A herbivorous, marsupial mammal (family Macropodidae) in which the lower incisor teeth are directed forwards and specialized for cutting and grinding tough plant material. Most kangaroos are grazers but some are browsers, and most have short front legs, very long hind legs, an elongated fourth metatarsal, and long, strong tails, allowing them to move efficiently by hopping, covering long distances at high speed. The 12 species (genus Dendrolagus) of tree-kangaroos, in contrast, have a longer tail, feet adapted for gripping, and are arboreal, moving clumsily on the ground, but with agility in the trees. There are about 60 species of kangaroos and wallabies, found only in Australia and New Guinea.