Simplify the following text for a Grade 9 native English-speaking person.
Original: The mid-Eocene saw the rise of large creodont and mesonychid predators to ecological prominence in Eurasia and North America ; the appearance of these new predators coincides with the decline of Gastornis and its relatives .
Simplified: The mid-Eocene saw the rise of large creodont and mesonychid predators in Eurasia and North America . The appearance of these new predators coincides with the decline of Gastornis and its relatives .