Experts believe that the 'Chihuahua' is the world's smallest breed of dog, and that the breed first appeared in Mexico. In fact, this endearing little animal is purportedly one of the oldest breed of dog in North America, to date. Found primarily in warmer climates, this dog weighs in at about two to six pounds, and measures about six to nine inches in height. The Chihuahua looks amazed and carries a surprised expression all the time, perhaps because of its round saucer like eyes, and its pointed ears that stand up! This small breed can be either long haired or short haired, and come in different colours, but most of these darlings are either tan or brown and white and black. Used as guard dogs, the Chihuahua is capable of taking on human intruders with a keen fighting spirit, belying its small size. Fiercely loyal and protective of its master, this small dog is ideal for the elderly or the physically challenged, since it does not require too much of maintenance.