1.
Precambrian
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The Precambrian is the earliest period of Earths history, set before the current Phanerozoic Eon. The Precambrian is a supereon that is subdivided into three eons of the time scale. It spans from the formation of Earth about 4.6 billion years ago to the beginning of the Cambrian Period, about 541 million years ago, the Precambrian accounts for 89% of geologic time. Relatively little is known about the Precambrian, despite it making up roughly seven-eighths of the Earths history, the Precambrian fossil record is poorer than that of the succeeding Phanerozoic, and fossils from that time are of limited biostratigraphic use. This is because many Precambrian rocks have been metamorphosed, obscuring their origins, while others have been destroyed by erosion. A stable crust was apparently in place by 4,412 Ma, the term Precambrian is recognized by the International Commission on Stratigraphy as a general term including the Archean and Proterozoic eons. It is still used by geologists and paleontologists for general discussions not requiring the more specific eon names and it was briefly called the Cryptozoic eon. A specific date for the origin of life has not been determined, carbon found in 3.8 billion year old rocks from islands off western Greenland may be of organic origin. Well-preserved microscopic fossils of bacteria older than 3.46 billion years have found in Western Australia. Probable fossils 100 million years older have been found in the same area, there is a fairly solid record of bacterial life throughout the remainder of the Precambrian. The oldest fossil evidence from that era of such complex life comes from the Lantian formation of the Ediacarian period, a very diverse collection of soft-bodied forms is found in a variety of locations worldwide and date to between 635 and 542 Ma. These are referred to as Ediacaran or Vendian biota, hard-shelled creatures appeared toward the end of that time span, marking the beginning of the Phanerozoic era. By the middle of the following Cambrian period, a diverse fauna is recorded in the Burgess Shale. The explosion in diversity of lifeforms during the early Cambrian is called the Cambrian explosion of life, while land seems to have been devoid of plants and animals, cyanobacteria and other microbes formed prokaryotic mats that covered terrestrial areas. Evidence of the details of plate motions and other activity in the Precambrian has been poorly preserved. It is generally believed that small proto-continents existed prior to 4280 Ma, the supercontinent, known as Rodinia, broke up around 750 Ma. A number of glacial periods have been identified going as far back as the Huronian epoch, one of the best studied is the Sturtian-Varangian glaciation, around 850–635 Ma, which may have brought glacial conditions all the way to the equator, resulting in a Snowball Earth. The atmosphere of the early Earth is not well understood, most geologists believe it was composed primarily of nitrogen, carbon dioxide, and other relatively inert gases, and was lacking in free oxygen
2.
Cambrian
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The Cambrian Period was the first geological period of the Paleozoic Era, of the Phanerozoic Eon. The Cambrian lasted 55.6 million years from the end of the preceding Ediacaran Period 541 million years ago to the beginning of the Ordovician Period 485.4 mya and its subdivisions, and its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latinised form of Cymru, the Welsh name for Wales, as a result, our understanding of the Cambrian biology surpasses that of some later periods. The rapid diversification of lifeforms in the Cambrian, known as the Cambrian explosion, most of the continents were probably dry and rocky due to a lack of vegetation. Shallow seas flanked the margins of several continents created during the breakup of the supercontinent Pannotia, the seas were relatively warm, and polar ice was absent for much of the period. The United States Federal Geographic Data Committee uses a barred capital C ⟨Є⟩ character similar to the capital letter Ukrainian Ye ⟨Є⟩ to represent the Cambrian Period, the proper Unicode character is U+A792 Ꞓ LATIN CAPITAL LETTER C WITH BAR. Despite the long recognition of its distinction from younger Ordovician Period rocks and older Supereon Precambrian rocks, the base of the Cambrian lies atop a complex assemblage of trace fossils known as the Treptichnus pedum assemblage. Pedum in Namibia, Spain and Newfoundland, and possibly, in the western USA, the stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, and probably in Spain. The Cambrian Period followed the Ediacaran Period and was followed by the Ordovician Period, the Cambrian is divided into four epochs and ten ages. Currently only two series and five stages are named and have a GSSP, because the international stratigraphic subdivision is not yet complete, many local subdivisions are still widely used. In some of these subdivisions the Cambrian is divided into three epochs with locally differing names – the Early Cambrian, Middle Cambrian and Furongian, rocks of these epochs are referred to as belonging to the Lower, Middle, or Upper Cambrian. Trilobite zones allow biostratigraphic correlation in the Cambrian, each of the local epochs is divided into several stages. The International Commission on Stratigraphy list the Cambrian period as beginning at 541 million years ago, the lower boundary of the Cambrian was originally held to represent the first appearance of complex life, represented by trilobites. The recognition of small shelly fossils before the first trilobites, and Ediacara biota substantially earlier and this formal designation allowed radiometric dates to be obtained from samples across the globe that corresponded to the base of the Cambrian. Early dates of 570 million years ago quickly gained favour, though the used to obtain this number are now considered to be unsuitable. A more precise date using modern radiometric dating yield a date of 541 ±0.3 million years ago, most continental land was clustered in the Southern Hemisphere at this time, but was drifting north. Large, high-velocity rotational movement of Gondwana appears to have occurred in the Early Cambrian, the sea levels fluctuated somewhat, suggesting there were ice ages, associated with pulses of expansion and contraction of a south polar ice cap. In Baltoscandia a Lower Cambrian transgression transformed large swathes of the Sub-Cambrian peneplain into a epicontinental sea, the Earth was generally cold during the early Cambrian, probably due to the ancient continent of Gondwana covering the South Pole and cutting off polar ocean currents
3.
Ordovician
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The Ordovician is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.2 million years from the end of the Cambrian Period 485.4 million years ago to the start of the Silurian Period 443.8 Mya. Lapworth recognized that the fauna in the disputed strata were different from those of either the Cambrian or the Silurian periods. It received international sanction in 1960, when it was adopted as a period of the Paleozoic Era by the International Geological Congress. Life continued to flourish during the Ordovician as it did in the earlier Cambrian period, invertebrates, namely molluscs and arthropods, dominated the oceans. The Great Ordovician Biodiversification Event considerably increased the diversity of life, fish, the worlds first true vertebrates, continued to evolve, and those with jaws may have first appeared late in the period. Life had yet to diversify on land, about 100 times as many meteorites struck the Earth during the Ordovician compared with today. The Ordovician Period began with a major extinction called the Cambrian–Ordovician extinction event and it lasted for about 42 million years and ended with the Ordovician–Silurian extinction event, about 443.8 Mya which wiped out 60% of marine genera. The dates given are recent radiometric dates and vary slightly from those found in other sources and this second period of the Paleozoic era created abundant fossils that became major petroleum and gas reservoirs. The boundary chosen for the beginning of both the Ordovician Period and the Tremadocian stage is highly significant and it correlates well with the occurrence of widespread graptolite, conodont, and trilobite species. The base of the Tremadocian allows scientists to relate these species not only to each other and this makes it easier to place many more species in time relative to the beginning of the Ordovician Period. A number of terms have been used to subdivide the Ordovician Period. In 2008, the ICS erected an international system of subdivisions. There exist Baltoscandic, British, Siberian, North American, Australian, the Ordovician Period in Britain was traditionally broken into Early, Middle and Late epochs. The corresponding rocks of the Ordovician System are referred to as coming from the Lower, Middle, the Floian corresponds to the lower Arenig, the Arenig continues until the early Darriwilian, subsuming the Dapingian. The Llanvirn occupies the rest of the Darriwilian, and terminates with it at the base of the Late Ordovician. The Sandbian represents the first half of the Caradoc, the Caradoc ends in the mid-Katian, during the Ordovician, the southern continents were collected into Gondwana. Gondwana started the period in equatorial latitudes and, as the period progressed, drifted toward the South Pole, the small continent Avalonia separated from Gondwana and began to move north towards Baltica and Laurentia, opening the Rheic Ocean between Gondwana and Avalonia
4.
Silurian
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The Silurian is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at 443.8 million years ago, to the beginning of the Devonian Period,419.2 Mya. As with other periods, the rock beds that define the periods start and end are well identified. The base of the Silurian is set at a major Ordovician-Silurian extinction event when 60% of marine species were wiped out, a significant evolutionary milestone during the Silurian was the diversification of jawed and bony fish. However, terrestrial life would not greatly diversify and affect the landscape until the Devonian, the Silurian system was first identified by British geologist Sir Roderick Impey Murchison, who was examining fossil-bearing sedimentary rock strata in south Wales in the early 1830s. He named the sequences for a Celtic tribe of Wales, the Silures, inspired by his friend Adam Sedgwick and this naming does not indicate any correlation between the occurrence of the Silurian rocks and the land inhabited by the Silures. As it was first identified, the Silurian series when traced farther afield quickly came to overlap Sedgwicks Cambrian sequence, however, charles Lapworth resolved the conflict by defining a new Ordovician system including the contested beds. An early alternative name for the Silurian was Gotlandian after the strata of the Baltic island of Gotland, the French geologist Joachim Barrande, building on Murchisons work, used the term Silurian in a more comprehensive sense than was justified by subsequent knowledge. He divided the Silurian rocks of Bohemia into eight stages and his interpretation was questioned in 1854 by Edward Forbes, and the later stages of Barrande, F, G and H, have since been shown to be Devonian. Despite these modifications in the groupings of the strata, it is recognized that Barrande established Bohemia as a classic ground for the study of the earliest fossils. The epoch is named for the town of Llandovery in Carmarthenshire, the Wenlock, which lasted from 433.4 ±1.5 to 427.4 ±2.8 mya, is subdivided into the Sheinwoodian and Homerian ages. It is named after Wenlock Edge in Shropshire, England, during the Wenlock, the oldest known tracheophytes of the genus Cooksonia, appear. The first terrestrial animals also appear in the Wenlock, represented by air-breathing millipedes from Scotland. The Ludlow, lasting from 427.4 ±1.5 to 423 ±2.8 mya, comprises the Gorstian stage, lasting until 425.6 million years ago, and it is named for the town of Ludlow in Shropshire, England. The Pridoli, lasting from 423 ±1.5 to 419.2 ±2.8 mya, is the final and it is named after one locality at the Homolka a Přídolí nature reserve near the Prague suburb Slivenec in the Czech Republic. Přídolí is the old name of a field area. The high sea levels of the Silurian and the flat land resulted in a number of island chains. The southern continents remained united during this period, the melting of icecaps and glaciers contributed to a rise in sea level, recognizable from the fact that Silurian sediments overlie eroded Ordovician sediments, forming an unconformity. The continents of Avalonia, Baltica, and Laurentia drifted together near the equator and this event is the Caledonian orogeny, a spate of mountain building that stretched from New York State through conjoined Europe and Greenland to Norway
5.
