The thylacine (Greek for "dog-headed pouched one") was the largest known carnivorous marsupial of modern times. It is commonly known as the Tasmanian tiger (because of its striped lower back) or the Tasmanian wolf. Native to continental Australia, Tasmania and New Guinea, it is believed to have become extinct in the 20th century. It was the last extant member of its family, Thylacinidae; specimens of other members of the family have been found in the fossil record dating back to the late Oligocene.

Surviving evidence suggests that it was a relatively shy, nocturnal creature with the general appearance of a medium-to-large-size dog, except for its stiff tail and abdominal pouch (reminiscent of a kangaroo) and dark transverse stripes that radiated from the top of its back, similar to those of a tiger. The thylacine was an apex predator, like the tigers and wolves of the Northern Hemisphere from which it obtained two of its common names. As a marsupial, it was not closely related to these placental mammals, but because of convergent evolution it displayed the same general form and adaptations. Its closest living relative is thought to be either the Tasmanian devil or the numbat. The thylacine was one of only two marsupials to have a pouch in both sexes (the other being the water opossum). The male thylacine had a pouch that acted as a protective sheath, covering his external reproductive organs while he ran through thick brush.

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