~210 million years agoReputable sourceWell documented
The First Mammals
On the timeline · around ~210 million years ago · Mesozoic
What happened
Tiny, shrew-like mammals such as Morganucodon evolved from mammal-like reptiles in the Late Triassic and Early Jurassic. Through the long age of the dinosaurs, mammals remained small and mostly nocturnal.
Why it matters
These unassuming creatures were the ancestors of all mammals — and they would inherit the Earth once the dinosaurs were gone.