The geological history of North America comprises the history of geological occurrences and emergence of life in North America during the interval of time spanning from the formation of the Earth through to the emergence of humanity and the start of prehistory. At the start of the Paleozoic Era, what is now "North" America was actually in the SouthernHemisphere. Marine life flourished in the country's many seas, although terrestrial life had not yet evolved. During the latter part of the Paleozoic, 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 Triassic, the first period of the Mesozoic Era, followed. Dinosaurs evolved and began their rise to dominance, quickly spreading into the United States. Soon, Pangaea began to split up and North America began drifting north and westward. During the latterJurassic, the floodplains of the western states were home to dinosaurs like Allosaurus, Apatosaurus, and Stegosaurus. During the Cretaceous, the Gulf of Mexico expanded until it split North America in half. Plesiosaurs and mosasaurs swam in its waters. Later into the period, it began to withdraw and the coastal plains of the western states were home to dinosaurs like Edmontosaurus, Triceratops, and Tyrannosaurus. Another mass extinction ended the reign of the dinosaurs.
The oldest known eukaryotes lived around 1.4 billion years ago during the Precambrian near Beck Spring in California. These were photosynthetic organisms and produced oxygen as a byproduct of their physiology. The Beck Spring eukaryotes and other Precambrian photosynthesizers released the oxygen that now makes the planet's atmosphere breathable.[1] Precambrian cyanobacteria remains from this age were preserved between Copper Harbor and Eagle Harbor on the shoreline of Lake Superior in the Upper Peninsula of Michigan.[2] The appearance of the first eukaryotic cells in the fossil record were relatively followed by evidence of complex multicellular life. Rocks in Nevada dating back to a billion years ago preserve trace fossils left behind by worms as they burrowed below the sediment.[3] Other complex Precambrian life forms were preserved in North Carolina[4] and Arizona.[5]
The Phanerozoic eon began following the Precambrian. The first major unit of time it contained was the Cambrian period of the Paleozoic era.[6] At the time, Earth's continents were in a very different arrangement and were generally smaller than they are today. The southeastern part of the US was connected to South America and Africa and located in the polar latitudes of the southern hemisphere. The western states were located near the equator.[7]
All known life during the Cambrian was aquatic so areas of the United States above sea level would have been sterile wastelands.[8]Trilobites are the most common kind of animal in the Cambrian fossil record.[9] Especially notable are the Elrathia of the Antelope Springs region of Utah.[10]Sponge-like archaeocyathids were common in Nevada.[9]Brachiopods, gastropods, and sponges were also important Cambrian animals.[11] Sea levels around North America dropped at the end of the Cambrian. Ecosystems in shallow water probably devastated.[12] The Cambrian ended with a mass extinction. Globally, brachiopods and gastropods lost much of their biodiversity, sponges lost about half of their families and almost three quarters of contemporary trilobite families vanished at the same time.[13]
Much of the continent would be submerged when the sea finally rose again.[12] The most common animal in the Ordovician fossil record seems to have been brachiopods. Large numbers flourished and were preserved in great detail near Cincinnati during the Middle Ordovician. Members of this fauna were preserved in Indiana, Kentucky, and Ohio.[14] Most known Ordovician trilobites are distinct from their Cambrian forebears as the few taxa surviving the mass extinction diversified once again.[15] During the Middle Ordovician, early armored jawlessfish called ostracoderms left behind fragmentary shards of bone in what is now the Rocky Mountains region.[16] Late in the Ordovician sea levels dropped.[17] Another mass extinction marked the end of the Ordovician. Globally, 25% of families disappeared. Major losses were experienced by brachiopods, fishes, echinoids, sponges and trilobites. This mass extinction was also most damaging to trilobites, which lost 50% of their families.[18]
