The only surviving examples of monotremes are all indigenous to Australia and New Guinea although there is evidence that they were once more widespread including some extinct species in South America. The extant monotreme species are the platypus and four species of echidnas.

Why are monotremes only found in Australia?

Why are monotremes, mammals that lay eggs rather than give birth to live young, only found in the isolated region of Australia and New Guinea? It is the isolation of this region that's key. 200 million years ago, Australia was situated on the far-reaches of Pangaea, the last supercontinent (Figure 10.3. 1).

Do all monotremes live in Australia?

Yet today no monotremes exist outside of Australia (and New Guinea), and no placental mammals that didn't fly or swim there—for example, bats or dugongs—exist in Australia except for rodents (which arrived only about five million years ago) and mammals that were introduced by people (who arrived by 60,000 years ago).