Smithsonian National Museum of Natural History Geologic Time The Story of a Changing Earth
Presented by the Department of Paleobiology.
The Eocene
Contents
Eocene Overview
Terrestrial Life during the Eocene
Marine Life in the Eocene
Shifting Continents and Changing Climates
Evidence
A fossil weevil from the Green River
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sample
Dawn horse
Uintathere
Brontothere
Miacis
Pseudocrypturus cereamaxis
Extinct whale
Snail shell
Poplar
Fern leaf
Palm leaf
March fly
Treehopper
Butterfly

references and links
Foundational Concepts
Dating Methods
Earth Processes
Life Processes
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Marine Life in the Eocene
One of the most remarkable aspects of the Eocene marine fossil record is the presence of the first whales. These earliest fossil whales, from rocks in Pakistan and India, suggest that whales are closely related to the even-toed ungulates (artiodactyls). Both artiodactyls and early whales have an unusual feature in that one of the ankle bones (the astragalus) is shaped like a double pulley. Archaic whales such as Ambulocetus and Pakicetus demonstrate the transition from a terrestrial to an aquatic way of life. Later in the Eocene, whales and sea cows (sirenians) adapted more completely to ocean life and spread worldwide. One type of archaic whale (Basilosaurus) achieved lengths of 60 feet.

Among the cartilaginous fishes, modern forms such as requiem sharks increased, while sand tiger sharks decreased. By the Middle Eocene, the giant sand tiger shark Otodus obliquus was extinct. Mako and giant-toothed white sharks first appeared at this time as well. However, bony fishes continued to dominate the seas, as they do today. Marine invertebrates were also more modern. Paleozoic Fauna animals such as brachiopods were uncommon, while cephalopods, echinoderms, snails, and bivalves thrived.

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Eocene Overview | Terrestrial Life during the Eocene | Marine Life in the Eocene
Shifting Continents and Changing Climates



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