1.
Glossary of leaf morphology
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The following is a defined list of terms which are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple or compound, the edge of the leaf may be regular or irregular, may be smooth or bearing hair, bristles or spines. For more terms describing other aspects of leaves besides their overall morphology see the leaf article, leaves of most plants include a flat structure called the blade or lamina, but not all leaves are flat, some are cylindrical. Leaves may be simple, with a leaf blade, or compound. In flowering plants, as well as the blade of the leaf, there may be a petiole and stipules, leaf structure is described by several terms that include, Being one of the more visible features, leaf shape is commonly used for plant identification. Edge and margin are both interchangeable in the sense that they refer to the perimeter of a leaf. Leaves may also be folded or rolled in various ways, the folding of leaves within a bud is vernation, ptyxis is the folding of an individual leaf in a bud
2.
Terreneuvian
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The Terreneuvian is the lowermost and oldest series of the Cambrian geological system. Its base is defined by the first appearance datum of the trace fossil Treptichnus pedum around 541 million years ago and its top is defined as the first appearance of trilobites in the stratigraphic record around 521 million years ago. This series was ratified by the International Commission on Stratigraphy in 2012. The Fortunian stage and presently unnamed Cambrian Stage 2 are the stages within this series, the Terreneuvian corresponds to the pre-trilobitic Cambrian. The name Terreneuvian is derived from Terre Neuve, a French name for the island of Newfoundland, Canada, the type locality of the Terreneuvian is in Fortune Head, at the northern edge of the Burin Peninsula, Newfoundland, Canada. The outcrops show a carbonate-siliciclastic succession which is mapped as the Chapel Island Formation, the Precambrian-Cambrian boundary lies 2.4 m above the base of the second member, which is the lowest occurrence of Treptichnus pedum. The traces can be seen on the surface of the sandstone layers. The first calcareous shelled skeletal fossils are 400 m above the boundary, the first trilobites appear 1400 m above the boundary, which corresponds to the beginning of the Branchian Series
3.
Holocene
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The Holocene is the geological epoch that began after the Pleistocene at approximately 11,700 years before present. The term Recent has often used as an exact synonym of Holocene. The Holocene is part of the Quaternary period and its name comes from the Ancient Greek words ὅλος and καινός, meaning entirely recent. It has been identified with the current warm period, known as MIS1, given these, a new term, Anthropocene, is specifically proposed and used informally only for the very latest part of modern history involving significant human impact. It is accepted by the International Commission on Stratigraphy that the Holocene started approximately 11,700 years ago, the epoch follows the Pleistocene and the last glacial period. The Holocene can be subdivided into five time intervals, or chronozones, based on climatic fluctuations, Preboreal, Boreal, Atlantic, Subboreal and they find a general correspondence across Eurasia and North America, though the method was once thought to be of no interest. The scheme was defined for Northern Europe, but the changes were claimed to occur more widely. The periods of the include a few of the final pre-Holocene oscillations of the last glacial period. Paleontologists have not defined any faunal stages for the Holocene, if subdivision is necessary, periods of human technological development, such as the Mesolithic, Neolithic, and Bronze Age, are usually used. However, the time periods referenced by these terms vary with the emergence of those technologies in different parts of the world, climatically, the Holocene may be divided evenly into the Hypsithermal and Neoglacial periods, the boundary coincides with the start of the Bronze Age in Europe. According to some scholars, a division, the Anthropocene, has now begun. Continental motions due to plate tectonics are less than a kilometre over a span of only 10,000 years, however, ice melt caused world sea levels to rise about 35 m in the early part of the Holocene. The sea level rise and temporary land depression allowed temporary marine incursions into areas that are now far from the sea, Holocene marine fossils are known, for example, from Vermont and Michigan. Other than higher-latitude temporary marine incursions associated with depression, Holocene fossils are found primarily in lakebed, floodplain. Holocene marine deposits along low-latitude coastlines are rare because the rise in sea levels during the period exceeds any likely tectonic uplift of non-glacial origin, post-glacial rebound in the Scandinavia region resulted in the formation of the Baltic Sea. The region continues to rise, still causing weak earthquakes across Northern Europe, the equivalent event in North America was the rebound of Hudson Bay, as it shrank from its larger, immediate post-glacial Tyrrell Sea phase, to near its present boundaries. Climate has been stable over the Holocene. It appears that this was influenced by the glacial ice remaining in the Northern Hemisphere until the later date
4.
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
5.
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
6.
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
7.
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
8.
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
9.
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
10.
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
11.
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
12.
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
13.
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
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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
17.
Kryptopterus vitreolus
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Kryptopterus vitreolus, known in the aquarium trade traditionally as the glass catfish and also as the ghost catfish or phantom catfish, is a small species of Asian glass catfish. It is commonly seen in the aquarium trade, but its taxonomy is confusing and was only fully resolved in 2013. It is endemic to Thailand, where found in south of the Isthmus of Kra that drain into the Gulf of Thailand. There are also unconfirmed reports from Penang in Malaysia, until 1989, it was considered to be the same as the glass catfish Kryptopterus bicirrhis, a larger species infrequently seen in the aquarium trade. The true K. minor, which is restricted to Borneo, has entered the aquarium trade. This is a transparent freshwater catfish with two long barbels, standard lengths may range up to 8 cm, but usually only reach around 6.5 cm in total length. They are transparent because, like all catfish, they are scaleless, most of their organs are located near the head, with a magnifying glass, their heart can be seen beating. When the light strikes the fish just right, it can create an iridescent rainbow color, during strong illness and after death, they turn milky white. The scientific species name vitreolus is derived from the Latin vitreus, among described species of Kryptopterus, only two other species, K. minor and K. piperatus, have clearly transparent bodies and both these are largely–if not entirely–absent from the aquarium trade. The body of others, including K. bicirrhis, are somewhat translucent or opaque. Native to rivers in Thailand, glass catfish prefer tanks with open swimming areas with a moderate current and planted areas that provide shelter. Due to their timid and non-aggressive nature, they should always be kept in a group of at least five, they can be kept with fish species of similar size. Glass catfish are highly sensitive to changes in quality and pH. The pH should be slightly acidic, water hardness should be low and they have a reputation for being finicky eaters, they prefer live food such as mosquito larvae, bloodworms and brine shrimp, but can be weaned to flake food with time. Kryptopterus species are different from most other catfish because they are free-swimming, glass catfish commonly favor dark places to being out in the open light. A small school of them may hide under elevated rocks, logs, sometimes, however, one or two may venture out into the open and swim in the upper level of the water. They can be enticed to do more often if the flow of water in the tank is arranged so that their favorite hiding spots are sheltered. Thus, they move in the open especially at feeding time
