Papua New Guinea notable feature in common for the two landmasses is the existence of several species of marsupial mammals, including some kangaroos and possums, which are not found elsewhere. Papua New Guinea is a megadiverse country. Many of the other islands within PNG territory, including New Britain, New Ireland, Bougainville, the Admiralty Islands, the Trobriand Islands, and the Louisiade Archipelago, were never linked to New Guinea by land bridges. As a consequence, they have their own flora and fauna; in particular, they lack many of the land mammals and flightless birds that are common to New Guinea and Australia. Australia and New
New Guinea is about the same amount as that found in the United States or Australia. A high percentage of New Guinea's species are endemic, and thousands are still unknown to science: probably well over 200,000 species of insect, between 11,000 and 20,000 plant species, and over 650 resident bird species. Most of these species are shared, at least in their origin, with the continent of Australia, which was until fairly recent geological times part of the same landmass (see Australia-New Guinea for an overview). The island is so large that it is considered 'nearly a continent' in terms of its biological