1.
Late 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
2.
Megaannum
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A year is the orbital period of the Earth moving in its orbit around the Sun. Due to the Earths axial tilt, the course of a year sees the passing of the seasons, marked by changes in weather, the hours of daylight, and, consequently, vegetation and soil fertility. In temperate and subpolar regions around the globe, four seasons are recognized, spring, summer, autumn. In tropical and subtropical regions several geographical sectors do not present defined seasons, but in the seasonal tropics, a calendar year is an approximation of the number of days of the Earths orbital period as counted in a given calendar. The Gregorian, or modern, calendar, presents its calendar year to be either a common year of 365 days or a year of 366 days, as do the Julian calendars. For the Gregorian calendar the average length of the year across the complete leap cycle of 400 years is 365.2425 days. The ISO standard ISO 80000-3, Annex C, supports the symbol a to represent a year of either 365 or 366 days, in English, the abbreviations y and yr are commonly used. In astronomy, the Julian year is a unit of time, it is defined as 365.25 days of exactly 86400 seconds, totalling exactly 31557600 seconds in the Julian astronomical year. The word year is used for periods loosely associated with, but not identical to, the calendar or astronomical year, such as the seasonal year, the fiscal year. Similarly, year can mean the period of any planet, for example. The term can also be used in reference to any long period or cycle, west Saxon ġēar, Anglian ġēr continues Proto-Germanic *jǣran. Cognates are German Jahr, Old High German jār, Old Norse ár and Gothic jer, all the descendants of the Proto-Indo-European noun *yeh₁rom year, season. Cognates also descended from the same Proto-Indo-European noun are Avestan yārǝ year, Greek ὥρα year, season, period of time, Old Church Slavonic jarŭ, Latin annus is from a PIE noun *h₂et-no-, which also yielded Gothic aþn year. Both *yeh₁-ro- and *h₂et-no- are based on verbal roots expressing movement, *h₁ey- and *h₂et- respectively, the Greek word for year, ἔτος, is cognate with Latin vetus old, from the PIE word *wetos- year, also preserved in this meaning in Sanskrit vat-sa- yearling and vat-sa-ras year. Derived from Latin annus are a number of English words, such as annual, annuity, anniversary, etc. per annum means each year, anno Domini means in the year of the Lord. No astronomical year has an number of days or lunar months. Financial and scientific calculations often use a 365-day calendar to simplify daily rates, in the Julian calendar, the average length of a year is 365.25 days. In a non-leap year, there are 365 days, in a year there are 366 days
3.
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
4.
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
5.
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
6.
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
7.
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
8.
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
9.
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
10.
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
11.
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
12.
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
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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
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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
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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
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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
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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
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Sarcopterygii
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The living sarcopterygians are the coelacanths and lungfish, additionally, all tetrapods are sarcopterygians or descendants of them. Early lobe-finned fishes are bony fish with fleshy, lobed, paired fins, the fins of lobe-finned fishes differ from those of all other fish in that each is borne on a fleshy, lobelike, scaly stalk extending from the body. The scales of sarcopterygians are true scaloids, consisting of lamellar bone surrounded by layers of bone, dentine-like cosmine. Pectoral and pelvic fins have articulations resembling those of tetrapod limbs and these fins evolved into the legs of the first tetrapod land vertebrates, amphibians. They also possess two dorsal fins with separate bases, as opposed to the dorsal fin of actinopterygians. The braincase of sarcopterygians primitively has a line, but this is lost in tetrapods. Many early sarcopterygians have a symmetrical tail, all sarcopterygians possess teeth covered with true enamel. Most species of lobe-finned fishes are extinct, the largest known lobe-finned fish was Rhizodus hibberti from the Carboniferous period of Scotland which may have exceeded 7 meters in length. Among the two groups of extant species, the coelacanths and the lungfishes, the largest species is the West Indian Ocean coelacanth, reaching 2 m in length, the largest lungfish is the African lungfish which can reach 2 m in length and weigh up to 50 kg. Taxonomists who subscribe to the approach include the grouping Tetrapoda within this group. The fin-limbs of lobe-finned fishes such as the show a strong similarity to the expected ancestral form of tetrapod limbs. The lobe-finned fishes apparently followed two different lines of development and are separated into two subclasses, the Rhipidistia and the Actinistia. The classification below follows Benton 2004, and uses a synthesis of rank-based Linnaean taxonomy, the earliest fossils of sarcopterygians, found in the uppermost Silurian, closely resembled the acanthodians. In the early–middle Devonian, while the predatory placoderms dominated the seas, in the Early Devonian, the sarcopterygians split into two main lineages — the coelacanths and the rhipidistians. The Rhipidistians, whose ancestors lived in the oceans near the river mouths, left the ocean world. They in turn split into two groups, the lungfish and the tetrapodomorphs. The lungfishs greatest diversity was in the Triassic period, today there are fewer than a dozen genera left, the lungfish evolved the first proto-lungs and proto-limbs, developing the ability to live outside a water environment in the middle Devonian. There are three hypotheses as to how they evolved their stubby fins
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Tetrapodomorpha
