118-445: Olenellus is an extinct genus of redlichiid trilobites , with species of average size (about 5 centimetres or 2.0 inches long). It lived during the Botomian and Toyonian stages ( Olenellus -zone), 522 to 510 million years ago , in what is currently North-America, part of the palaeocontinent Laurentia . Olenellus means small Olenus , after a genus belonging to
236-438: A food chain who lose their prey. "Species coextinction is a manifestation of one of the interconnectednesses of organisms in complex ecosystems ... While coextinction may not be the most important cause of species extinctions, it is certainly an insidious one." Coextinction is especially common when a keystone species goes extinct. Models suggest that coextinction is the most common form of biodiversity loss . There may be
354-657: A nautilus to the Royal Society that was more than two feet in diameter, and morphologically distinct from any known living species. Hooke theorized that this was simply because the species lived in the deep ocean and no one had discovered them yet. While he contended that it was possible a species could be "lost", he thought this highly unlikely. Similarly, in 1695, Sir Thomas Molyneux published an account of enormous antlers found in Ireland that did not belong to any extant taxa in that area. Molyneux reasoned that they came from
472-500: A polar climate ( ET ). The climate is generally very dry, with little precipitation, but is considerably wetter in the southeast. Precipitation is much greater in the mountains, and the snowpack continues to melt well into the summer, resulting in high water in July or August. Source: Environment Canada Except for the Arctic Ocean coastal plain and high elevations, most of Yukon is in
590-415: A species or a population is the variety of genetic information in its living members. A large gene pool (extensive genetic diversity ) is associated with robust populations that can survive bouts of intense selection . Meanwhile, low genetic diversity (see inbreeding and population bottlenecks ) reduces the range of adaptions possible. Replacing native with alien genes narrows genetic diversity within
708-436: A viable population for species preservation and possible future reintroduction to the wild, through use of carefully planned breeding programs . The extinction of one species' wild population can have knock-on effects, causing further extinctions. These are also called "chains of extinction". This is especially common with extinction of keystone species . A 2018 study indicated that the sixth mass extinction started in
826-474: A Lazarus species when extant individuals were described in 2019. Attenborough's long-beaked echidna ( Zaglossus attenboroughi ) is an example of a Lazarus species from Papua New Guinea that had last been sighted in 1962 and believed to be possibly extinct, until it was recorded again in November 2023. Some species currently thought to be extinct have had continued speculation that they may still exist, and in
944-616: A boom-and-bust industry. A small amount of natural gas is currently produced in the southeast, but little exploration has been done in other parts of the Yukon. It is believed that there are abundant natural gas fields in the Eagle Plains area along the Dempster Highway and possibly in the Whitehorse area, but distance from pipelines has hampered exploration. Global warming is affecting
1062-495: A cascade of coextinction across the trophic levels . Such effects are most severe in mutualistic and parasitic relationships. An example of coextinction is the Haast's eagle and the moa : the Haast's eagle was a predator that became extinct because its food source became extinct. The moa were several species of flightless birds that were a food source for the Haast's eagle. Extinction as
1180-429: A common ancestor with modern horses. Pseudoextinction is much easier to demonstrate for larger taxonomic groups. A Lazarus taxon or Lazarus species refers to instances where a species or taxon was thought to be extinct, but was later rediscovered. It can also refer to instances where large gaps in the fossil record of a taxon result in fossils reappearing much later, although the taxon may have ultimately become extinct at
1298-399: A fact that was accepted by most scientists. The primary debate focused on whether this turnover caused by extinction was gradual or abrupt in nature. Cuvier understood extinction to be the result of cataclysmic events that wipe out huge numbers of species, as opposed to the gradual decline of a species over time. His catastrophic view of the nature of extinction garnered him many opponents in
