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Paleontology in Utah
Paleontology in Utah refers to paleontological research occurring within or conducted by people from the U.S. state of Utah. Utah has a rich fossil record spanning almost all of the geologic column.〔 During the Precambrian, the area of northeastern Utah now occupied by the Uinta Mountains was a shallow sea which was home to simple microorganisms. During the early Paleozoic Utah was still largely covered in seawater. The state's Paleozoic seas would come to be home to creatures like brachiopods, fishes, and trilobites. During the Permian the state came to resemble the Sahara desert and was home to amphibians, early relatives of mammals, and reptiles. During the Triassic about half of the state was covered by a sea home to creatures like the cephalopod ''Meekoceras'', while dinosaurs whose footprints would later fossilize roamed the forests on land. Sand dunes returned during the Early Jurassic. During the Cretaceous the state was covered by the sea for the last time. The sea gave way to a complex of lakes during the Cenozoic era. Later, these lakes dissipated and the state was home to short-faced bears, bison, musk oxen, saber teeth, and giant ground sloths. Local Native Americans devised myths to explain fossils. Formally trained scientists have been aware of local fossils since at least the late 19th century. Major local finds include the bonebeds of Dinosaur National Monument. The Jurassic dinosaur ''Allosaurus fragilis'' is the Utah state fossil.
== Prehistory==
During the Precambrian, the area of northeastern Utah now occupied by the Uinta Mountains was a shallow sea which was home to simple microorganisms.〔 During the Paleozoic, most of Utah was covered by a shallow sea.〔 The life of Utah during the Cambrian period included brachiopods and trilobites like ''Elrathia''. Cambrian fossils are known from Antelope Springs, the House Range, Millard County in west central Utah.〔 Other Paleozoic marine life included algae, brachiopods, corals, snails, sponges, and trilobites.〔 Marine conditions continued into the Carboniferous.〔 Almost every kind of marine invertebrate could be found in Utah at this time. Fish were also present. This age is the best documented among the state's fossil record.〔 Later, during the Permian period, eastern Utah resembled the modern Sahara desert. Sediments deposited here are now known as the Cedar Mesa Formation.〔 One spectacular fossil trackway from this formation documents a possible predation event that occurred hundreds of millions of years ago. One small trackway of the ichnogenus ''Stenichnus'', left by an early reptile like a protorothyrid or a primitive amphibian like a microsaur, proceeds for a short distance before disappearing when its tracks meet a trackway left by a larger animal. These larger tracks of the ichnogenus ''Anomalopus'' were likely left by a predatory pelycosaur who may have eaten the ''Stenichnus'' trackmaker.〔
Sea levels in Utah dropped by the start of the Mesozoic, leaving only the western half of the state submerged. Life was abundant in the sea.〔 In Utah's Triassic marine ecosystems, ''Meekoceras'' was an especially common cephalopod. Its remains were preserved at what is now known as "Cephalopod Gulch" near Salt Lake City.〔 A series of floodplains filled the vacated eastern part of the state.〔 On land, the Triassic life included trees similar to those of Petrified Forest National Park.〔 Local dinosaurs left behind footprints that would later fossilize.〔 For the rest of the Mesozoic sea levels in the state would rise and fall. During a dry spell in the Jurassic the state was covered in sand dunes. Later the sea rose and covered much of the state. This sea was home to ammonites, brachiopods, clams, fish, marine reptiles, and snails. On land, Utah was still home to dinosaurs.〔 During the Middle Jurassic, eastern Utah was home to crocodilians. One small individual preserved in sediments now known as the Entrada Sandstone represents the only vertebrate body fossils known from western North America.〔 The Entrada Sandstone also preserves many footprints of mid-to-large sized carnivorous dinosaurs across more than thirty tracksites in the eastern part of the state.〔 These tracksites form "a single vast expanse of tracks covering an area of over 300 square miles", or roughly 1,000 square kilometers. This is known as the Moab megatracksite.〔 During the Late Jurassic a group of small to mid-sized ornithopods left behind another significant series of trackways that have since fossilized. These parallel trackways were laid down in sediments that would later become the Morrison Formation of the state's southeastern region, near the Arizona border. The tracks provide important clues to dinosaur social behavior.〔 During the Cretaceous significant volcanic activity occurred in Utah.〔 The Cretaceous was also the last period in geologic history that Utah was covered in sea water.〔 During the Early Cretaceous Utah was home to the pliosaurid ''Brachauchenius''. Western Interior Seaway researcher Michael J. Everhart has called it a "true 'sea monster'" of its time".〔 Nevertheless, most of the fossils from this time are the preserved remains of contemporary local terrestrial life.〔 Later during the ensuing Late Cretaceous epoch the ammonite ''Scaphites'' was especially common in Utah's marine environments.〔
Into the Cenozoic era, geologic processes elevated the state's topography. Utah was also host to a complex of large lakes. Many of these lakes' inhabitants fossilized. These massive lakes gradually vanished as the Cenozoic era proceeded.〔 The Uinta Basin region near the state's border with neighboring Wyoming has been a source of fossil bird tracks, fish, insects, and leaves dating back to the Eocene epoch of the Cenozoic era.〔 Later in the Cenozoic geologic uplift created the state's Basin and Range physiographic province. More recently, in the Quaternary, the state's many canyons were formed by rivers eroding through uplifted rock. Lake Bonneville formed and then largely dried out as local precipitation decreased. Its remnants are known as Great Salt Lake. Local wildlife included short-faced bears, bison, musk oxen, saber teeth, and giant ground sloths.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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