Amphibians are ectothermic, tetrapod vertebrates of the class Amphibia. Modern amphibians are all Lissamphibia, they inhabit a wide variety of habitats, with most species living within terrestrial, arboreal or freshwater aquatic ecosystems. Thus amphibians start out as larvae living in water, but some species have developed behavioural adaptations to bypass this; the young undergo metamorphosis from larva with gills to an adult air-breathing form with lungs. Amphibians use their skin as a secondary respiratory surface and some small terrestrial salamanders and frogs lack lungs and rely on their skin, they are superficially similar to lizards but, along with mammals and birds, reptiles are amniotes and do not require water bodies in which to breed. With their complex reproductive needs and permeable skins, amphibians are ecological indicators; 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, but were displaced by reptiles and other vertebrates. Over time, amphibians shrank in size and decreased in diversity, leaving only the modern subclass Lissamphibia; the three modern orders of amphibians are Anura and Apoda. The number of known amphibian species is 8,000, 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, but this is dwarfed by the extinct 9 m Prionosuchus from the middle Permian of Brazil. 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, which means "both kinds of life", ἀμφί meaning "of both kinds" and βιος meaning "life". The term was 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. Amphibia in its widest sense was divided into three subclasses, two of which are extinct: Subclass Lepospondyli† Subclass Temnospondyli† Subclass Lissamphibia Salientia: Jurassic to present—6,200 current species in 53 families Caudata: Jurassic to present—652 current species in 9 families Gymnophiona: Jurassic to present—192 current species in 10 families The actual number of species in each group depends on the taxonomic classification followed; the two most common systems are the classification adopted by the website AmphibiaWeb, University of California and the classification by herpetologist Darrel Frost and the American Museum of Natural History, available as the online reference database "Amphibian Species of the World". The numbers of species cited above follows Frost and the total number of known amphibian species as of March 31, 2019 is 8,000, of which nearly 90% are frogs. With the phylogenetic classification, the taxon Labyrinthodontia has been discarded as it is a polyparaphyletic group without unique defining features apart from shared primitive characteristics.
Classification varies according to the preferred phylogeny of the author and whether they use a stem-based or a node-based classification. Traditionally, amphibians as a class are defined as all tetrapods with a larval stage, while the group that includes the common ancestors of all living amphibians and all their descendants is called Lissamphibia; the phylogeny of Paleozoic amphibians is uncertain, Lissamphibia may fall within extinct groups, like the Temnospondyli or the Lepospondyli, in some analyses in the amniotes. This means that advocates of phylogenetic nomenclature have removed a large number of basal Devonian and Carboniferous amphibian-type tetrapod groups that were placed in Amphibia in Linnaean taxonomy, included them elsewhere under cladistic taxonomy. If the common ancestor of amphibians and amniotes is included in Amphibia, it becomes a paraphyletic group. All modern amphibians are included in the subclass Lissamphibia, considered a clade, a group of species that have evolved from a common ancestor.
The three modern orders are Anura and Gymnophiona. It has been suggested that salamanders arose separately from a Temnospondyl-like ancestor, that caecilians are the sister group of the advanced reptiliomorph amphibians, thus of amniotes. 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 from Arizona; the earliest salamander is Beiyanerpeton jianpingensis from the Late Jurassic of northeastern China. Authorities disagree as to whether Salientia is a superorder that includes the order Anura, or whether
Xenopus is a genus of aquatic frogs native to sub-Saharan Africa. Twenty species are described within it; the two best-known species of this genus are Xenopus laevis and Xenopus tropicalis, which are studied as model organisms for developmental biology, cell biology, toxicology and for modelling human disease and birth defects. The genus is known for its polyploidy, with some species having up to 12 sets of chromosomes. All species of Xenopus have flattened, somewhat egg-shaped and streamlined bodies, slippery skin; the frog's skin is smooth, but with a lateral line sensory organ. The frogs are all excellent swimmers and have powerful webbed toes, though the fingers lack webbing. Three of the toes on each foot have conspicuous black claws; the frog's eyes are on top of the head. The pupils are circular, they have tongues or eardrums. Unlike most amphibians, they have no haptoglobin in their blood. Xenopus species are aquatic, though they have been observed migrating on land to nearby bodies of water during times of drought or in heavy rain.
