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Paleontology in North Dakota refers to paleontological research occurring within or conducted by people from the U.S. state of North Dakota. During the early Paleozoic era most of North Dakota was covered by a sea home to brachiopods, corals, and fishes. The sea briefly left during the Silurian, but soon returned, until once more starting to withdraw during the Permian. By the Triassic some areas of the state were still under shallow seawater, but others were dry and hot. During the Jurassic subtropical forests covered the state. North Dakota was always at least partially under seawater during the Cretaceous. On land ''Sequoia'' grew. Later in the Cenozoic the local seas dried up and were replaced by subtropical swamps. Climate gradually cooled until the Ice Age, when glaciers entered the area and mammoths and mastodons roamed the local woodlands. Local Native Americans interpreted fossils as the remains of the water monster Unktehi or burrowing serpents killed by the thunderbirds. The first scientifically documented local fossils were collected during the Lewis and Clark expedition. Shipworm-bored petrified wood is the North Dakota state fossil. ==Prehistory== No Precambrian fossils are known from North Dakota, so the state's fossil record does not begin until the Paleozoic era. Large areas of North Dakota were under the sea during the early Paleozoic. During the Silurian the sea briefly withdrew from the state, although it was quickly re-inundated. Life in this sea included brachiopods, corals, fishes and molluscs. Sea levels continued to fluctuate throughout the remainder of the Paleozoic, and by the Permian period significant areas of the state were dry land. By the end of the Paleozoic the state was positioned near the equator.〔 During the Triassic much of the state was covered in shallow seawater, but the exposed terrestrial environments were very hot and dry. As the Triassic gave way to the Jurassic, North Dakota was becoming a series of plains covered in subtropical forests. Eventually these forests were also swallowed again by the sea. This sea was home to life like bivalves, echinoderms, foraminiferans, and gastropods. Throughout the Cretaceous North Dakota was either fully or partially submerged by sea water.〔〔 The Niobrara Formation of the Pembina Escarpment and Valley City region records the presence of fish during the Cretaceous with fossils of their scales and bones. The Cretaceous Pierre Shale can likewise be found in the Pembina Escarpment and Valley City area as well as the banks of the Missouri and Little Missouri rivers.〔 The Pierre Shale preserves later Cretaceous invertebrates like ammonites, clams, and snails. Contemporary fishes also left fossils of their scales.〔 Mosasaurs lived in the Late Cretaceous seas of North Dakota.〔 On land, dinosaurs were living along the coast of this sea.〔 Later in the Cretaceous, local North Dakotan vertebrates left behind fossil bones and on rare occasions impressions were preserved of leaves from the local flora in the Hell Creek Formation. These were also preserved in the area now occupied by the banks of the Missouri and Little Missouri rivers.〔 The Cretaceous ''Sequoia dakotensis'' left fossil cones in the area near Mandan. The same site preserved sections of petrified wood, some up to 50 lbs. Some of the petrified wood at this site bear the borings made by ancient ship worms.〔 Dinosaurs included the armored ''Edmontonia'', duck-billed ''Edmontosaurus'', ostrich dinosaurs, pachycephalosaurs, ''Triceratops'', and ''Tyrannosaurus''.〔 During the ensuing Paleocene epoch, corals and snails were preserved by sediments now known as the Cannonball Formation, however, such fossils are very rare. Freshwater clams and snails have also been found in other contemporary deposits in the state. On land, trees would later leave behind wood to petrify. Leaves are also among the state's Paleocene fossils.〔 Eocene plant fossils are known along the Knife River.〔 Freshwater clams and snails are known in the areas north and east of the Missouri River. The Cannonball deposits near Minot are the last marine deposits to have been left in the North American interior.〔 As the Cenozoic progressed, North Dakota's sea would give way to subtropical swamps.〔 Rich North Dakotan forests included plants like cycads, dawn redwoods, ferns, figs, and palms. The local vegetation left behind great coals deposits in the rock record. Throughout the remainder of the Cenozoic, North Dakota's climate cooled and dried. The state's swamps vanished and their inhabitants went extinct. In their place woodlands formed. The climate got colder still and eventually glacial activity reshaped the state's landscape. At this time North Dakota was home to mammoths and mastodons.〔 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 North Dakota」の詳細全文を読む スポンサード リンク
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