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The Tetrapodomorpha are a clade of vertebrates consisting of tetrapods and their closest sarcopterygian relatives that are more closely related to living tetrapods than to living lungfish. The Tetrapodamorpha minus the crown group Tetrapoda are the Stem Tetrapoda, among the characters defining tetrapodomorphs are modifications to the fins, notably a humerus with convex head articulating with the glenoid fossa. Another key trait is the internal nostril or choana, most fish have two pairs of nostrils, one on either side of the head for incoming water and another pair for outgoing water. Early tetrapodomorphs such as Kenichthys had excurrent nostrils that had migrated to the edge of the mouth, in later tetrapodomorphs, including tetrapods, the excurrent nostril is positioned inside the mouth, where it is known as the choana. Tetrapodomorph fossils are known from the early Devonian onwards, and include Osteolepis, Panderichthys, Kenichthys, after Benton,2004, and Swartz,2012. Older taxons that include late stem tetrapods and early tetrapods are the Labyrinthodontia and Ichthyostegalia, the cladogram is based on a phylogenetic analysis of 46 taxa using 204 characters by B. Swartz in 2012. P. E. Ahlberg & Z. Johanson, osteolepiforms and the ancestry of tetrapods. Michel Laurin, Marc Girondot & Armand de Ricqlès
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Type species
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A similar concept is used for suprageneric groups called a type genus. In botanical nomenclature, these terms have no standing under the code of nomenclature. In botany, the type of a name is a specimen which is also the type of a species name. The species name that has that type can also be referred to as the type of the genus name, names of genus and family ranks, the various subdivisions of those ranks, and some higher-rank names based on genus names, have such types. In bacteriology, a species is assigned for each genus. Every named genus or subgenus in zoology, whether or not currently recognized as valid, is associated with a type species. In practice, however, there is a backlog of untypified names defined in older publications when it was not required to specify a type, a type species is both a concept and a practical system that is used in the classification and nomenclature of animals. The type species represents the species and thus definition for a particular genus name. In the Glossary, type species is defined as The nominal species that is the type of a nominal genus or subgenus. The type species permanently attaches a formal name to a genus by providing just one species within that genus to which the name is permanently linked. The species name in turn is fixed, in theory, to a type specimen, for example, the type species for the land snail genus Monacha is Monacha cartusiana. That genus is placed within the family Hygromiidae. The type genus for that family is the genus Hygromia, the concept of the type species in zoology was introduced by Pierre André Latreille. The International Code of Zoological Nomenclature states that the name of the type species should always be cited. It gives an example in Article 67.1, Astacus marinus Fabricius,1775 was later designated as the type species of the genus Homarus, thus giving it the name Homarus marinus. However, the species of Homarus should always be cited using its original name. 3, the type of the genus name Elodes is quoted as the type of the species name Hypericum aegypticum, Glossary of scientific naming Genetypes – genetic sequence data from type specimens. Holotype Paratype Principle of Typification Type Type genus
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Species
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In biology, a species is the basic unit of biological classification and a taxonomic rank. A species is defined as the largest group of organisms in which two individuals can produce fertile offspring, typically by sexual reproduction. While this definition is often adequate, looked at more closely it is problematic, for example, with hybridisation, in a species complex of hundreds of similar microspecies, or in a ring species, the boundaries between closely related species become unclear. Other ways of defining species include similarity of DNA, morphology, all species are given a two-part name, a binomial. The first part of a binomial is the genus to which the species belongs, the second part is called the specific name or the specific epithet. For example, Boa constrictor is one of four species of the Boa genus, Species were seen from the time of Aristotle until the 18th century as fixed kinds that could be arranged in a hierarchy, the great chain of being. In the 19th century, biologists grasped that species could evolve given sufficient time, Charles Darwins 1859 book The Origin of Species explained how species could arise by natural selection. Genes can sometimes be exchanged between species by horizontal transfer, and species may become extinct for a variety of reasons. In his biology, Aristotle used the term γένος to mean a kind, such as a bird or fish, a kind was distinguished by its attributes, for instance, a bird has feathers, a beak, wings, a hard-shelled egg, and warm blood. A form was distinguished by being shared by all its members, Aristotle believed all kinds and forms to be distinct and unchanging. His approach remained influential until the Renaissance, when observers in the Early Modern period began to develop systems of organization for living things, they placed each kind of animal or plant into a context. Many of these early delineation schemes would now be considered whimsical, animals likewise that differ specifically preserve their distinct species permanently, one species never springs from the seed of another nor vice versa. In the 18th century, the Swedish scientist Carl Linnaeus classified organisms according to shared physical characteristics and he established the idea of a taxonomic hierarchy of classification based upon observable characteristics and intended to reflect natural relationships. At the time, however, it was widely believed that there was no organic connection between species, no matter how similar they appeared. However, whether or not it was supposed to be fixed, by the 19th century, naturalists understood that species could change form over time, and that the history of the planet provided enough time for major changes. Jean-Baptiste Lamarck, in his 1809 Zoological Philosophy, described the transmutation of species, proposing that a species could change over time, in 1859, Charles Darwin and Alfred Russel Wallace provided a compelling account of evolution and the formation of new species. Darwin argued that it was populations that evolved, not individuals and this required a new definition of species. Darwin concluded that species are what appear to be, ideas
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Genus