During the Silurian, warm, shallow seas covered most of North America. Illinois, Indiana, and Michigan were home to vast coral reefs.[17] The reefs of Indiana in particular are among the most diverse of the period on the entire continent.[19] The southeastern United States were still part of Gondwanaland during the Silurian.[20] Graptolites still inhabited the waters near the eastern coast of the United States but were not as big a component of the Silurian fauna as they used to be during the Ordovician.[21] As the Silurian progressed the seas covering most of the country would retreat. Only the Michigan and New York areas (then near the equator) were still inundated. However, these landlocked seas were not being replenished by freshwater and so gradually evaporated, leaving concentrated salt deposits in those regions.[17]
Devonian North America once again was home to seas that teemed with life. In fact Devonian marine life may have been more abundant and diverse than at any other point in the Paleozoic.[22]Glass sponges became abundant in western New York during the Devonian.[23] Especially notable are the marine fossils of Cuyahoga County, Ohio, which was home to more than 120 kinds of marine life. The local fishes alone left behind more than 50,000 fossils.[24] During the Late Devonian the oldest known seed-bearing plants grew in Pennsylvania. The plants responsible for leaving behind the local fossil seeds may have been seed ferns, plants whose fronds resemble ferns but who reproduce through seeds instead of spores.[25]Gilboa Forest, among the first in the world, formed in New York around this time.[26] The Devonian ended with another mass extinction. Globally, 25% of families were lost. Nearly every family of ammonoids, fishes, and amphibians became extinct. Most known families of coral and trilobite became extinct. Other taxa to suffer declines in diversity include brachiopods, bryozoans, crinoids, and ostracodes.[27]
The ensuing Mississippian has been nicknamed the Age of Crinoids because this group left behind such abundant fossils. Other common lifeforms include their relatives the blastoids.[28] The pinhead-sized foraminiferanEndothyra fed on seafloor detritus and was extremely abundant during the Mississippian. Some limestones in Illinois and Missouri that formed at this time are almost entirely composed of its remains.[29] Few fossils of terrestrial life are known from the Mississippian of North America.[30]
During the ensuing Pennsylvanian, the northward drift of Gondwanaland finally joined the southeastern United States to North America as Pangaea began to form. Mountain building raised the Ancestral Rockies in Colorado, Utah, and Wyoming. Seawaters left the interior of the country.[31] Densely vegetated swamps were widespread.[32] The largest insects in geologic history lived during the Pennsylvanian.[33] Giant salamander-like amphibians left behind footprints near Lawrence, Kansas that would later fossilize.[34] Fossil footprints from this time period were also preserved in eastern states like Alabama, Georgia, West Virginia, Ohio, and Pennsylvania where Carboniferous fossil footprints are known.[35]
The world's continents were joined as Pangaea throughout all of the Permian. Volcanic activity occurred on the west coast. Seas were present in the southwest and west coast.[36] The seas of Texas were home to massive reefs made of spined brachiopods jumbled together.[37] Seas that had previously covered Kansas, New Mexico and Texas began drying up and left behind salt deposits. The inner portions of the western United States had a hot dry climate. Sand dunes were common throughout the country.[36] The insects of the Permian were common and diverse, but smaller than those of the Pennsylvanian. An example of this bounty were the twenty different orders preserved at a site called Insect Hill near Elmo, Kansas.[38] Massive amphibians were not rare in the southwestern United States but were unable to stray too far from bodies of water.[39]Seymouria was a twenty inch long transitional form documenting the origin of reptiles from their amphibian-like forebears from Texas.[40] Reptiles were becoming common during the Permian.[41] Texas was also home to the pelycosaurs Dimetrodon and Edaphosaurus.[40] Late in the Permian therapsids became the dominant large-bodied terrestrial vertebrates. These were the precursors of mammals.[42]
