Does it seem suspicious to anyone else that the gray wolf, Canis lupus, somehow flourished in both North America and Europe? Although not technically a native species to the Americas, the gray wolf should not be the symbol of North American wildlife that it has become. That title should go to the extinct dire wolf, another awesome piece of Pleistocene megafauna:
Back when mammoths roamed the continent, a predator called the dire wolf (Canis dirus) preyed upon them. The dire wolf had a stronger bite and stockier build than the modern gray wolf, allowing it to overpower large mammals. It had a larger head relative to its body, meaning that there was more power in its bite. Its attack style was more akin to a bear's than a wolf's.
(It also has a fair amount of pop culture references, including a beast in Lineage II, a Grateful Dead song, and an attack called "Dire Bite" in Fossil Fighters.)
A canid that has a different attack style from the gray wolf? It's all in the dire wolf's physiology. Check out this video on dog attack styles to see exactly why, even though dogs are considered wolves, subtle anatomical differences affect how they attack.
The main weapon of any canid is its jaws. The stronger the bite, the more damage it can do. As the video demonstrates, yes, weight helps as well, but it ultimately boils down to jaw power and making the bite do as much damage as humanly (dogly?) possible.
So, why the hell did it die out?
It went extinct because of both competition with other predators (such as the gray wolf) and the general "humans suck" rule. There is an inverse relationship between humans and megafauna- that is, the more humans, the less megafauna. Humans kill giant mammals off because they are threats, food, or threats to our food. Competition for mammoth and bison meat from humans working in groups led to the dire wolf becoming extinct. The kicker is that humans probably learned to hunt in groups from observing pack-hunting canids.
Damn, we're douchebags.