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A genus is a taxonomic rank used in the biological classification of living and fossil organisms in biology. In the hierarchy of classification, genus comes above species. In binomial nomenclature, the name forms the first part of the binomial species name for each species within the genus. Felis catus and Felis silvestris are two species within the genus Felis, Felis is a genus within the family Felidae. The composition of a genus is determined by a taxonomist, the standards for genus classification are not strictly codified, so different authorities often produce different classifications for genera. Moreover, genera should be composed of units of the same kind as other genera. The term comes from the Latin genus, a noun form cognate with gignere, linnaeus popularized its use in his 1753 Species Plantarum, but the French botanist Joseph Pitton de Tournefort is considered the founder of the modern concept of genera. The scientific name of a genus may be called the name or generic epithet. It plays a role in binomial nomenclature, the system of naming organisms. The rules for the names of organisms are laid down in the Nomenclature Codes. The standard way of scientifically describing species and other lower-ranked taxa is by binomial nomenclature, the generic name forms its first half. For example, the gray wolfs binomial name is Canis lupus, with Canis being the name shared by the wolfs close relatives. The specific name is written in lower-case and may be followed by names in zoology or a variety of infraspecific names in botany. Especially with these names, when the generic name is known from context. Because animals are typically only grouped within subspecies, it is written as a trinomen with a third name. Dog breeds, meanwhile, are not scientifically distinguished, there are several divisions of plant species and therefore their infraspecific names generally include contractions explaining the relation. For example, the genus Hibiscus includes hundreds of other species apart from the Rose of Sharon or common garden hibiscus, Rose of Sharon doesnt have subspecies but has cultivars that carry desired traits, such as the bright white H. syriaca Diana. Hawaiian hibiscus, meanwhile, includes several separate species, since not all botanists agree on the divisions or names between species, it is common to specify the source of the name using author abbreviations
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Extinction
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In biology and ecology, extinction is the end of an organism or of a group of organisms, normally a species. The moment of extinction is considered to be the death of the last individual of the species, although the capacity to breed. Because a species range may be very large, determining this moment is difficult. This difficulty leads to such as Lazarus taxa, where a species presumed extinct abruptly reappears after a period of apparent absence. More than 99 percent of all species, amounting to five billion species. Estimates on the number of Earths current species range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described. More recently, in May 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described, the relationship between animals and their ecological niches has been firmly established. Mass extinctions are relatively rare events, however, isolated extinctions are quite common, only recently have extinctions been recorded and scientists have become alarmed at the current high rate of extinctions. Most species that become extinct are never scientifically documented, some scientists estimate that up to half of presently existing plant and animal species may become extinct by 2100. A dagger symbol next to a name is often used to indicate its extinction. A species is extinct when the last existing member dies, Extinction therefore becomes a certainty when there are no surviving individuals that can reproduce and create a new generation. Pinpointing the extinction of a species requires a definition of that species. If it is to be declared extinct, the species in question must be distinguishable from any ancestor or daughter species. Extinction of a plays a key role in the punctuated equilibrium hypothesis of Stephen Jay Gould. In ecology, extinction is often used informally to refer to local extinction, in which a species ceases to exist in the area of study. This phenomenon is known as extirpation. Local extinctions may be followed by a replacement of the species taken from other locations, species which are not extinct are termed extant. Those that are extant but threatened by extinction are referred to as threatened or endangered species, currently an important aspect of extinction is human attempts to preserve critically endangered species
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Myr
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The Malaysian ringgit is the currency of Malaysia. It is divided into 100 sen, the ringgit is issued by the Bank Negara Malaysia. In modern usage ringgit is used almost solely for the currency, to differentiate between the three currencies, the Malaysian currency is referred to as Ringgit Malaysia, hence the official abbreviation and currency symbol RM. Internationally, the ISO4217 currency code for Malaysian ringgit is MYR, the Malay names ringgit and sen were officially adopted as the sole official names in August 1975. Previously they had been known officially as dollars and cents in English and ringgit and sen in Malay, in the northern states of Peninsular Malaysia, denominations of 10 sen are called kupang in Malay, e. g.50 sen is 5 kupang. On 12 June 1967, the Malaysian dollar, issued by the new bank, Bank Negara Malaysia, replaced the Malaya. The new currency retained all denominations of its predecessor except the $10,000 denomination, and also brought over the colour schemes of the old dollar. In November 1967, five months after the introduction of the Malaysian dollar and this ended on 8 May 1973, when the Malaysian government withdrew from the agreement. The Monetary Authority of Singapore and the Brunei Currency and Monetary Board still maintain the interchangeability of their two currencies, as of 2009, in 1993, the currency symbol RM was introduced to replace the use of the dollar sign $. US$130 and RM1,000 worth of US$260. Despite these measures, the ringgit lost 50% of its value against the US dollar between 1997 and 1998, and suffered general depreciation against other currencies between December 2001 and January 2005. As of 4 September 2008, the ringgit has yet to regain its value circa 2001 against the Singapore dollar, the euro, the Australian dollar, and the British pound. On 21 July 2005, Bank Negara announced the end of the peg to the US dollar immediately after Chinas announcement of the end of the peg to the US dollar. According to Bank Negara, Malaysia allows the ringgit to operate in a float against several major currencies. Following the end of the peg, the ringgit appreciated to as high as 3.16 to the US dollar in April 2008. The ringgit had also enjoyed a period of appreciation against the Hong Kong dollar, the initial stability of the ringgit in the late-2000s had led to considerations to reintroduce the currency to foreign trading. As a result, the US dollar appreciated significantly to close at 3.43 to the MYR as of 4 September 2008, while other major currencies, including the renminbi and Hong Kong dollar, followed suit. The ringgit spiked at 3.73 to the US dollar by March 2009, before recovering to 3.00 to the US dollar by mid-2011. The first series of sen coins were introduced in 1967 in denominations of 1 sen,5 sen,10 sen,20 sen,50 sen, followed by the introduction of the 1 ringgit coin in 1971
25.