The Permian ended with the most destructive mass extinction in all of Earth's history. Globally up to 96% of all species may have disappeared.[43]Rugose and tabulate corals became extinct.[44] The cryptostome and trepostomebryozoans also became extinct at this time despite their long history of diversity and abundance earlier in the Paleozoic. Brachiopods suffered greatly and never regained their previous numbers or variety. Ammonoids lost all but one family. Eurypterids and trilobites became extinct. Blastoids became extinct. Crinoids lost all but one family. The echinoids just squeaked past; only one genus is known to have survived. Typical survivors were small detritivores and sediments feeders. The worst losses were among filter feeders and carnivores.[45]
The eastern United States was part of Pangaea's interior for most of the Triassic Period of the Mesozoic era. At the time, the area lay close to the equator and was connected to western Europe and Africa. The union of all of Earth's continents into a single land mass changed the way the atmosphere and oceans circulated. This left what is now the eastern US with a hot climate and pronounced seasons.[46] Much of the country was located at about 30 latitudinal degrees North, where there tends to be high atmospheric pressures and little precipitation. The western United States were largely covered in seawater during the Late Triassic. Mountain building and volcanic activity were ongoing in the same region.[47]
The Triassic saw the Earth's biosphere recovering from the end-Permian mass extinction.[46] After the Permian mass extinction, ammonoids were one of the first groups of marine invertebrates to become abundant and diverse again.[46][48] During the Middle Triassic the scleractinian corals typical of modern oceans appeared. During the Triassic, corals were rare in North America. Nevertheless, some were present on the west coast, although these corals did not congregate into reefs.[49] Ichthyosaurs were one of the most important groups of marine reptiles during the Triassic. Important ichthyosaur fossils of this age were preserved in Nevada.[50]
On land, North America's vegetation included plants like conifers, cycads, ferns, ginkgoes, and horsetails.[46] The Triassic vegetation of the east coast indicated swampy conditions in the local rift valleys. Arizona was home to a great forest that would later leave behind the area's famous petrified wood.[51] Reptiles first began claiming the ecological dominance of marine, terrestrial and aerial habitats during the Triassic that would earn the Mesozoic the nickname "the Age of Reptiles".[52]
The Late Triassic also saw the origin of the dinosaurs.[53]Dinosaurs left behind abundant fossils in the Four Corners region and this area is now known as one of the best sources of Late Triassic dinosaur fossils in the United States. Texas is also good source of dinosaur remains from this time.[54] The oldest dinosaur remains in the eastern US are about 225 million years old.[55] So, dinosaurs had reached the east coast of the United States not long after they evolved in the first place.[56]Fossil footprints are the most common kind of early dinosaur fossil in the eastern United States.[57]
As the Triassic ended, Pangaea was breaking up into separate continents again. Rift valleys formed along the east coast as the North American, European and African plates diverged.[58] This process created rifts down the east coast to Florida.[47] One of these rift valleys was inundated with ocean water and became the young Atlantic Ocean. Volcanism related to the tectonic processes fracturing Pangaea also left deposits in the eastern US.[59] At the end of the Triassic another mass extinction occurred.[58] Globally, this extinction event wiped out roughly one quarter of families. Conodonts went completely extinct. Ammonoids barely survived. Brachiopods lost much of their former diversity as well. On land, most families of amphibians and reptiles became extinct.[60]
The eastern coast of the US became warmer and wetter during the Early Jurassic because the newly formed Atlantic Ocean brought it into contact with more humid air.[58] Fossils spanning from the Late Triassic to Early Jurassic were preserved in the Newark Supergroup, which is found between the Canadian province Nova Scotia and South Carolina.[61] Rifting continued in the eastern part of the country during the Early Jurassic as the eastern United States drifted apart from Greenland and Europe. The Pacific Plate forced its way under the North American plate, triggering geologic upheaval, including volcanism, on the west coast.[62] Ichthyosaurs remained the dominant marine reptiles of the Early Jurassic, but as the Jurassic progressed that title was gradually transferred to the plesiosaurs.[63]
