The thylacine was relatively shy and nocturnal, with the general appearance of a medium-to-large-size dog, except for its stiff tail and abdominal pouch similar to that of a kangaroo, and dark transverse stripes that radiated from the top of its back, reminiscent of a tiger. The thylacine was a formidable apex predator, though exactly how large its prey animals were is disputed. Because of convergent evolution, it displayed an anatomy and adaptations similar to the tiger and wolf of the Northern Hemisphere, despite being unrelated. Its closest living relatives are the Tasmanian devil and the numbat. The thylacine was one of only two marsupials known to have a pouch in both sexes: the other (still extant) species is the water opossum from Central and South America. The pouch of the male thylacine served as a protective sheath, covering the external reproductive organs.