Latvia
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Latvia, officially the Republic of Latvia, is a country in the Baltic region of Northern Europe, one of the three Baltic states. It is bordered by Estonia to the north, Lithuania to the south, Russia to the east, Latvia has 1,957,200 inhabitants and a territory of 64,589 km2. The country has a seasonal climate. Latvia is a parliamentary republic established in 1918. The capital city is Riga, the European Capital of Culture 2014, Latvia is a unitary state, divided into 119 administrative divisions, of which 110 are municipalities and 9 are cities. Latvians and Livs are the people of Latvia. Latvian and Lithuanian are the two surviving Baltic languages. Despite foreign rule from the 13th to 20th centuries, the Latvian nation maintained its identity throughout the generations via the language, Latvia and Estonia share a long common history. Until World War II, Latvia also had significant minorities of ethnic Germans, Latvia is historically predominantly Protestant Lutheran, except for the Latgale region in the southeast, which has historically been predominantly Roman Catholic. The Russian population has brought a significant portion of Eastern Orthodox Christians. The Republic of Latvia was founded on 18 November 1918, however, its de facto independence was interrupted at the outset of World War II. The peaceful Singing Revolution, starting in 1987, called for Baltic emancipation of Soviet rule and it ended with the Declaration on the Restoration of Independence of the Republic of Latvia on 4 May 1990, and restoring de facto independence on 21 August 1991. Latvia is a democratic and developed country and member of the European Union, NATO, the Council of Europe, the United Nations, CBSS, the IMF, NB8, NIB, OECD, OSCE, and WTO. For 2014, Latvia was listed 46th on the Human Development Index and it used the Latvian lats as its currency until it was replaced by the euro on 1 January 2014. The name Latvija is derived from the name of the ancient Latgalians, one of four Indo-European Baltic tribes, henry of Latvia coined the Latinisations of the countrys name, Lettigallia and Lethia, both derived from the Latgalians. The terms inspired the variations on the name in Romance languages from Letonia. Around 3000 BC, the ancestors of the Latvian people settled on the eastern coast of the Baltic Sea. The Balts established trade routes to Rome and Byzantium, trading local amber for precious metals, by 900 AD, four distinct Baltic tribes inhabited Latvia, Curonians, Latgalians, Selonians, Semigallians, as well as the Livonians speaking a Finnic language
26.
Tristichopteridae
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Tristichopterids were a diverse and successful group of tetrapodomorph fishes living throughout the Middle and Late Devonian. They first appeared in the Givetian stage of the Middle Devonian, within the group sizes ranged from a few tens of centimeters to several meters. Some tristichopterids share some of the features of the elpistostegalians, an assemblage of fishes close to the origin of tetrapods. This mainly concerns the shape of the skull and a reduction in size of the posterior fins, an old and persistent notion is that Eusthenopteron was able to crawl onto land using its fins. However, there is no evidence supporting this idea. All tristichopterids went extinct by the end of Late Devonian, second tristichopterid from the Upper Devonian of Canowindra, New South Wales, Australia, and phylogeny of the Tristichopteridae. in Journal of Vertebrate Palaeontology 17, 563-673. New tristichopterid from the Mandagery Sandstone near Canowindra, N. S. W, in Transactions of the Royal Society of Edinburgh 88, 39-53
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Tetrapods
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The superclass Tetrapoda contains the four-limbed vertebrates known as tetrapods, it includes living and extinct amphibians, reptiles and mammals, as well as earlier extinct groups. The first tetrapods appeared by the late Devonian,367, the first tetrapods were primarily aquatic. Their descendants drove most amphibians to extinction as they began to dominate, the amniotes include the tetrapods that further evolved for flight—such as birds from among the dinosaurs, and bats from among the mammals. The change from a plan for breathing and navigating in water to a body plan enabling the animal to move on land is one of the most profound evolutionary changes known. It is also becoming increasingly well-understood as a result of more transitional fossil finds, many tetrapods have returned to partially aquatic or fully aquatic lives throughout the history of the group. Tetrapods can be defined in cladistics as the nearest common ancestor of all living amphibians and all living amniotes, the group so defined is the crown group, or crown tetrapods. The term tetrapodomorph is used for the definition, any animal that is more closely related to living amphibians, reptiles, birds. The group so defined is known as the total group. Stegocephalia is a larger group equivalent to some uses of the word tetrapod. Batrachomorphs are all sharing a more recent common ancestry with living amphibians than with living amniotes. Reptiliomorphs are all sharing a more recent common ancestry with living amniotes than with living amphibians. Tetrapoda includes four classes, amphibians, reptiles, mammals, however, that diversification process was interrupted at least a few times by major biological crises, such as the Permian–Triassic extinction event, which at least affected amniotes. As biodiversity has grown, so has the number of niches that tetrapods have occupied, the first tetrapods were aquatic and fed primarily on fish. Today, the Earth supports a diversity of tetrapods that live in many habitats. Tetrapods evolved from early bony fishes, specifically from the branch of lobe-finned fishes. The first tetrapods probably evolved in the Emsian stage of the Early Devonian from Tetrapodomorph fish living in water environments. The very earliest tetrapods would have been similar to Acanthostega, with legs and lungs as well as gills. The earliest tetrapods inhabited saltwater, brackish-water, and freshwater environments and these traits were shared with many early lobed-finned fishes
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Christian Heinrich Pander