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Vertebral column
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The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column houses the spinal canal, a cavity that encloses, there are about 50,000 species of animals that have a vertebral column. The human vertebral column is one of the most-studied examples, the articulating vertebrae are named according to their region of the spine. There are seven cervical vertebrae, twelve thoracic vertebrae and five lumbar vertebrae, the number of vertebrae in a region can vary but overall the number remains the same. The number of those in the region however is only rarely changed. There are ligaments extending the length of the column at the front and the back, the vertebrae in the human vertebral column are divided into different regions, which correspond to the curves of the spinal column. The articulating vertebrae are named according to their region of the spine, vertebrae in these regions are essentially alike, with minor variation. These regions are called the spine, thoracic spine, lumbar spine, sacrum. There are seven cervical vertebrae, twelve thoracic vertebrae and five lumbar vertebrae, the number of vertebrae in a region can vary but overall the number remains the same. The number of those in the region however is only rarely changed. The vertebrae of the cervical, thoracic and lumbar spines are independent bones, the vertebrae of the sacrum and coccyx are usually fused and unable to move independently. Two special vertebrae are the atlas and axis, on which the head rests, a typical vertebra consists of two parts, the vertebral body and the vertebral arch. The vertebral arch is posterior, meaning it faces the back of a person, together, these enclose the vertebral foramen, which contains the spinal cord. Because the spinal cord ends in the spine, and the sacrum and coccyx are fused. Two transverse processes and one process are posterior to the vertebral body. The spinous process comes out the back, one transverse process comes out the left, the spinous processes of the cervical and lumbar regions can be felt through the skin. Above and below each vertebra are joints called facet joints and these restrict the range of movement possible, and are joined by a thin portion of the neural arch called the pars interarticularis. In between each pair of vertebrae are two small holes called intervertebral foramina, the spinal nerves leave the spinal cord through these holes
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Spinal cord
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The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. The brain and spinal cord make up the central nervous system. The spinal cord begins at the bone and extends down to the space between the first and second lumbar vertebrae, it does not extend the entire length of the vertebral column. It is around 45 cm in men and around 43 cm long in women, also, the spinal cord has a varying width, ranging from 13 mm thick in the cervical and lumbar regions to 6.4 mm thick in the thoracic area. The enclosing bony vertebral column protects the relatively shorter spinal cord, the spinal cord is the main pathway for information connecting the brain and peripheral nervous system. The length of the cord is much shorter as compared to the length of the vertebral column. The human spinal cord extends from the magnum and continues through to the conus medullaris near the second lumbar vertebra. It is about 45 cm long in men and around 43 cm in women, ovoid-shaped, the cervical enlargement, located from C5 to T1 spinal segments, is where sensory input comes from and motor output goes to the arms. The lumbar enlargement, located between L1 and S3 spinal segments, handles input and motor output coming from and going to the legs. The spinal cord is continuous with the portion of the medulla. It does not run the length of the vertebral column in adults. It is made of 31 segments that contain sensory nerve root. The first cervical segment is very small and may be absent in most individuals. Nerve roots merge into 31 bilaterally symmetric pairs of spinal nerves, the peripheral nervous system is made up of these spinal roots, nerves, and ganglia. Dorsal root ganglia hold the bodies of dorsal root ganglia in the spinal ganglia related with that spinal segment. Ventral roots only have efferent fibers that arise from motor neurons whose cell bodies are found in the ventral horns of the spinal cord. The spinal cord are protected by three layers of tissue or membranes called meninges, that surround the canal, the dura mater is the outermost layer, and it forms a tough protective coating. Between the dura mater and the bone of the vertebrae is a space called the epidural space
20.
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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Eumetazoa
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Eumetazoa is a clade comprising all major animal groups except sponges, placozoa, and several other extinct or obscure life forms, such as Iotuba and Thectardis. Characteristics of eumetazoans include true tissues organized into layers, the presence of neurons. The clade is usually held to contain at least Ctenophora, Cnidaria, whether mesozoans belong is in dispute. Ctenophora now appear basal eumetazoa, and placozoa also appear to have emerged in eumetazoa, Eumetazoa would then be a basal Metazoan clade as sister of Porifera. Some phylogenists have speculated the sponges and eumetazoans evolved separately from single-celled organisms, however, genetic studies and some morphological characteristics, like the common presence of choanocytes, support a common origin. When treated as a formal taxon Eumetazoa is typically ranked as a subkingdom, the name Metazoa has also been used to refer to this group, but more often refers to the Animalia as a whole. Many classification schemes do not include a subkingdom Eumetazoa, over the last decade, the work of developmental biologists and molecular phylogeneticists spawned new ideas about bilaterian relationships resulting in a paradigm shift. The current widely accepted hypothesis, based on data, divides Bilateria into the following four superphylums, Deuterostomia, Ecdysozoa, Lophotrochozoa. The last three groups are collectively known as Protostomia. However, many skeptics emphasize the pitfalls and inconsistencies associated with the new data, in his 2001 book Animal Evolution, Interrelationships of the Living Phyla, he maintains the traditional divisions of Protostomia and Deuterostomia. It has been suggested that one type of clock and one approach to interpretation of the fossil record both place the evolutionary origins of eumetazoa in the Ediacaran. However, the earliest eumetazoans may not have left an impact on the fossil record. Tree of Life web project, US National Science Foundation, invertebrates and the Origin of Animal Diversity Evers, Christine A. 2005 Metazoa, the Animals Nielsen, C.2001, Animal Evolution, Interrelationships of the Living Phyla, 2nd edition,563 pp. Oxford Univ. Manuel, M. Alivon, E. Boury-Esnault N. Vacelet, J. Le-Parco, journal of Evolutionary Biology 14, 171–179. Peterson, Kevin J. McPeek, Mark A. & Evans, tempo & mode of early animal evolution, inferences from rocks, Hox, & molecular clocks
23.