They are found in lakes, swamps, potholes in streams, man-made reservoirs. Adult frogs are both predators and scavengers, since their tongues are unusable, the frogs use their small fore limbs to aid in the feeding process. Since they lack vocal sacs, they make clicks underwater. Males establish a hierarchy of social dominance in which one male has the right to make the advertisement call; the females of many species produce a release call, Xenopus laevis females produce an additional call when sexually receptive and soon to lay eggs. The Xenopus species are active during the twilight hours. During breeding season, the males develop ridge-like nuptial pads on their fingers to aid in grasping the female; the frogs' mating embrace is inguinal. Like many other anurans, they are used in laboratory as research subjects. Xenopus embryos and eggs are a popular model system for a wide variety of biological studies; this animal is used because of its powerful combination of experimental tractability and close evolutionary relationship with humans, at least compared to many model organisms.
Xenopus has long been an important tool for in vivo studies in molecular and developmental biology of vertebrate animals. However, the wide breadth of Xenopus research stems from the additional fact that cell-free extracts made from Xenopus are a premier in vitro system for studies of fundamental aspects of cell and molecular biology. Thus, Xenopus is the only vertebrate model system that allows for high-throughput in vivo analyses of gene function and high-throughput biochemistry. Furthermore, Xenopus oocytes are a leading system for studies of ion transport and channel physiology. Xenopus is a unique system for analyses of genome evolution and whole genome duplication in vertebrates, as different Xenopus species form a ploidy series formed by interspecific hybridization. Xenbase is the Model Organism Database for both Xenopus Xenopus tropicalis. In 1931, Lancelot Hogben noted that Xenopus laevis females ovulated when injected with the urine of pregnant women; this led to a pregnancy test, refined by South African researchers Hillel Abbe Shapiro and Harry Zwarenstein.
A female Xenopus frog injected with a woman's urine was put in a jar with a little water. If eggs were in the water a day it meant the woman was pregnant. Four years after the first Xenopus test, Zwarenstein's colleague, Dr Louis Bosman, reported that the test was accurate in more than 99% of cases. From the 1930s to the 1950s, thousands of frogs were exported across the world for use in these pregnancy tests. All modes of Xenopus research are used in direct studies of human disease genes and to study the basic science underlying initiation and progression of cancer. Xenopus embryos for in vivo studies of human disease gene function: Xenopus embryos are large and manipulated, moreover, thousands of embryos can be obtained in a single day. Indeed, Xenopus was the first vertebrate animal for which methods were developed to allow rapid analysis of gene function using misexpression. Injection of mRNA in Xenopus that led to the cloning of interferon. Moreover, the use of morpholino-antisense oligonucleotides for gene knockdowns in vertebrate embryos, now used, was first developed by Janet Heasman using Xenopus.
In recent years, these approaches have played in important role in studies of human disease genes. The mechanism of action for several genes mutated in human cystic kidney disorders have been extensively studied in Xenopus embryos, shedding new light on the link between these disorders and Wnt signaling. Xenopus embryos have provided a rapid test bed for validating newly discovered disease genes. For example, studies in Xenopus confirmed and elucidated the role of PYCR1 in cutis laxa with progeroid features. Transgenic Xenopus for studying transcriptional regulation of human disease genes: Xenopus embryos develop so transgenesis in Xenopus is a rapid and effective method for analyzing genomic regulatory sequences. In a recent study, mutations in the SMAD7 locus were revealed to associate with human colorectal cancer; the mutations lay in
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present. As with other older geologic periods, the rock beds that define the epoch are well identified but the exact dates of the start and end of the epoch are uncertain; the name Oligocene was coined in 1854 by the German paleontologist Heinrich Ernst Beyrich. The Oligocene is followed by the Miocene Epoch; the Oligocene is the final epoch of the Paleogene Period. The Oligocene is considered an important time of transition, a link between the archaic world of the tropical Eocene and the more modern ecosystems of the Miocene. Major changes during the Oligocene included a global expansion of grasslands, a regression of tropical broad leaf forests to the equatorial belt; the start of the Oligocene is marked by a notable extinction event called the Grande Coupure. By contrast, the Oligocene–Miocene boundary is not set at an identified worldwide event but rather at regional boundaries between the warmer late Oligocene and the cooler Miocene.
