The Palaeocene or Paleocene ("Old New", from Greek palaios, "older", kainos "new") is the first epoch of the Paleogene period of the modern Cenozoic era. The Palaeocene starts with the K-Pg Extinction event which wiped out the Non-avian dinosaurs and ended with the Palaeocene-Eocene Thermal Maximum, which resulted in a mass extinction of deep-sea algae and a major turnover of mammals on land around 55.8 Mya. The Palaeocene starts around 66-65 Mya to 56-54 Mya (according to different sources, it ended 56 according to some sources, 54 according to others).
The K-Pg Extinction Event ended up with new niches vacant, which resulted in an explosive evolutionary radiation of mammals, birds, snakes, fish and crocodiles, with many new bird orders and families appearing. The earliest owls appeared in France and North America during the Late Palaeocene.