The eastern grey kangaroo (Macropus giganteus: gigantic large-foot; also great grey kangaroo or forester kangaroo) is a marsupial found in the eastern third of Australia, with a population of several million. Although a large M. giganteus kangaroo male can typically weigh up to 69 kg (152 lb) and have a length of well over 2 m (6 ft 7 in), the scientific name is misleading as the red kangaroo of the semi-arid inland is larger, weighing up to 90 kg (200 lb).
Kangaroos are marsupials from the subfamily Macropodinae (macropods, meaning "large foot"). In common use, the term is used to describe the largest species from this family, the red kangaroo, as well as the antilopine kangaroo, eastern grey kangaroo, and western grey kangaroo. Kangaroos are indigenous to Australia and New Guinea. The Australian government estimates that 42.8 million kangaroos lived within the commercial harvest areas of Australia in 2019, down from 53.2 million in 2013.
As with the terms "wallaroo" and "wallaby", "kangaroo" refers to a paraphyletic grouping of species. All three terms refer to members of the same taxonomic family, Macropodidae, and are distinguished according to size. The largest species in the family are called "kangaroos" and the smallest are generally called "wallabies". The term "wallaroos" refers to species of an intermediate size. There are also the tree-kangaroos, another type of macropod which inhabit the upper branches of trees in the tropical rainforests of New Guinea, far northeastern Queensland, and some of the islands in the region. A general idea of the relative size of these informal terms could be:
The pouch is a distinguishing feature of female marsupials and monotremes, and rarely in males as well, such as in the yapok and the extinct thylacine. The name marsupial is derived from the Latin marsupium, meaning "pouch". This is due to the occurrence of epipubic bones, a pair of bones projecting forward from the pelvis. Marsupials give birth to a live but relatively undeveloped foetus called a joey. When the joey is born it crawls from inside the mother to the pouch. The pouch is a fold of skin with a single opening that covers the teats. Inside the pouch, the blind offspring attaches itself to one of the mother's teats and remains attached for as long as it takes to grow and develop to a juvenile stage.
Epipubic bones are a pair of bones projecting forward from the pelvic bones of modern marsupials, monotremes and fossil mammals like multituberculates, and even basal eutherians (the ancestors of placentals, who lack them).They first occur in non-mammalian cynodonts such as tritylodontids, suggesting that they are a synapomorphy between them and Mammaliformes.
They were first described as early as 1698, but to date, their function(s) remain unresolved. Epipubic bones are often called marsupial bones because they support the mother's pouch in modern marsupials ("marsupium" is Latin for "pouch").