After sequencing five genomes from dire wolf fossils between 50,000 and 13,000 years old, the researchers found that the animals belonged to a much older lineage of dogs. Dire wolves, it now appeared, had evolved in the Americas and had no close kinship with the gray wolves from Eurasia; the last time gray wolves and dire wolves shared a common ancestor was about 5.7 million years ago.
The strong resemblance between the two, the researchers say, is a case of convergent evolution, whereby different species develop similar adaptations—or even appearances—thanks to a similar way of life. Sometimes such convergence is only rough, such as both birds and bats evolving wings despite their differing anatomy. In the case of dire and gray wolves, lives of chasing large herbivores to catch some meat on the hoof resulted in two different canid lineages independently producing wolflike forms.
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The new findings also add layers to experts’ ruminations on why dire wolves eventually disappeared as the last ice age closed. These predators became specialized in hunting camels, horses, bison and other herbivores in North America over millions of years. As those prey sources disappeared, so did the dire wolves. “In contrast to gray wolves, which are a model for adaptation,” Perri says, “dire wolves appear to be much less flexible to deal with changing environments and prey.”
Nor did dire wolves leave a genetic legacy beyond the decaying DNA in their ancient bones. Although canids such as wolves and coyotes often create hybrids, dire wolves apparently did not do so with any other canids that remain alive today. Perri, Mitchell and their colleagues found no DNA evidence of interbreeding between dire wolves and gray wolves or coyotes. Dire wolves were genetically isolated from other canids, Mitchell notes, so “hybridization couldn’t provide a way out” because dire wolves were probably unable to produce viable offspring with the recently arrived wolves from Eurasia.
By 13,000 years ago, dire wolves were facing extinction. Evolving in the harsh, variable environments of Eurasia may have given gray wolves an edge, Zazula notes, “while the big, bad dire wolves got caught off guard relaxing in southern California at the end of the ice age.” But what might sound like the end of the dire wolf’s story is really only the beginning. Preserved genes have shown that dire wolves and their ancestors were top dogs in the Americas for more than five million years—and the early chapters of their story are waiting to be rewritten.