Australasian marsupials (Australidelphia)
Marsupials are found living in Australasia (Australian continent, Tasmania, New Guinea and nearby islands) and the Americas. There are 334 extant species of marsupials living today and 70% occur in Australasia. In Australasia, marsupials are found in Australia, Tasmania and New Guinea; throughout the Maluku Islands, Timor and Sulawesi to the west of New Guinea, and in the Bismarck Archipelago (including the Admiralty Islands) and Solomon Islands to the east of New Guinea.
Phylogeny and Evolution of Australian marsupials
Marsupials are distinguished from other mammals (eutherians) and monotremes mainly by their mode of reproduction. Marsupial young are born in an altricial, undeveloped state and very very minute and need to be nourished for prolonged periods by their mother’s milk, often protected within a maternal pouch (marsupium).
The living marsupials may be broadly divided into the Ameridelphia (including the Paucituberculata or shrew opossums, and the Didelphimorphia or “true” opossums) and the Australidelphia (Australian and New Guinean species, and also include the Microbiotheria from southern South America). The timing of divergence of marsupial and placental lineages is controversial, with estimates of at least 160 My being suggested (Yu et al. 2012; Weisbecker and Beck 2015). Molecular dating estimates place the basal marsupial divergence in the Late Cretaceous (around 77 My; Yu et al. 2012) and periods of acceleration in marsupial diversification are thought to have occurred in the early Paleocene to early Eocene among the Australian lineages.