Paleontology

A

Paleocene Epoch

The Paleocene Epoch (65 million to 56 million years ago) marks the beginning of the Cenozoic Era. A number of groups of Paleocene mammals are known. All of them appear to have developed in northern Asia and to have migrated to other parts of the world. These primitive mammals had many features in common. They were small, with no species exceeding the size of a small modern bear. They were four-footed, with five toes on each foot, and they walked on the soles of their feet. Almost all of them had slim heads with narrow muzzles and small brain cavities. The predominant mammals of the period were members of three groups that are now extinct. They were the creodonts, meat-eating mammals that were not ancestral to modern carnivores; the amblypods, which were small, heavy-bodied animals; and the condylarths, which were light-bodied herbivorous animals with small brains. The Paleocene groups that have survived are the marsupials, the insectivores, the primates, and the rodents.

B

Eocene Epoch

During the Eocene Epoch (56 million to 34 million years ago), a number of direct evolutionary ancestors of modern animals appeared. Among these animals—all of which were small in stature—were the horse, rhinoceros, camel, rodent, and monkey. The creodonts and amblypods continued to develop during the epoch, but the condylarths became extinct before it ended. The first aquatic mammals, ancestors of modern whales, also appeared in Eocene times, as did such modern birds as eagles, pelicans, quail, and vultures. Changes in vegetation during the Eocene Epoch were limited chiefly to the migration of types of plants in response to climate changes.

C

Oligocene Epoch

During the Oligocene Epoch (34 million to 23 million years ago), most of the archaic mammals from earlier epochs of the Cenozoic Era disappeared. In their place appeared representatives of a large number of modern mammalian groups. The creodonts became extinct, and the first true carnivores, resembling dogs and cats, evolved. The first anthropoid apes also lived during this time, but they became extinct in North America by the end of the epoch. Two groups of animals that are now extinct flourished during the Oligocene Epoch: the titanotheres, which are related to the rhinoceros and the horse; and the oreodonts, which were small grazing animals.

D

Miocene Epoch

The development of mammals during the Miocene Epoch (23 million to 5.3 million years ago) was influenced by an important evolutionary development in the plant kingdom: the spread of grasses. These plants, which were ideally suited for forage, encouraged the growth and development of grazing animals such as horses, camels, and rhinoceroses, which were abundant during the epoch. During the Miocene Epoch, the mastodon evolved, and in Europe and Asia a gorilla-like ape, Dryopithecus, was common. Various types of carnivores, including cats and wolflike dogs, ranged over many parts of the world.

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E

Pliocene and Pleistocene Epochs

The paleontology of the Pliocene Epoch (5.3 million to 1.8 million years ago) does not differ much from that of the Miocene, although the period is regarded by many zoologists as the climax of the Age of Mammals. The Pleistocene Epoch (1.8 million to 11,500 years ago) in both Europe and North America was marked by an abundance of large mammals, most of which were basically modern in type. Among them were buffalo, elephants, mammoths, and mastodons. Mammoths and mastodons became extinct before the end of the epoch. In Europe, antelope, lions, and hippopotamuses also appeared. Carnivores included badgers, foxes, lynx, otters, pumas, and skunks, as well as now-extinct species such as the giant saber-toothed tiger. In North America, the first bears made their appearance as migrants from Asia. The armadillo and ground sloth migrated from South America to North America, and the musk-ox ranged southward from the Arctic regions. Modern human beings also emerged during this epoch.

See also Geology and individual articles on the eras, periods, and epochs mentioned.