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#17328688616551416-473: A few frogs . Yukon is sparsely populated, with about 30,000 inhabitants in a territory almost as large as Spain or Sweden. Population density is 0.06 people per km . Close to three quarters of the population is in the Whitehorse area, and the rest live in a number of other communities . All except Old Crow are accessible by road. The capital, Whitehorse, is also the largest city with more than two thirds of
1534-708: A higher risk of extinction and die out faster than less sexually dimorphic species, the least sexually dimorphic species surviving for millions of years while the most sexually dimorphic species die out within mere thousands of years. Earlier studies based on counting the number of currently living species in modern taxa have shown a higher number of species in more sexually dimorphic taxa which have been interpreted as higher survival in taxa with more sexual selection, but such studies of modern species only measure indirect effects of extinction and are subject to error sources such as dying and doomed taxa speciating more due to splitting of habitat ranges into more small isolated groups during
1652-405: A large range, a lack of individuals of both sexes (in sexually reproducing species), or other reasons. Pinpointing the extinction (or pseudoextinction ) of a species requires a clear definition of that species . If it is to be declared extinct, the species in question must be uniquely distinguishable from any ancestor or daughter species, and from any other closely related species. Extinction of
1770-592: A later point. The coelacanth , a fish related to lungfish and tetrapods , is an example of a Lazarus taxon that was known only from the fossil record and was considered to have been extinct since the end of the Cretaceous Period . In 1938, however, a living specimen was found off the Chalumna River (now Tyolomnqa) on the east coast of South Africa. Calliostoma bullatum , a species of deepwater sea snail originally described from fossils in 1844 proved to be
1888-587: A mathematical model that falls in all positions. By contrast, conservation biology uses the extinction vortex model to classify extinctions by cause. When concerns about human extinction have been raised, for example in Sir Martin Rees ' 2003 book Our Final Hour , those concerns lie with the effects of climate change or technological disaster. Human-driven extinction started as humans migrated out of Africa more than 60,000 years ago. Currently, environmental groups and some governments are concerned with
2006-456: A natural part of the evolutionary process. Only recently have extinctions been recorded and scientists have become alarmed at the current high rate of extinctions . Most species that become extinct are never scientifically documented. Some scientists estimate that up to half of presently existing plant and animal species may become extinct by 2100. A 2018 report indicated that the phylogenetic diversity of 300 mammalian species erased during
2124-441: A new mega-predator or by transporting animals and plants from one part of the world to another. Such introductions have been occurring for thousands of years, sometimes intentionally (e.g. livestock released by sailors on islands as a future source of food) and sometimes accidentally (e.g. rats escaping from boats). In most cases, the introductions are unsuccessful, but when an invasive alien species does become established,
2242-610: A population a higher chance in the short term of surviving an adverse change in conditions. Effects that cause or reward a loss in genetic diversity can increase the chances of extinction of a species. Population bottlenecks can dramatically reduce genetic diversity by severely limiting the number of reproducing individuals and make inbreeding more frequent. Extinction sometimes results for species evolved to specific ecologies that are subjected to genetic pollution —i.e., uncontrolled hybridization , introgression and genetic swamping that lead to homogenization or out-competition from
2360-407: A race of animals to become extinct. A series of fossils were discovered in the late 17th century that appeared unlike any living species. As a result, the scientific community embarked on a voyage of creative rationalization, seeking to understand what had happened to these species within a framework that did not account for total extinction. In October 1686, Robert Hooke presented an impression of
2478-502: A reduction in agricultural productivity. Furthermore, increased erosion contributes to poorer water quality by elevating the levels of sediment and pollutants in rivers and streams. Habitat degradation through toxicity can kill off a species very rapidly, by killing all living members through contamination or sterilizing them. It can also occur over longer periods at lower toxicity levels by affecting life span, reproductive capacity, or competitiveness. Habitat degradation can also take