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Heinz Christian Pander, also Christian Heinrich Pander, was a Baltic German biologist and embryologist born in Riga. In 1817 he received his doctorate from the University of Würzburg, in 1820 he took part in a scientific expedition to Bokhara as a naturalist. In 1826 he became a member of the St. Petersburg Academy of Sciences, Pander studied the chick embryo and discovered the germ layers. Because of these findings, he is considered by many to be the founder of embryology and his work in embryology was continued by Karl Ernst von Baer, who expanded Panders concept of germ layers to include all vertebrates. Pander performed important studies in the field of paleontology, being known for his research on fossils found in the Devonian and Silurian geological strata of the Baltic regions. His study of trilobites from this age led to the adjective Panderian, first used by the Canadian palaeontologist, Pander is credited as the first scientist to describe primitive creatures known as conodonts. Today the Pander Society is an association of palaeontologists and stratigraphers with a common interest in the study of conodonts. Panders eponyms are, Panders islands or blood islands Beiträge zur Entwickelungsgeschichte des Hühnchens im Eye, Beiträge zur Naturkunde aus den Ostseeprovinzen Rußlands, Dorpat. Vergleichende Osteologie seven volumes, with Eduard Joseph dAlton, Bonn, Beiträge zur geognosie des russischen reiches,1830. Monographie der Fossilen Fische des silurischen Systems der Russisch-Baltischen Gouvernements, St. Petersburg, ueber die Placodermen des devonischen Systems,1857. Über die ctenodopterinen des devonischen systems,1858 Über die saurodipterinen, dendrodonten, glyptolepiden und cheirolepiden des devonischen systems,1860, list of Baltic German scientists Gilbert, Developmental biology Latvian Technical and Scientific Achievements
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Lepidotrichia
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Fins are usually the most distinctive features of a fish. Apart from the tail or caudal fin, fish fins have no connection with the spine and are supported only by muscles. Their principal function is to help the fish swim, Fins located in different places on the fish serve different purposes such as moving forward, turning, keeping an upright position or stopping. Most fish use fins when swimming, flying fish use pectoral fins for gliding, for every type of fin, there are a number of fish species in which this particular fin has been lost during evolution. Bony fishes form a group called Osteichthyes. They have skeletons made of bone, and can be contrasted with cartilaginous fishes which have made of cartilage. Bony fishes are divided into ray-finned and lobe-finned fish, most fish are ray-finned, an extremely diverse and abundant group consisting of over 30,000 species. It is the largest class of vertebrates in existence today, in the distant past, lobe-finned fish were abundant. Nowadays they are extinct, with only eight living species. Bony fish have fin spines and rays called lepidotrichia and they typically have swim bladders, which allows the fish to create a neutral balance between sinking and floating without having to use its fins. However, these are absent in species, and have developed into primitive lungs in the lungfishes. Bony fishes also have an operculum, which helps them breathe without having to use fins to swim, lobe-finned fishes are a class of bony fishes called Sarcopterygii. They have fleshy, lobed, paired fins, which are joined to the body by a single bone, the fins of lobe-finned fish differ from those of all other fish in that each is borne on a fleshy, lobelike, scaly stalk extending from the body. Pectoral and pelvic fins have articulations resembling those of tetrapod limbs and these fins evolved into legs of the first tetrapod land vertebrates, amphibians. They also possess two dorsal fins with separate bases, as opposed to the dorsal fin of ray-finned fish. The coelacanth is another lobe-finned fish which is still extant and it is thought to have evolved into roughly its current form about 408 million years ago, during the early Devonian. Locomotion of the coelacanths is unique to their kind, to move around, coelacanths most commonly take advantage of up or downwellings of the current and drift. They use their fins to stabilize their movement through the water
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Tiktaalik
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Tiktaalik /tɪkˈtɑːlᵻk/ is a monospecific genus of extinct sarcopterygian from the late Devonian period, about 375 Ma ago, having many features akin to those of tetrapods. Tiktaalik has a possibility of being a representative of the transition from fish to amphibians. It and similar animals may possibly be the ancestors of the broad swath of all vertebrate terrestrial fauna, amphibians, reptiles, birds. The first well-preserved Tiktaalik fossils were found in 2004 on Ellesmere Island in Nunavut, Tiktaalik provides insights on the features of the extinct closest relatives of the tetrapods. Unlike many previous, more fishlike transitional fossils, the fins of Tiktaalik have basic wrist bones, however, the proximal series can be directly compared to the ulnare and intermedium of tetrapods. The bones of the show large muscle facets, suggesting that the fin was both muscular and had the ability to flex like a wrist joint. These wrist-like features would have helped anchor the creature to the bottom in fast moving current, also notable are the spiracles on the top of the head, which suggest the creature had primitive lungs as well as gills. This attribute would have been useful in water, where higher water temperature would lower oxygen content. This development may have led to the evolution of a more robust ribcage, the more robust ribcage of Tiktaalik would have helped support the animal’s body any time it ventured outside a fully aquatic habitat. Tiktaalik also lacked a characteristic that most fishes have—bony plates in the area that restrict lateral head movement. This makes Tiktaalik the earliest known fish to have a neck and this would give the creature more freedom in hunting prey either on land or in the shallows. The fossil discovered in 2004 did not include the rear fins and it had rows of sharp teeth of a predator fish, and its neck could move independently of its body, which is not common in other fish. The discoverers said that in all likelihood, Tiktaalik flexed its proto-limbs primarily on the floor of streams and may have pulled itself onto the shore for brief periods. In 2014, the discovery of the pelvic girdle was announced, it was strongly built, indicating the animal could have used them for moving in shallow water. And maybe occasionally, using its very specialized fins, for moving up overland, and thats what is particularly important here. The animal is developing features which eventually allow animals to exploit land. Tiktaalik roseae is the species classified under the genus. Tiktaalik lived approximately 375 million years ago and its mixture of primitive fish and derived tetrapod characteristics led one of its discoverers, Neil Shubin, to characterize Tiktaalik as a fishapod