Devonian
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The Devonian is a geologic period and system of the Paleozoic, spanning 60 million years from the end of the Silurian,419.2 million years ago, to the beginning of the Carboniferous,358.9 Mya. It is named after Devon, England, where rocks from this period were first studied, the first significant adaptive radiation of life on dry land occurred during the Devonian. Free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents, by the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants appeared. Various terrestrial arthropods also became well-established, Fish reached substantial diversity during this time, leading the Devonian to often be dubbed the Age of Fish. The first ray-finned and lobe-finned bony fish appeared, while the placodermi began dominating almost every aquatic environment. The ancestors of all four-limbed vertebrates began adapting to walking on land, as their strong pectoral, in the oceans, primitive sharks became more numerous than in the Silurian and Late Ordovician. The first ammonites, species of molluscs, appeared, trilobites, the mollusk-like brachiopods and the great coral reefs, were still common. The Late Devonian extinction which started about 375 million years ago severely affected marine life, killing off all placodermi, and all trilobites, save for a few species of the order Proetida. The palaeogeography was dominated by the supercontinent of Gondwana to the south, the continent of Siberia to the north, while the rock beds that define the start and end of the Devonian period are well identified, the exact dates are uncertain. According to the International Commission on Stratigraphy, the Devonian extends from the end of the Silurian 419.2 Mya, another common term is Age of the Fishes, referring to the evolution of several major groups of fish that took place during the period. Older literature on the Anglo-Welsh basin divides it into the Downtonian, Dittonian, Breconian and Farlovian stages, in the Late Devonian, by contrast, arid conditions were less prevalent across the world and temperate climates were more common. The Devonian Period is formally broken into Early, Middle and Late subdivisions, the rocks corresponding to those epochs are referred to as belonging to the Lower, Middle and Upper parts of the Devonian System. Early Devonian The Early Devonian lasted from 419.2 ±2.8 to 393.3 ±2.5 and began with the Lochkovian stage, which lasted until the Pragian. It spanned from 410.8 ±2.8 to 407.6 ±2.5, and was followed by the Emsian, which lasted until the Middle Devonian began,393. 3±2.7 million years ago. Middle Devonian The Middle Devonian comprised two subdivisions, first the Eifelian, which gave way to the Givetian 387. 7±2.7 million years ago. Late Devonian Finally, the Late Devonian started with the Frasnian,382.7 ±2.8 to 372.2 ±2.5, during which the first forests took shape on land. The first tetrapods appeared in the record in the ensuing Famennian subdivision. This lasted until the end of the Devonian,358. 9±2.5 million years ago, the Devonian was a relatively warm period, and probably lacked any glaciers
6.
Carboniferous
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The Carboniferous is a geologic period and system that spans 60 million years from the end of the Devonian Period 358.9 million years ago, to the beginning of the Permian Period,298.9 Mya. The name Carboniferous means coal-bearing and derives from the Latin words carbō and ferō, and was coined by geologists William Conybeare and William Phillips in 1822. Based on a study of the British rock succession, it was the first of the system names to be employed. The Carboniferous is often treated in North America as two periods, the earlier Mississippian and the later Pennsylvanian. Terrestrial life was established by the Carboniferous period. Amphibians were the dominant land vertebrates, of one branch would eventually evolve into amniotes. Arthropods were also common, and many were much larger than those of today. Vast swaths of forest covered the land, which would eventually be laid down, the atmospheric content of oxygen also reached their highest levels in geological history during the period, 35% compared with 21% today, allowing terrestrial invertebrates to evolve to great size. A major marine and terrestrial extinction event, the Carboniferous rainforest collapse, occurred in the middle of the period, the later half of the period experienced glaciations, low sea level, and mountain building as the continents collided to form Pangaea. In the United States the Carboniferous is usually broken into Mississippian and Pennsylvanian subperiods, the Silesian is roughly contemporaneous with the late Mississippian Serpukhovian plus the Pennsylvanian. In Britain the Dinantian is traditionally known as the Carboniferous Limestone, the Namurian as the Millstone Grit, and the Westphalian as the Coal Measures and Pennant Sandstone. There was also a drop in south polar temperatures, southern Gondwanaland was glaciated throughout the period and these conditions apparently had little effect in the deep tropics, where lush swamps, later to become coal, flourished to within 30 degrees of the northernmost glaciers. Mid-Carboniferous, a drop in sea level precipitated a major extinction, one that hit crinoids. This sea level drop and the unconformity in North America separate the Mississippian subperiod from the Pennsylvanian subperiod. This happened about 323 million years ago, at the onset of the Permo-Carboniferous Glaciation, the Carboniferous was a time of active mountain-building, as the supercontinent Pangaea came together. The southern continents remained tied together in the supercontinent Gondwana, which collided with North America–Europe along the present line of eastern North America, in the same time frame, much of present eastern Eurasian plate welded itself to Europe along the line of the Ural mountains. Most of the Mesozoic supercontinent of Pangea was now assembled, although North China, the Late Carboniferous Pangaea was shaped like an O. There were two major oceans in the Carboniferous—Panthalassa and Paleo-Tethys, which was inside the O in the Carboniferous Pangaea, other minor oceans were shrinking and eventually closed - Rheic Ocean, the small, shallow Ural Ocean and Proto-Tethys Ocean
7.
Permian
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The Permian is a geologic period and system which spans 46.7 million years from the end of the Carboniferous Period 298.9 million years ago, to the beginning of the Triassic Period 252.2 Mya. It is the last period of the Paleozoic Era, the following Triassic Period belongs to the Mesozoic Era, the concept of the Permian was introduced in 1841 by geologist Sir Roderick Murchison, who named it after the city of Perm. The Permian witnessed the diversification of the early amniotes into the groups of the mammals, turtles, lepidosaurs. The world at the time was dominated by two known as Pangaea and Siberia, surrounded by a global ocean called Panthalassa. The Carboniferous rainforest collapse left behind vast regions of desert within the continental interior, amniotes, who could better cope with these drier conditions, rose to dominance in place of their amphibian ancestors. The Permian ended with the Permian–Triassic extinction event, the largest mass extinction in Earths history, in which nearly 90% of marine species and it would take well into the Triassic for life to recover from this catastrophe. Recovery from the Permian-Triassic extinction event was protracted, on land, the term Permian was introduced into geology in 1841 by Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil, the region now lies in the Perm Krai of Russia. This could have in part caused the extinctions of marine species at the end of the period by severely reducing shallow coastal areas preferred by many marine organisms. During the Permian, all the Earths major landmasses were collected into a supercontinent known as Pangaea. The Cimmeria continent rifted away from Gondwana and drifted north to Laurasia, a new ocean was growing on its southern end, the Tethys Ocean, an ocean that would dominate much of the Mesozoic Era. Large continental landmass interiors experience climates with extreme variations of heat and cold, deserts seem to have been widespread on Pangaea. Such dry conditions favored gymnosperms, plants with seeds enclosed in a cover, over plants such as ferns that disperse spores in a wetter environment. The first modern trees appeared in the Permian, the climate in the Permian was quite varied. At the start of the Permian, the Earth was still in an Ice Age, glaciers receded around the mid-Permian period as the climate gradually warmed, drying the continents interiors. In the late Permian period, the drying continued although the temperature cycled between warm and cool cycles, Permian marine deposits are rich in fossil mollusks, echinoderms, and brachiopods. By the close of the Permian, trilobites and a host of other groups became extinct. Terrestrial life in the Permian included diverse plants, fungi, arthropods, the period saw a massive desert covering the interior of Pangaea
8.
Triassic
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The Triassic is a geologic period and system which spans 50.9 million years from the end of the Permian Period 252.17 million years ago, to the beginning of the Jurassic Period 201.3 Mya. The Triassic is the first period of the Mesozoic Era, both the start and end of the period are marked by major extinction events. Therapsids and archosaurs were the terrestrial vertebrates during this time. A specialized subgroup of archosaurs, called dinosaurs, first appeared in the Late Triassic, the vast supercontinent of Pangaea existed until the mid-Triassic, after which it began to gradually rift into two separate landmasses, Laurasia to the north and Gondwana to the south. The global climate during the Triassic was mostly hot and dry, however, the climate shifted and became more humid as Pangaea began to drift apart. The end of the period was marked by yet another mass extinction, the Triassic-Jurassic extinction event. The Triassic is usually separated into Early, Middle, and Late Triassic Epochs, from the east, along the equator, the Tethys sea penetrated Pangaea, causing the Paleo-Tethys Ocean to be closed. Later in the mid-Triassic a similar sea penetrated along the equator from the west, the remaining shores were surrounded by the world-ocean known as Panthalassa. All the deep-ocean sediments laid down during the Triassic have disappeared through subduction of oceanic plates, thus, the supercontinent Pangaea was rifting during the Triassic—especially late in that period—but had not yet separated. In North America, for example, marine deposits are limited to a few exposures in the west, thus Triassic stratigraphy is mostly based on organisms that lived in lagoons and hypersaline environments, such as Estheria crustaceans. At the beginning of the Mesozoic Era, Africa was joined with Earths other continents in Pangaea, Africa shared the supercontinents relatively uniform fauna which was dominated by theropods, prosauropods and primitive ornithischians by the close of the Triassic period. Late Triassic fossils are found throughout Africa, but are common in the south than north. The time boundary separating the Permian and Triassic marks the advent of an event with global impact. At Paleorrota geopark, located in Rio Grande do Sul, Brazil, in these formations, one of the earliest dinosaurs, Staurikosaurus, as well as the mammal ancestors Brasilitherium and Brasilodon have been discovered. The Triassic continental interior climate was hot and dry, so that typical deposits are red bed sandstones and evaporites. Pangaeas large size limited the effect of the global ocean, its continental climate was highly seasonal, with very hot summers. The strong contrast between the Pangea supercontinent and the global ocean triggered intense cross-equatorial monsoons, the best studied of such episodes of humid climate, and probably the most intense and widespread, was the Carnian Pluvial Event. On land, the vascular plants included the lycophytes, the dominant cycadophytes, ginkgophyta, ferns, horsetails
9.
