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Mesozoic era
Mesozoic era [Gr.,=middle life], major division of geologic time (see Geologic Timescale , table) from 65 to 225 million years ago. Great crustal disturbances that marked the close of the Paleozoic and the beginning of the Mesozoic eras brought about drastic changes in the topography of North Amer...
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Cenozoic era
Cenozoic 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 present) periods. Early i...
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ammonite
ammonite , one of a type of extinct marine cephalopod mollusk, related to the nautilus and resembling it in having an elaborately coiled and chambered shell. Unlike the interiors of nautilus shells, the chambers of ammonite shells display intricately shaped septa and sutures. The type included n...
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cephalopod
cephalopod , member of the class Cephalopoda, the most highly organized group of mollusks (phylum Mollusca ), and including the squids , octopuses , cuttlefish , and nautiluses . The class as a whole has become adapted for a free-swimming existence. Cephalopods are able to move about rapidly, a...
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Plesiosaurus
Plesiosaurus , genus of extinct predatory marine reptiles that arose in the Triassic period of geologic time and continued into the Jurassic and Cretaceous periods. Plesiosaurs became extinct at the close of the Mesozoic era. Fossilized skeletons of them have been found in North America, Europe, and...
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Geologic Timescale
Geologic Timescale
Geologic Timescale
Era
Period
Epoch
Approximate duration (millions of years)
Approximate number of years ago (millions of years)
Not an era but the time preceding the Cambrian.
Cenozoic
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continental drift
continental drift geological theory that the relative positions of the continents on the earth's surface have changed considerably through geologic time. Though first proposed by American geologist Frank Bursley Taylor in a lecture in 1908, the first detailed theory of continental drift was put for...
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Karroo
Karroo or Karoo , the semiarid plateaus of South Africa. The Little Karroo, in Western Cape, is located N of the Langeberg and Outeniqua Ranges and extends c.200 mi (320 km) from east to west at an altitude of 1,000 to 2,000 ft (305-610 m). It is separated from the Great Karroo, in Western C...
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tuatara
tuatara or tuatera , lizardlike reptile , Sphenodon punctatus, last survivor of the reptilian order Rhynchocephalia, which flourished in the early Mesozoic era before the rise of the dinosaurs. Also called sphenodon, it is found on islands off the New Zealand coast and in Karori Wildlife Sanc...
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mammal
mammal an animal of the highest class of vertebrates, the Mammalia. The female has mammary glands, which secrete milk for the nourishment of the young after birth. In the majority of mammals the body is partially or wholly covered with hair; the heart has four chambers, and only the left aortic arc...
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