Answer the following question given this paragraph: 

By about 320 million years ago, early amniotes had diverged into two groups, called synapsids and sauropsids. Synapsids were amniotes that eventually gave rise to mammals. Sauropsids were amniotes that evolved into reptiles, dinosaurs, and birds. The two groups of amniotes differed in their skulls. The earliest known reptile, pictured in Figure below , dates back about 315 million years.


Q: How many years ago did early amniotes diverge into two groups?


A:
320 million years