Oligocene faunal stages from youngest to oldest are: The Paleogene Period general temperature decline is interrupted by an Oligocene 7-million-year stepwise climate change. A deeper 8.2 °C, 400,000-year temperature depression leads the 2 °C, seven-million-year stepwise climate change 33.5 Ma. The stepwise climate change began 32.5 Ma and lasted through to 25.5 Ma, as depicted in the PaleoTemps chart. The Oligocene climate change was a global increase in ice volume and a 55 m decrease in sea level with a related temperature depression; the 7-million-year depression abruptly terminated within 1–2 million years of the La Garita Caldera eruption at 28–26 Ma. A deep 400,000-year glaciated Oligocene Miocene boundary event is recorded at McMurdo Sound and King George Island. During this epoch, the continents continued to drift toward their present positions. Antarctica became more isolated and developed an ice cap. Mountain building in western North America continued, the Alps started to rise in Europe as the African plate continued to push north into the Eurasian plate, isolating the remnants of the Tethys Sea.
A brief marine incursion marks the early Oligocene in Europe. Marine fossils from the Oligocene are rare in North America. There appears to have been a land bridge in the early Oligocene between North America and Europe, since the faunas of the two regions are similar. Sometime during the Oligocene, South America was detached from Antarctica and drifted north towards North America, it allowed the Antarctic Circumpolar Current to flow cooling the Antarctic continent. Angiosperms continued their expansion throughout the world as tropical and sub-tropical forests were replaced by temperate deciduous forests. Open plains and deserts became more common and grasses expanded from their water-bank habitat in the Eocene moving out into open tracts; however at the end of the period, grass was not quite common enough for modern savannas. In North America, subtropical species dominated with cashews and lychee trees present, temperate trees such as roses and pines were common; the legumes spread, while sedges and ferns continued their ascent.
More open landscapes allowed animals to grow to larger sizes than they had earlier in the Paleocene epoch 30 million years earlier. Marine faunas became modern, as did terrestrial vertebrate fauna on the northern continents; this was more as a result of older forms dying out than as a result of more modern forms evolving. Many groups, such as equids, rhinos and camelids, became more able to run during this time, adapting to the plains that were spreading as the Eocene rainforests receded; the first felid, originated in Asia during the late Oligocene and spread to Europe. South America was isolated from the other continents and evolved a quite distinct fauna during the Oligocene; the South American continent became home to strange animals such as pyrotheres and astrapotheres, as well as litopterns and notoungulates. Sebecosuchians, terror birds, carnivorous metatheres, like the borhyaenids remained the dominant predators. Brontotheres died out in the Earliest Oligocene, creodonts died out outside Africa and the Middle East at the end of the period.
Multituberculates, an ancient lineage of primitive mammals that originated back in the Jurassic became extinct in the Oligocene, aside from the gondwanatheres. The Oligocene was home to a wide variety of strange mammals. A good example of this would be the White River Fauna of central North America, which were a semiarid prairie home to many different types of endemic mammals, including entelodonts like Archaeotherium, running rhinoceratoids, three-toed equids, nimravids and early canids like Hesperocyon. Merycoidodonts, an endemic American group, were diverse during this time. In Asia during the Oligocene, a group of running rhinoceratoids gave rise to the indricotheres, like Paraceratherium, which were the largest land mammals to walk the Earth; the marine animals of Oligocene oceans resembled today's fauna, such as the bivalves. Calcareous cirratulids appeared in the Oligocene; the fossil record of marine mammals is a little spotty during this time, not as well known as the Eocene o
University of Alberta
The University of Alberta is a public research university located in Edmonton, Canada. It was founded in 1908 by Alexander Cameron Rutherford, the first premier of Alberta, Henry Marshall Tory, its first president, its enabling legislation is the Post-secondary Learning Act. The university is considered a “Comprehensive academic and research university”, which means that it offers a range of academic and professional programs, which lead to undergraduate and graduate level credentials, have a strong research focus; the university comprises four campuses in Edmonton, the Augustana Campus in Camrose, a staff centre in downtown Calgary. The original north campus consists of 150 buildings covering 50 city blocks on the south rim of the North Saskatchewan River valley, directly across from downtown Edmonton. 39,000 students from Canada and 150 other countries participate in 400 programs in 18 faculties. The University of Alberta is a major economic driver in Alberta; the university's impact on the Alberta economy is an estimated $12.3 billion annually, or five per cent of the province's gross domestic product.
