The vertebrate fauna of Australian Mediterranean-type ecosystems are not unusually diverse, nor are many endemic. Instead, the majority are populations of more typically arid or mesic habitat species whose ranges extend into Southwestern or South Australia. The majority of the vertebrates have relatively broad ecological niches rather than specialized requirements unique to the Mediterranean-climate regions.
The Mediterranean-climate mammal fauna includes only 57 species, 12 of these endemic. Interpreting the patterns of distribution of large mammals is difficult, however, because of the strong impact of both Aboriginal and European peoples. The extinction of a large megafauna in the late Quaternary left the Australian continent without large grazers or predators.
Bird diversity is also relatively low, with 285 species regularly present. Ten of these are endemic. Most notable among these endemics is the black swan (Cygnus atratus), shown on the state emblem for Western Australia.
Diversity is high among reptiles in southwestern Australia, an evolutionary consequence that stems in part from the low mammal diversity. Of the 177 native species, 27 areendemic. Amphibians include 33 native species, with 19 endemic species and four endemic genera.
With only small areas of riverine or freshwater habitat, fish diversity in Southwestern Australia is low. Only 20 native species are present but half of these are endemic. These include three endemic genera and one endemic family.