The stratigraphic unit known as the Morrison Formation was deposited during the Late Jurassic.[64] These sediments are now exposed in Arizona, New Mexico, Oklahoma, Utah, Colorado, Wyoming, South Dakota, and Montana.[65] At the time, this region of the country was home to forests of conifers, ginkgos, and tree ferns. Coal would later form from the remains of these plants.[66] Local mammals diversified significantly during the Jurassic. The Morrison Formation is the best source of Jurassic mammal fossils in North America.[67] Local dinosaurs included the ornithopodCamptosaurus, the sauropodsApatosaurus and Diplodocus, and the theropodAllosaurus.[68] Unlike many periods of geologic history the Jurassic did not end in a mass extinction. There were, however, lesser extinction events going on at the time, with notable losses occurring among ammonoids and dinosaurs.[69]
During the Early Cretaceous the Gulf of Mexico began gradually expanding northward.[70] On land, the eastern United States resembled the modern Mississippi Delta. It was a lowlying plain divided by rivers. A thick coat of vegetation covered the region in plants like club mosses, conifers, cycads, ferns, ginkgoes, horsetails, and early flowers.[71]
During the Late Cretaceous the Gulf of Mexico had expanded through North America until reaching Alaska.[70] Up to half of the continent's modern surface area may have been submerged by this sea.[72] This is called the Western Interior Seaway.[73] It covered the majority of states like Texas, New Mexico, Oklahoma, Colorado, Kansas, Nebraska, the Dakotas, and Wyoming.[74] The seafloor was smooth and probably never submerged by more than 600 feet of water. A great diversity of invertebrates flourished both on the bottom and in the water column. Examples include ammonites, giant clams, crinoids, rudists, and squid. Vertebrate life included bony fishes, mosasaurs, plesiosaurs, sharks, and turtles.[75] Areas now occupied by the plains of the east coast from New Jersey southward as well as the Gulf coast region were covered in seawater during the Cretaceous.[76] Sea levels reached their highest level in all of geologic history during the Cretaceous, although they declined before the period ended.[77] Scleractinian corals were more diverse during the Cretaceous than they are today. Back then coral reefs formed along the Gulf coast.[78] Rudist bivalves also constructed reefs in the Gulf coast region.[79] Another bivalve, Exogyra, was so common its fossils are found in almost every Cretaceous marine deposit.[80] During the Cretaceous, the dominant group of living fishes, the teleosts, first achieved ascendency over their holostean forebears.[81] The aquatic toothed bird Hesperornis is the only known Cretaceous bird whose remains are found with any frequency in North America.[82]
Near the end of the Cretaceous, the Western Interior Seaway began to withdraw. This regression would end up resulting in both halves of North America reuniting. As the seaway withdrew, a coastal plain expanded southward into the northern part of the western interior.[83] Powerful geologic forces began to fold and distort the rocks of Idaho, Utah, and Wyoming, beginning the processes that would form the Rocky Mountains.[84] Rivers flowing across the eastern part of what is now Montana, deposited the sediments now known as the Hell Creek Formation. At the time, Montana was home to some of the most famous dinosaurs; creatures like Edmontosaurus, Pachycephalosaurus, Triceratops, and Tyrannosaurus.[83] Despite the western upheaval, the eastern US had achieved geological stability by the Late Cretaceous.[72] The weather was uniformly warm and rainy throughout the year.[85] Flowering plants were now common and fossil of broadleaf trees and shrubs were preserved in Late Cretaceous rocks.[85]
After the Cretaceous, a new era of geologic time began; the Cenozoic era, which means the era of "recent life". Traditionally, the first period of the Cenozoic was called the Tertiary,[131] however recent recommendations of the International Commission on Stratigraphy discourage its use, with the correspondent time span divided between the earlier Paleogene and the more recent Neogene periods.[132] The geologic turmoil on the west coast was maintained as the Pacific Plate continued to slide under the North American Plate.[133] During the early part of the Cenozoic period climates were much warmer than they are today. Latitudes as high as South Dakota had a subtropical climate until as recently as the end of the Oligocene.[134]
