On Old Earth, the first epoch of the Cenozoic Era, lasting from 65 to 57 million years ago. It was preceded by the last epoch of the Cretaceous and followed by the Eocene. Life on land included many new forms of mammals, though few of the types that dominate in modern times. Many of these resembled modern rodents or opossums but walked plantigrade and had short legs and relatively small brains. Few were larger than a bear and many were much smaller. There were some very large ground-dwelling birds, both predatory and carnivorous. Invertebrate life was quite similar to that of modern times to the uneducated eye. Dense forests covered most of the land and extended nearly to the poles. Seasonal variations were small.