The University of Alberta is a leading institution for the study of Ukraine and is home to the Canadian Institute of Ukrainian Studies. The University of Alberta has graduated more than 275,000 alumni, including Governor General Roland Michener; the university is a member of the Alberta Rural Development Network, the Association for the Advancement of Sustainability in Higher Education and the Sustainability Tracking, Assessment & Rating System. The University of Alberta, a single, public provincial university, was chartered in 1906 in Edmonton, Alberta with the University Act in the first session of the new Legislative Assembly, with Premier Alexander C. Rutherford as its sponsor; the university was modelled on the American state university, with an emphasis on extension work and applied research. The governance was modelled on Ontario's University of Toronto Act of 1906: a bicameral system consisting of a senate responsible for academic policy, a board of governors controlling financial policy and having formal authority in all other matters.
The president, appointed by the board, was to provide a link between the two bodies and perform institutional leadership. Heated wrangling took place between the cities of Calgary and Edmonton over the location of the provincial capital and of the university, it was stated that the capital would be north of the North Saskatchewan River and that the university would be in a city south of it. The city of Edmonton became the capital and the then-separate city of Strathcona on the south bank of the river, where Premier Alexander Rutherford lived, was granted the university; when the two cities were amalgamated in 1912, Edmonton became both the political and academic capital. With Henry Marshall Tory as its first president, the University of Alberta started operation in 1908. Forty-five students attended classes in English and modern languages, on the top floor of the Queen Alexandra Elementary School in Strathcona, while the first campus building, Athabasca Hall, was under construction. In a letter to Alexander Cameron Rutherford in early 1906, while he was in the process of setting up McGill University College in Vancouver, Tory wrote, "If you take any steps in the direction of a working University and wish to avoid the mistakes of the past, mistakes which have fearfully handicapped other institutions, you should start on a teaching basis."Under Tory's guidance, the early years were marked by recruitment of professors and construction of the first campus buildings.
Today, he has a building named after him. Percy Erskine Nobbs & Frank Darling designed the master plan for the University of Alberta in 1909–10. Nobbs designed the Arts Building and Power House. With Cecil S. Burgess, Nobbs designed the Provincial College of Medicine. Architect Herbert Alton Magoon designed several buildings on campus, including St. Stephen's Methodist College and the residence for professor Rupert C. Lodge; the University of Alberta awarded its first degrees in 1912, the same year it established the Department of Extension. The Faculty of Medicine was established the following year, the Faculty of Agriculture began in 1915, but along with these early milestones came the First World War and the global influenza pandemic of 1918, whose toll on the university resulted in a two-month suspension of classes in the fall of 1918. Despite these setbacks, the university continued to grow. By 1920, it had two schools, it awarded a range of degrees: Bachelor of Arts, Bachelor of Science, Bachelor of Science in Agriculture, Bachelor of Laws, Bachelor of Pharmacy, Bachelor of Divinity, Master of Arts, Master of Science, Doctor of Laws.
There were 851 male students and 251 female students, 171 academic staff, including 14 women. The Breton Soil Plots were established at the faculty of agriculture from 1929 – present to provide agricultural research on fertilization, crop rotations and farming practices on Gray-Luvisolic soils, which cover many regions in western Canada; the University of Alberta spearheaded an extraordinary rate of volunteerism in the Province of Alberta to the First World War from its medical faculty. Experience gained was used by returning veteran
The Pleistocene is the geological epoch which lasted from about 2,588,000 to 11,700 years ago, spanning the world's most recent period of repeated glaciations. The end of the Pleistocene corresponds with the end of the last glacial period and with the end of the Paleolithic age used in archaeology; the Pleistocene is the first epoch of the Quaternary Period or sixth epoch of the Cenozoic Era. In the ICS timescale, the Pleistocene is divided into four stages or ages, the Gelasian, Middle Pleistocene and Upper Pleistocene. In addition to this international subdivision, various regional subdivisions are used. Before a change confirmed in 2009 by the International Union of Geological Sciences, the time boundary between the Pleistocene and the preceding Pliocene was regarded as being at 1.806 million years Before Present, as opposed to the accepted 2.588 million years BP: publications from the preceding years may use either definition of the period. Charles Lyell introduced the term "Pleistocene" in 1839 to describe strata in Sicily that had at least 70% of their molluscan fauna still living today.
