Lasting 42 million years, the Paleogene is most notable as being the time in which mammals evolved from relatively small, simple forms into a large group of diverse animals in the wake of the Cretaceous-Tertiary extinction event that ended the preceding Cretaceous Period.. 
jẹ́ ará Nàìjíríààìtọ́kasí àwọn Ọjọ́ìbí níàwọn ara Nàìjíríà..