Simplify the following text for a Grade 10 native English-speaking person.
Original: A classic example of this is the replacement of the non-avian dinosaurs with mammals at the end of the Cretaceous , and of brachiopods by bivalves at the Permo-Triassic boundary .
Simplified: A classic example of this is the replacement of the non-avian dinosaurs at the end of the Cretaceous with mammals in the Palaeocene .