Kangaroos have large, powerful hind legs, large feet adapted for leaping, a long muscular tail for balance, and a small head. Like most marsupials, female kangaroos have a pouch called a marsupium in which joeys complete postnatal development.Larger kangaroos have adapted much better than smaller macropods to land clearing for pastoral agriculture and habitat changes brought to the Australian landscape by humans. Many of the smaller species are rare and endangered, whilst the larger kangaroos are relatively plentiful.The kangaroo is an unofficial symbol of Australia and appears as an emblem on the Australian coat of arms and on some of its currency and is used by some of Australia's well known organisations, including Qantas and the Royal Australian Air Force.The kangaroo is important to both Australian culture and the national image, and consequently there are numerous popular culture references.