Jurassic
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The Jurassic is a geologic period and system that spans 56.3 million years from the end of the Triassic Period 201.3 million years ago to the beginning of the Cretaceous Period 145 Mya. The Jurassic constitutes the middle period of the Mesozoic Era, also known as the Age of Reptiles, the start of the period is marked by the major Triassic–Jurassic extinction event. The Jurassic is named after the Jura Mountains within the European Alps, by the beginning of the Jurassic, the supercontinent Pangaea had begun rifting into two landmasses, Laurasia to the north and Gondwana to the south. This created more coastlines and shifted the continental climate from dry to humid, on land, the fauna transitioned from the Triassic fauna, dominated by both dinosauromorph and crocodylomorph archosaurs, to one dominated by dinosaurs alone. The first birds also appeared during the Jurassic, having evolved from a branch of theropod dinosaurs, other major events include the appearance of the earliest lizards, and the evolution of therian mammals, including primitive placentals. Crocodilians made the transition from a terrestrial to a mode of life. The oceans were inhabited by marine reptiles such as ichthyosaurs and plesiosaurs, the chronostratigraphic term Jurassic is directly linked to the Jura Mountains. The name Jura is derived from the Celtic root jor, which was Latinised into juria, the Jurassic period is divided into the Early Jurassic, Middle, and Late Jurassic epochs. The Jurassic System, in stratigraphy, is divided into the Lower Jurassic, Middle, the separation of the term Jurassic into three sections goes back to Leopold von Buch. The Jurassic North Atlantic Ocean was relatively narrow, while the South Atlantic did not open until the following Cretaceous period, the Tethys Sea closed, and the Neotethys basin appeared. Climates were warm, with no evidence of glaciation, as in the Triassic, there was apparently no land over either pole, and no extensive ice caps existed. In contrast, the North American Jurassic record is the poorest of the Mesozoic, the Jurassic was a time of calcite sea geochemistry in which low-magnesium calcite was the primary inorganic marine precipitate of calcium carbonate. Carbonate hardgrounds were thus very common, along with calcitic ooids, calcitic cements, the first of several massive batholiths were emplaced in the northern American cordillera beginning in the mid-Jurassic, marking the Nevadan orogeny. Important Jurassic exposures are found in Russia, India, South America, Japan, Australasia. As the Jurassic proceeded, larger and more groups of dinosaurs like sauropods and ornithopods proliferated in Africa. Middle Jurassic strata are well represented nor well studied in Africa. Late Jurassic strata are also poorly represented apart from the spectacular Tendaguru fauna in Tanzania, the Late Jurassic life of Tendaguru is very similar to that found in western North Americas Morrison Formation. During the Jurassic period, the primary living in the sea were fish
10.
Cretaceous
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The Cretaceous is a geologic period and system that spans 79 million years from the end of the Jurassic Period 145 million years ago to the beginning of the Paleogene Period 66 Mya. It is the last period of the Mesozoic Era, the Cretaceous Period is usually abbreviated K, for its German translation Kreide. The Cretaceous was a period with a warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct marine reptiles, ammonites and rudists, during this time, new groups of mammals and birds, as well as flowering plants, appeared. The Cretaceous ended with a mass extinction, the Cretaceous–Paleogene extinction event, in which many groups, including non-avian dinosaurs, pterosaurs. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary, the name Cretaceous was derived from Latin creta, meaning chalk. The Cretaceous is divided into Early and Late Cretaceous epochs, or Lower and Upper Cretaceous series, in older literature the Cretaceous is sometimes divided into three series, Neocomian, Gallic and Senonian. A subdivision in eleven stages, all originating from European stratigraphy, is now used worldwide, in many parts of the world, alternative local subdivisions are still in use. As with other geologic periods, the rock beds of the Cretaceous are well identified. No great extinction or burst of diversity separates the Cretaceous from the Jurassic and this layer has been dated at 66.043 Ma. A140 Ma age for the Jurassic-Cretaceous boundary instead of the usually accepted 145 Ma was proposed in 2014 based on a study of Vaca Muerta Formation in Neuquén Basin. Víctor Ramos, one of the authors of the study proposing the 140 Ma boundary age sees the study as a first step toward formally changing the age in the International Union of Geological Sciences, due to the high sea level there was extensive space for such sedimentation. Because of the young age and great thickness of the system. Chalk is a type characteristic for the Cretaceous. It consists of coccoliths, microscopically small calcite skeletons of coccolithophores, the group is found in England, northern France, the low countries, northern Germany, Denmark and in the subsurface of the southern part of the North Sea. Chalk is not easily consolidated and the Chalk Group still consists of sediments in many places. The group also has other limestones and arenites, among the fossils it contains are sea urchins, belemnites, ammonites and sea reptiles such as Mosasaurus. In southern Europe, the Cretaceous is usually a marine system consisting of competent limestone beds or incompetent marls
11.
Paleogene
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The Paleogene is a geologic period and system that spans 43 million years from the end of the Cretaceous Period 66 million years ago to the beginning of the Neogene Period 23.03 Mya. It is the beginning of the Cenozoic Era of the present Phanerozoic Eon and this period consists of the Paleocene, Eocene and Oligocene epochs. The terms Paleogene System and lower Tertiary System are applied to the rocks deposited during the Paleogene Period. By dividing the Tertiary Period into two periods instead of directly into five epochs, the periods are more comparable to the duration of periods of the preceding Mesozoic and Paleozoic Eras. The trend was caused by the formation of the Antarctic Circumpolar Current. During the Paleogene, the continued to drift closer to their current positions. India was in the process of colliding with Asia, subsequently forming the Himalayas, the Atlantic Ocean continued to widen by a few centimeters each year. Africa was moving north to meet with Europe and form the Mediterranean, inland seas retreated from North America early in the period. Australia had also separated from Antarctica and was drifting towards Southeast Asia, mammals began a rapid diversification during this period. Some of these mammals would evolve into forms that would dominate the land, while others would become capable of living in marine, specialized terrestrial. Those that took to the oceans became modern cetaceans, while those that took to the trees became primates, the group to which humans belong. Birds, which were well established by the end of the Cretaceous. In comparison to birds and mammals, most other branches of life remained unchanged during this period. As the Earth cooled, tropical plants became less numerous and were now restricted to equatorial regions, deciduous plants, which could survive through the seasonal climates the world was now experiencing, became more common. The Paleogene is notable in the context of offshore oil drilling, and especially in Gulf of Mexico oil exploration and these rock formations represent the current cutting edge of deep-water oil discovery. Lower Tertiary explorations to date include, Kaskida Oil Field Tiber Oil Field Jack 2 Paleogene Microfossils, 180+ images of Foraminifera
12.
Neogene
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The Neogene is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period 23.03 million years ago to the beginning of the present Quaternary Period 2.58 Mya. The Neogene is sub-divided into two epochs, the earlier Miocene and the later Pliocene, some geologists assert that the Neogene cannot be clearly delineated from the modern geological period, the Quaternary. During this period, mammals and birds continued to evolve into modern forms. Early hominids, the ancestors of humans, appeared in Africa near the end of the period, some continental movement took place, the most significant event being the connection of North and South America at the Isthmus of Panama, late in the Pliocene. This cut off the ocean currents from the Pacific to the Atlantic ocean. The global climate cooled considerably over the course of the Neogene, the terms Neogene System and upper Tertiary System describe the rocks deposited during the Neogene Period. The continents in the Neogene were very close to their current positions, the Isthmus of Panama formed, connecting North and South America. The Indian subcontinent continued to collide with Asia, forming the Himalayas, sea levels fell, creating land bridges between Africa and Eurasia and between Eurasia and North America. The global climate became seasonal and continued an overall drying and cooling trend which began at the start of the Paleogene. The ice caps on both poles began to grow and thicken, and by the end of the period the first of a series of glaciations of the current Ice Age began, marine and continental flora and fauna have a modern appearance. The reptile group Choristodera became extinct in the part of the period. Mammals and birds continued to be the dominant terrestrial vertebrates, the first hominids, the ancestors of humans, appeared in Africa and spread into Eurasia. In response to the cooler, seasonal climate, tropical plant species gave way to deciduous ones, grasses therefore greatly diversified, and herbivorous mammals evolved alongside it, creating the many grazing animals of today such as horses, antelope, and bison. The Neogene traditionally ended at the end of the Pliocene Epoch, just before the definition of the beginning of the Quaternary Period. However, there was a movement amongst geologists to also include ongoing geological time in the Neogene, by dividing the Cenozoic Era into three periods instead of seven epochs, the periods are more closely comparable to the duration of periods in the Mesozoic and Paleozoic eras. The International Commission on Stratigraphy once proposed that the Quaternary be considered a sub-era of the Neogene, with a date of 2.58 Ma. In the 2004 proposal of the ICS, the Neogene would have consisted of the Miocene and Pliocene epochs, thus the Neogene Period ends bounding the succeeding Quaternary Period at 2.58 Mya. Digital Atlas of Neogene Life for the Southeastern United States — by San Jose State University via Web Archive
13.
Taxonomy (biology)
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Taxonomy is the science of defining groups of biological organisms on the basis of shared characteristics and giving names to those groups. The exact definition of taxonomy varies from source to source, but the core of the remains, the conception, naming. There is some disagreement as to whether biological nomenclature is considered a part of taxonomy, the broadest meaning of taxonomy is used here. The word taxonomy was introduced in 1813 by Candolle, in his Théorie élémentaire de la botanique, the term alpha taxonomy is primarily used today to refer to the discipline of finding, describing, and naming taxa, particularly species. In earlier literature, the term had a different meaning, referring to morphological taxonomy, ideals can, it may be said, never be completely realized. They have, however, a value of acting as permanent stimulants. Some of us please ourselves by thinking we are now groping in a beta taxonomy, turrill thus explicitly excludes from alpha taxonomy various areas of study that he includes within taxonomy as a whole, such as ecology, physiology, genetics, and cytology. He further excludes phylogenetic reconstruction from alpha taxonomy, thus, Ernst Mayr in 1968 defined beta taxonomy as the classification of ranks higher than species. This activity is what the term denotes, it is also referred to as beta taxonomy. How species should be defined in a group of organisms gives rise to practical and theoretical problems that are referred to as the species problem. The scientific work of deciding how to define species has been called microtaxonomy, by extension, macrotaxonomy is the study of groups at higher taxonomic ranks, from subgenus and above only, than species. While some descriptions of taxonomic history attempt to date taxonomy to ancient civilizations, earlier works were primarily descriptive, and focused on plants that were useful in agriculture or medicine. There are a number of stages in scientific thinking. Early taxonomy was based on criteria, the so-called artificial systems. Later came systems based on a complete consideration of the characteristics of taxa, referred to as natural systems, such as those of de Jussieu, de Candolle and Bentham. The publication of Charles Darwins Origin of Species led to new ways of thinking about classification based on evolutionary relationships and this was the concept of phyletic systems, from 1883 onwards. This approach was typified by those of Eichler and Engler, the advent of molecular genetics and statistical methodology allowed the creation of the modern era of phylogenetic systems based on cladistics, rather than morphology alone. Taxonomy has been called the worlds oldest profession, and naming and classifying our surroundings has likely been taking place as long as mankind has been able to communicate
14.