Bilateria
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In contrast, radially symmetrical animals like jellyfish have a topside and a downside, but no identifiable front or back. The bilateria are a group of animals, including the majority of phyla but not sponges, cnidarians, placozoans. For the most part, bilateral embryos are triploblastic, having three germ layers, endoderm, mesoderm, and ectoderm. Nearly all are symmetrical, or approximately so, the most notable exception is the echinoderms, which achieve near-radial symmetry as adults. Except for a few phyla, bilaterians have complete digestive tracts with a separate mouth, some bilaterians lack body cavities, while others display primary body cavities or secondary cavities. The hypothetical most recent common ancestor of all bilateria is termed the Urbilaterian, the nature of the first bilaterian is a matter of debate. The first evidence of bilateria in the record comes from trace fossils in Ediacaran sediments. Earlier fossils are controversial, the fossil Vernanimalcula may be the earliest known bilaterian, fossil embryos are known from around the time of Vernanimalcula, but none of these have bilaterian affinities. Burrows believed to have created by bilaterian life forms have been found in the Tacuarí Formation of Uruguay. There are two main superphyla of Bilateria, the deuterostomes include the echinoderms, hemichordates, chordates, and a few smaller phyla. The protostomes include most of the rest, such as arthropods, annelids, mollusks, flatworms, there are a number of differences, most notably in how the embryo develops. In particular, the first opening of the embryo becomes the mouth in protostomes, many taxonomists now recognize at least two more superphyla among the protostomes, Ecdysozoa and Lophotrochozoa. Within the latter, some researchers also recognize another superphylum, Platyzoa, the arrow worms have proven particularly difficult to classify, with some taxonomists placing them among the deuterostomes and others placing them among the protostomes. The two most recent studies to address the question of chaetognath origins support protostome affinities, a modern consensus phylogeny for Bilateria is shown below, although the position of certain clades are still controversial and the tree has changed considerably between 2000 and 2010. Nodes marked with * have received broad consensus, a prominent alternative tree is championed by Nielsen. Embryological origins of the mouth and anus Tree of Life web project — Bilateria University of California Museum of Paleontology — Systematics of the Metazoa
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Nephrozoa
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Nephrozoa is a major clade of bilaterians including deuterostomes and protostomes. It is the extant sister clade of Xenacoelomorpha, the majority of bilaterian animals are split into two groups, the protostomes and deuterostomes. It seems very likely that the 555 million year old Kimberella was a member of the protostomes, balavoine, G. Adoutte, A.1998, One or three Cambrian radiations. Economou, A. D. Telford, M. J.2008, Testing the new animal phylogeny, molecular phylogenetics and evolution,49, 23-31. Baguñà, J. Riutort, M.2002, The Nemertodermatida are basal bilaterians and not members of the Platyhelminthes
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Deuterostome
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Deuterostomes are any members of a superphylum of animals. It is a clade of Protostomia, with which it forms the Nephrozoa clade. Deuterostomes are also known as enterocoelomates because their coelom develops through enterocoely, the phylum Chaetognatha may belong here, but molecular studies have placed them in the protostomes more often. Extinct deuterostome groups may include the phylum Vetulicolia, echinodermata and Hemichordata form the clade Ambulacraria. In both deuterostomes and protostomes, a zygote first develops into a ball of cells, called a blastula. In deuterostomes, the early divisions occur parallel or perpendicular to the polar axis and this is called radial cleavage, and also occurs in certain protostomes, such as the lophophorates. Most deuterostomes display indeterminate cleavage, in which the fate of the cells in the developing embryo are not determined by the identity of the parent cell. Thus, if the first four cells are separated, each cell is capable of forming a small larva, and if a cell is removed from the blastula. In deuterostomes the mesoderm forms as evaginations of the gut that pinch off. Both the Hemichordata and Chordata have gill slits, and primitive fossil echinoderms also show signs of gill slits, a hollow nerve cord is found in all chordates, including tunicates. Some hemichordates also have a nerve cord. In the early stage, it looks like the hollow nerve cord of chordates. It could have resembled the small group of Cambrian urochordate deuterostomes named Vetulicolia, the defining characteristic of the deuterostome is the fact that the blastopore becomes the anus, whereas in protostomes the blastopore becomes the mouth. The deuterostome mouth develops at the end of the embryo from the blastopore. The majority of more complex than jellyfish and other Cnidarians are split into two groups, the protostomes and deuterostomes. It seems likely that the 555 million year old Kimberella was a member of the protostomes. e, during the later part of the Ediacaran Era. The oldest discovered proposed deuterostome is Saccorhytus coronarius, which lived approximately 540 million years ago, the researchers that made the discovery believe that the Saccorhytus is a common ancestor to all previously-known deuterostomes. Fossils of one major group, the echinoderms, are quite common from the start of Series 2 of the Cambrian,521 million years ago
26.
Ernst Haeckel
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The published artwork of Haeckel includes over 100 detailed, multi-colour illustrations of animals and sea creatures. As a philosopher, Ernst Haeckel wrote Die Welträtsel, the genesis for the term world riddle, Ernst Haeckel was born on 16 February 1834, in Potsdam. In 1852, Haeckel completed studies at the Domgymnasium, the high school of Merseburg. He then studied medicine in Berlin and Würzburg, particularly with Albert von Kölliker, Franz Leydig, Rudolf Virchow, together with Hermann Steudner he attended botany lectures in Würzburg. In 1857, Haeckel attained a doctorate in medicine, and afterwards he received a license to practice medicine, the occupation of physician appeared less worthwhile to Haeckel, after contact with suffering patients. Between 1859 and 1866, Haeckel worked on many phyla such radiolarians, poriferans, during a trip to the Mediterranean, Haeckel named nearly 150 new species of radiolarians. In 1867, he married Agnes Huschke and their son Walter was born in 1868, their daughters Elizabeth in 1871 and Emma in 1873. In 1869, he traveled as a researcher to Norway, in 1871 to Croatia, and in 1873 to Egypt, Turkey, Haeckel retired from teaching in 1909, and in 1910 he withdrew from the Evangelical church. Haeckels wife, Agnes, died in 1915, and Haeckel became substantially frailer, with a broken leg and he sold his Villa Medusa in Jena in 1918 to the Carl Zeiss foundation, and it presently contains a historic library. Haeckel died on 9 August 1919, Haeckels political beliefs were influenced by his affinity for the German Romantic movement coupled with his acceptance of a form of Lamarckism. Rather than being a strict Darwinian, Haeckel believed that the characteristics of an organism were acquired through interactions with the environment and he believed the social sciences to be instances of applied biology, and that phrase was picked up and used for Nazi propaganda. In 1905, Haeckel founded a group called the Monist League to promote his religious and this group lasted until 1933 and included such notable members as Wilhelm Ostwald, Georg von Arco, Helene Stöcker and Walter Arthur Berendsohn. Haeckel was the first person known to use the term First World War. Shortly after the start of the war Haeckel wrote, There is no doubt that the course, Haeckel was a zoologist, an accomplished artist and illustrator, and later a professor of comparative anatomy. For example, Haeckel described and named hypothetical ancestral microorganisms that have never been found and he was one of the first to consider psychology as a branch of physiology. He also proposed the kingdom Protista in 1866 and his chief interests lay in evolution and life development processes in general, including development of nonrandom form, which culminated in the beautifully illustrated Kunstformen der Natur. Haeckel did not support natural selection, rather believing in Lamarckism and it proposed a link between ontogeny and phylogeny, summed up by Haeckel in the phrase ontogeny recapitulates phylogeny. His concept of recapitulation has been refuted in the form he gave it, the strong recapitulation hypothesis views ontogeny as repeating forms of the ancestors, while weak recapitulation means that what is repeated is the ancestral embryonic development process
27.
