Outline the evolution of monotreme, marsupial, and placental mammals.

Evolution of Monotreme: About 150 million years ago, the first monotreme have evolved. Early fossils of monotreme have been found in Australia.  A genus called steropodon is an example.

Evolution of Marsupial: About 150 million years ago, the first marsupial have evolved. A genus called sinodelphys which was about 6 inches long is an example of earliest found extinct genus.

Evolution of Placental mammals: About 110 million years ago, the earliest placental mammal have evolved. The extinct genus eomaia is an example of this. It was only 4 inches long.