Animal
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Animals are multicellular, eukaryotic organisms of the kingdom Animalia. The animal kingdom emerged as a clade within Apoikozoa as the group to the choanoflagellates. Animals are motile, meaning they can move spontaneously and independently at some point in their lives and their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later in their lives. All animals are heterotrophs, they must ingest other organisms or their products for sustenance, most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion, about 542 million years ago. Animals can be divided broadly into vertebrates and invertebrates, vertebrates have a backbone or spine, and amount to less than five percent of all described animal species. They include fish, amphibians, reptiles, birds and mammals, the remaining animals are the invertebrates, which lack a backbone. These include molluscs, arthropods, annelids, nematodes, flatworms, cnidarians, ctenophores, the study of animals is called zoology. The word animal comes from the Latin animalis, meaning having breath, the biological definition of the word refers to all members of the kingdom Animalia, encompassing creatures as diverse as sponges, jellyfish, insects, and humans. Aristotle divided the world between animals and plants, and this was followed by Carl Linnaeus, in the first hierarchical classification. In Linnaeuss original scheme, the animals were one of three kingdoms, divided into the classes of Vermes, Insecta, Pisces, Amphibia, Aves, and Mammalia. Since then the last four have all been subsumed into a single phylum, in 1874, Ernst Haeckel divided the animal kingdom into two subkingdoms, Metazoa and Protozoa. The protozoa were later moved to the kingdom Protista, leaving only the metazoa, thus Metazoa is now considered a synonym of Animalia. Animals have several characteristics that set apart from other living things. Animals are eukaryotic and multicellular, which separates them from bacteria and they are heterotrophic, generally digesting food in an internal chamber, which separates them from plants and algae. They are also distinguished from plants, algae, and fungi by lacking cell walls. All animals are motile, if only at life stages. In most animals, embryos pass through a stage, which is a characteristic exclusive to animals. With a few exceptions, most notably the sponges and Placozoa and these include muscles, which are able to contract and control locomotion, and nerve tissues, which send and process signals
15.
Chordate
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Chordates are deuterostomes, as during the embryo development stage the anus forms before the mouth. They are also bilaterally symmetric coelomates, in the case of vertebrate chordates, the notochord is usually replaced by a vertebral column during development, and they may have body plans organized via segmentation. There are also additional extinct taxa, the Vertebrata are sometimes considered as a subgroup of the clade Craniata, consisting of chordates with a skull, the Craniata and Tunicata compose the clade Olfactores. Of the more than 65,000 living species of chordates, the worlds largest and fastest animals, the blue whale and peregrine falcon respectively, are chordates, as are humans. Fossil chordates are known from at least as early as the Cambrian explosion, Hemichordata, which includes the acorn worms, has been presented as a fourth chordate subphylum, but it now is usually treated as a separate phylum. The Hemichordata, along with the Echinodermata, form the Ambulacraria, the Chordata and Ambulacraria form the superphylum Deuterostomia, composed of the deuterostomes. Attempts to work out the relationships of the chordates have produced several hypotheses. All of the earliest chordate fossils have found in the Early Cambrian Chengjiang fauna. Because the fossil record of early chordates is poor, only molecular phylogenetics offers a prospect of dating their emergence. However, the use of molecular phylogenetics for dating evolutionary transitions is controversial and it has also proved difficult to produce a detailed classification within the living chordates. Attempts to produce family trees shows that many of the traditional classes are paraphyletic. While this has been known since the 19th century, an insistence on only monophyletic taxa has resulted in vertebrate classification being in a state of flux. Although the name Chordata is attributed to William Bateson, it was already in prevalent use by 1880, ernst Haeckel described a taxon comprising tunicates, cephalochordates, and vertebrates in 1866. Though he used the German vernacular form, it is allowed under the ICZN code because of its subsequent latinization, among the vertebrate sub-group of chordates the notochord develops into the spine, and in wholly aquatic species this helps the animal to swim by flexing its tail. In fish and other vertebrates, this develops into the spinal cord, the pharynx is the part of the throat immediately behind the mouth. In fish, the slits are modified to form gills, a muscular tail that extends backwards behind the anus. This is a groove in the wall of the pharynx. In filter-feeding species it produces mucus to gather food particles, which helps in transporting food to the esophagus and it also stores iodine, and may be a precursor of the vertebrate thyroid gland
16.
Charles Doolittle Walcott
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Charles Doolittle Walcott was an American paleontologist, administrator of the Smithsonian Institution from 1907 to 1927, and geologist. He became known for his discovery in 1909 of well-preserved fossils in the Burgess Shale of British Columbia, Canada and he was described by Stephen Jay Gould as the finest symbol that I have ever encountered for the embodiment of conventional beliefs. Walcott was born in New York Mills, New York and his grandfather, Benjamin S. Walcott, moved from Rhode Island in 1822. His father, also Charles Doolittle Walcott, died when Charles Jr. was only two, Walcott was the youngest of four children. He was interested in nature from an age, collecting minerals and bird eggs and, eventually. He attended various schools in the Utica area but left at the age of eighteen without completing high school and his interest in fossils solidified as he became a commercial fossil collector. On January 9,1872, Walcott married Lura Ann Rust and she died on January 23,1876. He lost this job after two years but was recruited to the newly formed US Geological Survey as a geological assistant. In 1876, he became the assistant to James Hall, State Geologist of New York, Walcott also became a member of the American Association for the Advancement of Science. In 1879, Walcott joined the US Geological Survey and rose to become its director in 1894 and he married Helena Breese Stevens in 1888. They had four children between 1889 and 1896, Charles Doolittle Walcott, Sydney Stevens Walcott, Helena Breese Walcott, Walcott was elected to the National Academy of Sciences in 1896. In 1902, he met with Andrew Carnegie and became one of the founders and incorporators of the Carnegie Institution of Washington and he served in various administrative and research positions in that organization. In 1921 Walcott was awarded the inaugural Mary Clark Thompson Medal from the National Academy of Sciences, Walcott became Secretary of the Smithsonian Institution in 1907 after the death of Samuel Pierpont Langley, holding the latter post until his own death. He was succeeded by Charles Greeley Abbot, because of Walcotts responsibilities at the Smithsonian, he resigned as director of the United States Geological Survey. As part of the celebration of Darwins birth, Walcott was awarded an honorary doctorate by the University of Cambridge in 1909. He served as president of the American Association for the Advancement of Science in 1923 and he was an advisor to then-president, Theodore Roosevelt. Walcott had an interest in the movement and assisted its efforts. In 1910, the year after his discovery of Cambrian fossils in the Burgess shale, Walcott returned to the area accompanied by his sons Stuart and Sidney
17.
Binomial nomenclature
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Such a name is called a binomial name, a binomen, binominal name or a scientific name, more informally it is also called a Latin name. The first part of the name identifies the genus to which the species belongs, for example, humans belong to the genus Homo and within this genus to the species Homo sapiens. The formal introduction of system of naming species is credited to Carl Linnaeus. But Gaspard Bauhin, in as early as 1623, had introduced in his book Pinax theatri botanici many names of genera that were adopted by Linnaeus. Although the general principles underlying binomial nomenclature are common to these two codes, there are differences, both in the terminology they use and in their precise rules. Similarly, both parts are italicized when a binomial name occurs in normal text, thus the binomial name of the annual phlox is now written as Phlox drummondii. In scientific works, the authority for a name is usually given, at least when it is first mentioned. In zoology Patella vulgata Linnaeus,1758, the original name given by Linnaeus was Fringilla domestica, the parentheses indicate that the species is now considered to belong in a different genus. The ICZN does not require that the name of the person who changed the genus be given, nor the date on which the change was made, in botany Amaranthus retroflexus L. – L. is the standard abbreviation used in botany for Linnaeus. – Linnaeus first named this bluebell species Scilla italica, Rothmaler transferred it to the genus Hyacinthoides, the ICN does not require that the dates of either publication be specified. Prior to the adoption of the binomial system of naming species. Together they formed a system of polynomial nomenclature and these names had two separate functions. First, to designate or label the species, and second, to be a diagnosis or description, such polynomial names may sometimes look like binomials, but are significantly different. For example, Gerards herbal describes various kinds of spiderwort, The first is called Phalangium ramosum, Branched Spiderwort, is aptly termed Phalangium Ephemerum Virginianum, Soon-Fading Spiderwort of Virginia. The Latin phrases are short descriptions, rather than identifying labels, the Bauhins, in particular Caspar Bauhin, took some important steps towards the binomial system, by pruning the Latin descriptions, in many cases to two words. The adoption by biologists of a system of binomial nomenclature is due to Swedish botanist and physician Carl von Linné. It was in his 1753 Species Plantarum that he first began using a one-word trivial name together with a generic name in a system of binomial nomenclature. This trivial name is what is now known as an epithet or specific name
18.
Cephalochordate
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A cephalochordate is an animal in the chordate subphylum, Cephalochordata. They are characterized as chordates, as they possess all 5 of the chordate characteristics during larval stages and this includes, notocord, dorsal nerve cord, endostyle, pharynx and post-anal tail. Cephalochordates are represented in the oceans by the Amphioxiformes. Along with its sister phylum, Urochordata, Cephalochordata can be classified as belonging to the taxon Protochordata, the members of this subphylum are very small and have no hard parts, making their fossils difficult to find. Fossilized species have found in very old rocks predating vertebrates. There is a famous fossil shale from the Middle Cambrian, the Burgess Shale of British Columbia, recently, a different cephalochordate fossil has been found in south China. It dates to the early Cambrian period, and is the earliest known fossil of the cephalochordate lineage, members of this lineage have numerous gill slits, and have separate sexes. Phylogeny is based on a combination of studies of extinct and extant species, cephalochordates employ a filter feeding system to consume microorganisms. The oral hood serves as the entrance for food particles, and possesses buccal cirri, epithelial cilia lining the mouth and pharynx form a specialized wheel organ situated at the dorsal and posterior end of the cavity. The motion of the cilia resembles the motion of a wheel, hence the organs name. Behind this organ is the velum, which acts as a filter before food enters the pharynx. The food particles adhere to secreted mucus on the bars before being brought to the epibranchial groove on the dorsal side of the pharynx. Following this, the food is transferred to the gut, and this excess water passes through the atriopore and is then excreted from the body
19.