Cephalochordate
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A cephalochordate is an animal in the chordate subphylum, Cephalochordata. They are characterized as chordates, as they possess all 5 of the chordate characteristics during larval stages and this includes, notocord, dorsal nerve cord, endostyle, pharynx and post-anal tail. Cephalochordates are represented in the oceans by the Amphioxiformes. Along with its sister phylum, Urochordata, Cephalochordata can be classified as belonging to the taxon Protochordata, the members of this subphylum are very small and have no hard parts, making their fossils difficult to find. Fossilized species have found in very old rocks predating vertebrates. There is a famous fossil shale from the Middle Cambrian, the Burgess Shale of British Columbia, recently, a different cephalochordate fossil has been found in south China. It dates to the early Cambrian period, and is the earliest known fossil of the cephalochordate lineage, members of this lineage have numerous gill slits, and have separate sexes. Phylogeny is based on a combination of studies of extinct and extant species, cephalochordates employ a filter feeding system to consume microorganisms. The oral hood serves as the entrance for food particles, and possesses buccal cirri, epithelial cilia lining the mouth and pharynx form a specialized wheel organ situated at the dorsal and posterior end of the cavity. The motion of the cilia resembles the motion of a wheel, hence the organs name. Behind this organ is the velum, which acts as a filter before food enters the pharynx. The food particles adhere to secreted mucus on the bars before being brought to the epibranchial groove on the dorsal side of the pharynx. Following this, the food is transferred to the gut, and this excess water passes through the atriopore and is then excreted from the body
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Pikaia
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Pikaia gracilens is an extinct cephalochordate animal known from the Middle Cambrian Burgess Shale of British Columbia. Sixteen specimens are known from the Greater Phyllopod bed, where they comprised 0. 03% of the community and it resembled the lancelet and perhaps swam much like an eel. Pikaia is a primitive chordate that lacked a head and averaged about 1 1⁄2 inches in length. Pikaia had a pair of large, antenna-like tentacles on its head, and a series of short appendages, in these ways, it differs from the living lancelet. The tentacles on its head may be comparable to those in the present-day hagfish, although primitive, Pikaia shows the essential prerequisites for vertebrates. When alive, Pikaia was a compressed, leaf-shaped animal with a tail fin. The muscles lie on side of a flexible structure resembling a rod that runs from the tip of the head to the tip of the tail. It likely swam by throwing its body into a series of S-shaped, zigzag curves, similar to the movement of eels, fish inherited the same swimming movement and these adaptations may have allowed Pikaia to filter particles from the water as it swam along. Pikaia was probably a slow swimmer, since it lacks the fast-twitch fibers that are associated with rapid swimming in modern chordates, on the basis of these findings, they constructed a new scenario for chordate evolution. P. gracilens was discovered by Charles Walcott and first described by him in 1911 and it was named after Pika Peak, a mountain in Alberta, Canada. Based on the obvious and regular segmentation of the body, Walcott classified it as a polychaete worm and its anatomy closely resembles the modern creature Branchiostoma. Much debate on whether Pikaia is an ancestor, its worm-like appearance notwithstanding. It looks like a worm that has been flattened sideways, the notochord, a flexible rod-like structure that runs along the back of the animal, lengthens and stiffens the body so that it can be flexed from side to side by the muscle blocks for swimming. In the fish and all subsequent vertebrates, the forms the backbone. The backbone strengthens the body, supports strut-like limbs, and protects the vital dorsal nerve cord, a Pikaia lookalike, the lancelet Branchiostoma, still exists today. With a notochord and paired muscle blocks, the lancelet and Pikaia belong to the group of animals from which the vertebrates descended. Molecular studies have refuted earlier hypotheses that lancelets might be the closest living relative to the vertebrates, instead favoring tunicates in this position. Other living and fossil groups, such as worms and graptolite, are more primitive, called the hemichordates
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Lancelet
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They are the modern representatives of the subphylum Cephalochordata, formerly thought to be the sister group of the craniates. In Asia, they are harvested commercially as food for humans and they are an important object of study in zoology as they provide indications about the evolutionary origins of the vertebrates. Lancelets serve as an intriguing comparison point for tracing how vertebrates have evolved and adapted, although lancelets split from vertebrates more than 520 million years ago, their genomes hold clues about evolution, particularly how vertebrates have employed old genes for new functions. They are regarded as similar to the archetypal vertebrate form, the first representative organism of the group to be described was Branchiostoma lanceolatum. It was described by Peter Simon Pallas in 1774 as molluscan slugs in the genus Limax and it was not until 1834 that Gabriel Costa brought the phylogenetic position of the group closer to the agnathan vertebrates, including it in the new genus Branchiostoma. In 1836, Yarrel renamed the genus as Amphioxus, now considered a synonym of the genus Branchiostoma. Today, the term amphioxus is still used as a name for the Amphioxiformes, along with lancelet. A non-technical review of all aspects of biology is, Stokes, M. D. and Holland. The genome of the Florida lancelet has been sequenced, lancelets are typically 5 centimetres long, or 7 centimetres at the longest. They have a translucent, somewhat fish-like body, but without any paired fins or other limbs, a relatively poorly developed tail fin is present, so they are not especially good swimmers. While they do possess some cartilage-like material stiffening the gill slits, mouth, in common with vertebrates, lancelets have a hollow nerve cord running along the back, pharyngeal slits and a tail that runs past the anus. Also like vertebrates, the muscles are arranged in blocks called myomeres, unlike vertebrates, the dorsal nerve cord is not protected by bone but by a simpler notochord made up of a cylinder of cells that are closely packed to form a toughened rod. The lancelet notochord, unlike the vertebrate spine, extends into the head and this gives the subphylum its name. The nerve cord is only larger in the head region than in the rest of the body. However, developmental gene expression and Transmission electron microscopy indicate the presence of a diencephalic forebrain, a possible midbrain, lancelets have two known kinds of light-sensing structures, Joseph cells, and Hesse organs, as well as a frontal eye and lamellar body. The frontal eye is thought to be light-sensitive, although this has not been confirmed by electrophysiological measurement. The lamellar body, a homologue of the pineal body, was once thought to be light-sensitive. All of these organs and structures are located in the tube, with the frontal eye at the front, followed by the lamellar body, the Joseph cells
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Tunicate
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A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata, which is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords. The subphylum was at one time called Urochordata, and the term urochordates is still used for these animals. Some tunicates live as solitary individuals, but others replicate by budding and become colonies and they are marine filter feeders with a water-filled, sac-like body structure and two tubular openings, known as siphons, through which they draw in and expel water. During their respiration and feeding, they take in water through the incurrent siphon, various species are commonly known as sea squirts, sea pork, sea livers, or sea tulips. The earliest probable species of tunicate appears in the record in the early Cambrian period. Their name derives from their outer covering or tunic, which is formed from proteins and carbohydrates. In some species, it is thin, translucent, and gelatinous, while in others it is thick, tough, about 2,150 species of tunicate exist in the worlds oceans, living mostly in shallow water. The most numerous group is the ascidians, fewer than 100 species of these are found at greater than 200 m. Some are solitary animals leading a sessile existence attached to the seabed, but others are colonial and a few are pelagic. Some are supported by a stalk, but most are attached directly to a substrate and they are found in a range of solid or translucent colours and may resemble seeds, grapes, peaches, barrels, or bottles. One of the largest is a stalked sea tulip, Pyura pachydermatina, the Tunicata were established by Jean-Baptiste Lamarck in 1816. In 1881, Francis Maitland Balfour introduced a name for the same group, Urochorda. Accordingly, the current trend is to abandon the name Urochorda or Urochordata in favour of the original Tunicata, and it is accepted as valid by the World Register of Marine Species but not by the Integrated Taxonomic Information System. Various common names are used for different species, sea tulips are tunicates with colourful bodies supported on slender stalks. Sea squirts are so named because of their habit of contracting their bodies sharply, sea liver and sea pork get their names from the resemblance of their dead colonies to pieces of meat. Tunicates are more related to craniates, than to lancelets, echinoderms, hemichordates. The clade consisting of tunicates and vertebrates is called Olfactores, although the traditional classification is provisionally accepted, newer evidence suggests the Ascidiacea are an artificial group of paraphyletic status. Undisputed fossils of tunicates are rare, the best known and earliest unequivocally identified species is Shankouclava shankouense from the Lower Cambrian Maotianshan Shale at Shankou village, Anning, near Kunming
