The Paleogene era opened with the most dramatic reset in the past 250 million years. Sixty-six million years ago, an asteroid impact and massive volcanic eruptions ended the reign of non-avian dinosaurs, erasing roughly 75 percent of all species from the planet. From this devastation emerged a transformed world—warmer, wetter, and ripe for evolutionary experimentation. The Paleogene spans 43 million years of reconstruction, divided into three epochs: the Paleocene, Eocene, and Oligocene. During this time, Earth's continents continued their slow drift toward modern positions, and dense tropical forests blanketed landscapes from pole to pole.
Mammals seized the opportunity left by the dinosaurs' extinction. Within ten million years, they diversified from small, shrew-like creatures into an astonishing array of forms: early whales took to the seas, horses the size of house cats galloped across forest floors, and the first primates climbed through canopy branches. Birds, the surviving dinosaur lineage, radiated into thousands of species, including giant flightless predators that temporarily claimed the top carnivore role on several continents. Flowering plants consolidated their dominance, and grasslands began their slow spread across the continents during the Oligocene.
The Paleogene established the biological foundation of our modern world. By its close, 23 million years ago, most major mammal groups—carnivores, rodents, elephants, bats, and primates—had appeared. Global temperatures began a long cooling trend that would eventually culminate in the ice ages. The stage was set for the Neogene, when grasslands would reshape ecosystems and our own ancestors would take their first upright steps.
Key Events
66 Mya
Mass Extinction Ends the Mesozoic Era
63 Mya
Mammals Rapidly Diversify Into Empty Niches
56 Mya
Paleocene-Eocene Thermal Maximum Spikes Temperatures
50 Mya
India Collides With Asia, Himalayas Begin
47 Mya
Early Whales Transition to Marine Life
34 Mya
Antarctic Ice Sheets Form, Climate Cools
25 Mya
Grasslands Spread Across Continental Interiors
Life in the Paleogene
The Paleogene era opened in the aftermath of the asteroid impact that ended the dinosaurs, leaving a world of ecological vacuums waiting to be filled. Mammals, previously small and nocturnal, rapidly diversified into niches once dominated by reptiles. Within 10 million years, the first whales swam coastal waters, early horses no larger than dogs browsed forest floors, and primates established themselves in tropical canopies.
Birds emerged as the dominant land vertebrates in some regions, with terror birds standing over 2 meters tall as apex predators in South America. Crocodilians, turtles, and snakes persisted largely unchanged, while giant insects briefly returned in oxygen-rich Eocene forests.
The World of the Paleogene
The Paleogene opened with the continents still drifting apart from the breakup of Pangaea—South America and Australia remained connected to Antarctica, while India raced northward toward its collision with Asia around 50 million years ago, an impact that began raising the Himalayas. The Tethys Sea, a vast equatorial ocean separating Africa and Eurasia, dominated global marine circulation until Africa's northward movement progressively closed it, while the Atlantic Ocean continued widening as the Americas pulled away from Europe and Africa. What distinguished the Paleogene from the preceding Cretaceous was the absence of the Western Interior Seaway that had split North America, and from the following Neogene, the still-open connections between Antarctica and its neighboring continents—passages that, once severed around 34 million years ago, triggered the Antarctic Circumpolar Current and plunged the planet into the icehouse conditions
Continent Configuration
The supercontinent Gondwana continued breaking apart as South America separated from Antarctica, Australia drifted northward from Antarctica, and India collided with Asia to begin forming the Himalayas, while the Atlantic Ocean widened steadily between the Americas and Europe-Africa.
Notable Seaways
Atlantic Ocean · Tethys Sea · Southern Ocean · Arctic Ocean