The first mammal-like animals
Tiny nocturnal insectivores appear, and spend the next 160 million years staying out of the way.
- When
- Known to
- ± 3 million years
- Era
- Triassic, Mesozoic
By around 225 million years ago cynodonts have given rise to mammaliaforms — shrew-sized, probably nocturnal, with differentiated teeth, enlarged brains for their size, and likely fur and milk. A 225-million-year-old jaw joint fossil has pushed key mammalian features earlier still. They remain small and inconspicuous throughout the age of dinosaurs, but the lineage never dies out.