Sea level fell throughout the Cenozoic.[134] Areas of Cenozoic North America that were covered by seawater tended to be areas near the modern coasts.[135] The Cannonball Sea near Minot, North Dakota was the last of the North American interior.[136] Cenozoic marine invertebrates are best known from deposits near the coasts and tend to resemble modern forms. Solitary corals became common, but coral reefs formed only around the Gulf of Mexico.[137]Sharks were common during the Cenozoic.[138] From Eocene times onward they began increasing in size.[139]
The beginning of the Cenozoic was also the beginning of the Age of Mammals. The small shrew-like generalist insectivores that survived the Late Cretaceous extinction event began diversifying into the mammals that dominate the modern world's terrestrial ecosystems.[140] The creodonts, which first appeared in the Paleocene, were among the first mammals to specialize in carnivory.[141] The coastal region of the southeastern states, like Alabama[142] and Mississippi[143] were covered in seawater and home to the primitive whale Basilosaurus during the Eocene. The diversity of mammalian carnivores on land increased from the Eocene to the Miocene.[141]
Around the same time, camels were becoming common in North America, although they were just barely bigger than modern rabbits during the Eocene. Early camels had four toes.[144] During the early part of the Eocene the first primitive horses also began appearing. Among the earliest was Eohippus, a small animal with four toes on the front feet and three on the rear.[145] A group of mammals called oreodonts also appeared during the Eocene.[146] By the Oligocene, camels were the size of sheep and had only two toes.[144] Gradually over time horses also lost toes, but unlike camels, horses' were reduced to a single digit.[145] By the Oligocene their teeth had adapted to endure abrasion from silica in their increasingly grassy diets.[145] Horses gradually became common throughout the country.[145] Large numbers of oreodonts grazed in the badlands of South Dakota by the middle of the Cenozoic.[146] Oreodonts were vaguely pig like and about the size of modern goats. Their numbers peaked during the Oligocene.[146] The largest mammals of Oligocene North America were the rhinoceros-like titanotheres. One spectacular example was the abundant Brontotherium of South Dakota, which could be up to 8 feet tall at the shoulder. Despite their early success, by the end of the epoch the entire group became extinct.[147]
Following the Oligocene temperatures began to decline, and with it warm-weather vegetation was forced southward into lower latitudes.[134] By the Miocene some sharks, which had been increasing in size since the Eocene, were over 60 feet long.[139]Mastodons arrived in North America by crossing the Bering land bridge from the old world during the Miocene as well.[148] The oreodonts became extinct during the Pliocene.[146] By the time the Pliocene ended more modern carnivores like wolves and cats appeared. Notable among the latter group were the saber-toothed cats.[141]Woolly mammoths became abundant across the US during the late Cenozoic.[148] During the late Pleistocene, the large volumes of water were held frozen as part of glaciers. This caused a drop in sea level, which exposed a land bridge between Asia and Alaska. Humans crossed over this bridge and started becoming abundant in North America between 11,000 and 12,000 years ago.[149] Despite withstanding the fluctuating climate and concomitant advance and retreat of glaciers, around 10,000 years ago around 32 genera of large mammals suddenly became extinct.[150] Horses were locally extirpated during these end-Pleistocene megafauna extinctions.[145] Some paleontologists attribute these extinctions to the arrival of early humans, who over hunted the local large game. Under this model, the disappearance of saber-toothed cats and other contemporary predators would be explained by the loss of their primary source of food. However, this explanation is still controversial.[151]
↑ Ogg, James G.; Gradstein, F. M; Gradstein, Felix M. (2004). A geologic time scale 2004. Cambridge, UK: Cambridge University Press. ISBN0-521-78142-6.
The Mesozoic Era is the second-to-last era of Earth's geological history, lasting from about 252 to 66 million years ago, comprising the Triassic, Jurassic and Cretaceous Periods. It is characterized by the dominance of gymnosperms and of archosaurian reptiles, such as the dinosaurs; a hot greenhouse climate; and the tectonic break-up of Pangaea. The Mesozoic is the middle of the three eras since complex life evolved: the Paleozoic, the Mesozoic, and the Cenozoic.