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Laccognathus
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Laccognathus is an extinct genus of amphibious lobe-finned fish from Europe and North America. They existed from the Middle Devonian to the Late Devonian, the name comes from Greek for pitted jaw. Species of Laccognathus were characterized by the presence of three large pits on the surface of the lower jaw which may have had sensory functions. It is the origin of the name, from Greek λάκκος and γνάθος. Laccognathus grew to approximately 1–2 metres in length and they had very short dorsoventrally flattened heads, less than one-fifth the length of the body. Like other sarcopterygians, their fins arise from pairs of fleshy lobes, the skeleton of Laccognathus was structured such that large areas of the skin were stretched out over solid plates of bone. This bone was composed of particularly dense fibers—so dense that cutaneous respiration was not a likely trait exhibited by Laccognathus, rather, the dense ossifications may have served to retain water inside the body as Laccognathus traveled on land between bodies of water. Laccognathus are classified under the family Holoptychiidae in the extinct order Porolepiformes and they are not direct ancestors of tetrapods like the clade Tetrapodomorpha, but instead belong to the clade Dipnomorpha. Their closest living descendants are the members of the subclass Dipnoi, the following are the species classified under Laccognathus. A fourth undescribed species recovered from the Middle Devonian of Latvia may exist, †Laccognathus panderi Gross,1941 Recovered from the Middle Devonian and Late Devonian formations of various parts of eastern Europe. †Laccognathus grossi Vorobyeva,2006 Recovered from the Middle Devonian Gauja Formation of Latvia, †Laccognathus embryi Downs et al.2011 Recovered from Late Devonian Fram Formation of Ellesmere Island, Canada, the same locality from which Tiktaalik was found. Holoptychius Sarcopterygii List of sarcopterygians List of prehistoric bony fish
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Dipterus
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Dipterus is an extinct genus of lungfish from the late Devonian period of Australia, Europe and North America. In most respects, Dipterus, which was about 35 centimetres long, like its ancestor Dipnorhynchus, it had tooth-like plates on its palate instead of real teeth. However, unlike its relatives, in which the dorsal, caudal. It mostly ate invertebrates, and had lungs, not an air bladder and these were more developed in Dipterus and are still seen in modern-day lungfish. The genus was established by Adam Sedgwick & Roderick Murchison in the year 1828
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Eusthenopteron
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Eusthenopteron is a genus of prehistoric sarcopterygian which has attained an iconic status from its close relationships to tetrapods. Early depictions of this show it emerging onto land, however paleontologists now widely agree that it was a strictly aquatic animal. The genus Eusthenopteron is known from species that lived during the Late Devonian period. Eusthenopteron was first described by J. F. Whiteaves in 1881, as part of a collection of fishes from Miguasha. Anatomically, Eusthenopteron shares many features in common with the earliest known tetrapods. Largest individuals grew up to 1.8 m in length and it shares a similar pattern of skull roofing bones with forms such as Ichthyostega and Acanthostega. Eusthenopteron, like other tetrapodomorph fishes, had internal nostrils, which are one of the traits of tetrapodomorphs. It also had labyrinthodont teeth, characterized by infolded enamel, which all of the earliest known tetrapods as well. Like other fish-like sarcopterygians, Eusthenopteron possessed a two-part cranium, which hinged at mid-length along an intracranial joint, eusthenopterons notoriety comes from the pattern of its fin endoskeleton, which bears a distinct humerus, ulna, and radius and femur, tibia, and fibula. These appendicular long bones had epiphyseal growth plates that allowed substantial longitudinal growth through endochondral ossification and these six appendicular bones also occur in tetrapods and are a synapomorphy of a large clade of sarcopterygians, possibly Tetrapodomorpha. Similarly, its elasmoid scales lack superficial odontodes composed of dentine and enamel, the earliest known fossilised evidence of bone marrow has been found in Eusthenopteron, which may be the origin of bone marrow in tetrapods. Eusthenopteron differs significantly from some later Carboniferous tetrapods in the apparent absence of a larval stage. In even the smallest known specimen of Eusthenopteron foordi, the cover all of the fins. This might indicate that Eusthenopteron developed directly, with the hatchling already attaining the general form of the adult. Gogonasus Tiktaalik, an even more tetrapod-like sarcopterygian, S. Cote, R. Carroll, R. Cloutier, L. Bar-Sagi. Vertebral development in the Devonian Sarcopterygian fish Eusthenopteron foordi and the polarity of vertebral evolution in non-amniote tetrapods, Devonian Fishes and Plants of Miguasha, Quebec, Canada. Basic Structure and Evolution of Vertebrates
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Elpistostege
