Diatryma (Gastornis gigantea): Eocene 55 MYA Megistotherium osteothlastes: Miocene 23 MYA Hyaenodon horridus: late Eocene-early Oligocene 42-16 MYA Smilodon gracilis: Pleistocene Andrewsarchus mongoliensis: Eocene 42-36 MYA Amphicyon giganteus: Bear-dog: Oligocene to Miocene 16.8-7.2 MYA