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Paleontology in Montana refers to paleontological research occurring within or conducted by people from the U.S. state of Montana. The fossil record in Montana stretches all the way back to the Precambrian. During the Late Precambrian, western Montana was covered by a warm, shallow sea where local bacteria formed stromatolites and bottom-dwelling marine life left tracks on the sediment that would later fossilize. This sea remained in place during the early Paleozoic, although withdrew during the Silurian and Early Devonian, leaving a gap in the local rock record until its return. This sea was home to creatures including brachiopods, conodonts, crinoids, fish, and trilobites. During the Carboniferous the state was home to an unusual cartilaginous fish fauna. Later in the Paleozoic the sea began to withdraw, but with a brief return during the Permian. During the Triassic Montana was again covered in a sea whose inhabitants are the state's only known fossils from this time. Much of Montana remained covered by seawater into the Late Jurassic, but exposed areas were greened by a flora of conifers, cycads, ferns, and ginkgoes. This coastal plain was home to dinosaurs including the ornithopod ''Camptosaurus'', the sauropods ''Apatosaurus'' and ''Diplodocus'', and the theropod ''Allosaurus''. During the early Cretaceous the state was home to its first flowering plants as well as predators such as ''Deinonychus''. Later the Western Interior Seaway, home to creatures such as mosasaurs and plesiosaurs, came to cover the state. On land, the duckbilled ''Maiasaura'' formed vast nesting colonies. By the end of the Cretaceous Montana was home to some of the most famous dinosaurs; creatures such as ''Edmontosaurus'', ''Triceratops'', and ''Tyrannosaurus''. During the early Cenozoic the sea began to withdraw from the state. Plants, insects, dogs, and titanotheres are preserved from this time. Later inhabitants would include arctocyonids, insectivores, multituberculates, pantodonts, primates, and taeniodonts. As the Cenozoic proceeded the climate cooled until the Ice Age started and glaciers entered the state. At this time mammoths, musk oxen, and dire wolves lived in the areas of the state not covered by glaciers. Local Native Americans have been devising mythical explanations for fossils or applying them for practical purposes thousands of years. The first scientific collection of local fossils began in the mid 19th century. Other important discoveries include the plant and insect fossils of Ruby Valley and ''Deinonychus'', which triggered the Dinosaur Renaissance. The Cretaceous Duck-billed dinosaur ''Maiasaura peeblesorum'' is the Montana state fossil. ==Prehistory== The fossil record in Montana stretches all the way back to the Precambrian.〔 During the Late Precambrian, western Montana was covered by a warm, shallow sea. This sea was home to stromatolites and to bottom-dwelling marine life whose tracks on the benthic sediment would later fossilize.〔 Montanan life of the time included arthropods, blue-green algae, conularians, fungi, and worms. Their fossils were preserved in what are now known as Glacier National Park. The worms left trace fossils such as burrow fillings and trails through the sediment.〔 During the ensuing Cambrian period the state was still largely covered by sea water. Montana's Cambrian sea was home to algae, invertebrates, and even some of the first known vertebrates.〔 Later, Cambrian trilobites left behind remains in Nixon Gulch, Horseshoe Hills north of Manhattan, Sawtooth-Lewis and Clark ranges west of Augusta, and the Bridger Range north of Bozeman.〔 The sea eventually withdrew from the state and most of Montana's Silurian and Early Devonian sediments were lost to erosion. During the Late Devonian nearly the entire state was again inundated by the sea. Montana's Late Devonian sea was home to brachiopods, conodonts, crinoids, fish, molluscs, and sponges.〔 Seas continued to cover the state into the Carboniferous period. At that time, the state was home to a bewildering array of cartilaginous fishes.〔 Further into the Paleozoic, Mississippian brachiopods, bryozoans, and corals left behind fossils in the Bridger Range and at Shell Mountain south of Big Timber.〔 Later in the Carboniferous, during the Pennsylvanian epoch, the sea began to retreat. Geological uplift was raising the elevation of the northern and northwestern regions of the state. Montana was covered by the sea again for a short interval of the Permian period.〔 During the Early Triassic, Montana was located about thirty degrees of latitude north of the equator.〔 The sea returned twice to cover significant areas of Montana during the ensuing Triassic period. The state's only known contemporary fossils are the remains of this sea's inhabitants.〔 On land Montana was hot and dry. At the time, the far southwesternmost corner of Montana was covered by a small extension of the shallow sea that covered the western coast of North America and stretched into northern Canada. South central Montana, by contrast, was a desert divided by streams. Outside of these regions little is known because sediments were being eroded rather than deposited.〔 During the Jurassic, the sea returned to cover the state. The sea was gradually filled in by sediments eroded away from areas of higher elevation in the western region of the state.〔 During the Late Jurassic, most of Montana was covered in seawater, similar to that which covered the southwestern corner during the Triassic.〔 Ironically, at this point in time the southwestern area of the state contained an island.〔 This sea would have been home to cephalopods, crinoids, ichthyosaurs, and pelecypods. At the time, Montana was located at about 40 degrees Latitude.〔 The state's flora consisted of conifers, cycads, ferns, and ginkgoes.