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Craniate
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A craniate is a member of the Craniata, a proposed clade of chordate animals with a skull of hard bone or cartilage. Included in the clade are the vertebrates, and non-vertebrate chordates with skulls, living representatives are the Myxini, Hyperoartia, and the much more numerous Gnathostomata. The craniate head consists of a brain, sense organs, including eyes, in addition to distinct crania, craniates possess many derived characteristics, which have allowed for more complexity to follow. In general, craniates are much more active than tunicates and lancelets and, as a result, have greater metabolic demands, aquatic craniates have gill slits, which are connected to muscles and nerves that pump water through the slits, engaging in both feeding and gas exchange. Muscles line the canal, moving food through the canal. Craniates have cardiovascular systems that include a heart with two or more chambers, red cells, and oxygen transporting hemoglobin, as well as kidneys. Linnaeus used the terms Craniata and Vertebrata interchangeably to include lampreys, jawed fishes, hagfishes were classified as Vermes, possibly representing a transitional form between worms and fishes. Dumeril grouped hagfishes and lampreys in the taxon Cyclostomi, characterized by horny teeth borne on an apparatus, a large notochord as adults. Cyclostomes were regarded as either degenerate cartilaginous fishes or primitive vertebrates, cope coined the name Agnatha for a group that included the cyclostomes and a number of fossil groups in which jaws could not be observed. Vertebrates were subsequently divided into two major sister-groups, the Agnatha and the Gnathostomata, stensiö suggested that the two groups of living agnathans arose independently from different groups of fossil agnathans. e. On this basis Janvier proposed to use the names Vertebrata and Craniata as two distinct and nested taxa, the argument is that, if Cyclostomata is indeed monophyletic, Vertebrata would return to its old content and the name Craniata, being superfluous, would become a junior synonym. Lines show probable evolutionary relationships, including extinct taxa, which are denoted with a dagger, the positions of the Lancelet, Tunicate, and Craniata clades are as reported in the scientific journal Nature. Note that this cladogram, in showing the extant cyclostomes as paraphyletic, is contradicted by all recent molecular data. Extinct genera Haikouella and Haikouichthys Campbell, Neil A. Reece, cleveland P. Hickman, J. Roberts, L. S. Keen, S. L. Larson, A. & Eisenhour, D. J. Animal Diversity, Fourth Edition. CS1 maint, Uses authors parameter Cracraft, Joel, Donoghue, new York, Oxford University Press US. Delarbre, Christiane, Gallut, C, Barriel, V, Janvier, P, Gachelin, G, complete Mitochondrial DNA of the Hagfish, Eptatretus burgeri, The Comparative Analysis of Mitochondrial DNA Sequences Strongly Supports the Cyclostome Monophyly. Parker, T. J. Haswell, W. A
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Palaeospondylus
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Palaeospondylus gunni is a mysterious, fish-like fossil vertebrate. Its fossils are described from Achannaras slate quarry in Caithness, Scotland, the fossil as preserved is carbonized, and indicates an eel-shaped animal of up to 6 centimetres in length. The skull, which must have consisted of hardened cartilage, exhibits pairs of nasal and auditory capsules, with a gill-apparatus below its hinder part, the phylogeny of this bizarre fossil has puzzled scientists since its discovery in 1890, and many taxonomies have been suggested. In 2004, researchers proposed that Palaeospondylus was a larval lungfish, previously it had been classified as a larval tetrapod, unarmored placoderm, an agnathan, and a chimera. Prehistoric fish Orcadian Basin This article incorporates text from a now in the public domain, Chisholm, Hugh
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Zhongxiniscus
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Zhongxiniscus is a genus of primitive chordate from eastern Yunnan that lived during the Early Cambrian. Known from a specimen, it had a small, broad and short. It possessed S-shaped myomeres, numbering roughly seven per one millimeter of length, two triangular fins are evident on the dorsal margin. For these reasons, Zhongxiniscus is tentatively considered to be an intermediate form between Cathaymyrus and the two vertebrates Haikouichthys and Myllokunmingia, luo, Huilin, Hu, Sinxue, Chen, Liangzhong. New Early Cambrian Chordates from Haikou, Kunming
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Vetulicolia
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Vetulicolia is an extinct taxon, either phylum or subphylum in rank, encompassing several Cambrian organisms. All vetulicolians lack preserved appendages of any kind, having no legs, feelers, the area where the anterior and posterior parts join is constricted. Their affinity has been uncertain, they have considered to represent stem- and crown-group arthropods, stem-group vertebrates. The general scientific consensus formerly considered them early limbless arthropods, recently examined Vetulicolian fossils show the presence of notochord-like structures. Therefore, it can be concluded that vetulicolians are crown-group chordates, as originally proposed, the phylum included the Didazoonidae and the Vetulicolidae. Other groups which may be related include the yunnanozoans, the taxonomic placement of the Vetulicolians remains controversial. Dominguez and Jefferies have argued, based on analysis, that Vetulicola is a urochordate. However, recent research have confirmed a close to urochordates for Vetulicolians. Some groups, like the genus Vetulicola, were more streamlined than other groups, because all vetulicolians had mouths which had no features for chewing or grasping, it is automatically assumed that they were not predators. Because of their gill slits, many regard the vetulicolians as being planktivores. The sediment infills in the guts of their fossils have led some to suggest that they were deposit feeders and this idea has been contested, as deposit feeders tend to have straight guts, whereas the hindguts of vetulicolians were spiral-shaped. Some researchers propose that the vetulicolians were selective deposit-feeders which actively swam from one region of the seafloor to another, phylum Chordata Subphylum Vetulicolia Class Vetulicolida Genus NesonektrisN. Aldridgei Family Vetulicolidae Genus Vetulicola V. rectangulata V. cuneata V. gangtoucunensis V. monile Genus OoedigeraO
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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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Phylum
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In biology, a phylum is a taxonomic rank below kingdom and above class. Traditionally, in botany the term division was used instead of phylum, although from 1993 the International Code of Nomenclature for algae, fungi, depending on definitions, the kingdom Animalia contains approximately 35 phyla, Plantae contains about 12, and Fungi contains around 7. Current research in phylogenetics is uncovering the relationships between phyla, which are contained in larger clades, like Ecdysozoa and Embryophyta, the definitions of zoological phyla have changed from their origins in the six Linnaean classes and the four embranchements of Georges Cuvier. Haeckel introduced the term phylum, based on the Greek word phylon, in plant taxonomy, Eichler classified plants into five groups, named divisions. Informally, phyla can be thought of as grouping organisms based on general specialization of body plan, the most important objective measure in the above definitions is the certain degree—how unrelated do organisms need to be to be members of different phyla. The minimal requirement is that all organisms in a phylum should be more closely related to one another than to any other group. So phyla can be merged or split if it becomes apparent that they are related to one another or not, a definition of a phylum based on body plan has been proposed by paleontologists Graham Budd and Sören Jensen. By Budd and Jensens definition, a phylum is defined by a set of shared by all its living representatives. This approach brings some small problems—for instance, ancestral characters common to most members of a phylum may have been lost by some members, also, this definition is based on an arbitrary point of time, the present. However, as it is based, it is easy to apply to the fossil record. A greater problem is that it relies on a decision about which groups of organisms should be considered as phyla. However, proving that a fossil belongs to the group of a phylum is difficult. Furthermore, organisms in the group of a phylum can possess the body plan of the phylum without all the characteristics necessary to fall within it. This weakens the idea that each of the phyla represents a body plan. A classification using this definition may be affected by the chance survival of rare groups. Representatives of many modern phyla did not appear until long after the Cambrian, the kingdom Plantae is defined in various ways by different biologists. All definitions include the living embryophytes, to which may be added the two green algae divisions, Chlorophyta and Charophyta, to form the clade Viridiplantae. The table below follows the influential Cavalier-Smith system in equating Plantae with Archaeplastida, a group containing Viridiplantae, the definition and classification of plants at the division level also varies from source to source, and has changed progressively in recent years
