Eocene epoch


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Related to Eocene epoch: Oligocene epoch, Paleocene epoch, Paleogene, Miocene epoch

Eocene epoch

(ē`əsēn'), second epoch of the Tertiary periodTertiary period
, name for the major portion of the Cenozoic era, the most recent of the geologic eras (see Geologic Timescale, table) from around 26 to 66 million years ago. The name Tertiary was first applied about the middle of the 18th cent.
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 in the Cenozoic eraCenozoic era
, last major division of geologic time (see Geologic Timescale, table) lasting from 65 million years ago to the present. The Cenozoic is divided into the Tertiary (from 65 million years ago until 2 million years ago) and Quaternary (2 million years ago to the
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 of geologic time, from approximately 54.9 to 38 million years ago. The Eocene in North America was marked by the submergence of the Great Valley of California and a portion of the Atlantic and Gulf coastal plain extending from New Jersey to Texas and into the present Mississippi River valley as far north as S Illinois. There was also extensive sediment deposition in the Rocky Mt. region. Eocene sedimentary formations along the Atlantic-Gulf coast are chiefly sands, clays, and marls, with some limestone and lignite; in California, Oregon, and Washington they consist of shale and sandstone, with oil and coal. The Badlands of the West are partly cut into Eocene rock formations, e.g., the Wasatch, Green River, Bridger, and Uinta formations, which contain great quantities of volcanic ash and, in some districts, oil-producing shale. The Green River formation of SW Wyoming is noted for its freshwater fossil fish. The brightly colored Wasatch formation makes up the spectacular pillars of Bryce Canyon National Park. Interpretation of Eocene rock strata is based on the succession of beds in Belgian, French, and English basins, which became type areas. The Norwegian-Greenland Sea began to open during the Eocene, and a great inundation from the Mediterranean covered most of S Europe, N Africa, and SW Asia, depositing nummulitic limestone, which is prominent in the Alps and Carpathians and from which the stones of the Pyramids were quarried. Mammals became the dominant animals, and the ancestors of the common animals of Europe and North America made their appearance, possibly as immigrants from other regions. Eocene mammals included ancestral rhinoceroses, tapirs, camels, pigs, rodents, monkeys, whales, and the ancestral horse, eohippus, as well as animals such as the titanothere, which have since become extinct. The vegetation of the Eocene was fairly modern; the climate was warm.
References in periodicals archive ?
5 million years ago, just after the end of the Eocene epoch.
The nearest major extinction came some 2 million years later, at the end of the Eocene epoch.
Even so, these resilient mammals went extinct about 35 million years ago, at the end of the Eocene epoch.
Previous analyses of cores drilled in this region revealed ice-rafted debris dating back to the middle Eocene epoch, prompting suggestions that ice appeared in the Arctic about 46 million years ago.
He looked through the North American mammal record to see how species responded to three periods of extreme climate change during the last 40 million years: a global cooling during the Eocene epoch, 37 million years ago; a severe cooling in the early Oligocene, at 33 million years ago; and a drying in the Miocene at 7.
Before the cooling occurred at the end of the Eocene epoch, the Earth was warm and wet, and even the north and south poles experienced subtropical climates.
Indeed, the ostrich has its origins in the Eocene epoch, about 55 million years ago.
Paleontologists have discovered fossils of cat-sized horses that scampered across northwestern Wyoming about 50 million years ago, during the Eocene epoch.
Leaf-eating did not happen overnight," Strahl told SCIENCE NEWS, adding that some fossil evidence indicates the hoatzin may have originated in the Eocene epoch, predating mammal foregut fermenters.
During the Eocene epoch, a long rift cleaved the plate and cut off its northern section, which held the Broken Ridge part of the plateau.
The 53-million-year-old fossils combine features of two major primate groups from the Eocene epoch, which lasted from about 53 million to 37 million years ago.
What enticed so many people was Petuch's idea that the evolution of the United States' largest tropical wetland began when an asteriod slammed into the region 36 million years ago, at the end of the Eocene epoch.