Modern mammal groups diverge
The three surviving mammal lineages — monotremes, marsupials and placentals — split from one another.
- When
- Known to
- ± 8 million years
- Era
- Jurassic, Mesozoic
Dating from the Yanliao fossils places the origin of crown mammals in the Middle Jurassic, with the egg-laying monotreme line separating first and the marsupial and placental lines dividing later. All three remain small and mostly nocturnal for another hundred million years. The Jurassic is where the deep structure of the modern mammal family tree is set.