ground down and they actually move forward in the mouth before they eventually fall out, and are replaced by new teeth that grow in the back.[5] This process is known as polyphyodonty and, amongst other mammals, only occurs in elephants and manatees.
The large kangaroos have adapted much better than the 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, while kangaroos are relatively plentiful, despite a common misconception to the contrary.[6][7]
The kangaroo along with the koala are symbols of Australia. A kangaroo appears on the Australian coat of arms[8] and on some of its currency,[9] and is used as a logo for some of Australia's most well-known organisations, such as Qantas,[10] and as the roundel of the Royal Australian Air Force.[11] The kangaroo is important to both Australian culture and the national image, and consequently there are numerous popular culture references.
Wild kangaroos are shot for meat, leather hides, and to protect grazing land.[12] Kangaroo meat has perceived health benefits for human consumption compared with traditional meats due to the low level of fat on kangaroos.[13] with the Phalangeridae from the Middle Miocene.[27] This ancestor was likely arboreal and lived in the canopies of the extensive forests that covered most of Australia at that time, when the climate was much wetter, and fed on leaves and stems.[28] From the Late Miocene through the Pliocene and into the Pleistocene the climate got drier, which led to a decline of forests and expansion of grasslands. At this time, there was a radiation of macropodids characterised by enlarged body size and adaptation to the low quality grass diet with the development of foregut fermentation.[28] The most numerous early macropods, the Balbaridae and the Bulungamayinae, became extinct in the Late Miocene around 5–10 mya.[29] There is dispute over the relationships of the two groups to modern kangaroos and rat-kangaroos. Some argue that the balbarines were the ancestors of rat-kangaroos and the bulungamayines were the ancestors of kangaroos.[30] while others hold the contrary view.[31]