The Paleogene is a geologic period and system that began 66 million years ago and ended 23 million years ago. It is the first of three periods in the Cenozoic Era, preceding the Neogene Period and followed by the Quaternary Period. The Paleogene spans from the end of the Mesozoic Era to the beginning of the Neogene.
The Paleogene Period was characterized by global warming, which resulted in widespread tropical climates; it also featured drastic changes in flora and fauna. The climate abruptly cooled at around 34 Ma, during what is known as “the Paleocene-Eocene Thermal Maximum” (PETM). This event caused mass extinctions and rapid evolution among surviving species.
During this time, mammals had diversified into many new forms, including ancestral forms of primates, elephants, horses, pigs, rabbits and rodents. Birds also diversified during this time – one notable example being the early appearance of ducks. Reptiles were less diverse during this time than they had been during previous periods; however, some groups such as snakes underwent adaptive radiation to fill newly vacant ecological niches.
Paleogene rocks are distributed worldwide; however, most outcrops are found in areas that were once part of ancient continents such as Europe or North America. Notable exceptions include Australia, India, Africa,-, Antarctica, New Zealand, Japan, Greenland, and parts of Southeast Asia.-.