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Elpistostege is an extinct genus of tetrapod-like vertebrate that lived in the Late Devonian period. Fossils of its skull and a part of its backbone have been found in rocks of the Escuminac Formation in Quebec, a complete specimen of the animal has since been found in the same formation. An analysis conducted by Swartz in 2012 found Elpistostege to be the sister taxon of Tiktaalik, both were found to be primitive members of the group Stegocephalia, along with other primitive stem-tetrapods. Elpistostege at Palaeos History of Elpistostege Recent Discovery of an entire well-preserved fossil of Elpistostege watsoni
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Basal (phylogenetics)
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In phylogenetics, basal is the direction of the base of a rooted phylogenetic tree or cladogram. Clade C may be described as basal within a larger clade D if its root is linked to the root of D. If C is a clade within D that has the lowest taxonomic rank of all basal clades within D, C may be described as the basal taxon of that rank within D. While there must always be two or more equally basal clades sprouting from the root of every cladogram, those clades may differ widely in rank or species diversity. In general, clade A is more basal than clade B if B is a subgroup of the group of A. Within large groups, basal may be used loosely to mean closer to the root than the great majority of. A core clade is a clade representing all but the clade of lowest rank within a larger clade. While basal applies to clades, characters or traits are considered derived if they are absent in a basal group. This assumption only holds if the basal group is a good analogy for the last common ancestor of the group. Ancestral or plesiomorphic are preferred to primitive, which may carry false connotations of inferiority or a lack of complexity, within the primate family Hominidae, gorillas are a sister group to common chimpanzees, bonobos and humans. These five species form a clade, the subfamily Homininae, of which Gorilla is the basal genus, however, if the analysis is not restricted to genera, the Homo plus Pan clade is also basal. This semantic ambiguity is discussed in the Criticism section, moreover, orangutans are a sister group to Homininae and are the basal genus in the family as a whole. Subfamilies Homininae and Ponginae are both basal within Hominidae, but given that there are no subfamilies in the cladogram it is unlikely the term would be applied to either. In general, a statement to the effect that one group is basal, or branches off first, if that level cannot be specified a more detailed description of the relevant sister groups may be needed. In this example, orangutans differ from the genera in their Eurasian range. This fact plus their basal status provides a hint that the most recent common ancestor of extant great apes may have been Eurasian, despite the ubiquity of the usage of the term, some systematists believe its application to extant groups is unnecessary and misleading. This is because a pair of branches of a phylogenetic tree are equally ranked. The term tends to be applied when one branch is less diverse than another branch and this situation raises an equivocal usage for the term basal in that it also refers to the direction of the root of the tree
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Gnathostomata
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Gnathostomata /ˌneɪθoʊstoʊˈmɑːtə/ are the jawed vertebrates. The term derives from Greek, γνάθος jaw + στόμα mouth, gnathostome diversity comprises roughly 60,000 species, which accounts for 99% of all living vertebrates. Another is an immune system that uses VJ recombination to create antigen recognition sites. It is now assumed that Gnathostomata evolved from ancestors that possessed a pair of both pectoral and pelvic fins. The Osteostraci are generally considered the taxon of Gnathostomata. The mouth could then grow bigger and wider, making it possible to capture larger prey and this close and open mechanism would, with time, become stronger and tougher, being transformed into real jaws. Newer research suggests that a branch of Placoderms was most likely the ancestor of present-day gnathostomes and it also indicates that spiny sharks and Chondrichthyes represent a single sister group to the bony fishes. Late Ordovician-aged microfossils of what have been identified as scales of either acanthodians or shark-like fishes, undeniably unambiguous gnathostome fossils, mostly of primitive acanthodians, begin appearing by the early Silurian, and become abundant by the start of the Devonian. Some classification systems have used the term Amphirhina and it is a sister group of the jawless craniates Agnatha. Tree of Life discussion of Gnathostomata The Gill Arches, Meckels Cartilage
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Osteichthyes
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Osteichthyes /ˌɒstiːˈɪkθi. iːz/, popularly referred to as the bony fish, is a diverse taxonomic group of fish that have skeletons primarily composed of bone tissue, as opposed to cartilage. The vast majority of fish are members of Osteichthyes, which is a diverse and abundant group consisting of 45 orders. It is the largest class of vertebrates in existence today, the group Osteichthyes is divided into the ray-finned fish and lobe-finned fish. The oldest known fossils of fish are about 420 million years ago. Osteichthyes can be compared to Euteleostomi, in paleontology, the terms are synonymous. However, recently published phylogenetic trees treat the Osteichthyes as a clade, bony fish are characterized by a relatively stable pattern of cranial bones, rooted, medial insertion of mandibular muscle in the lower jaw. The head and pectoral girdles are covered with large dermal bones, the eyeball is supported by a sclerotic ring of four small bones, but this characteristic has been lost or modified in many modern species. The labyrinth in the ear contains large otoliths. The braincase, or neurocranium, is divided into anterior and posterior sections divided by a fissure. Early bony fish had simple lungs which helped them breathe in low-oxygen water, in many bony fish these have evolved into swim bladders, which help the body create a neutral balance between sinking and floating. They do not have fin spines, but instead support the fin with lepidotrichia and they also have an operculum, which helps them breathe without having to