Burgess Shale
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The Burgess Shale Formation is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the preservation of the soft parts of its fossils. At 508 million years old, it is one of the earliest fossil beds containing soft-part imprints, the rock unit is a black shale and crops out at a number of localities near the town of Field in Yoho National Park and the Kicking Horse Pass. Another outcrop is in Kootenay National Park 42 km to the south, the Burgess Shale was discovered by palaeontologist Charles Walcott on 30 August 1909, towards the end of the seasons fieldwork. He returned in 1910 with his sons, daughter, and wife, the significance of soft-bodied preservation, and the range of organisms he recognised as new to science, led him to return to the quarry almost every year until 1924. At that point, aged 74, he had amassed over 65,000 specimens, describing the fossils was a vast task, pursued by Walcott until his death in 1927. Walcott, led by scientific opinion at the time, attempted to categorise all fossils into living taxa, and as a result and it was not until 1962 that a first-hand reinvestigation of the fossils was attempted, by Alberto Simonetta. Indeed, many of the present had bizarre anatomical features. Examples include Opabinia, with five eyes and a snout like a vacuum hose and Hallucigenia. With Parks Canada and UNESCO recognising the significance of the Burgess Shale, collections continued to be made by the Royal Ontario Museum. The curator of invertebrate palaeontology, Desmond Collins, identified a number of additional outcrops and these localities continue to yield new organisms faster than they can be studied. Stephen Jay Goulds book Wonderful Life, published in 1989, brought the Burgess Shale fossils to the publics attention, Goulds interpretation of the diversity of Cambrian fauna relied heavily on Simon Conway Morriss reinterpretation of Charles Walcotts original publications. However, Conway Morris strongly disagreed with Goulds conclusions, arguing that almost all the Cambrian fauna could be classified into modern day phyla, the Burgess Shale has attracted the interest of paleoclimatologists who want to study and predict long-term future changes in Earths climate. See also Future of the Earth, after the Burgess Shale site was registered as a World Heritage Site in 1980, it was included in the Canadian Rocky Mountain Parks WHS designation in 1984. In February 2014, the discovery was announced of another Burgess Shale outcrop in Kootenay National Park to the south, in just 15 days of field collecting in 2013,50 animal species were unearthed at the new site. The fossil-bearing deposits of the Burgess Shale correlate to the Stephen formation, the beds were deposited at the base of a cliff about 160 m tall, below the depth agitated by waves during storms. This vertical cliff was composed of the reefs of the Cathedral Formation. Later reactivation of faults at the base of the led to its disintegration from about 509 million years ago
20.
British Columbia
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British Columbia is the westernmost province of Canada, with a population of more than four million people located between the Pacific Ocean and the Rocky Mountains. British Columbia is also a component of the Pacific Northwest and the Cascadia bioregion, along with the U. S. states of Idaho, Oregon, Washington and Alaska. The first British settlement in the area was Fort Victoria, established in 1843, subsequently, on the mainland, the Colony of British Columbia was founded by Richard Clement Moody and the Royal Engineers, Columbia Detachment, in response to the Fraser Canyon Gold Rush. Port Moody is named after him, in 1866, Vancouver Island became part of the colony of British Columbia, and Victoria became the united colonys capital. In 1871, British Columbia became the province of Canada. Its Latin motto is Splendor sine occasu, the capital of British Columbia remains Victoria, the fifteenth-largest metropolitan region in Canada, named for the Queen who created the original European colonies. The largest city is Vancouver, the third-largest metropolitan area in Canada, the largest in Western Canada, in October 2013, British Columbia had an estimated population of 4,606,371. British Columbia evolved from British possessions that were established in what is now British Columbia by 1871, First Nations, the original inhabitants of the land, have a history of at least 10,000 years in the area. Today there are few treaties and the question of Aboriginal Title, notably, the Tsilhqotin Nation has established Aboriginal title to a portion of their territory, as a result of the recent Supreme Court of Canada decision. BCs economy is diverse, with service producing industries accounting for the largest portion of the provinces GDP and it is the endpoint of transcontinental railways, and the site of major Pacific ports that enable international trade. Though less than 5% of its vast 944,735 km2 land is arable and its climate encourages outdoor recreation and tourism, though its economic mainstay has long been resource extraction, principally logging, farming, and mining. Vancouver, the provinces largest city and metropolitan area, also serves as the headquarters of many western-based natural resource companies and it also benefits from a strong housing market and a per capita income well above the national average. The Northern Interior region has a climate with very cold winters. The climate of Vancouver is by far the mildest winter climate of the major Canadian cities, the provinces name was chosen by Queen Victoria, when the Colony of British Columbia, i. e. the Mainland, became a British colony in 1858. The current southern border of British Columbia was established by the 1846 Oregon Treaty, British Columbias land area is 944,735 square kilometres. British Columbias rugged coastline stretches for more than 27,000 kilometres and it is the only province in Canada that borders the Pacific Ocean. British Columbias capital is Victoria, located at the tip of Vancouver Island. Only a narrow strip of the Island, from Campbell River to Victoria, is significantly populated, much of the western part of Vancouver Island and the rest of the coast is covered by thick, tall and sometimes impenetrable temperate rainforest
21.
Lancelet
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They are the modern representatives of the subphylum Cephalochordata, formerly thought to be the sister group of the craniates. In Asia, they are harvested commercially as food for humans and they are an important object of study in zoology as they provide indications about the evolutionary origins of the vertebrates. Lancelets serve as an intriguing comparison point for tracing how vertebrates have evolved and adapted, although lancelets split from vertebrates more than 520 million years ago, their genomes hold clues about evolution, particularly how vertebrates have employed old genes for new functions. They are regarded as similar to the archetypal vertebrate form, the first representative organism of the group to be described was Branchiostoma lanceolatum. It was described by Peter Simon Pallas in 1774 as molluscan slugs in the genus Limax and it was not until 1834 that Gabriel Costa brought the phylogenetic position of the group closer to the agnathan vertebrates, including it in the new genus Branchiostoma. In 1836, Yarrel renamed the genus as Amphioxus, now considered a synonym of the genus Branchiostoma. Today, the term amphioxus is still used as a name for the Amphioxiformes, along with lancelet. A non-technical review of all aspects of biology is, Stokes, M. D. and Holland. The genome of the Florida lancelet has been sequenced, lancelets are typically 5 centimetres long, or 7 centimetres at the longest. They have a translucent, somewhat fish-like body, but without any paired fins or other limbs, a relatively poorly developed tail fin is present, so they are not especially good swimmers. While they do possess some cartilage-like material stiffening the gill slits, mouth, in common with vertebrates, lancelets have a hollow nerve cord running along the back, pharyngeal slits and a tail that runs past the anus. Also like vertebrates, the muscles are arranged in blocks called myomeres, unlike vertebrates, the dorsal nerve cord is not protected by bone but by a simpler notochord made up of a cylinder of cells that are closely packed to form a toughened rod. The lancelet notochord, unlike the vertebrate spine, extends into the head and this gives the subphylum its name. The nerve cord is only larger in the head region than in the rest of the body. However, developmental gene expression and Transmission electron microscopy indicate the presence of a diencephalic forebrain, a possible midbrain, lancelets have two known kinds of light-sensing structures, Joseph cells, and Hesse organs, as well as a frontal eye and lamellar body. The frontal eye is thought to be light-sensitive, although this has not been confirmed by electrophysiological measurement. The lamellar body, a homologue of the pineal body, was once thought to be light-sensitive. All of these organs and structures are located in the tube, with the frontal eye at the front, followed by the lamellar body, the Joseph cells
22.
Eel
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An eel is any fish belonging to the order Anguilliformes, which consists of four suborders,20 families,111 genera and about 800 species. The term eel is used for some other similarly shaped fish, such as electric eels and spiny eels. Eels are elongated fish, ranging in length from 5 cm in the eel to 4 m in the slender giant moray. Adults range in weight from 30 g to well over 25 kg and they possess no pelvic fins, and many species also lack pectoral fins. The dorsal and anal fins are fused with the caudal fin, eels swim by generating body waves which travel the length of their bodies. They can swim backwards by reversing the direction of the wave, most eels live in the shallow waters of the ocean and burrow into sand, mud, or amongst rocks. A majority of eel species are nocturnal, thus are rarely seen, sometimes, they are seen living together in holes, or eel pits. Some species of eels live in deeper water on the continental shelves. Only members of the Anguilla regularly inhabit fresh water, but they, too, the heaviest true eel is the European conger. The maximum size of species has been reported as reaching a length of 3 m. Other eels are longer, but do not weigh as much, such as the giant moray which reaches 4 m. Eels begin life as flat and transparent larvae, called leptocephali, Eel larvae drift in the surface waters of the sea, feeding on marine snow, small particles that float in the water. Eel larvae then metamorphose into glass eels and then become elvers before finally seeking out their juvenile, freshwater elvers travel upstream and are forced to climb up obstructions, such as weirs, dam walls, and natural waterfalls. Lady Colin Campbell found, at Ballisodare, the eel fisheries were greatly improved by the hanging of loosely plaited grass ladders over barriers and this classification follows FishBase in dividing the eels into 20 families. Additional families included in other classifications are noted below the family with which they are synomized in the Fish Base system, identifying the origin of the freshwater species has been problematic. Genomic studies indicate they are a group which originated among the deep-sea eels. The electric eel of South America is not a true eel, freshwater eels and marine eels are commonly used in Japanese cuisine, foods such as unadon and unajū are popular, but expensive. Eels are also popular in Chinese cuisine, and are prepared in many different ways
23.
Vertebrate
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Vertebrates /ˈvɜːrtᵻbrᵻts/ comprise all species of animals within the subphylum Vertebrata /-ɑː/. Vertebrates represent the majority of the phylum Chordata, with currently about 66,000 species described. Vertebrates include the fish and the jawed vertebrates, which include the cartilaginous fish. A bony fish known as the lobe-finned fishes is included with tetrapods, which are further divided into amphibians, reptiles, mammals. Extant vertebrates range in size from the frog species Paedophryne amauensis, at as little as 7.7 mm, to the blue whale, vertebrates make up less than five percent of all described animal species, the rest are invertebrates, which lack vertebral columns. The vertebrates traditionally include the hagfish, which do not have proper vertebrae due to their loss in evolution, though their closest living relatives, hagfish do, however, possess a cranium. For this reason, the vertebrate subphylum is sometimes referred to as Craniata when discussing morphology, molecular analysis since 1992 has suggested that hagfish are most closely related to lampreys, and so also are vertebrates in a monophyletic sense. Others consider them a group of vertebrates in the common taxon of craniata. The word origin of vertebrate derives from the Latin word vertebratus, the Proto-Indo-European language origins are still unclear. Vertebrate is derived from the vertebra, which refers to any of the bones or segments of the spinal column. All vertebrates are built along the basic body plan, a stiff rod running through the length of the animal, with a hollow tube of nervous tissue above it. In all vertebrates, the mouth is found at, or right below, the remaining part of the body continuing after the anus forms a tail with vertebrae and spinal cord, but no gut. However, a few vertebrates have secondarily lost this anatomy, retaining the notochord into adulthood, such as the sturgeon, jawed vertebrates are typified by paired appendages, but this trait is not required in order for an animal to be a vertebrate. All basal vertebrates breathe with gills, the gills are carried right behind the head, bordering the posterior margins of a series of openings from the pharynx to the exterior. Each gill is supported by a cartilagenous or bony gill arch, the bony fish have three pairs of arches, cartilaginous fish have five to seven pairs, while the primitive jawless fish have seven. The vertebrate ancestor no doubt had more arches than this, as some of their relatives have more than 50 pairs of gills. In amphibians and some primitive fishes, the larvae bear external gills. These are reduced in adulthood, their function taken over by the gills proper in fishes, some amphibians retain the external larval gills in adulthood, the complex internal gill system as seen in fish apparently being irrevocably lost very early in the evolution of tetrapods
24.