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#17328688616552596-486: A result of climate change has been confirmed by fossil studies. Particularly, the extinction of amphibians during the Carboniferous Rainforest Collapse , 305 million years ago. A 2003 review across 14 biodiversity research centers predicted that, because of climate change, 15–37% of land species would be "committed to extinction" by 2050. The ecologically rich areas that would potentially suffer
2714-479: A species (or replacement by a daughter species) plays a key role in the punctuated equilibrium hypothesis of Stephen Jay Gould and Niles Eldredge . In ecology , extinction is sometimes used informally to refer to local extinction , in which a species ceases to exist in the chosen area of study, despite still existing elsewhere. Local extinctions may be made good by the reintroduction of individuals of that species taken from other locations; wolf reintroduction
2832-439: A species may come suddenly when an otherwise healthy species is wiped out completely, as when toxic pollution renders its entire habitat unliveable; or may occur gradually over thousands or millions of years, such as when a species gradually loses out in competition for food to better adapted competitors. Extinction may occur a long time after the events that set it in motion, a phenomenon known as extinction debt . Assessing
2950-404: A species or group of species. "Just as each species is unique", write Beverly and Stephen C. Stearns , "so is each extinction ... the causes for each are varied—some subtle and complex, others obvious and simple". Most simply, any species that cannot survive and reproduce in its environment and cannot move to a new environment where it can do so, dies out and becomes extinct. Extinction of
3068-518: A subsequent report, IPBES listed unsustainable fishing, hunting and logging as being some of the primary drivers of the global extinction crisis. In June 2019, one million species of plants and animals were at risk of extinction. At least 571 plant species have been lost since 1750, but likely many more. The main cause of the extinctions is the destruction of natural habitats by human activities, such as cutting down forests and converting land into fields for farming. A dagger symbol (†) placed next to
3186-406: A third on Aishihik Lake . While Yukon is mostly covered with forests, most of the trees are small and take a long time to grow and regenerate because of the dry cold climate. There is a considerable amount of small scale logging , but the only area that can sustain industrial forestry is in the southeast with its wetter climate. However, distance from markets and fluctuating prices have resulted in
3304-472: Is Arctic in territory north of Old Crow , subarctic in the region, between Whitehorse and Old Crow, and humid continental climate south of Whitehorse and in areas close to the British Columbia border. Most of the territory is boreal forest with tundra being the main vegetation zone only in the extreme north and at high elevations. The territory is about the shape of a right triangle, bordering
3422-517: Is also evidence to suggest that this event was preceded by another mass extinction, known as Olson's Extinction . The Cretaceous–Paleogene extinction event (K–Pg) occurred 66 million years ago, at the end of the Cretaceous period; it is best known for having wiped out non-avian dinosaurs , among many other species. According to a 1998 survey of 400 biologists conducted by New York 's American Museum of Natural History , nearly 70% believed that
3540-490: Is also the recipient of airborne pollutants from other parts of the world, especially persistent organic pollutants . Consumption of the liver of certain wild animals and fish is no longer recommended because of these. Locally, mine reclamation and dealing with mine tailings that cause acid mine drainage left over from mine closures is a major problem and is likely to cost hundreds of millions of dollars to clean up. In an effort to encourage natural resource exploration,
3658-444: Is an example of this. Species that are not globally extinct are termed extant . Those species that are extant, yet are threatened with extinction, are referred to as threatened or endangered species . Currently, an important aspect of extinction is human attempts to preserve critically endangered species. These are reflected by the creation of the conservation status "extinct in the wild" (EW) . Species listed under this status by
Olenellus - Misplaced Pages Continue