The Phanerozoic is the current and the latest of the four geologic eons in the Earth's geologic time scale, covering the time period from 538.8 million years ago to the present. It is the eon during which abundant animal and plant life has proliferated, diversified and colonized various niches on the Earth's surface, beginning with the Cambrian period when animals first developed hard shells that can be clearly preserved in the fossil record. The time before the Phanerozoic, collectively called the Precambrian, is now divided into the Hadean, Archaean and Proterozoic eons.
The Triassic is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago (Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is the first and shortest period of the Mesozoic Era. Both the start and end of the period are marked by major extinction events. The Triassic Period is subdivided into three epochs: Early Triassic, Middle Triassic and Late Triassic.
Paleontology in North Carolina refers to paleontological research occurring within or conducted by people from the U. S. state of North Carolina. Fossils are common in North Carolina. According to author Rufus Johnson, "almost every major river and creek east of Interstate 95 has exposures where fossils can be found". The fossil record of North Carolina spans from Eocambrian remains that are 600 million years old, to the Pleistocene 10,000 years ago.
Paleontology in Virginia refers to paleontological research occurring within or conducted by people from the U.S. state of Virginia. The geologic column in Virginia spans from the Cambrian to the Quaternary. During the early part of the Paleozoic, Virginia was covered by a warm shallow sea. This sea would come to be inhabited by creatures like brachiopods, bryozoans, corals, and nautiloids. The state was briefly out of the sea during the Ordovician, but by the Silurian it was once again submerged. During this second period of inundation the state was home to brachiopods, trilobites and entire reef systems. During the mid-to-late Carboniferous the state gradually became a swampy environment.
Paleontology in Maryland refers to paleontological research occurring within or conducted by people from the U.S. state of Maryland. The invertebrate fossils of Maryland are similar to those of neighboring Delaware. For most of the early Paleozoic era, Maryland was covered by a shallow sea, although it was above sea level for portions of the Ordovician and Devonian. The ancient marine life of Maryland included brachiopods and bryozoans while horsetails and scale trees grew on land. By the end of the era, the sea had left the state completely. In the early Mesozoic, Pangaea was splitting up. The same geologic forces that divided the supercontinent formed massive lakes. Dinosaur footprints were preserved along their shores. During the Cretaceous, the state was home to dinosaurs. During the early part of the Cenozoic era, the state was alternatingly submerged by sea water or exposed. During the Ice Age, mastodons lived in the state.
Paleontology in Delaware refers to paleontological research occurring within or conducted by people from the U.S. state of Delaware. There are no local rocks of Precambrian, Paleozoic, Triassic, or Jurassic age, so Delaware's fossil record does not begin until the Cretaceous period. As the Early Cretaceous gave way to the Late Cretaceous, Delaware was being gradually submerged by the sea. Local marine life included cephalopods like Belemnitella americana, and marine reptiles. The dwindling local terrestrial environments were home to a variety of plants, dinosaurs, and pterosaurs. Along with New Jersey, Delaware is one of the best sources of Late Cretaceous dinosaur fossils in the eastern United States. Delaware was still mostly covered by sea water through the Cenozoic era. Local marine life included manatees, porpoises, seals, and whales. Delaware was worked over by glaciers during the Ice Age. The Cretaceous belemnite Belemnitella americana is the Delaware state fossil.
Paleontology in South Carolina refers to paleontological research occurring within or conducted by people from the U.S. state of South Carolina. Evidence suggests that at least part of South Carolina was covered by a warm, shallow sea and inhabited by trilobites during the Cambrian period. Other than this, little is known about the earliest prehistory of South Carolina because the Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, and Jurassic, are missing from the state's local rock record. The earliest fossils of South Carolina date back to the Cretaceous, when the state was partially covered by seawater. Contemporary fossils include marine invertebrates and the remains of dinosaur carcasses that washed out to sea. On land, a wide variety of trees grew. Sea levels rose and fell throughout the ensuing Cenozoic era. Local marine life included invertebrates, fish, sharks, whales. The first scientifically accurate identification of vertebrate fossils in North America occurred in South Carolina. In 1725, African slaves digging in a swamp uncovered mammoth teeth, which they recognized as originating from an elephant-like animal.