This distinguished it from the older Pliocene epoch, which Lyell had thought to be the youngest fossil rock layer. He constructed the name "Pleistocene" from the Greek πλεῖστος, pleīstos, "most", καινός, kainós, "new"; the Pleistocene has been dated from 2.588 million to 11,700 years BP with the end date expressed in radiocarbon years as 10,000 carbon-14 years BP. It covers most of the latest period of repeated glaciation, up to and including the Younger Dryas cold spell; the end of the Younger Dryas has been dated to about 9640 BC. The end of the Younger Dryas is the official start of the current Holocene Epoch. Although it is considered an epoch, the Holocene is not different from previous interglacial intervals within the Pleistocene, it was not until after the development of radiocarbon dating, that Pleistocene archaeological excavations shifted to stratified caves and rock-shelters as opposed to open-air river-terrace sites. In 2009 the International Union of Geological Sciences confirmed a change in time period for the Pleistocene, changing the start date from 1.806 to 2.588 million years BP, accepted the base of the Gelasian as the base of the Pleistocene, namely the base of the Monte San Nicola GSSP.
The IUGS has yet to approve a type section, Global Boundary Stratotype Section and Point, for the upper Pleistocene/Holocene boundary. The proposed section is the North Greenland Ice Core Project ice core 75° 06' N 42° 18' W; the lower boundary of the Pleistocene Series is formally defined magnetostratigraphically as the base of the Matuyama chronozone, isotopic stage 103. Above this point there are notable extinctions of the calcareous nanofossils: Discoaster pentaradiatus and Discoaster surculus; the Pleistocene covers the recent period of repeated glaciations. The name Plio-Pleistocene has, in the past, been used to mean the last ice age; the revised definition of the Quaternary, by pushing back the start date of the Pleistocene to 2.58 Ma, results in the inclusion of all the recent repeated glaciations within the Pleistocene. The modern continents were at their present positions during the Pleistocene, the plates upon which they sit having moved no more than 100 km relative to each other since the beginning of the period.
According to Mark Lynas, the Pleistocene's overall climate could be characterized as a continuous El Niño with trade winds in the south Pacific weakening or heading east, warm air rising near Peru, warm water spreading from the west Pacific and the Indian Ocean to the east Pacific, other El Niño markers. Pleistocene climate was marked by repeated glacial cycles in which continental glaciers pushed to the 40th parallel in some places, it is estimated. In addition, a zone of permafrost stretched southward from the edge of the glacial sheet, a few hundred kilometres in North America, several hundred in Eurasia; the mean annual temperature at the edge of the ice was −6 °C. Each glacial advance tied up huge volumes of water in continental ice sheets 1,500 to 3,000 metres thick, resulting in temporary sea-level drops of 100 metres or more over the entire surface of the Earth. During interglacial times, such as at present, drowned coastlines were common, mitigated by isostatic or other emergent motion of some regions.
The effects of glaciation were global. Antarctica was ice-bound throughout the Pleistocene as well as the preceding Pliocene; the Andes were covered in the south by the Patagonian ice cap. There were glaciers in New Tasmania; the current decaying glaciers of Mount Kenya, Mount Kilimanjaro, the Ruwenzori Range in east and central Africa were larger. Glaciers existed to the west in the Atlas mountains. In the northern hemisphere, many glaciers fused into one; the Cordilleran ice sheet covered the North American northwest. The Fenno-Scandian ice sheet rested including much of Great Britain. Scattered domes stretched across Siberi
The Pliocene Epoch is the epoch in the geologic timescale that extends from 5.333 million to 2.58 million years BP. It is the youngest epoch of the Neogene Period in the Cenozoic Era; the Pliocene is followed by the Pleistocene Epoch. Prior to the 2009 revision of the geologic time scale, which placed the four most recent major glaciations within the Pleistocene, the Pliocene included the Gelasian stage, which lasted from 2.588 to 1.806 million years ago, is now included in the Pleistocene. As with other older geologic periods, the geological strata that define the start and end are well identified but the exact dates of the start and end of the epoch are uncertain; the boundaries defining the Pliocene are not set at an identified worldwide event but rather at regional boundaries between the warmer Miocene and the cooler Pliocene. The upper boundary was set at the start of the Pleistocene glaciations. Charles Lyell gave the Pliocene its name in Principles of Geology; the word pliocene comes from the Greek words πλεῖον and καινός and means "continuation of the recent", referring to the modern marine mollusc fauna.
