While undisputably a marsupial, the thylacine bears a remarkable resemblance to the common dog. The primary visible distinctions between the two are its tail, which smoothly extends off the body like a kangaroo; several stripes ordered vertically across its hind quarters; and its amazingly large gape of mouth. Of course it also has a pouch.
Though it is presumed extinct, sightings are still occasionally claimed in Tasmania, Australia, and the British Isles(!) See also Cryptozoology.
http://livingplanet.virtualave.net/thylacine/thylacine.htm