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Paleontology in the United States refers to paleontological research occurring within or conducted by people from the United States. Paleontologists have found that at the start of the Paleozoic era, what is now "North" America was actually in the southern hemisphere. Marine life flourished in the country's many seas. Later the seas were largely replaced by swamps, home to amphibians and early reptiles. When the continents had assembled into Pangaea drier conditions prevailed. The evolutionary precursors to mammals dominated the country until a mass extinction event ended their reign. The Mesozoic era followed and the dinosaurs began their rise to dominance, spreading into the country before Pangaea split up. During the latter Jurassic Morrison Formation dinosaurs lived in the western states. During the Cretaceous, the Gulf of Mexico expanded until it split North America in half. Plesiosaurs and mosasaurs swam in its waters. Later it began to withdraw and the western states were home to the Hell Creek dinosaurs. Another mass extinction ended the reign of the dinosaurs. The Cenozoic era began afterward. The inland sea of the Cretaceous vanished and mammals came to dominate the land. The western states were home to primitive camels and horses as well as the carnivorous creodonts. Soon mammals had entered the oceans and the early whale ''Basilosaurus'' swam the coastal waters of the southeast. Rhino-like titanotheres dominated Oligocene South Dakota. From this point on the climate in the United States cooled until the Pleistocene, when glaciers spread. Saber-toothed cats, woolly mammoths, mastodons, and dire wolves roamed the land. Humans arrived across a land bridge between Siberia and Alaska and may have played a role in hunting these animals into extinction. Native Americans have been familiar with fossils for thousands of year, but the first major fossil discovery to attract the attention of formally trained scientists were the Ice Age fossils of Kentucky's Big Bone Lick. These fossils were studied by eminent intellectuals like France's George Cuvier and local statesmen like Benjamin Franklin, Thomas Jefferson, and George Washington. By the beginning of the 19th century, Dinosaur footprints were discovered near the country's east coast. Later in the century, as more dinosaur fossils were uncovered, eminent paleontologists Edward Drinker Cope and Othniel Charles Marsh were embroiled in a bitter rivalry to collect the most fossils and name the most new species. Early in the 20th century major finds continued, such as the Ice Age mammals of the La Brea Tar Pits. Mid-to-late twentieth century discoveries in the United States triggered the Dinosaur Renaissance as the discovery of the bird-like ''Deinonychus'' overturned misguided notions of dinosaurs as plodding lizard-like animals, highlighting their sophisticated physiology and apparent relationship with birds. Other notable finds in the United States include ''Maiasaura'', which provided early evidence for parental care in dinosaurs and "''Seismosaurus''", the largest known dinosaur. ==Prehistory== (詳細はPrecambrian, the areas now composing the United States were home to the first known eucaryotes, whose remains were preserved in California. Other simple Precambrian life is known from Michigan,〔 while more complex forms in Arizona〔 and North Carolina.〔 During the Cambrian, the land masses now composing the United States were separate and located in the southern hemisphere.〔 Trilobites are the most characteristic animal of the time,〔 and are especially abundant in Utah.〔 Ordovician America was still home to a wide variety of marine invertebrates. An important fauna was preserved in the states of Indiana, Kentucky, and Ohio in the Cincinnati region.〔 Life in Silurian America was especially diverse around the coral reefs of Indiana.〔 It was also the time of New York's famous sea scorpion, ''Eurypterus''.〔 Fishes diversified greatly during the Devonian.〔 On land the first known seed plants appeared in Pennsylvania and some of the world's first forests appeared in New York.〔 Mississippian America was once more covered in seas,〔 now notably home to abundant crinoids.〔 During the Pennsylvanian America was largely terrestrial〔 and vast swamps expanded across the country〔 which were home to amphibians.〔 Reptiles were appearing around this time.〔 Into the Permian the continents had collided uniting into a single supercontinent called Pangaea. Much of the country was dry.〔 Precursors to mammals like ''Dimetrodon'' and ''Edaphosaurus'' lived in Texas.〔 At the end of the Permian the largest mass extinction in earth's history occurred, killing some 96% of species on the planet.〔 During the Triassic, the Mesozoic era began.〔 Ichthyosaurs entered the sea and achieved large sizes in Nevada.〔 The Petrified Forest appeared in the southwest.〔 The dinosaurs appeared and achieved dominance on land〔 while pterosaurs flew overhead.〔 Into the Jurassic, plesiosaurs began usurping marine dominance from the ichthyosaurs.〔 Dinosaurs continued to diversify on land and increase in size.〔 A vast complex of floodplains covered the western United States〔 that was home to iconic creatures like ''Allosaurus'',〔 ''Apatosaurus'',〔 ''Ceratosaurus'',〔 and ''Stegosaurus''.〔 During the Early Cretaceous dinosaur faunas began to change.〔 Around the same time sea levels began to gradually rise and the Gulf of Mexico extended up into Alaska, dividing North America in two.〔 This formed the Western Interior Seaway,〔 where ichthyosaurs and plesiosaurs gradually gave way to mosasaurs.〔 Overhead pterosaurs like ''Pteranodon'' of Kansas achieved vast wingspans.〔 Before the end of the Cretaceous the seaway began to retreat and the coastal plains of Montana and the Dakotas were home to iconic dinosaurs like ''Edmontosaurus'', ''Triceratops'', and ''Tyrannosaurus rex''.〔 Soon however, the marine reptiles, dinosaurs, and pterosaurs that dominated the planet went extinct, likely because a meteor impact destabilized the planet's ecosystems.〔 After the extinction of the dominant reptile groups, the Cenozoic〔 ushered in the Age of Mammals.〔 Sea levels continued to decline〔 until the vast Western Interior Seaway was reduced to a small inland body in North Dakota.〔 Mammals were beginning to diversify and dominate the land.〔 The creodonts, forerunners of modern carnivores, arose to prominence during the Paleocene.〔 During the Eocene the western states were home to small primitive camels〔 and horses.〔 Over time both groups got larger and lost several toes.〔〔 Even by the late Eocene mammals had entered the oceans and the great primitive whale ''Basilosaurus'' swam in the coastal waters of the southeastern states like Alabama〔 and Mississippi.〔 Rhino-like titanotheres dominated the South Dakota badlands of the Oligocene.〔 From this point on the climate in the United States cooled〔 until the iconic Ice Age mammals of the Pleistocene like saber-toothed cats, woolly mammoths, mastodons and dire wolves〔 spread across the continent in advance of glaciers.〔 Humans arrived across a land bridge between Siberia and Alaska〔 and may have played a role in hunting these animal into extinction.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Paleontology in the United States」の詳細全文を読む スポンサード リンク
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