ABSTRACT
Today, the biogeographical region comprising Australia, New Guinea and the adjacent islands is the only part of the globe where representatives of all three major extant mammalian clades occur together – namely, monotremes, mar supials and placentals (Flannery 1995b; Van Dyck and Strahan 2008; Wilson and Reeder 2005). Monotremes (ve species) are currently found nowhere else, while > 240 described marsupial species comprise ~40% of the total terrestrial mammal diversity in the region. Placentals dominate the mammal faunas of most continental landmasses, but in Australia and New Guinea only two placental clades have achieved moderate diversity: murine rodents (> 160 species; ~25% of the total) and bats (> 130 species; ~20% of the total). Most other non-marine placental clades seem to have been entirely absent from Australia and New Guinea prior to human-related introductions during the Holocene. This unique overall pattern of mammalian biodiversity, so different from that seen elsewhere in the world, has fascinated a long line of researchers, including Darwin and Wallace themselves.
