Palaeodiversity and relationships of all groups of Australian mammals are reviewed. The fossil record spanning this time is of variable quality. 'Dark Ages' about which nothing is known in terms of Australian mammal evolution include the late Triassic to late Jurassic, late Cretaceous to late Paleocene and middle Eocene to middle Oligocene. Very little is known about the early Cretaceous and late Miocene. The late Oligocene to middle Miocene record documents the highest levels of biodiversity known for the continent, comparable to that which characterises the lowland rainforests of Borneo and Brazil. Order Monotremata spans at least the last 110 million years and includes four families. The enigmatic Ausktribosphenos from 115 million-year-old sediments in Victoria may represent an archaic monotreme, specialised peramurid or previously undocumented order of mammals but is unlikely to represent a placental as suggested in the initial description. Order Microbiotheria is represented in the early Eocene (~55 mya) by two genera similar in morphology to early Eocene taxa from Argentina. Order Peramelemorphia spans the early Eocene to Holocene and includes at least five families. Order Dasyuromorphia spans at least the late Oligocene to Holocene and includes at least three families. Other dasyuromorphian-like marsupials are indeterminate in terms of family-level affinities. Order Notoryctemorphia spans the early Miocene to Holocene with one family. Order Yalkaparidontia spans the late Oligocene to middle Miocene with one genus. Order Diprotodontia spans the late Oligocene to Holocene, represented throughout by three major groups: Phalangerida (eight families), Vombatomorphia (seven families) and Macropodoidea (at least three families). A possible placental condylarth (Tingamarra) has been recorded from the early Eocene. An archaeonycteridid bat (Australonycteris) is known from the early Eocene. Among bats, the late Oligocene to middle Miocene is dominated by rhinolophoids, many of which have European, Asian and African affinities. Mystacinids, megadermatids, hipposiderids and molossids are well-represented in the Oligocene to Miocene deposits. Vespertilionids are uncommon in the Oligocene to Miocene but become more diverse in the Pliocene to Holocene. Emballonurids and rhinolophids appear for the first time in the Plio-Pleistocene. Pteropodids are unknown prior to the Holocene. Murids span the early Pliocene to Holocene. In the oldest assemblage at Riversleigh, one undescribed lineage resembles archaic forms otherwise only known from the fossil records of Africa and Eurasia.
