Mammals and reptiles part ways
The amniote line divides into two branches — one leads to reptiles and birds, the other to us.
- When
- Known to
- ± 10 million years
- Era
- Carboniferous, Paleozoic
Early amniotes split into sauropsids, ancestral to all reptiles and birds, and synapsids, ancestral to mammals. The division is marked by the number of openings in the skull behind the eye. For the next hundred million years the synapsids are the larger and more successful branch; only after the end-Permian extinction do the sauropsids take over.