Paleontology in New Jersey refers to paleontological research in the U.S. state of New Jersey. The state is especially rich in marine deposits.
Paleontology in Georgia refers to paleontological research occurring within or conducted by people from the U.S. state of Georgia. During the early part of the Paleozoic, Georgia was largely covered by seawater. Although no major Paleozoic discoveries have been uncovered in Georgia, the local fossil record documents a great diversity of ancient life in the state. Inhabitants of Georgia's early Paleozoic sea included corals, stromatolites, and trilobites. During the Carboniferous local sea levels dropped and a vast complex of richly vegetated delta formed in the state. These swampy deltas were home to early tetrapods which left behind footprints that would later fossilize. Little is known of Triassic Georgia and the Jurassic is absent altogether from the state's rock record. During the Cretaceous, however, southern Georgia was covered by a sea that was home to invertebrates and fishes. On land, the tree Araucaria grew, and dinosaurs inhabited the state. Southern Georgia remained submerged by shallow seawater into the ensuing Paleogene and Neogene periods of the Cenozoic era. These seas were home to small coral reefs and a variety of other marine invertebrates. By the Pleistocene the state was mostly dry land covered in forests and grasslands home to mammoths and giant ground sloths. Local coal mining activity has a history of serendipitous Carboniferous-aged fossil discoveries. Another major event in Georgian paleontology was a 1963 discovery of Pleistocene fossils in Bartow County. Shark teeth are the Georgia state fossil.
Paleontology in Connecticut refers to paleontological research occurring within or conducted by people from the U.S. state of Connecticut. Apart from its famous dinosaur tracks, the fossil record in Connecticut is relatively sparse. The oldest known fossils in Connecticut date back to the Triassic period. At the time, Pangaea was beginning to divide and local rift valleys became massive lakes. A wide variety of vegetation, invertebrates and reptiles are known from Triassic Connecticut. During the Early Jurassic local dinosaurs left behind an abundance of footprints that would later fossilize.
Paleontology in Vermont comprises paleontological research occurring within or conducted by people from the U.S. state of Vermont. Fossils are generally uncommon in Vermont. Nevertheless, however, significant finds have been made in the state. Very few fossils are known in Vermont east of the Green Mountains due to the type of rock underlying that area. During the early part of the Paleozoic era, Vermont was covered by a warm, shallow sea that would end up being home to creatures like brachiopods, corals, crinoids, ostracoderms, and trilobites. There are no rocks in the state from the Carboniferous, Permian, Triassic, or Jurassic periods. The few Cretaceous rocks present contain no fossils. The Paleogene and Neogene periods are also absent from the local rock record. During the Ice Age, glaciers scoured the state. At times the state was inundated by seawater, allowing marine mammals to venture in. After the seawater drained away the state was home to mastodons. Local fossils had already attracted scientific attention by the mid-19th century when mastodon remains were found in Rutland County. In 1950 a major Paleozoic invertebrate find occurred. The Pleistocene Beluga whale Delphinapterus leucas is the Vermont state fossil.
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.
Paleontology in Nebraska refers to paleontological research occurring within or conducted by people from the U.S. state of Nebraska. Nebraska is world-famous as a source of fossils. During the early Paleozoic, Nebraska was covered by a shallow sea that was probably home to creatures like brachiopods, corals, and trilobites. During the Carboniferous, a swampy system of river deltas expanded westward across the state. During the Permian period, the state continued to be mostly dry land. The Triassic and Jurassic are missing from the local rock record, but evidence suggests that during the Cretaceous the state was covered by the Western Interior Seaway, where ammonites, fish, sea turtles, and plesiosaurs swam. The coasts of this sea were home to flowers and dinosaurs. During the early Cenozoic, the sea withdrew and the state was home to mammals like camels and rhinoceros. Ice Age Nebraska was subject to glacial activity and home to creatures like the giant bear Arctodus, horses, mammoths, mastodon, shovel-tusked proboscideans, and Saber-toothed cats. Local Native Americans devised mythical explanations for fossils like attributing them to water monsters killed by their enemies, the thunderbirds. After formally trained scientists began investigating local fossils, major finds like the Agate Springs mammal bone beds occurred. The Pleistocene mammoths Mammuthus primigenius, Mammuthus columbi, and Mammuthus imperator are the Nebraska state fossils.
