How and when did wolves evolve? It's a question science has yet to answer conclusively because, evolutionarily speaking, the development of the modern day wolf isn't clear. What's generally believed is that about 60 million years ago during what's referred to as the Paleocene times wolves began their development as a specialized genus of cursorial, or hunt-by-chasing, carnivore. Approximately 8 million years later primitive carnivores known as Miacids appeared in the Lower Tertiary. The Tertiary period lasted about 65 million years and is often called "the age of the rise of mammals." Miacids ranged from gopher to dog size and had evolved from Cretaceous insectivores.

So, small rodent-like insectivores are included in the wolf's ancestry. Much later, creodonts emerged. These animals are described as walking on five toes, having partially retractile claws, partially opposable thumbs on the forefeet and long thick tails. In his book Of Wolves And Men, Barry Holstun Lopez hypothesizes that creodonts "perhaps looked like long-legged otters, dwelt in forests, and may have slept in trees." Of course evolution continued and some creodonts eventually transformed. These transformations eventually moved out onto plains and prairies becoming wolves, bears, badgers, skunks and weasels. Those that remained behind in the forests became saber-toothed tigers, leopards and cheetahs. 

By about 20 million years ago during what's called the Miocene times, the two superfamilies of carnivores, canines and felines, were distinct. This is really when the more recognizable ancestors of the wolf emerged. Lopez describes them as having "specialized shearing teeth" with the bones of their lower legs having fused "as flexibility in the limbs...gave way for rigidity for strength in the chase." In Tomarctus, one ancestor of the wolf, the fifth toe on the hind leg became vestigial and the dew claw was born. Apparently Tomarctus lived much like the wild dogs and wolves of today. It's described as a stealthy predator with short prick ears and a long tail that was used to maintain balance.   

Dire Wolf  [Source: National Geographic Wild]


Above Diagram Source: Little Big History Of The Canine

The Dire Wolf was about the same length as the Gray Wolf but about 25 percent heavier, weighing 125 to 175 pounds. Some scientific estimates place it at up to 200 pounds.

Dire Wolves' bones were broader and connected to larger muscles. They had proportionately shorter legs, shorter and broader heads and deeper jaws with very large carnassial (meat-shearing) teeth. Some  males had larger and more menacing fangs than females.

Dire Wolves are known as hypercarnivores because their diet consisted of at least 70 percent meat (just like the saber-toothed cats they co-existed with).

Paleontologists speculate the Dire Wolf may have been a "bone crushing" canid, crushing its prey's bones and eating the marrow inside.

Tooth analyses of Dire Wolves indicates that prehistoric horses formed the bulk of their diet. They also fed on bison, mastodons, ancient camels and giant ground sloths. 

Paleontologist Francois Therrien calculated the Dire Wolf's bite contained 129 percent of the force of today's Gray Wolves.

Dire Wolves had smaller brain cases than Gray Wolves so were likely not as smart.

The Dire Wolf was genetically distinct from the Gray Wolf. They share a common ancestor but Gray and Dire Wolves lie on two separate and diverging branches on the evolutionary tree.

Dire Wolf

As Robert H. Busch outlines in his book The Wolf Almanac, research by Robert Wayne at the University of California suggests that a number of wolf-like canids diverged from a common ancestor about two to three million years ago. Early in the Pleistocene period, about a million years ago, the first Gray Wolf, Canis lupus​, probably appeared in Eurasia.  It's thought to have migrated to North America about 750,000 years ago. Evolving even earlier, the Dire Wolf, Canis dirus, was larger and heavier. It co-existed with the Gray Wolf in North America for approximately 400,000 years. Many believe that as the Dire Wolf's main prey became extinct due to climactic change about 16,000 years ago the Dire Wolf itself eventually died out. Consequently, about 7,000 years ago, the Gray Wolf became the prime canine predator in North America. It was classified as Canis lupus by Swedish scientist Carl von Linne in 1758. 

Why did Canis lupus survive while Canis dirus  did not? In his book The Great American Wolf, Bruce Hampton theorizes that since the Dire Wolf was "[built] more for power than speed and used to preying on relatively sedentary megaherbivores, dirus simply may have been unable to catch the smaller and faster ungulates that ascended as larger ones disappeared." In contrast, lupus was fast, with social behaviorism better equipped to meet the changing world. Hampton writes that perhaps the Dire Wolf was "less tolerant and more aggressive toward members of its own species."

Although the Dire Wolf appears to have hunted in large packs, these packs were probably less mobile and less far-ranging than those of the co-existing Gray Wolf. Ill-equipped to catch the faster prey that Gray Wolves lived upon, Hampton compares Dire Wolves to hyenas in that they may have resorted more and more to scavenging, "a survival strategy considered less versatile than that practiced by self-supporting carnivores." If in fact scavenging became the lifestyle of Dire Wolves, it proved insufficient to maintain their survival once megaherbivores, their original prey, completely died out.