Re:Monotremes and Marsupials vs Placentals (Score 1)

This is heavily coloured by placental chauvinism.

We now know that placental mammals were present in Australia before it was isolated by the breakup of Gondwana ~50 million years ago. Unlike marsupials and monotremes, these placentals did not persist into the present.

The introduction of various placental mammals into Australia in the last 200 years has been a large factor in the extinction of a number of marsupial species. However, these introductions have also a large factor in a similar number of extinctions of Australian placentals - rodent species whose ancestors managed the sea journey from Asia in the last few million years.

Neither data point suggests placental "superiority".

While monotreme diversity is extremely limited, one monotreme, the Short-beaked Echidna, is rather successful - ranging over the entirety of Australia and occupying habitats as diverse as alpine grasslands, desert and tropical rainforests. Few placentals can make such claims.