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Pharyngeal slit
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Pharyngeal slits are filter-feeding organs found in Invertebrate chordates and hemichordates living in aquatic environments. These repeated segments are controlled by similar developmental mechanisms, some hemichordate species can have as many as 200 gill slits. Pharyngeal slits resembling gill slits are present during the embryonic stages of tetrapod development. However, it is now accepted that it is the pharyngeal pouches. Gill slits are, at stage of life, found in all chordates. In vertebrates, the arches are derived from all three germ layers. Neural crest cells enter these arches where they contribute to features such as bone. However, the existence of pharyngeal structures before neural crest cells evolved is indicated by the existence of neural crest-independent mechanisms of pharyngeal arch development, the first, most anterior pharyngeal arch gives rise to the oral jaw. The second arch becomes the hyoid and jaw support, in fish, the other posterior arches contribute to the brachial skeleton, which support the gills, in tetrapods the anterior arches develop into components of the ear, tonsils, and thymus. The genetic and developmental basis of pharyngeal arch development is well characterized and it has been shown that Hox genes and other developmental genes such as dlx are important for patterning the anterior/posterior and dorsal/ventral axes of the branchial arches. Some fish species have jaws in their throat, known as pharyngeal jaws, the presence of pharyngeal slits in hemichordates led to debates of whether this structure was homologous to the slits found in chordates or a result of convergent evolution. With the placement of hemichordates and echinoderms as a group to chordates. Intriguingly, extant echinoderms lack pharyngeal structures, but fossil records reveal that ancestral forms of echinoderms had gill-like structures, applying excess retinoic acid leads to the absence of gill slits in developing Amphioxus, suggesting that retinoic acid may act through the same mechanism in vertebrates and amphioxus. These studies indicate that the slits found in hemichordates and chordates are indeed homologous in a molecular sense
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Tail
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The tail is the section at the rear end of an animals body, in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals, reptiles, tailed objects are sometimes referred to as caudate and the part of the body associated with or proximal to the tail are given the adjective caudal. Animal tails are used in a variety of ways and they provide a source of locomotion for fish and some other forms of marine life. Many land animals use their tails to brush away flies and other biting insects, tails are also used for social signaling. Some species tails are armored, and some, such as those of scorpions, some species of lizard can detach their tails from their bodies. This can help them to escape predators, which are either distracted by the wriggling, tails cast in this manner generally grow back over time, though the replacement is typically darker in colour than the original. Most birds tails end in long feathers called rectrices and these feathers are used as a rudder, helping the bird steer and maneuver in flight, they also help the bird to balance while it is perched. In some species—such as birds of paradise, lyrebirds, and most notably peafowl—modified tail feathers play an important role in courtship displays, the extra-stiff tail feathers of other species, including woodpeckers and woodcreepers, allow them to brace themselves firmly against tree trunks. The tails of grazing animals, such as horses, are used both to sweep away insects and positioned or moved in ways that indicate the physical or emotional state. Human embryos have a tail measures about one-sixth of the size of the embryo itself. As the embryo develops into a fetus, the tail is absorbed by the growing body, humans have a tail bone attached to the pelvis, formed of fused vertebrae, usually four, at the bottom of the vertebral column. Rump Empennage, the tail of an aircraft
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Symmetry in biology
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Symmetry in biology is the balanced distribution of duplicate body parts or shapes within the body of an organism. In nature and biology, symmetry is always approximate, for example plant leaves, while considered symmetrical, symmetry creates a class of patterns in nature, where the near-repetition of the pattern element is by reflection or rotation. The body plans of most multicellular organisms exhibit some form of symmetry, whether radial, bilateral, a small minority, notably among the sponges, exhibit no symmetry. Radially symmetric organisms resemble a pie where several cutting planes produce roughly identical pieces, such an organism exhibits no left or right sides. They have a top and a surface only. Most radially symmetric animals are symmetrical about an axis extending from the center of the oral surface, radial symmetry is especially suitable for sessile animals such as the sea anemone, floating animals such as jellyfish, and slow moving organisms such as starfish. Animals in the phyla cnidaria and echinodermata are radially symmetric, although many sea anemones and some corals have bilateral symmetry defined by a single structure, many flowers are radially symmetric or actinomorphic. Roughly identical flower parts – petals, sepals, and stamens occur at intervals around the axis of the flower. Many viruses have radial symmetries, their coats being composed of a small number of protein molecules arranged in a regular pattern to form polyhedrons, spheres. Tetramerism is a variant of radial symmetry found in jellyfish, which have four canals in an otherwise radial body plan, pentamerism, another variant of radial symmetry, means the organism is in five parts around a central axis, 72° apart. Among animals, only the echinoderms such as sea stars, sea urchins, being bilaterian animals, however, they initially develop with mirror symmetry as larvae, then gain pentaradial symmetry later. Flowering plants show fivefold symmetry in many flowers and in various fruits and this is well seen in the arrangement of the five carpels in an apple cut transversely. Hexamerism is found in the corals and sea anemones which are divided into two based on their symmetry. The most common corals in the subclass Hexacorallia have a body plan, their polyps have sixfold internal symmetry. Octamerism is found in corals of the subclass Octocorallia and these have polyps with eight tentacles and octameric radial symmetry. The octopus, however, has symmetry, despite its eight arms. Spherical symmetry occurs in an if it is able to be cut into two identical halves through any cut that runs through the organisms center. Organisms which show approximate spherical symmetry include the green alga Volvox
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Coelom
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The coelom is the main body cavity in most animals and is positioned inside the body to surround and contain the digestive tract and other organs. In developed animals, it is lined with a mesodermal epithelium, in other animals, such as molluscs, it remains undifferentiated. Coelom formation begins in the gastrula stage, the developing digestive tube of an embryo forms as a blind pouch called the archenteron. In Protostomes, the forms by a process known as schizocoely. The space between the layer and the visceral layer is known as the coelom or body cavity. In Deuterostomes, the forms by enterocoely, mesoderm buds from the walls of the archenteron. The evolutionary origin of the coelom is uncertain, the oldest known animal to have had a body cavity was the Vernanimalcula. Current hypothesis include, The acoelomate theory, which states that evolved from an acoelomate ancestor. The enterocoel theory, which states that evolved from gastric pouches of cnidarian ancestors. This is supported by research on flatworms and small worms recently discovered in marine fauna A coelom can absorb shock or provide a hydrostatic skeleton. It can also support a system in the form of coelomocytes that may either be attached to the wall of the coelom or may float about in it freely. The fluid inside the coelom is known as coelomic fluid and this is circulated by mesothelial cilia or by contraction of muscles in the body wall which are themselves of mesin. This scheme was followed by a number of textbooks and some general classifications. However, some authors of recent molecular phylogeny studies misleadingly called this classification scheme as the traditional, the complete mesoderm lining allows organs to be attached to each other so that they can be suspended in a particular order while still being able to move freely within the cavity. Most bilateral animals, including all the vertebrates, are coelomates, Pseudocoelomate animals have a pseudocoelom, which is a fluid filled body cavity. Tissue derived from mesoderm only partly lines the fluid filled body cavity of these animals, thus, although organs are held in place loosely, they are not as well organized as in a coelomate. All pseudocoelomates are protostomes, however, not all protostomes are pseudocoelomates, an example of a Pseudocoelomate is the roundworm. Pseudocoelomate animals are referred to as Hemocoel and Blastocoelomate