H. W. Fowler called the term Pliocene a "regrettable barbarism" and an indication that "a good classical scholar" such as Lyell should have requested a philologist's help when coining words. To summarize the usage of these "regrettable barbarisms" in the labelling of the Cenozoic era: with the understanding that these are all new relative to the Mesozoic and Paleozoic eras. In the official timescale of the ICS, the Pliocene is subdivided into two stages. From youngest to oldest they are: Piacenzian Zanclean The Piacenzian is sometimes referred to as the Late Pliocene, whereas the Zanclean is referred to as the Early Pliocene. In the system of North American Land Mammal Ages include Hemphillian, Blancan; the Blancan extends forward into the Pleistocene. South American Land Mammal Ages include Montehermosan and Uquian. In the Paratethys area the Pliocene contains the Romanian stages; as usual in stratigraphy, there are many other local subdivisions in use. In Britain the Pliocene is divided into the following stages: Gedgravian, Pre-Ludhamian, Thurnian, Bramertonian or Antian, Pre-Pastonian or Baventian and Beestonian.
In the Netherlands the Pliocene is divided into these stages: Brunssumian C, Reuverian A, Reuverian B, Reuverian C, Tiglian A, Tiglian B, Tiglian C1-4b, Tiglian C4c, Tiglian C5, Tiglian C6 and Eburonian. The exact correlations between these local stages and the ICS stages is still a matter of detail; the global average temperature in the mid-Pliocene was 2–3 °C higher than today, carbon dioxide levels were the same as today, global sea level was 25 m higher. The northern hemisphere ice sheet was ephemeral before the onset of extensive glaciation over Greenland that occurred in the late Pliocene around 3 Ma; the formation of an Arctic ice cap is signaled by an abrupt shift in oxygen isotope ratios and ice-rafted cobbles in the North Atlantic and North Pacific ocean beds. Mid-latitude glaciation was underway before the end of the epoch; the global cooling that occurred during the Pliocene may have spurred on the disappearance of forests and the spread of grasslands and savannas. Continents continued to drift, moving from positions as far as 250 km from their present locations to positions only 70 km from their current locations.
South America became linked to North America through the Isthmus of Panama during the Pliocene, making possible the Great American Interchange and bringing a nearly complete end to South America's distinctive large marsupial predator and native ungulate faunas. The formation of the Isthmus had major consequences on global temperatures, since warm equatorial ocean currents were cut off and an Atlantic cooling cycle began, with cold Arctic and Antarctic waters dropping temperatures in the now-isolated Atlantic Ocean. Africa's collision with Europe formed the Mediterranean Sea, cutting off the remnants of the Tethys Ocean; the border between the Miocene and the Pliocene is the time of the Messinian salinity crisis. Sea level changes exposed the land bridge between Asia. Pliocene marine rocks are well exposed in the Mediterranean and China. Elsewhere, they are exposed near shores. During the Pliocene parts of southern Norway and southern Sweden, near sea level rose. In Norway this rise elevated the Hardangervidda plateau to 1200 m in the Early Pliocene.