3776-568: Is at the northern end of the Pacific Flyway . Other than the burbot and northern pike , most of the large fish found in Yukon rivers, lakes and streams are salmonids . Four species of Pacific salmon ( Chinook , sockeye , coho and chum ) breed in Yukon rivers and lakes in the Pacific and Yukon River watersheds. The Yukon River has the longest freshwater migration route of any salmon; Chinook salmon swim over 3,000 kilometres from its mouth in
3894-709: Is common. The northern part of Yukon has continuous permafrost, while it is widespread in the central part. Even the southern Yukon has scattered patches of permafrost. Two major faults , the Denali Fault and the Tintina Fault have created major valleys called trenches : the Shakwak Trench and the Tintina Trench . The Shakwak Trench separates the Kluane ranges from other mountain ranges north of it. The Haines Highway and
4012-585: Is difficult to demonstrate unless one has a strong chain of evidence linking a living species to members of a pre-existing species. For example, it is sometimes claimed that the extinct Hyracotherium , which was an early horse that shares a common ancestor with the modern horse , is pseudoextinct, rather than extinct, because there are several extant species of Equus , including zebra and donkey ; however, as fossil species typically leave no genetic material behind, one cannot say whether Hyracotherium evolved into more modern horse species or merely evolved from
4130-805: Is dominated by the Kluane icefields in Kluane National Park and Reserve , the largest non-polar icefields in the Poles . Kluane National Park also contains eight of Canada's ten highest mountains, including the five highest, all in the Saint Elias Mountains . A number of glaciers flow out of the icefields, including the Logan Glacier , the Hubbard Glacier and the Kaskawulsh Glacier . Permafrost
4248-417: Is estimated as 100 to 1,000 times "background" rates (the average extinction rates in the evolutionary time scale of planet Earth), faster than at any other time in human history, while future rates are likely 10,000 times higher. However, some groups are going extinct much faster. Biologists Paul R. Ehrlich and Stuart Pimm , among others, contend that human population growth and overconsumption are
4366-417: Is estimated that there are currently around 8.7 million species of eukaryotes globally, and possibly many times more if microorganisms , such as bacteria , are included. Notable extinct animal species include non-avian dinosaurs , saber-toothed cats , dodos , mammoths , ground sloths , thylacines , trilobites , golden toads , and passenger pigeons . Through evolution , species arise through
4484-643: Is of aboriginal origin. There is no Inuit population in Yukon, although there was a population along the Arctic Ocean coast within historic times. The Inuit were decimated by disease and disappeared in the 19th century. In 1984, the Government of Canada included the Yukon North Slope within the Inuvialuit Settlement Region under the auspices of the Inuvialuit . The following table presents
4602-753: Is on the Beaufort Sea . Its western boundary is 141° west longitude . Its ragged eastern boundary mostly follows the divide between the Yukon River Basin and the Mackenzie River watershed to the east in the Mackenzie Mountains . Except for the coastal plain on the Beaufort Sea ( Arctic Ocean ) coast, most of Yukon is part of the American Cordillera . The terrain includes mountain ranges , plateaus and river valleys . The southwest
4720-592: Is the destruction of ocean floors by bottom trawling . Diminished resources or introduction of new competitor species also often accompany habitat degradation. Global warming has allowed some species to expand their range, bringing competition to other species that previously occupied that area. Sometimes these new competitors are predators and directly affect prey species, while at other times they may merely outcompete vulnerable species for limited resources. Vital resources including water and food can also be limited during habitat degradation, leading to extinction. In
4838-525: Is the most important determinant of genus extinction at background rates but becomes increasingly irrelevant as mass extinction arises. Limited geographic range is a cause both of small population size and of greater vulnerability to local environmental catastrophes. Extinction rates can be affected not just by population size, but by any factor that affects evolvability , including balancing selection , cryptic genetic variation , phenotypic plasticity , and robustness . A diverse or deep gene pool gives
Olenellus - Misplaced Pages Continue
4956-415: Is the territorial bird and is common everywhere. Other common resident birds include bald eagles ( Haliaeetus leucocephalus ), golden eagles ( Aquila chrysaetos ), gyrfalcon ( Falco rusticolus ) and peregrine falcon ( Falco peregrinus ), five species of grouse ( spruce grouse , blue grouse , ruffed grouse , ptarmigan , and white-tailed ptarmigan ). Many migratory birds breed in the Yukon, as it