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Metamerism (biology)
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In animals, metameric segments are referred to as somites or metameres. In plants, they are referred to as metamers or, more concretely, in animals, metamery is defined as a mesodermal event resulting in serial repetition of unit subdivisions of ectoderm and mesoderm products. Endoderm is not involved in metamery, segmentation is not the same concept as metamerism. Segmentation can be confined only to ectodermally derived tissue, e. g. in the Cestoda tapeworms, metamerism is far more important biologically since it results in metameres, also called somites, that play a critical role in advanced locomotion. Metamerism can be divided into two categories, homonymous metamery is a strict serial succession of metameres. It can be grouped into two more known as pseudometamerism and true metamerism. An example of pseudometamerism is in class Cestoda, the tapeworm is composed of many repeating segments primarily for reproduction and basic nutrient exchange. Each segment acts independently from each other which is why it is not considered true metamerism, another worm, the Earthworm in class Annelid can be an example of true metamerism. In each segment of the worm, a repetition of organs, what differentiates the Annelids from Cestoda is that the segments in the Earthworm all work together for the whole organism. It is believed that segmentation evolved for reasons including a higher degree of motion. Taking the Earthworm for example, the segmentation of the muscular tissue allows the worm to move in an inching pattern, the circular muscles work to allow the segments elongate one by one and the Longitudinal muscles then work to shorten the elongated segments. This pattern continues down the entirety of the worm allowing it to inch along the surface, each segment is allowed to work independently but towards the movement of the whole worm. Heteronomous metamery is the condition where metameres have grouped together to perform similar tasks, the extreme example of this is the insect head, thorax, and abdomen. The process that results in the grouping of metameres is called tagmatization, in organisms with highly derived tagmata, such as the insects, much of the metamerism within a tagma may not be trivially distinguishable. It may have to be sought in structures that do not necessarily reflect the grouped metameric function, in addition, an animal may be classified as pseudometameric meaning that it has clear internal metamerism but no corresponding external metamerism as is seen, for example, in Monoplacophora. Humans and other chordates are conspicuous examples of organisms that have metameres intimately grouped into tagmata, in the Chordata the metameres of each tagma are fused to such an extent that few repetitive features are directly visible. Intensive investigation is necessary to discern the metamerism in the tagmata of such organisms, examples of detectable evidence of vestigially metameric structures include branchial arches and cranial nerves. A metamer is one of several segments that share in the construction of a shoot, in the metameristic model, a plant consists of a series of phytons or phytomers, each consisting of an internode and its upper node with the attached leaf
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Vertebrate
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Vertebrates /ˈvɜːrtᵻbrᵻts/ comprise all species of animals within the subphylum Vertebrata /-ɑː/. Vertebrates represent the majority of the phylum Chordata, with currently about 66,000 species described. Vertebrates include the fish and the jawed vertebrates, which include the cartilaginous fish. A bony fish known as the lobe-finned fishes is included with tetrapods, which are further divided into amphibians, reptiles, mammals. Extant vertebrates range in size from the frog species Paedophryne amauensis, at as little as 7.7 mm, to the blue whale, vertebrates make up less than five percent of all described animal species, the rest are invertebrates, which lack vertebral columns. The vertebrates traditionally include the hagfish, which do not have proper vertebrae due to their loss in evolution, though their closest living relatives, hagfish do, however, possess a cranium. For this reason, the vertebrate subphylum is sometimes referred to as Craniata when discussing morphology, molecular analysis since 1992 has suggested that hagfish are most closely related to lampreys, and so also are vertebrates in a monophyletic sense. Others consider them a group of vertebrates in the common taxon of craniata. The word origin of vertebrate derives from the Latin word vertebratus, the Proto-Indo-European language origins are still unclear. Vertebrate is derived from the vertebra, which refers to any of the bones or segments of the spinal column. All vertebrates are built along the basic body plan, a stiff rod running through the length of the animal, with a hollow tube of nervous tissue above it. In all vertebrates, the mouth is found at, or right below, the remaining part of the body continuing after the anus forms a tail with vertebrae and spinal cord, but no gut. However, a few vertebrates have secondarily lost this anatomy, retaining the notochord into adulthood, such as the sturgeon, jawed vertebrates are typified by paired appendages, but this trait is not required in order for an animal to be a vertebrate. All basal vertebrates breathe with gills, the gills are carried right behind the head, bordering the posterior margins of a series of openings from the pharynx to the exterior. Each gill is supported by a cartilagenous or bony gill arch, the bony fish have three pairs of arches, cartilaginous fish have five to seven pairs, while the primitive jawless fish have seven. The vertebrate ancestor no doubt had more arches than this, as some of their relatives have more than 50 pairs of gills. In amphibians and some primitive fishes, the larvae bear external gills. These are reduced in adulthood, their function taken over by the gills proper in fishes, some amphibians retain the external larval gills in adulthood, the complex internal gill system as seen in fish apparently being irrevocably lost very early in the evolution of tetrapods
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Fish
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A fish is any member of a group of animals that consist of all gill-bearing aquatic craniate animals that lack limbs with digits. They form a group to the tunicates, together forming the olfactores. Included in this definition are the living hagfish, lampreys, and cartilaginous, tetrapods emerged within lobe-finned fishes, so cladistically they are fish as well. However, traditionally fish are rendered obsolete or paraphyletic by excluding the tetrapods, because in this manner the term fish is defined negatively as a paraphyletic group, it is not considered a formal taxonomic grouping in systematic biology. The traditional term pisces is considered a typological, but not a phylogenetic classification, the earliest organisms that can be classified as fish were soft-bodied chordates that first appeared during the Cambrian period. Although they lacked a true spine, they possessed notochords which allowed them to be more agile than their invertebrate counterparts, fish would continue to evolve through the Paleozoic era, diversifying into a wide variety of forms. Many fish of the Paleozoic developed external armor that protected them from predators, the first fish with jaws appeared in the Silurian period, after which many became formidable marine predators rather than just the prey of arthropods. Fish are abundant in most bodies of water and they can be found in nearly all aquatic environments, from high mountain streams to the abyssal and even hadal depths of the deepest oceans. With 33,100 described species, fish exhibit greater species diversity than any group of vertebrates. Fish are an important resource for humans worldwide, especially as food, commercial and subsistence fishers hunt fish in wild fisheries or farm them in ponds or in cages in the ocean. They are also caught by fishers, kept as pets, raised by fishkeepers. Fish have had a role in culture through the ages, serving as deities, religious symbols, fish do not represent a monophyletic group, and therefore the evolution of fish is not studied as a single event. Early fish from the record are represented by a group of small, jawless. Jawless fish lineages are mostly extinct, an extant clade, the lampreys may approximate ancient pre-jawed fish. The first jaws are found in Placodermi fossils, the diversity of jawed vertebrates may indicate the evolutionary advantage of a jawed mouth. It is unclear if the advantage of a hinged jaw is greater biting force, improved respiration, fish may have evolved from a creature similar to a coral-like sea squirt, whose larvae resemble primitive fish in important ways. The first ancestors of fish may have kept the form into adulthood. Fish are a group, that is, any clade containing all fish also contains the tetrapods
