Simplify the following text for a Grade 10 native English-speaking person.
Original: Very early in the evolutionary history of amniotes , basal amniotes evolved into two main lines of amniotes , the synapsids and the sauropsids , both of which persist into the modern era .
Simplified: Very early in the evolutionary history of amniotes , they split into two main lines , the synapsids and the sauropsids , both of which persist into the modern era .