Tentacle
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In zoology, a tentacle is a flexible, mobile, elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs, anatomically, the tentacles of animals work mainly like muscular hydrostats. Most forms of tentacles are used for grasping and feeding, many are sensory organs, variously receptive to touch, vision, or to the smell or taste of particular foods or threats. Examples of such tentacles are the eye stalks of various kinds of snails, some kinds of tentacles have both sensory and manipulatory functions. The word tentillum literally means little tentacle, however, irrespective of size, it usually refers to a side branch of a larger tentacle. In some cases such tentilla are specialised for particular functions, for example, in the Cnidaria tentilla usually bear cnidocytes, many molluscs have tentacles of one form or another. Both pairs are fully retractable muscular hydrostats, but they are not used for manipulation or prey capture, some marine snails such as abalone and top snails, Trochidae, have numerous small tentacles around the edge of the mantle. These are known as pallial tentacles, among cephalopods, squid have spectacular tentacles. They take the form of highly mobile muscular hydrostats with various appendages such as suction disks, up to the early twentieth century tentacles were interchangeably called arms. The modern convention however, is to speak of appendages as tentacles when they have relatively thin peduncles or stalks with clubs at their tips, in contrast the convention refers to the relatively shorter appendages as arms. By this definition the eight appendages of octopuses, though quite long, in terms of this article however, both types of organs count as tentacles because in relevant ways they are structurally and functionally similar. The tentacles of the giant squid and colossal squid have powerful suckers, the teeth of the giant squid resemble bottle caps, and function like tiny, hole saws, while the tentacles of the colossal squid wield two long rows of swiveling, tri-pointed hooks. Cnidarians, such as jellyfish, sea anemones, Hydra and coral have numerous hair-like tentacles, cnidarians have huge numbers of cnidocytes on their tentacles. In medusoid form, the floats on water so that the tentacles hang down in a ring around the mouth. In polyp form, such as sea anemone and coral, the body is below with the tentacles pointed upwards, many species of the jellyfish-like ctenophores have two tentacles, while some have none. Their tentacles have adhesive structures called colloblasts or lasso cells, the colloblasts burst open when prey comes in contact with the tentacle, releasing sticky threads that secure the food. The tentacles of the Lions mane jellyfish may be up to 120 feet long and they are hollow and are arranged in 8 groups of between 70 and 150. The longer tentacles are equipped with cnidocytes whose venom paralyses and kills prey, the smaller tentacles guide food into the mouth
25.
Hagfish
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Hagfish, the class Myxini, are eel-shaped, slime-producing marine fish. They are the known living animals that have a skull. Along with lampreys, hagfish are jawless, they are the group to vertebrates. The classification of hagfish has been controversial, the issue is whether the hagfish is a degenerate type of vertebrate-fish, or represents a stage that precedes the evolution of the vertebral column. The original scheme groups hagfish and lampreys together as cyclostomes, as the oldest surviving class of vertebrates alongside gnathostomes, an alternative scheme proposed that jawed vertebrates are more closely related to lampreys than to hagfish, and introduces the category craniata to group vertebrates near hagfish. Recent DNA evidence has supported the original scheme, Hagfish average about 0.5 m in length. The largest known species is Eptatretus goliath with a recorded at 127 cm, while Myxine kuoi. Hagfish have elongated, eel-like bodies, and paddle-like tails, the skin is naked and covers the body like a loosely fitting sock. They have cartilaginous skulls and tooth-like structures composed of keratin, colors depend on the species, ranging from pink to blue-grey, and black or white spots may be present. Eyes are simple eyespots, not compound eyes that can resolve images, Hagfish have no true fins and have six or eight barbels around the mouth and a single nostril. Instead of vertically articulating jaws like Gnathostomata, they have a pair of horizontally moving structures with tooth-like projections for pulling off food, the mouth of the hagfish has two pairs of horny, comb-shaped teeth on a cartilaginous plate that protracts and retracts. These teeth are used to food and draw it toward the pharynx. Hagfish are long and vermiform, and can exude copious quantities of a milky, the typical species Myxine glutinosa was named for this slime. When captured and held, e. g. by the tail, they secrete the microfibrous slime, which expands into up to 20 litres of sticky, gelatinous material when combined with water. This singular behavior may assist them in extricating themselves from the jaws of predatory fish or from the interior of their own prey, recently, the slime was reported to entrain water in its microfilaments, creating a slow-to-dissipate, viscoelastic substance, rather than a simple gel. It has been proven to impair the function of a predator fishs gills, in this case, the hagfishs mucus would clog up the predators gills, disabling their ability to breathe. The predator would release the hagfish as it focused less on eating and it is because of the mucus that there are very few marine predators that target the hagfish. The other known predators of hagfish are varieties of birds or mammals, free-swimming hagfish also slime when agitated and later clear the mucus off by way of the same travelling-knot behavior
26.
Alberta
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Alberta is a western province of Canada. With an estimated population of 4,196,457 as of July 1,2015, it is Canadas fourth-most populous province and its area is about 660,000 square kilometres. Alberta and its neighbour Saskatchewan were districts of the Northwest Territories until they were established as provinces on September 1,1905, the premier has been Rachel Notley since May 2015. Alberta is bounded by the provinces of British Columbia to the west and Saskatchewan to the east, the Northwest Territories to the north, and the U. S. state of Montana to the south. Alberta is one of three Canadian provinces and territories to only a single U. S. state and one of only two landlocked provinces. About 290 km south of the capital is Calgary, the largest city in Alberta, Calgary and Edmonton centre Albertas two census metropolitan areas, both of which have populations exceeding one million, while the province has 16 census agglomerations. Tourist destinations in the province include Banff, Canmore, Drumheller, Jasper, Alberta is named after Princess Louise Caroline Alberta, the fourth daughter of Victoria, Queen of Canada, and Albert, Prince Consort. Princess Louise was the wife of John Campbell, Marquess of Lorne, Lake Louise and Mount Alberta were also named in her honour. Alberta, with an area of 661,848 km2, is the fourth largest province after Quebec, Ontario and British Columbia. To the south, the borders on the 49th parallel north, separating it from the US state of Montana. The province extends 1,223 km north to south and 660 km east to west at its maximum width, with the exception of the semi-arid steppe of the south-eastern section, the province has adequate water resources. There are numerous rivers and lakes used for swimming, fishing, there are three large lakes, Lake Claire in Wood Buffalo National Park, Lesser Slave Lake, and Lake Athabasca which lies in both Alberta and Saskatchewan. The longest river in the province is the Athabasca River which travels 1,538 km from the Columbia Icefield in the Rocky Mountains to Lake Athabasca, the largest river is the Peace River with an average flow of 2161 m3/s. The Peace River originates in the Rocky Mountains of northern British Columbia and flows through northern Alberta and into the Slave River, Albertas capital city, Edmonton, is located approximately in the geographic centre of the province. It is the most northerly city in Canada, and serves as a gateway. The region, with its proximity to Canadas largest oil fields, has most of western Canadas oil refinery capacity, Calgary is located approximately 280 km south of Edmonton and 240 km north of Montana, surrounded by extensive ranching country. Almost 75% of the population lives in the Calgary–Edmonton Corridor. The land grant policy to the served as a means to populate the province in its early years
27.
Polychaete
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The Polychaeta /ˌpɒlɪˈkiːtə/ or polychaetes are a paraphyletic class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, as such, polychaetes are sometimes referred to as bristle worms. More than 10,000 species are described in this class, common representatives include the lugworm and the sandworm or clam worm Alitta. Only 168 species are known from fresh waters, polychaetes are segmented worms, generally less than 10 cm in length, although ranging at the extremes from 1 mm to 3 m. They can sometimes be brightly coloured, and may be iridescent or even luminescent, each segment bears a pair of paddle-like and highly vascularized parapodia, which are used for movement and, in many species, act as the worms primary respiratory surfaces. Bundles of bristles, called setae, project from the parapodia, however, polychaetes vary widely from this generalised pattern, and can display a range of different body forms. The head, or prostomium, is well developed, compared with other annelids. It projects forward over the mouth, which lies on the animals underside. The head normally includes two to four pair of eyes, although species are blind. These are typically fairly simple structures, capable of distinguishing only light and dark, the head also includes a pair of antennae, tentacle-like palps, and a pair of pits lined with cilia, known as nuchal organs. These latter appear to be chemoreceptors, and help the worm to seek out food, the outer surface of the body wall consists of a simple columnar epithelium covered by a thin cuticle. Underneath this, in order, are a layer of connective tissue, a layer of circular muscle, a layer of longitudinal muscle. Additional oblique muscles move the parapodia, in most species the body cavity is divided into separate compartments by sheets of peritoneum between each segment, but in some species its more continuous. In general, however, they possess a pair of jaws, in some species, the pharynx is modified into a lengthy proboscis. The digestive tract is a tube, usually with a stomach part way along. The smallest species, and those adapted to burrowing, lack gills, most other species have external gills, often associated with the parapodia. A simple but well-developed circulatory system is usually present, the two main blood vessels furnish smaller vessels to supply the parapodia and the gut. Blood flows forward in the vessel, above the gut
28.
