According to Gray Wolf Conservation, wolves have four legs, along with foxes, coyotes and domestic dogs. HowStuffWorks.com also showcases various four-legged amphibians such as the tree frog, an amphibian with pads at the ends of their fingers to help them climb.
According to Wikipedia.org, quadrupeds are animals that move on four legs. Other quadrupeds are cats, cattle and reptiles. Animals whose limbs have been modified because of evolution are known as tetrapods. Tetrapods have quadruped ancestors, but they cannot be classified as four-legged animals in the traditional sense.
PBS notes that humans were once quadrupeds as apes, but evolution has changed man into a bipedal creature. This was a process that took millions of years, and experts are not sure when the change took place. Apes such as gorillas are classified as quadrupeds since they rely on all four limbs to move around. The shape and structure of the pelvis defines humanity. Wikipedia mentions various cases of quadrupedalism in humans in Chile and Turkey. This is due to such factors as brain impairment and learning how to walk on all-fours as infants.
Crystal Graphics shows various quadrupeds such as deer, warthogs, bison, bears and wild boars. Zebras and rhinos also have four limbs. Other domestic animals such as horses and sheep have four limbs as well. Dinosaurs such as the brachiosaurus and the mamenchisaurus also had four limbs.