Macropodids are the most diverse group of marsupial herbivores ever to have evolved. They have been the subject of more phylogenetic studies than any other marsupial family, yet relationships of several key clades remain uncertain. Two important problem areas have been the position of the merrnine (Lagostrophus fasciatus) and the phylogenetic proximity of tree-kangaroos and rock-wallabies. Our osteological analysis revealed strong support for a plesiomorphic clade (Lagostrophinae subfam. nov.) containing Lagostrophus and Troposodon, which is likely to have originated in the early Miocene. The extinct short-faced kangaroos (Sthenurinae) emerged in the middle Miocene as the sister lineage to a clade containing all other living kangaroos and wallabies (Macropodinae). New Guinea forest wallabies (Dorcopsini trib. nov.) are the most plesiomorphic macropodines; the other two main lineages include tree-kangaroos and rock-wallabies (Dendrolagini), and 'true' kangaroos and wallabies (Macropodini). These phylogenetic outcomes are broadly consistent with the results of recent molecular studies, although conflicts remain over the relative positions of some macropodins (e.g. Setonix, Onychogalea, and Wallabia). Given the presence of derived dendrolagins and macropodins in early Pliocene localities, it is probable that most macropodine genera originated in the late Miocene. Key functional-adaptive trajectories within the craniodental and locomotory systems of the dominant macropodid lineages represent varying responses to the spread of drier, open habitats following the Miocene Climatic Optimum.

How well the ecology, zoogeography and evolution of modern biotas is understood depends substantially on knowledge of the Pleistocene. Australia has one of the most distinctive, but least understood, Pleistocene faunas. Records from the western half of the continent are especially rare. Here we report on a diverse and exceptionally well preserved middle Pleistocene vertebrate assemblage from caves beneath the arid, treeless Nullarbor plain of south-central Australia. Many taxa are represented by whole skeletons, which together serve as a template for identifying fragmentary, hitherto indeterminate, remains collected previously from Pleistocene sites across southern Australia. A remarkable eight of the 23 Nullarbor kangaroos are new, including two tree-kangaroos. The diverse herbivore assemblage implies substantially greater floristic diversity than that of the modern shrub steppe, but all other faunal and stable-isotope data indicate that the climate was very similar to today. Because the 21 Nullarbor species that did not survive the Pleistocene were well adapted to dry conditions, climate change (specifically, increased aridity) is unlikely to have been significant in their extinction.

Bandicoots and bilbies (Peramelemorphia) represent a distinct lineage within the marsupial adaptive radiation, which despite several curious anatomical traits has received little morphological attention. Many bandicoot species (family Peramelidae) dig for subterranean food, while bilbies (family Thylacomyidae) employ their forelimbs to dig extensive burrow systems for shelter. In the current study, dissections of the southern brown bandicoot (Isoodon obesulus) (n = 7) and greater bilby (Macrotis lagotis) (n = 4) provide the first anatomical descriptions of forelimb musculature in these species. The anatomical arrangement of forelimb muscles in I. obesulus and M. lagotis differs from that of other marsupials and corresponds to the aclaviculate pectoral girdle and modified arrangement of digits in the study species. Comparative and functional interpretations indicate that the forelimb of I. obesulus is well equipped for scratch digging and demonstrates muscular modifications in order to generate large out-forces. The bones of the forelimb, and in particular the antebrachium, are relatively short, stout bones, improving both their resistance to mechanical forces and providing a mechanical advantage via a reduced out-lever length. There has been an increase in the absolute volume of muscles employed during digging, thereby increasing the magnitude of the in-force. Increased in-lever lengths have been achieved via the migration of muscle insertions, including the elongate olecranon for the insertion of the m. triceps brachii, and the distal migration of the humeral attachments of the teres major, latissimus dorsi and superficial pectoral muscles.