National Museum of Natural History
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The National Museum of Natural History is a natural history museum administered by the Smithsonian Institution, located on the National Mall in Washington, D. C. Opened in 1910, the museum on the National Mall was one of the first Smithsonian buildings constructed exclusively to hold the national collections and research facilities. The main building has an area of 1,500,000 square feet with 325,000 square feet of exhibition and public space. The museums collections contain over 126 million specimens of plants, animals, fossils, minerals, rocks, meteorites, human remains, the United States National Museum was founded in 1846 as part of the Smithsonian Institution. The museum was housed in the Smithsonian Institution Building, which is better known today as the Smithsonian Castle. A formal exhibit hall opened in 1858, the growing collection led to the construction of a new building, the National Museum Building. Covering a then-enormous 2.25 acres, it was built in just 15 months at a cost of $310,000, congress authorized construction of a new building on June 28,1902. The regents began considering sites for the new building in March, the D. C. architectural firm of Hornblower & Marshall was chosen to design the structure. Testing of the soil for the foundations was set for July 1903, the Natural History Building opened its doors to the public on March 17,1910, in order to provide the Smithsonian Institution with more space for collections and research. The building was not fully completed until June 1911, the structure cost $3.5 million dollars. The Neoclassical style building was the first structure constructed on the side of the National Mall as part of the 1901 McMillan Commission plan. In addition to the Smithsonians natural history collection, it housed the American history, art. Between 1981 and 2003, the National Museum of Natural History had 11 permanent, there were six directors alone between 1990 and 2002. Turnover was high as the directors were disenchanted by low levels of funding. Robert W. Fri was named the director in 1996. One of the largest donations in Smithsonian history was made during Fris tenure, kenneth E. Behring donated $20 million in 1997 to modernize the museum. Fri resigned in 2001 after disagreeing with Smithsonian leadership over the reorganization of the scientific research programs. J. Dennis OConnor, Provost of the Smithsonian Institution was named acting director of the museum on July 25,2001, eight months later, OConner resigned to become the vice president of research and dean of the graduate school at the University of Maryland
29.
Paleontology
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Paleontology or palaeontology is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene Epoch. It includes the study of fossils to determine organisms evolution and interactions with each other, paleontological observations have been documented as far back as the 5th century BC. The science became established in the 18th century as a result of Georges Cuviers work on comparative anatomy, and developed rapidly in the 19th century. The term itself originates from Greek παλαιός, palaios, i. e. old, ancient, ὄν, on, i. e. being, creature and λόγος, logos, i. e. speech, thought, study. Paleontology lies on the border between biology and geology, but differs from archaeology in that it excludes the study of modern humans. It now uses techniques drawn from a range of sciences, including biochemistry, mathematics. The final quarter of the 20th century saw the development of molecular phylogenetics, molecular phylogenetics has also been used to estimate the dates when species diverged, but there is controversy about the reliability of the molecular clock on which such estimates depend. The simplest definition is the study of ancient life, paleontology is one of the historical sciences, along with archaeology, geology, astronomy, cosmology, philology and history itself. This means that it aims to describe phenomena of the past, hence it has three main elements, description of the phenomena, developing a general theory about the causes of various types of change, and applying those theories to specific facts. Sometimes the smoking gun is discovered by an accident during other research. Paleontology lies on the boundary between biology and geology since paleontology focuses on the record of past life but its source of evidence is fossils. In addition paleontology often uses techniques derived from other sciences, including biology, osteology, ecology, chemistry, techniques developed in engineering have been used to analyse how ancient organisms might have worked, for example how fast Tyrannosaurus could move and how powerful its bite was. As knowledge has increased, paleontology has developed specialised subdivisions, vertebrate paleontology concentrates on fossils of vertebrates, from the earliest fish to the immediate ancestors of modern mammals. Invertebrate paleontology deals with fossils of such as molluscs, arthropods. Paleobotany focuses on the study of plants, but traditionally includes the study of fossil algae. Palynology, the study of pollen and spores produced by plants and protists. Micropaleontology deals with all microscopic fossil organisms, regardless of the group to which they belong, one example is the development of oxygenic photosynthesis by bacteria, which hugely increased the productivity and diversity of ecosystems. This also caused the oxygenation of the atmosphere, together, these were a prerequisite for the evolution of the most complex eukaryotic cells, from which all multicellular organisms are built
30.
Cuticle
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A cuticle /ˈkjuːtɪkəl/, or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of cuticle are non-homologous, differing in their origin, structure, function, in human anatomy, cuticle refers to several structures. In zoology, the cuticle or cuticula is a multi-layered structure outside the epidermis of many invertebrates, notably roundworms and arthropods. The main structural components of the cuticle are proteins, highly cross-linked collagens and specialised insoluble proteins known as cuticlins, together with glycoproteins. The rigidity is a function of the types of proteins and the quantity of chitin, the more acidic the protein is, the softer the cuticle. It is believed that the cells and hemocytes produce protein and also monitors the timing. Often, in the cuticle of arthropods, structural coloration-producing nanostructures are observed, in botany, plant cuticles are protective, hydrophobic, waxy coverings produced by the epidermal cells of leaves, young shoots and all other aerial plant organs. Cuticles minimize water loss and effectively reduce pathogen entry due to their waxy secretion, the main structural components of plant cuticles are the unique polymers cutin and/or cutan, impregnated with wax. The cuticles of plants function as permeability barriers for water and water-soluble materials, the cuticle both prevents plant surfaces from becoming wet and helps to prevent plants from drying out. Xerophytic plants such as cactus have very thick cuticles to help them survive in their arid climates, plants that live in range of seas spray also may have thicker cuticles that protect them from the toxic effects of salt. Some plants, particularly adapted to life in damp or aquatic environments, have an extreme resistance to wetting. A well-known example is the Sacred Lotus and this adaptation is not purely the physical and chemical effect of a waxy coating, however, it depends largely on the microscopic shape of the surface. The effect is to reduce wetting of the surface substantially, structural coloration is also observed in the cuticles of plants (see, as an example, the so-called marble berry, Pollia condensata. Cuticle is one used for the outer layer of tissue of a mushrooms basidiocarp. The alternative term pileipellis, Latin for skin of a cap might be technically preferable and it is the part removed in peeling mushrooms. On the other hand, some terminology in mycology makes finer distinctions. Be that as it may, the pileipellis is distinct from the trama, the fleshy tissue of a mushroom or similar fruiting body, and also from the spore-bearing tissue layer
31.
Chengjiang County
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Chengjiang County is in Yuxi, Yunnan Province, China, just north of Fuxian Lake. These fossils are considered one of the most important fossil finds of the 20th century and they contain an exquisite degree of detail, cover a diverse range of fauna, and are significant in attempts to understand the evolution of life on Earth. The fossils were first discovered by Henri Mansuy and Jaques Deprat who described them in 1912, previously he was a professor at the Palaeontological Institute, Chinese Academy of Sciences, Nanjing. Chengjiang is a county having rich phosphate deposits above and below the formation holding the lagerstätte. Efforts were made to close the region to mining in a bid to support the bid for listing as a World Heritage Site. A consequence of this was renewed mining efforts in the region, which threatened the fossil-bearing strata due to erosion, slumping of overburden, and simple destruction by the mining efforts. Guang, Hou Xian, Aldridge, Richard J. Bergstrom, Jan, Siveter, David J. Siveter, the Cambrian Fossils of Chengjiang, China, The Flowering of Early Animal Life. Book Review - The Cambrian Fossils of Chengjiang, China, in PalArchs Journal of Vertebrate Paleontology
32.
Haikouichthys
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Haikouichthys /ˌhaɪkuːˈɪkθɪs/ is an extinct genus of craniate believed to have lived 525 million years ago, during the Cambrian explosion of multicellular life. Haikouichthys had a skull and other characteristics that have led paleontologists to label it a true craniate. Cladistic analysis indicates that the animal is probably a basal chordate or a basal craniate, Haikouichthys is about 2.5 cm long and is narrower than Myllokunmingia, another putative chordate that comes from the same beds. The fossil was recovered among the Chengjiang fauna, in one of a series of Lagerstätten sites where thousands of exquisitely preserved soft-bodied fossils have already been found, following the discovery of the holotype, additional Lower Cambrian fossils of Haikouichthys ercaicunensis have been discovered. The animal has a head and tail. The head has at least six and perhaps nine probable gills, there are a number of segments with rear directed chevrons in the tail. There is a prominent dorsal fin with fin radials similar, but not comparable, to those of hagfish, the fin radials seem to angle forward toward the end thought on the basis of internal structures to be the head. This happens with a few modern fish but is an uncommon arrangement, there are 13 circular structures along the bottom that may be gonads, slime organs, or something else entirely
33.
Myllokunmingia
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Myllokunmingia is a genus of basal chordate from the Lower Cambrian Maotianshan shales of China, thought to be a vertebrate, although this is not conclusively proven. It is 28 mm long and 6 mm high and it is among the oldest possible craniates, found in the lower Cambrian Chengjiang. It appears to have a skull and skeletal structures made of cartilage, there is no sign of biomineralization of the skeletal elements. The holotype was found in the Yuanshan member of the Qiongzhusi Formation in the Eoredlichia Zone near Haikou at Ercaicun, Kunming City, Yunnan, the animal has a distinct head and trunk with a forward sail-like dorsal fin and a ventral finfold further back. The head has five or six gill pouches with hemibranchs, in the trunk there are 25 segments with rearward-facing chevrons. There is a notochord, a pharynx and a tract that may run all the way to the rear tip of the animal. The mouth cannot be clearly identified, there may be a pericardial cavity. There is only one specimen, which has the tip of the buried in sediment. Only one species is known – Myllokunmingia fengjiaoa, related creatures are Haikouichthys and Zhongjianichthys
34.
Crown group
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It is thus a clade, a group consisting of a species and all its descendants. Though formulated in the 1970s, the term was not commonly used until its reintroduction in 2000 by Graham Budd and it is not necessary for a species to have living descendants in order for it to be included in the crown group. Extinct side branches on the tree that are descended from the most recent common ancestor of living members will still be part of a crown group. Although considered to be birds, Archaeopteryx and other groups are not included in the crown group, as they fall outside the Neornithes clade. An alternative definition does not require any members of a group to be extant. The first definition forms the basis of this article, often, the crown group is given the designation crown-, to separate it from the group as commonly defined. Crown-Aves and Crown-Mammalia therefore differ slightly in content from the definition of Aves. This has caused confusion in the literature. Thus, a host of prefixes have been defined to describe various branches of the phylogenetic tree relative to extant organisms, a pan-group or total group is the crown group and all organisms more closely related to it than to any other extant organisms. In a tree analogy, it is the group and all branches back to the split with the closest branch to have living members. The Pan-Aves thus contain the living birds and all more closely related to birds than to crocodilians. The phylogenetic lineage leading back from Neornithes to the point where it merges with the crocodilian lineage, pan-Mammalia consists of all mammals and their fossil ancestors back to the phylogenetic split from the remaining amniotes. Pan-Mammalia is thus a name for Synapsida. A stem group is a group composed of a pan-group or total group, above. This leaves primitive relatives of the groups, back along the phylogenetic line to the last common ancestor of the crown group. It follows from the definition that all members of a group are extinct. Alternatively, the stem group is sometimes used in a narrower sense to cover just the members of the traditional taxon falling outside the crown group. Permian synapsids like Dimetrodon and Anteosaurus are stem mammals in the wider sense, stem birds perhaps constitute the most cited example of a stem group, as the phylogeny of this group is fairly well known
35.
