Australasian and Oceanian fauna

Australia is the only continent in which marsupials have been free to evolve without competition from the more advanced placental mammals until almost the present day. In the course of evolution, and with the entire continent at their disposal, the ancestral marsupials were able to exploit every ecological niche.

Marsupials The burrowing niche was occupied by the bandicoots, wombats, marsupial mice, and marsupial mole; the running niche was taken by kangaroos and wallabies; the climbing niche by tree kangaroos, possums, cuscuses, and the koala; and the flying niche by gliders and flying possums.

Monotremes An exception was the aquatic niche, already filled by the duck-billed platypus. Together with the echidnas, or spiny anteaters, the platypus belongs to an even more ancient order of mammals – the monotremes – only a little removed from the reptiles from which they sprang.

Convergent evolution This great flowering of the marsupials resulted in some notable instances of evolutionary convergence (the evolution along comparable lines of unrelated species to the point where they share similar behaviour and physical appearance). It is scarcely surprising that European settlers bestowed such names as ‘mouse’, ‘mole’, ‘cat’, and ‘wolf’ on the native marsupials, naming them after the placental animals with which they were familiar.

Examples of convergent evolution include the wombats, which are powerful burrowers resembling badgers; the marsupial mole, which is strikingly similar to the placental golden moles of Africa; the kangaroos and wallabies, which fill the grazing niche elsewhere occupied by hoofed mammals; the Tasmanian wolf or thylacine (now probably extinct), which resembles a placental wolf and hunts in a similar manner by running down its prey; the Tasmanian devil, which has powerful bone-crushing jaws and fills a role comparable to the hyena; the numbat, whose powerful claws, small mouth, and long tongue – adaptations to a diet of termites – resemble those of the placental anteaters; the cuscus, which looks and behaves rather like certain prosimians; the koala, which occupies a niche similar to the leaf-eating primates; and the gliders, which resemble flying squirrels and flying lemurs.

Birds The processes of adaptive radiation are almost as evident in the Australian birds as in the marsupials: the parrots, in particular, have occupied diverse ecological niches, some of which are elsewhere filled not only by completely different types of birds but even by mammals.

The megapodes provide a further link with the past. They bury their eggs as reptiles do but, in marked contrast to the reptiles, they have evolved highly sophisticated patterns of behaviour. Megapodes construct large mounds of vegetation in which to incubate their eggs, the male bird carefully controlling the temperature of this compost heap.

The birds of paradise are a group of about 40 species inhabiting New Guinea. Their brilliant plumage and elaborate courtship displays are unrivalled, though the courtship display and vocalisations of the lyrebird are almost equally elaborate.

Flightless birds include the Australian emu, the New Guinea cassowary, and the New Zealand kiwi, the only living relative of the gigantic moas, which at one time were the dominant species of New Zealand. Other flightless birds include the takahe, the parrot-like kea, and the kakapo, a nocturnal ground parrot.

Reptiles The tuatara, living on a few small islands off the coast of New Zealand, is the only living representative of a once-large order of reptiles which has remained almost unchanged since its origins in the Triassic, 200 million years ago.