Paleogene
adjective
Pa·leo·gene ˈpā-lē-ə-ˌjēn 
especially British
ˈpa- : of, relating to, or being the earlier part of the Tertiary including the Paleocene, Eocene, and Oligocene or the corresponding series of rocks
Paleogene noun
Word History
Etymology
borrowed from German paläogen, adjective, from paläo- paleo- + -gen (in neogen neogene)
Note: Term introduced by the German geologist Carl Friedrich Naumann (1797-1873) in Lehrbuch der Geognosie, 2. Auflage, 3. Band (Leipzig, 1866), p 8.
First Known Use
1882, in the meaning defined above