Branchiostoma
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Branchiostoma is one of the few living genera of lancelets. It is the genus of family Branchiostomidae. These small vaguely eel- or snake-like animals are close relatives of vertebrates, like all lancelets, they are filter feeders that hide in the sediment most of the time. The genus inhabits coastal waters throughout the world, media related to Branchiostoma at Wikimedia Commons Branchiostoma
36.
Tunicate
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A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata, which is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords. The subphylum was at one time called Urochordata, and the term urochordates is still used for these animals. Some tunicates live as solitary individuals, but others replicate by budding and become colonies and they are marine filter feeders with a water-filled, sac-like body structure and two tubular openings, known as siphons, through which they draw in and expel water. During their respiration and feeding, they take in water through the incurrent siphon, various species are commonly known as sea squirts, sea pork, sea livers, or sea tulips. The earliest probable species of tunicate appears in the record in the early Cambrian period. Their name derives from their outer covering or tunic, which is formed from proteins and carbohydrates. In some species, it is thin, translucent, and gelatinous, while in others it is thick, tough, about 2,150 species of tunicate exist in the worlds oceans, living mostly in shallow water. The most numerous group is the ascidians, fewer than 100 species of these are found at greater than 200 m. Some are solitary animals leading a sessile existence attached to the seabed, but others are colonial and a few are pelagic. Some are supported by a stalk, but most are attached directly to a substrate and they are found in a range of solid or translucent colours and may resemble seeds, grapes, peaches, barrels, or bottles. One of the largest is a stalked sea tulip, Pyura pachydermatina, the Tunicata were established by Jean-Baptiste Lamarck in 1816. In 1881, Francis Maitland Balfour introduced a name for the same group, Urochorda. Accordingly, the current trend is to abandon the name Urochorda or Urochordata in favour of the original Tunicata, and it is accepted as valid by the World Register of Marine Species but not by the Integrated Taxonomic Information System. Various common names are used for different species, sea tulips are tunicates with colourful bodies supported on slender stalks. Sea squirts are so named because of their habit of contracting their bodies sharply, sea liver and sea pork get their names from the resemblance of their dead colonies to pieces of meat. Tunicates are more related to craniates, than to lancelets, echinoderms, hemichordates. The clade consisting of tunicates and vertebrates is called Olfactores, although the traditional classification is provisionally accepted, newer evidence suggests the Ascidiacea are an artificial group of paraphyletic status. Undisputed fossils of tunicates are rare, the best known and earliest unequivocally identified species is Shankouclava shankouense from the Lower Cambrian Maotianshan Shale at Shankou village, Anning, near Kunming
37.
Acorn worms
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The acorn worms or Enteropneusta are a hemichordate class of invertebrates consisting of one order of the same name. Their closest relatives are the echinoderms, there are about 90 species of acorn worm in the world, the main species for research being Saccoglossus kowalevskii. Until recently, it was thought that all species lived in the sediment on the seabed, some of these worms may grow to be very long, one particular species may reach a length of 2.5 metres, although most acorn worms are much smaller. Due to secretions containing elements like iodine, the animals have a iodoform-like smell, most acorn worms range from 9 to 45 centimetres in length, with the largest species, Balanoglossus gigas, reaching 1.5 metres or more. The body is made up of three parts, an acorn-shaped proboscis, a short fleshy collar that lies behind it. The creatures mouth is located at the collar behind the proboscis, the skin is covered with cilia as well as glands that secrete mucus. Some produce a compound that gives them a medicinal smell and might protect them from bacteria. Acorn worms move only sluggishly, using ciliary action and peristalsis of the proboscis, many acorn worms are detritus feeders, eating sand or mud and extracting organic detritus. Others feed on organic material suspended in the water, which they can draw into the mouth using the cilia on the gill bars, a groove lined with cilia lies just in front of the mouth and directs suspended food into the mouth and may allow the animal to taste. The mouth cavity is tubular, with a narrow diverticulum or stomochord extending up into the proboscis and this diverticulum was once thought to be homologous with the notochord of chordates, hence the name hemichordate for the phylum. The mouth opens posteriorly into a pharynx with a row of gill slits along either side, the remainder of the digestive system consists of an oesophagus and intestine, there is no stomach. In some families there are openings in the surface of the oesophagus connecting to the external surface, through which water from the food can be squeezed. Digestion occurs in the intestine, with material being pulled through by cilia. Acorn worms breathe by drawing in oxygenated water through their mouth, the water then flows out the animals gills which are on its trunk. Thus, the acorn worm breathes about the way as fish. Acorn worms have a circulatory system, in which the blood flows through the tissues sinuses. A dorsal blood vessel in the mesentery above the gut and delivers blood to a sinus in the proboscis that contains a muscular sac acting as a heart. Unlike the hearts of most other animals, however, this structure is a closed fluid-filled vesicle whose interior does not connect directly to the blood system, nonetheless, it does regularly pulsate, helping to push blood through the surrounding sinuses
38.
Graptolithina
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Graptolithina is a class of hemichordate animal, the members of which are known as graptolites. Graptolites are colonial animals known chiefly as fossils from the Upper Cambrian through the Lower Carboniferous, a possible early graptolite, Chaunograptus, is known from the Middle Cambrian. The name graptolite comes from the Greek graptos, meaning written, Linnaeus originally regarded them as pictures resembling fossils rather than true fossils, though later workers supposed them to be related to the hydrozoans. More recent work places them near the pterobranchs, possibly within, one analysis suggests that the Pterobranchia represent extant graptolites. The name graptolite originates from the genus Graptolithus, which was used by Linnaeus in 1735 for inorganic mineralizations and crustations which resembled actual fossils. In 1768, in the 12th volume of Systema Naturae, he included G. sagittarius and G. scalaris, respectively a possible plant fossil and a possible graptolite. In his 1751 Skånska Resa, he included a figure of a fossil or graptolite of a kind currently thought to be a type of Climacograptus. Later workers used the name to refer to a group of organisms. Graptolithus was officially abandoned in 1954 by the ICZN, partly because of its purpose as a grouping for inorganic mimicries of fossils. Comparisons are drawn with the modern hemichordates Cephalodiscus and Rhabdopleura, Cephalodiscus numbers about 18 species, and was first discovered in 1882. Graptolites are common fossils and have a worldwide distribution, the preservation, quantity and gradual change over a geologic time scale of graptolites allows the fossils to be used to date strata of rocks throughout the world. They are important index fossils for dating Palaeozoic rocks as they evolved rapidly with time, british geologists can divide the rocks of the Ordovician and Silurian periods into graptolite biozones, these are generally less than one million years in duration. A worldwide ice age at the end of the Ordovician eliminated most graptolites except the neograptines, diversification from the neograptines that survived the Ordovician glaciation began around 2 million years later. Graptolites are also used to water depth and temperature during the graptolites lifetimes. Each graptolite colony is known as a rhabdosome and has a number of branches originating from an initial individual. Each subsequent individual is housed within a tubular or cup-like structure, in some colonies, there are two sizes of theca, and it has been suggested that this difference is due to sexual dimorphism. The number of branches and the arrangement of the thecae are important features in the identification of graptolite fossils and their general shape has been compared with that of a hacksaw blade. Most of the dendritic or many-branched types are classified as dendroid graptolites and they appear earlier in the fossil record, and were generally sessile animals
39.
Hemichordate
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Hemichordata is a phylum of marine deuterostome animals, generally considered the sister group of the echinoderms. They appear in the Lower or Middle Cambrian and include two main classes, Enteropneusta, and Pterobranchia, a third class, Planctosphaeroidea, is known only from the larva of a single species, Planctosphaera pelagica. The extinct class Graptolithina is closely related to the pterobranchs, acorn worms are solitary worm-shaped organisms. They generally live in burrows and are deposit feeders, but some species are filter feeders. Many are well known for their production and accumulation of various halogenated phenols, pterobranchs are filter-feeders, mostly colonial, living in a collagenous tubular structure called a coenecium. The body plan of hemichordates is characterized by a tripartite organization, the anteroposterior axis is divided into three parts, the anterior prosome, the intermediate mesosome, and the posterior metasome. The body of worms is worm-shaped and divided into an anterior proboscis, an intermediate collar. The proboscis is a muscular and ciliated organ used in locomotion and in the collection, the mouth is located between the proboscis and the collar. The trunk is the longest part of the animal and it contains the pharynx, which is perforated with gill slits, the esophagus, a long intestine, and a terminal anus. A post-anal tail is present in juvenile member of the worm family Harrimaniidae. The prosome of pterobranchs is specialized into a muscular and ciliated cephalic shield used in locomotion, the mesosome extends into one pair or several pairs of tentaculated arms used in filter feeding. The metasome, or trunk, contains a looped digestive tract, gonads, in the genus Cephalodiscus, asexually produced individuals stay attached to the contractile stalk of the parent individual until completing their development. In the genus Rhabdopleura, zooids are connected to the rest of the colony via a common stolon system. A hollow neural tube exists among some species, probably a primitive trait that they share with the ancestor of chordata. Some species biomineralize in calcium carbonate, the hemichordates are the closest extant phylogenetic relatives of chordates among the invertebrates. Thus these marine worms, described to be the group of the echinoderms, are of great interest for the study of the origins of chordate development. There are several species of hemichordates, with a diversity of embryological development among these species. Hemichordates are classically known to develop in two ways, both directly and indirectly, hemichordates are a phylum composed of two classes, the enteropneusts and the pterobranchs, both being forms of marine worm
40.
Metaspriggina
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Metaspriggina is a genus of chordate initially known from two specimens in the Middle Cambrian Burgess Shale and 44 specimens found in 2012 at the Marble Canyon bed in Kootenay National Park. Whilst named after the Ediacaran organism Spriggina, later work has shown the two to be unrelated and it lacked fins and it had a weakly developed cranium, but it did possess two well-developed upward-facing eyes with nostrils behind them. Metaspriggina also possessed a notochord, along with seven pairs of pharyngeal bars, the largest specimens are 10 centimetres in length. The exceptional preservation at Marble Canyon also preserved muscle detail, showing that the animal moved with a swimming motion. In Metaspriggina the myomeral configuration has an additional ventral chevron, the discovery of pharyngeal bars makes Metaspriggina the oldest known animal to have this feature. The first pair of pharyngeal bars later evolved to form the upper and lower jaws of vertebrates, new fossil find pinpoints the origin of jaws in vertebrates
. PMID 22695332.
