Mammals
Saw the most organism diversification of the period. After the events of the extinction of most of the dinosaurs, the remaining became mammals and formed the different organisms we see such as birds, fish, and the many different organisms we see in the Animalia Kingdom. The mammals after the age of the reptile grew in power and significance and with the forests as their home they grew and grew apart as well. The first primates were formed in this period being able to climb the trees and use mechanical functions as time progressed.
Birds
Birds were also a big group in the paleogene period, many flightless birds were also present but when the mammals grew larger and many species were formed, flightless birds dwindled and many birds we know today were existing in this period. Since the birds had tough beaks it was easy to break nuts and go into small crevices to get insects, and when flight capabilities are involved the birds can get away from harm.
Cetaceans
Whales were one of the mammals that took the seas. evolving into the whales we see now forming fins and muscular tails to be able to swim through the ocean. Whales than were some of the biggest mammals and near the end of the period they began to grow teeth and form another phyla in the animalia kingdom.