolf. Larger and stronger than the modern gray wolf, this beast had bigger teeth and more powerful jaws, built to kill very large prey.
This uber-wolf was discovered by Jennifer Leonard and colleagues from the University of California, Los Angeles. The group were studying the remains of ancient gray wolves, frozen in permafrost in eastern Beringia, a region that includes Alaska and northwest Canada. These freezer-like conditions preserved the bodies very well, and the team found themselves in a unique position. They could not only analyse the bones of an extinct species, but they could extract DNA from said bones, and study its genes too.
For their first surprise, they found that these ancient wolves were genetically distinct from modern ones. They analysed mitochondrial DNA from 20 ancient wolves and none of them was a match for over 400 modern individuals. Today's wolves are clearly not descendants of these prehistoric ones, which must have died out completely. The two groups shared a common ancestor, but lie on two separate and diverging branches on the evolutionary tree.
The genes were not the only differences that Leonard found. When she analysed the skulls of the Beringian wolves, she found that their heads were shorter and broader. Their jaws were deeper than usual and were filled with very large carnassials, the large meat-shearing teeth that characterise dogs, cats and other carnivores (the group, not meat-eaters in general).
This was the skull of a hypercarnivore, adapted to eat only meat and to kill prey much larger than itself using bites of tremendous force. Leonard even suggests that the mighty mammoths may have been on their menu.
Once prey was dismembered, the wolves would have left no bones to waste. With its large jaws, it could crush the bones of recent kills, or scavenge in times between hunts. Today, spotted hyenas lead a similar lifestyle. The wolves' teeth also suggest that bone-crushing was par for the course. The teeth of almost all the specimens showed significant wear and tear, and fractures were very common.
Their powerful jaws allowed the Beringian wolves to quickly gobble down carcasses, bones and all, before having to fend off the competition. And back then, the competition included many other fearsome and powerful hunters, including the American lion and the short-faced bear, the largest bear to have ever lived.
Leonard suggests that the ancestor of today's gray wolf reached the New World by crossing the Bering land bridge from Asia to Alaska. There, it found a role as a middle-sized hunter, sandwiched between a smaller species, the coyote, and a larger one, the dire wolf. When the large dire wolves died out, the gray wolf split into two groups. One filled the evolutionary gap left behind by the large predators by evolved stronger skulls and teeth. The other carried on in the 'slender and fast' mold.
But in evolution, the price of specialisation is vulnerability to extinction. When its large prey animals vanished in the Ice Age, so too did the large bone-crushing gray wolf. Its smaller and more generalised cousin, with its more varied diet, lived to hunt another day.
Similar things happened in other groups of meat-eaters. The American lion and sabre-toothed cats went extinct, but the more adaptable puma and bobcat lived on. The massive short-faced bear disappeared, while the smaller and more opportunistic brown and black bears survived. Leonard's findings suggests that the casualties of the last Ice Age extinction were more numerous than previously thought. What other predators still remain to be found in the permafrost?
Reference: Leonard, Vila, Fox-Dobbs, Koch. Wayne & van Valkenburgh. 2007. Megafaunal extinctions and the disappearance of a specialized wolf ecomorph. Curr Biol doi:10.1016/j.cub.2007.05.072
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