swim. Bony fish have no placoid scales, most have smooth and overlapping ganoid, cycloid or ctenoid scales. Traditionally, Osteichthyes is considered a class, recognised on having a swim bladder, under this classification systems, the Osteichthyes are paraphyletic with regard to land vertebrates as the common ancestor of all Osteichthyes includes tetrapods amongst its descendants. The largest subclass, the Actinopterygii are monophyletic, but with the inclusion of the smaller sub-class Sarcopterygii and this has led to an alternative classification, splitting the Osteichthyes into two full classes. Paradoxically, Sarcopterygii is under this scheme monophyletic, as it includes the tetrapods, most bony fish belong to the ray-finned fish. The phylogeny of living bony fishes is shown in the cladogram, for the majority this is their sole or main means of respiration. Lungfish and other species are capable of respiration through lungs or vascularized swim bladders. Other species can respire through their skin, intestines, and/or stomach, Osteichthyes are primitively ectothermic, meaning that their body temperature is dependent on that of the water
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Clade
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A clade is a group of organisms that consists of a common ancestor and all its lineal descendants, and represents a single branch on the tree of life. The common ancestor may be an individual, a population, a species, clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect evolutionary history as populations diverged and evolved independently, over the last few decades, the cladistic approach has revolutionized biological classification and revealed surprising evolutionary relationships among organisms. Increasingly, taxonomists try to avoid naming taxa that are not clades, the term clade was coined in 1957 by the biologist Julian Huxley to refer to the result of cladogenesis, a concept Huxley borrowed from Bernhard Rensch. Many commonly named groups are clades, for example, rodents or insects, because in each case, their name refers to a common ancestor with all its descendant branches. Rodents, for example, are a branch of mammals that split off after the end of the period when the clade Dinosauria stopped being the dominant terrestrial vertebrates 66 million years ago, the original population and all its descendants are a clade. The rodent clade corresponds to the order Rodentia, and insects to the class Insecta and these clades include smaller clades, such as chipmunk or ant, each of which consists of even smaller clades. The clade rodent is in included in the mammal, vertebrate. The phenomenon of convergent evolution is, however, responsible for cases where there are misleading similarities in the morphology of groups that evolved from different lineages. The publication of Darwins theory of evolution in 1859 gave this view increasing weight, thomas Henry Huxley, an early advocate of evolutionary theory, proposed a revised taxonomy based on clades. For example, he grouped birds with reptiles, based on fossil evidence, german biologist Emil Hans Willi Hennig is considered to be the founder of cladistics. Taxonomists have increasingly worked to make the taxonomic system reflect evolution, when it comes to naming, however, this principle is not always compatible with the traditional rank-based nomenclature. For these and other reasons, phylogenetic nomenclature has been developed, a clade is by definition monophyletic, meaning that it contains one ancestor and all its descendants. The ancestor can be known or unknown, any and all members of a clade can be extant or extinct, the science that tries to reconstruct phylogenetic trees and thus discover clades is called phylogenetics or cladistics, the latter term coined by Ernst Mayr, derived from clade. The results of analyses are tree-shaped diagrams called cladograms, they. Three methods of defining clades are featured in phylogenetic nomenclature, node-, stem-, the relationship between clades can be described in several ways, A clade located within a clade is said to be nested within that clade. In the diagram, the clade, i. e. the apes. Two clades are sisters if they have a common ancestor
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Rhizodontida
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Rhizodonts lived in tropical rivers and freshwater lakes and were the dominant predators of their age. They reached huge sizes - the largest known species, Rhizodus hibberti from Europe and North America, was an estimated 7 m in length, making it the largest freshwater fish known. The upper jaw had a row of small teeth on the maxilla and premaxilla, medium-sized fangs on the ectopterygoid and dermopalatine bones. On the lower jaw were marginal teeth on the dentary, with fangs on the three coronoids and a tusk at the symphysial tip of the dentary. Apparently, the left and right mandibles rotated inwards towards each other on biting and this may have been a kinetic mechanism to dig the marginal teeth more deeply into the prey, to help grip slippery or struggling items. Rhizodonts trunk was elongated, with pelvic, two dorsal and anal fins much reduced and placed posteriorly The anal and second dorsal fins formed a part of the tail. The lateral line system was elaborated on the skull and pectoral girdle - in Strepsodus the main trunk line also had several subsidiary lines running parallel to it. This probably helped rhizodonts detect prey in the turbid, swampy environments where they lived, rhizodont pelvic fins are known only from external morphology. They are smaller than the fins and positioned toward the rear of the body. In comparison to the fins, the pectoral fins were much enlarged. They had an internal skeleton surrounded by robust, largely unsegmented lepidotrichia. This turned the pectoral fin into a broad paddle, the cladogram presented below is based on studies compiled by Mikko Haaramo for the Mikkos Phylogeny Archive Judging from their anatomy, rhizodonts had an extremely powerful bite. Their prey probably included large sharks, lungfish, and other lobe-finned fishes, a complete primitive rhizodont from Australia. Johanson, Z. and Ahlberg, P. E. Devonian rhizodontids and tristichopterids from East Gondwana, classification after Benton, M. J. Vertebrate Palaeontology, 3rd ed. Oxford, Blackwell Publishing
