Summary:
- The earliest mammals evolved from cynodonts.
- Mammals continued to evolve.
- Monotreme mammals probably split off from other mammals first.
- They were followed by marsupials.
- Placental mammals probably evolved last.
- Early monotreme fossils have been found in Australia.
- An example is a genus called Steropodon, shown in Figure below.
- It may have been the ancestor of the platypus.
- The ancestor of placental mammals may be the extinct genus Eomaia.
- It was a tree climber and probably ate insects and worms.