|
Paleontology in Nevada refers to paleontological research occurring within or conducted by people from the U.S. state of Nevada. Nevada has a rich fossil record of plants as well as both invertebrate and vertebrate animal life.〔 During the Late Precambrian eastern and southern Nevada was being gradually covered by a shallow sea that was home to blue-green bacteria. During the early Paleozoic a variety of local aquatic invertebrates inhabited both freshwater (molluscs) and salt water (graptolites). By the Carboniferous reefs formed despite a drop in local sea levels and a variety of plants flourished on land. Sea levels continued to drop into the early Mesozoic although ammonites and ichthyosaurs inhabited regions still submerged by the sea. Sea levels continued to drop through the Jurassic. An island chain where ''Sequoia'' trees grew emerged during the Cretaceous, but little else is known. Woodlands covered the state during the early part of the Cenozoic era. The state would come to be home to camels, horses, mammoths, and giant ground sloths. Local Native Americans devised myths to explain fossils. By the late 19th century local fossils had attracted the attention of formally trained scientists. Nevertheless, very little organized paleontology has been done within Nevada, and much of that has been carried on by out of state researchers. Consequently, there are few fossils displayed within Nevada. Among the institutions that do house fossils within the state is the Nevada State Museum, Las Vegas.〔 The Triassic ichthyosaur ''Shonisaurus popularis'' is the Nevada state fossil.〔 ==Prehistory== During the Late Precambrian eastern and southern Nevada was being gradually covered by a shallow sea. Blue-green bacteria from this time period were preserved in those areas of the state.〔 More than 500 kinds of Paleozoic invertebrates are known to have inhabited Nevada during the Cambrian, Devonian, and Carboniferous periods of the Paleozoic era. Most of the invertebrates known from this time were freshwater mollusks.〔 The sea continued to expand into the state through the Devonian. During that period northwestern Nevada's sea began to get deeper, gradually becoming an ocean basin. These deeper water areas of Devonian Nevada were home to drifting animals like graptolites. The shallower water regions were home to reefs. Near the end of the Devonian an interval of mountain building called the Antler Orogeny began.〔 The Antler Orogeny continued into the Early Carboniferous. Dropping sea levels exposed regions of Nevada as dry land. Environments of eastern Nevada included lagoons and beaches. Local plant life were preserved in rocks formed by these deposits. Northern and northeastern Nevada were still home to reef habitats. Northwestern Nevada was still a deep ocean. Its abundant plankton left behind many fossils.〔 Nevada's sea level continued to drop during the Triassic period. However, the western part of the state was still relatively deep. It was home to a rich ammonite and ichthyosaur fauna.〔 During the Triassic, many invertebrates lived and died in the area now occupied by the Shoshone Mountains. Their fossils are scientifically significant as many are now used as index fossils or were completely unknown to science before their discovery here.〔 By the Jurassic, the only deep marine habitats of Nevada were in the northwestern part of the state. Central Nevada was only under shallow water and the eastern and southern parts of the state were characterized by other types of environment.〔 During the Cretaceous, a volcanic island chain formed in far western Nevada. Contemporary plant fossils from Nevada include "twigs" of petrified wood preserved in Eureka County. These may be the remnants of ancient ''Sequoia'' trees.〔 Local dinosaurs included armored dinosaurs, possible duck-billed dinosaurs and relatives of the horned dinosaurs.〔 During the Cenozoic geologic upheaval created the state's basin and range physiographic province. Woodlands harboring trees like oak, redwood, and willow formed in Nevada. Local wildlife included creatures like horses, mammoths, and rhinos. Volcanic eruptions regularly shook the state during the Cenozoic.〔 Some of Nevada's Miocene life was preserved in the sediments composing what are now known as the Truckie Beds of the Kawich Mountains northeast of modern Reno. Local bodies of fresh water were inhabited by mollusks at the time. On land Nevada was home to a variety of mammals including both mastodons and rhinoceroses.〔 As the Cenozoic continued, Nevada's Sierra Nevada Mountains were raised. Volcanic activity was still ongoing. Local wildlife included camels, horses, mammoths, and giant ground sloths.〔 Nevada's trace fossil record from the Pleistocene is very rich. One site preserved the footprints of a diverse menagerie of creatures including birds, giant sloths, horses, lions, mastodons, and wolves.〔 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 Nevada」の詳細全文を読む スポンサード リンク
|