〔 South of Montana's sea was a coastal plain split by streams flowing west from areas of higher elevation to the east. This coastal plain was home to dinosaurs including the ornithopod ''Camptosaurus'', the sauropods ''Apatosaurus'' and ''Diplodocus'', and the theropod ''Allosaurus''. These sediments deposited what is now known as the Morrison Formation.〔 For thirty million years following the deposition of the Morrison Formation sediments in Montana were being eroded rather than deposited. Seawater was still present in Montana, now extending as an embayment down from the Arctic Circle. Rivers were still flowing into the local sea, but the local dinosaur fauna was very different. Carnivores living here included ''Deinonychus'' and ''Microvenator''. Herbivores included ''Sauropelta'' and ''Tenontosaurus''. Around this time flowering plants would make their first appearance in the state.〔 During the middle part of the Cretaceous Montana was partially covered by the Western Interior Seaway. Significant volcanic eruptions occurred in Montana during the time of the Western Interior Seaway.〔 This sea was home to cephalopods, clams, and plesiosaurs. The sediments deposited by this sea compose what is now called the Colorado Group. No dinosaur fossils are known to have been preserved in the Colorado group in Montana, but outside the state occasional discoveries have been made. Southwestern Montana was dry land, but none of those deposits have yielded dinosaur fossils yet.〔 85 million years ago the Western Interior Seaway withdrew slightly leaving western Montana as a coastal plain. Dinosaurs were present but rarely left fossilized remains. The sea was home to animals such as cephalopods, gastropods, mosasaurs, pelecypods, and plesiosaurs.〔 During the Campanian Stage of the Late Cretaceous the coastal plain bordering the Western Interior Seaway was lined with rivers and dotted with a few lakes. These bodies of water deposited the sediments that later became the Two Medicine Formation. Nearby volcanoes were erupting, depositing ash that would later become bentonite. The climate was semiarid. The flora of the coastal plain included conifer forests, deciduous trees, and ferns. A diverse array of dinosaurs lived in Montana at this time. Duckbilled hadrosaurs were common inhabitants of Montana's Campanian coastal plains.〔 ''Maiasaura'' is one example.〔 Montana has an especially good fossil record of ceratopsid dinosaurs.〔 Examples of contemporary local ceratopsians include ''Einiosaurus''. The theropods ''Daspletosaurus'' and ''Troodon'' were also present. Both ''Maiasaura'' and ''Troodon'' are known to have formed nesting colonies in the area.〔 Late Cretaceous fossil dinosaur footprints are surprisingly rare in Montana compared to other western states with contemporary deposits. This might be due to the local ancient environments not being well suited for track preservation or merely because scientists have not yet looked in the right places.〔 Early in the Maastrichtian the Western Interior Seaway expanded its boundaries somewhat. It was home to cephalopods, clams, crustaceans, fishes, gastropods, mosasaurs, and plesiosaurs.〔 Later in the Maastrichtian stage, volcanic activity was still ongoing in the Elkhorn region and the Western Interior Seaway began to withdraw. This regression would end up resulting in both halves of North America reuniting. As the seaway withdrew the area closest to the Rocky Mountains became an expanding desert. Eastern Montana was hot and humid, by contrast, as the coastal plain was also expanding as a result of the marine regression. By the late Maastrichtian stage large rivers flowed across the eastern part of the state, depositing the sediments that would one day become the Hell Creek Formation. At the time, Montana was home to some of the most famous dinosaurs; creatures including ''Edmontosaurus'', ''Pachycephalosaurus'', ''Triceratops'', and ''Tyrannosaurus''.〔 During the early Cenozoic era, the sea began to retreat from Montana for the last time. Extreme tectonic activity helped form local mountains and raised much of the state's elevation. Local levels of precipitation rose and fell. Montana was home to creatures like dogs and titanotheres.〔 The Tertiary deposits from the southwestern part of the state are one of the best sources of plant and insect fossils in North America. More than two hundred species of plants, insects, and fishes are known from these deposits. The flora included water lilies and lotuses.〔 During the Tertiary Montana was home to swamps that would later leave coal behind.〔 The invertebrate fauna consisted of ants, bees, beetles, earwigs, caddis flies, crane flies, damsel flies, lantern flies, mayflies, grasshoppers, leafhoppers, mosquitoes, snails, and wasps. Contemporary vertebrate fossils included feathers and, once in a while, a bird.〔 Among the Oligocene flora of Montana were ailanthus, ash, beech, cattails, cedar, cinquefoil, dogwood, elm, ferns, milfoil fernbush, gooseberry, climbing grapes, grasses, greenbriers, horsetails, ironwood, katsura tree, liverwort, mountain mahogany, maple, false mermaid, mosses, oak, pennycress, pondweed, dawn redwood, roses, sedges, smoke tree, snowberry, spiraea, false strawberry, and vetches. Similar floras are known from the Florissant of Colorado and Oregon.〔 Montana's Miocene plants and mollusks left behind remains at Bear Butte, northwest of Melville in Sweet Grass County's Fort Union Beds.〔 The Miocene mammals preserved in the Fort Union beds included arctocyonids, insectivores, multituberculates, pantodonts, primates, taeniodonts.〔 During the Miocene Montana was also home to camels and horses.〔 Later into the Cenozoic Montana became colder and wetter. Glacial activity scoured the state. At this time mammoths, musk oxen, and dire wolves lived in the areas of the state not covered by glaciers.〔 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 Montana」の詳細全文を読む スポンサード リンク
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