The Paleogene Period is a division of the geological timescale that lasted from about 66 to 23 million years ago, following the extinction of the dinosaurs. This period is significant for the diversification of mammals, the development of modern plant species, and the establishment of many of the Earth’s current ecosystems.
Reference: Berggren, W. A., & Pearson, P. N. (2005). “A Revised Tropical to Subtropical Paleogene Planktonic Foraminiferal Zonation.” Journal of Foraminiferal Research, 35(4), 279-298.