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 . 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 .