Simplify the following text for a Grade 7 native English-speaking person.
Original: Morganucodon is regarded as very primitive , for its lower jaw retains some of the bones found in its reptilian ancestors in a very reduced form , rather than being composed solely of the dentary .
Simplified: Morganucodon is regarded as very basal ( = primitive ) . Its lower jaw has some of the bones found in its synapsid ancestors in a very reduced form .