| Oldfieldthomasiidae(noun, fauna, eocene, extinction) |
| Oligocene genus extinction(expression, extinction, period, geochronology) |
| Omomyidae(noun, fauna, extinction, oligocene) |
| Orohippus(noun, fauna, eocene, extinction) |
| Oromerycidae(noun, fauna, eocene, extinction) |
| Oxyaena(noun, fauna, eocene, extinction) |
| Oxytoma(noun, fauna, extinction, paleocene) |
| Pachyaena(noun, fauna, eocene, extinction) |
| Pakicetidae(noun, fauna, eocene, extinction) |
| Palaeoamasiidae(noun, fauna, eocene, extinction) |
| Palaeochiropterygidae(noun, fauna, eocene, extinction) |
| Palaeoglaux(noun, fauna, eocene, extinction) |
| Palaeolagus(noun, fauna, extinction, oligocene) |
| Palaeonictis(noun, fauna, eocene, extinction) |
| Palaeoryctidae(noun, fauna, extinction, paleocene) |
| Palaeotheriidae(noun, fauna, extinction, oligocene) |
| Palaeotherium(noun, fauna, eocene, extinction) |
| Palimphyes(noun, fauna, extinction, oligocene) |
| Pantolestidae(noun, fauna, extinction, oligocene) |
| Paracathartes(noun, fauna, eocene, extinction) |