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Amphibian
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Amphibians are ectothermic, tetrapod vertebrates of the class Amphibia. They inhabit a variety of habitats, with most species living within terrestrial, fossorial, arboreal or freshwater aquatic ecosystems. Thus amphibians typically start out as larvae living in water, the young generally undergo metamorphosis from larva with gills to an adult air-breathing form with lungs. Amphibians use their skin as a respiratory surface and some small terrestrial salamanders and frogs lack lungs. They are superficially similar to lizards but, along with mammals and birds, reptiles are amniotes, the earliest amphibians evolved in the Devonian period from sarcopterygian fish with lungs and bony-limbed fins, features that were helpful in adapting to dry land. They diversified and became dominant during the Carboniferous and Permian periods, over time, amphibians shrank in size and decreased in diversity, leaving only the modern subclass Lissamphibia. The three modern orders of amphibians are Anura, Urodela, and Apoda, the number of known amphibian species is approximately 7,000, of which nearly 90% are frogs. The smallest amphibian in the world is a frog from New Guinea with a length of just 7.7 mm. The largest living amphibian is the 1.8 m Chinese giant salamander, the study of amphibians is called batrachology, while the study of both reptiles and amphibians is called herpetology. The word amphibian is derived from the Ancient Greek term ἀμφίβιος, the term was initially used as a general adjective for animals that could live on land or in water, including seals and otters. Traditionally, the class Amphibia includes all tetrapod vertebrates that are not amniotes, the numbers of species cited above follows Frost and the total number of known amphibian species is over 7,000, of which nearly 90% are frogs. With the phylogenetic classification, the taxon Labyrinthodontia has been discarded as it is a group without unique defining features apart from shared primitive characteristics. Classification varies according to the phylogeny of the author and whether they use a stem-based or a node-based classification. The phylogeny of Paleozoic amphibians is uncertain, and Lissamphibia may possibly fall within groups, like the Temnospondyli or the Lepospondyli. If the common ancestor of amphibians and amniotes is included in Amphibia, all modern amphibians are included in the subclass Lissamphibia, which is usually considered a clade, a group of species that have evolved from a common ancestor. The three modern orders are Anura, Caudata, and Gymnophiona, although the fossils of several older proto-frogs with primitive characteristics are known, the oldest true frog is Prosalirus bitis, from the Early Jurassic Kayenta Formation of Arizona. It is anatomically similar to modern frogs. The oldest known caecilian is another Early Jurassic species, Eocaecilia micropodia, the earliest salamander is Beiyanerpeton jianpingensis from the Late Jurassic of northeastern China
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Reptile
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Reptiles are tetrapod animals in the class Reptilia, comprising todays turtles, crocodilians, snakes, amphisbaenians, lizards, tuatara, and their extinct relatives. The study of these traditional reptile orders, historically combined with that of amphibians, is called herpetology. Because some reptiles are more related to birds than they are to other reptiles. For this reason, many scientists prefer to consider the birds part of Reptilia as well. Some early examples include the lizard-like Hylonomus and Casineria, in addition to the living reptiles, there are many diverse groups that are now extinct, in some cases due to mass extinction events. In particular, the K–Pg extinction wiped out the pterosaurs, plesiosaurs, ornithischians, and sauropods, as well as species of theropods, crocodyliforms. Modern non-avian reptiles inhabit every continent with the exception of Antarctica, several living subgroups are recognized, Testudines, approximately 400 species, Sphenodontia,1 species, Squamata, over 9,600 species, Crocodilia,25 species, and Aves,10,000 species. Reptiles are tetrapod vertebrates, creatures that either have four limbs or, unlike amphibians, reptiles do not have an aquatic larval stage. As amniotes, reptile eggs are surrounded by membranes for protection and transport, many of the viviparous species feed their fetuses through various forms of placenta analogous to those of mammals, with some providing initial care for their hatchlings. In the 18th century, the reptiles were, from the outset of classification, the terms reptile and amphibian were largely interchangeable, reptile being preferred by the French. Josephus Nicolaus Laurenti was the first to use the term Reptilia for an expanded selection of reptiles. Today, the two groups are commonly treated under the same heading as herptiles. He subsequently proposed the names of Sauropsida and Ichthyopsida for the two groups. In 1866, Haeckel demonstrated that vertebrates could be divided based on their strategies, and that reptiles, birds. The terms Sauropsida and Theropsida were used again in 1916 by E. S, Goodrich to distinguish between lizards, birds, and their relatives on the one hand and mammals and their extinct relatives on the other. Goodrich supported this division by the nature of the hearts and blood vessels in each group, according to Goodrich, both lineages evolved from an earlier stem group, Protosauria in which he included some animals today considered reptile-like amphibians, as well as early reptiles. Watson observed that the first two groups diverged very early in history, so he divided Goodrichs Protosauria between them. He also reinterpreted Sauropsida and Theropsida to exclude birds and mammals, thus his Sauropsida included Procolophonia, Eosuchia, Millerosauria, Chelonia, Squamata, Rhynchocephalia, Crocodilia, thecodonts, non-avian dinosaurs, pterosaurs, ichthyosaurs, and sauropterygians
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Bird
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Birds, a subgroup of Reptiles, are the last living examples of Dinosaurs. Birds live worldwide and range in size from the 5 cm bee hummingbird to the 2.75 m ostrich. They rank as the class of tetrapods with the most living species, at ten thousand. Birds are the closest living relatives of crocodilians, the fossil record indicates that birds evolved from feathered ancestors within the theropod group of saurischian dinosaurs. True birds first appeared during the Cretaceous period, around 100 million years ago, Birds, especially those in the southern continents, survived this event and then migrated to other parts of the world while diversifying during periods of global cooling. Primitive bird-like dinosaurs that lie outside class Aves proper, in the broader group Avialae, have been found dating back to the mid-Jurassic period, around 170 million years ago. Birds have wings which are more or less developed depending on the species, the digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds, have evolved for swimming. Many species annually migrate great distances, Birds are social, communicating with visual signals, calls, and bird songs, and participating in such social behaviours as cooperative breeding and hunting, flocking, and mobbing of predators. The vast majority of species are socially monogamous, usually for one breeding season at a time, sometimes for years. Other species have breeding systems that are polygynous or, rarely, Birds produce offspring by laying eggs which are fertilised through sexual reproduction. They are usually laid in a nest and incubated by the parents, most birds have an extended period of parental care after hatching. Some birds, such as hens, lay eggs even when not fertilised, songbirds, parrots, and other species are popular as pets. Guano is harvested for use as a fertiliser, Birds prominently figure throughout human culture. About 120–130 species have become extinct due to human activity since the 17th century, human activity threatens about 1,200 bird species with extinction, though efforts are underway to protect them. Recreational birdwatching is an important part of the ecotourism industry, the first classification of birds was developed by Francis Willughby and John Ray in their 1676 volume Ornithologiae. Carl Linnaeus modified that work in 1758 to devise the taxonomic classification system currently in use, Birds are categorised as the biological class Aves in Linnaean taxonomy. Phylogenetic taxonomy places Aves in the dinosaur clade Theropoda, Aves and a sister group, the clade Crocodilia, contain the only living representatives of the reptile clade Archosauria
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