Smithsonian National Museum of Natural History Geologic Time The Story of a Changing Earth
Presented by the Department of Paleobiology.
The Pliocene
Contents
Overview
Life in the Pliocene
Tectonics during the Pliocene
Climate Cycles during the Pliocene
Evidence
Ostracode, a member of a group of crustaceans
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sample
Henryhowella
Pterygocythereis
references and links
Foundational Concepts
Dating Methods
Earth Processes
Life Processes
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Glossary Credits Email Us


Life in the Pliocene
During the Pliocene, the Panamanian land bridge linked North and South America, allowing terrestrial species to migrate between the two continents. This event is called the Great American Faunal Interchange, a time when two long-isolated faunas came into contact. Sixteen native southern genera moved to the north, including armadillos, giant ground sloths, flightless predatory birds, marsupials (including opossums), and porcupines. At the same time, 23 native northern genera moved south, including cats, dogs, bears, tapirs, camels, and certain rodents. The exchange was not a balanced one, however. Many more South American immigrant species became extinct, perhaps as a result of competition and the inability to adapt to new conditions. As a result, many North American species now live in South America, but few South American imports still survive in the north.

Migrations also continued between Asia and North America via the Bering land bridge. Mastodons and true horses (Equus) were among these migrating mammals. Rodents appear to have reached Australia from the Indonesian archipelago at this time. The one-toed horse Equus was common in North America, along with armored glyptodonts and many species of camels. The once-common oreodonts had dwindled in number, and North American rhinos became extinct.

Also during the Pliocene, several early bipedal ancestors of humans co-existed in the African landscape. Early evidence of human ancestors comes from East African fossil localities in the rift valley sites of Ethiopia, Kenya, and Tanzania. The well-known fossil "Lucy" was discovered in 1974 in Hadar, Ethiopia. This member of the hominid lineage, named Australopithecus afarensis, was found in sediments dating to over 3 million years ago. Meanwhile, at Laetoli, Tanzania, human-like footprints were left by two individuals in a volcanic deposit over 3 million years ago. These discoveries indicate that human bipedalism must be even older, and new evidence suggests it may be as old as 6 to 7 million years.

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Overview | Life in the Pliocene | Tectonics during the Pliocene
Climate Cycles during the Pliocene



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