Paleontology in Texas refers to paleontological research occurring within or conducted by people from the U.S. state of Texas. Author Marian Murray has said that "Texas is as big for fossils as it is for everything else." Some of the most important fossil finds in United States history have come from Texas. Fossils can be found throughout most of the state. The fossil record of Texas spans almost the entire geologic column from Precambrian to Pleistocene. Shark teeth are probably the state's most common fossil. During the early Paleozoic era Texas was covered by a sea that would later be home to creatures like brachiopods, cephalopods, graptolites, and trilobites. Little is known about the state's Devonian and early Carboniferous life. Evidence indicates that during the late Carboniferous the state was home to marine life, land plants and early reptiles. During the Permian, the seas largely shrank away, but nevertheless coral reefs formed in the state. The rest of Texas was a coastal plain inhabited by early relatives of mammals like Dimetrodon and Edaphosaurus. During the Triassic, a great river system formed in the state that was inhabited by crocodile-like phytosaurs. Little is known about Jurassic Texas, but there are fossil aquatic invertebrates of this age like ammonites in the state. During the Early Cretaceous local large sauropods and theropods left a great abundance of footprints. Later in the Cretaceous, the state was covered by the Western Interior Seaway and home to creatures like mosasaurs, plesiosaurs, and few icthyosaurs. Early Cenozoic Texas still contained areas covered in seawater where invertebrates and sharks lived. On land the state would come to be home to creatures like glyptodonts, mammoths, mastodons, saber-toothed cats, giant ground sloths, titanotheres, uintatheres, and dire wolves. Archaeological evidence suggests that local Native Americans knew about local fossils. Formally trained scientists were already investigating the state's fossils by the late 1800s. In 1938, a major dinosaur footprint find occurred near Glen Rose. Pleurocoelus was the Texas state dinosaur from 1997 to 2009, when it was replaced by Paluxysaurus jonesi after the Texan fossils once referred to the former species were reclassified to a new genus.
Paleontology in Idaho refers to paleontological research occurring within or conducted by people from the U.S. state of Idaho. The fossil record of Idaho spans much of the geologic column from the Precambrian onward. During the Precambrian, bacteria formed stromatolites while worms left behind trace fossils. The state was mostly covered by a shallow sea during the majority of the Paleozoic era. This sea became home to creatures like brachiopods, corals and trilobites. Idaho continued to be a largely marine environment through the Triassic and Jurassic periods of the Mesozoic era, when brachiopods, bryozoans, corals, ichthyosaurs and sharks inhabited the local waters. The eastern part of the state was dry land during the ensuing Cretaceous period when dinosaurs roamed the area and trees grew which would later form petrified wood.
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.
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 and animal life spanning the past 650 million years of time. The earliest fossils from the state are from Esmeralda County, and are Late Proterozoic in age and represent stromatolite reefs of cyanobacteria, amongst these reefs were some of the oldest known shells in the fossil record, the Cloudina-fauna. Much of the Proterozoic and Paleozoic fossil story of Nevada is that of a warm, shallow, tropical sea, with a few exceptions towards the Late Paleozoic. As such many fossils across the state are those of marine animals, such as trilobites, brachiopods, bryozoans, honeycomb corals, archaeocyaths, and horn corals.
Paleontology in California refers to paleontologist research occurring within or conducted by people from the U.S. state of California. California contains rocks of almost every age from the Precambrian to the Recent.
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.
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