After the Mesozoic Era ended, the Paleogene period started. During this period, the Earth was still recovering from the devastating meteor strike that defined the Cretaceous extinction. The mammals, formerly small, nocturnal, rodent-like creatures, had started to diversify in order to fill the niches the dinosaurs left behind, while the birds also flourished in order to rule the skies after the pterosaurs' extinction; as well as this, this period is split into three major epochs, the Paleocene (early Paleogene), Eocene (mid-Paleogene), and Oligocene (late Paleogene). During the Paleocene, the mammals and birds had continued to remain small (only diversifying later in the epoch); the reptiles, however, had still managed to attain respectable sizes and a near-global distribution even after the end of their Cretaceous heydays. The Eocene was when the mammals had already diversified to take up many different niches, from hoofed herbivores that fed from low-growing vegetation and agile predators that preyed on everything they could find to arboreal primates that used their prehensile fingers and toes to move around from tree to tree; most important of them all were a large group of small, hoofed predators that had slowly returned to an aquatic lifestyle, and would soon evolve into the first whales. During the Oligocene, the climate had significantly cooled down from the hot temperatures of the Eocene; with the cooling temperatures came the decline of tropical forests and the rise of more open habitats such as deserts and scrublands, which caused a diversification and decline of various classes of animals. Soon, climate change and a continental drift would sweep this period, driving many species to extinction and giving rise to the Neogene.
Lasted from 66-23.03 mya
Paleocene Animals (note that those are not all the ones that exist)[]
- Cerrejonisuchus
- Carbonemys
- Anthracosuchus
- Acherontisuchus
- Titanoboa
Eocene Animals (note that those are not all the ones that exist)[]
- Gastornis
- Physogaleus
- Mongolonyx
- Leptictidium
- Titanomyrma
- Godinotia
- Andrewsarchus
- Ambulocetus
- Propalaeotherium
- Palaeotherium
- Anthropornis
- Hyaenodon
- Dorudon
- Basilosaurus
- Llanocetus
- Cynodictis
- Entelodon
- Mongolestes
- Embolotherium
- Moeritherium
- Anoplotherium
- Arsinoitherium
- Sarkastodon
- Otodus auriculatus
- Paraceratherium
- Palaeeudyptes
Oligocene Animals (note that those are not all the ones that exist)[]
- Apidium
- Chalicotherium
- Pelagornis
- Quinkana