In Southern Sweden similar movements elevated the South Swedish highlands leading to a deflection of the ancient Eridanos river from its original path across south-central Sweden into a course south of Sweden. The change to a cooler, seasonal climate had considerable impacts on Pliocene vegetation, reducing tropical species worldwide. Deciduous forests proliferated, coniferous forests and tundra covered much of the north, grasslands spread on all continents. Tropical forests were limited to a tight band around the equator, in addition to dry savannahs, deserts appeared in Asia and Africa. Both marine and co
Russia the Russian Federation, is a transcontinental country in Eastern Europe and North Asia. At 17,125,200 square kilometres, Russia is by far or by a considerable margin the largest country in the world by area, covering more than one-eighth of the Earth's inhabited land area, the ninth most populous, with about 146.77 million people as of 2019, including Crimea. About 77 % of the population live in the European part of the country. Russia's capital, Moscow, is one of the largest cities in the world and the second largest city in Europe. Extending across the entirety of Northern Asia and much of Eastern Europe, Russia spans eleven time zones and incorporates a wide range of environments and landforms. From northwest to southeast, Russia shares land borders with Norway, Estonia, Latvia and Poland, Ukraine, Azerbaijan, China and North Korea, it shares maritime borders with Japan by the Sea of Okhotsk and the U. S. state of Alaska across the Bering Strait. However, Russia recognises two more countries that border it, Abkhazia and South Ossetia, both of which are internationally recognized as parts of Georgia.
The East Slavs emerged as a recognizable group in Europe between the 3rd and 8th centuries AD. Founded and ruled by a Varangian warrior elite and their descendants, the medieval state of Rus arose in the 9th century. In 988 it adopted Orthodox Christianity from the Byzantine Empire, beginning the synthesis of Byzantine and Slavic cultures that defined Russian culture for the next millennium. Rus' disintegrated into a number of smaller states; the Grand Duchy of Moscow reunified the surrounding Russian principalities and achieved independence from the Golden Horde. By the 18th century, the nation had expanded through conquest and exploration to become the Russian Empire, the third largest empire in history, stretching from Poland on the west to Alaska on the east. Following the Russian Revolution, the Russian Soviet Federative Socialist Republic became the largest and leading constituent of the Union of Soviet Socialist Republics, the world's first constitutionally socialist state; the Soviet Union played a decisive role in the Allied victory in World War II, emerged as a recognized superpower and rival to the United States during the Cold War.
The Soviet era saw some of the most significant technological achievements of the 20th century, including the world's first human-made satellite and the launching of the first humans in space. By the end of 1990, the Soviet Union had the world's second largest economy, largest standing military in the world and the largest stockpile of weapons of mass destruction. Following the dissolution of the Soviet Union in 1991, twelve independent republics emerged from the USSR: Russia, Belarus, Uzbekistan, Azerbaijan, Kyrgyzstan, Tajikistan and the Baltic states regained independence: Estonia, Lithuania, it is governed as a federal semi-presidential republic. Russia's economy ranks as the twelfth largest by nominal GDP and sixth largest by purchasing power parity in 2018. Russia's extensive mineral and energy resources are the largest such reserves in the world, making it one of the leading producers of oil and natural gas globally; the country is one of the five recognized nuclear weapons states and possesses the largest stockpile of weapons of mass destruction.
Russia is a great power as well as a regional power and has been characterised as a potential superpower. It is a permanent member of the United Nations Security Council and an active global partner of ASEAN, as well as a member of the Shanghai Cooperation Organisation, the G20, the Council of Europe, the Asia-Pacific Economic Cooperation, the Organization for Security and Co-operation in Europe, the World Trade Organization, as well as being the leading member of the Commonwealth of Independent States, the Collective Security Treaty Organization and one of the five members of the Eurasian Economic Union, along with Armenia, Belarus and Kyrgyzstan; the name Russia is derived from Rus', a medieval state populated by the East Slavs. However, this proper name became more prominent in the history, the country was called by its inhabitants "Русская Земля", which can be translated as "Russian Land" or "Land of Rus'". In order to distinguish this state from other states derived from it, it is denoted as Kievan Rus' by modern historiography.
The name Rus itself comes from the early medieval Rus' people, Swedish merchants and warriors who relocated from across the Baltic Sea and founded a state centered on Novgorod that became Kievan Rus. An old Latin version of the name Rus' was Ruthenia applied to the western and southern regions of Rus' that were adjacent to Catholic Europe; the current name of the country, Россия, comes from the Byzantine Greek designation of the Rus', Ρωσσία Rossía—spelled Ρωσία in Modern Greek. The standard way to refer to citizens of Russia is rossiyane in Russian. There are two Russian words which are commonly