Once the world’s most widely distributed land mammal, the gray wolf, or timber wolf, was systematically eradicated from the continental United States in the 20th century and was added to the endangered species list in 1973. Gray wolves are considered a “keystone†species — one with a dramatic effect on its environment. For example, the recent reintroduction of gray wolves to Yellowstone National Park has led to the recovery of the entire ecosystem, from vegetation to beavers to hawks and eagles. The animal is the direct descendent of the ancestor to dogs. Wolves are distinguished from dogs by their long, powerful muzzle, yellow eyes, longer legs, larger paws (which are slightly webbed for walking more easily on snow) and bigger teeth. The wolf has a two-layered coat, which is generally gray, but can vary in color from white to black