There are hundreds of different breeds of dogs, one of which, a Newfoundland breed, has webbed feet and a water-resistant coat. This breed was created to rescue drowning people and to help fisherman haul nets.
Dog breeds are divided into the sporting, non-sporting, working, herding, terrier, toy, hound and miscellaneous classes. Toy or lap dogs include the Pomeranian and Pekingese. Some popular breeds are the Border Collie, Golden Retriever, St. Bernard, German Shepherd and Labrador Retriever. Dogs have been bred for reasons such as herding animals, aiding fishermen, hunting animals and pulling sleds. Greyhounds are bred for racing, and can run up to 45 miles per hour. Despite the differences in breeds, all dogs are descended from wolves.
Dogs have a better sense of smell and hearing than humans, and are able to differentiate aromas and pick up small concentrations of odors. They can also swivel their ears to pick up sounds that humans cannot. Dogs have vibrissae, whiskers on their faces that act as sensors. They also have special membranes over their eyes that allow them to see in complete darkness. Although most dogs have pink tongues and bark, both the Shar Pei and Chow Chow have black tongues, and the Basenji breed is barkless. About two-thirds of dogs are mixed breeds, and about a third are purebred.