5074-746: The Alaska Highway north of Haines Junction are built in the Shakwak Trench. The Tintina Trench bisects the Yukon from northwest to southeast and its edges have rich mineral deposits including the Klondike gold and the lead - zinc deposits near Faro . The volcanoes in Yukon are part of the circle of volcanoes around the Pacific Ocean known as the Pacific Ring of Fire . Yukon includes more than 100 separate volcanic centres that have been active during
5192-532: The American state of Alaska to the west, the Northwest Territories to the east and British Columbia to the south. Yukon covers 482,443 km , of which 474,391 km is land and 8,052 km is water, making it the forty-first largest subnational entity in the world , and, among the fifty largest, the least populous. Yukon is bounded on the south by the 60th parallel of latitude . Its northern coast
5310-808: The Carmacks area. The world's largest known deposit of tungsten is in the Macmillan Pass area in the Mackenzie Mountains near the Northwest Territories border. Non-metallic minerals mined have included jade and barite . The fur trade was very important to the Yukon First Nation economy, but low prices and the impact of animal rights activists have devastated the traditional economy. There are three hydroelectric generating stations in Yukon: one at Schwatka Lake in Whitehorse, another near Mayo and
5428-530: The Carrara Formation , Funeral Mountains , Resting Spring Range , Eagle mountain, Grapevine Mountains , Salt Spring Hills); and in Nevada ( Nevada Test Site , Desert Range ). O. crassimarginatus has been collected in the middle Upper Olenellus -zone of Vermont (Parkers Quarry, Parker Slate, Georgia); and ½ mile South of East Petersburg; 2 miles North of York and Fruitville, 3 miles North of Lancaster (all in
5546-674: The Dempster Highway . Yukon mountain ranges include: Most of the territory is in the watershed of its namesake, the Yukon River , which flows into the Bering Sea . Southern Yukon is dotted with a large number of large, long and narrow glacier-fed alpine lakes , most of which flow into the Yukon River system. The larger lakes include: Teslin Lake , Atlin Lake , Tagish Lake , Marsh Lake , Lake Laberge , Kusawa Lake , Kluane Lake . Bennett Lake on
5664-474: The International Union for Conservation of Nature (IUCN) are not known to have any living specimens in the wild and are maintained only in zoos or other artificial environments. Some of these species are functionally extinct, as they are no longer part of their natural habitat and it is unlikely the species will ever be restored to the wild. When possible, modern zoological institutions try to maintain
5782-545: The Kinzers Shale). O. fowleri has been collected from the final layer of the Upper Olenellus -zone of Nevada (Pioche Formation). O. getzi is found in Upper Olenellus -zone of Pennsylvania (2 miles North of York, and Noah Getz Farm, 1 mile North of Rohrerstown, Kinzers Shale). O. howelli occurs in the final layer of the Upper Olenellus -zone of Nevada (Pioche Formation). O. nevadensis has been collected in
5900-687: The Klondike Gold Rush of 1898. Placer gold is found in many streams and rivers, and there is an active placer mining industry in the Klondike and many other parts of Yukon to this day. Other minerals that have been actively mined include copper in the Whitehorse area, lead and zinc in Faro , silver , zinc and lead in the Mayo / Keno City area, asbestos in Clinton Creek , and copper, gold, and coal in
6018-520: The Klondike Gold Rush trail is a smaller lake flowing into Tagish Lake. Other rivers flow either directly into the Pacific Ocean or directly or indirectly into the Arctic Ocean . The Alsek -Tatshenshini drainage flows directly into the Pacific from southwestern Yukon. A number of rivers in northern Yukon flow directly into the Arctic Ocean. The two main Yukon rivers flowing into the Mackenzie River in
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#17328688616556136-477: The Late Pleistocene could take up to 5 to 7 million years to restore mammal diversity to what it was before the human era. Extinction of a parent species where daughter species or subspecies are still extant is called pseudoextinction or phyletic extinction. Effectively, the old taxon vanishes, transformed ( anagenesis ) into a successor, or split into more than one ( cladogenesis ). Pseudoextinction
6254-679: The Olenellus -zone of Pennsylvania (2 miles North of York, Fruitville; 3 miles North of Lancaster; Getz Quarry; 1 mile North of Rohrerstown; ½ mile South of East Petersburg; all in the Kinzers Shale). O. romensis occurs in the middle Upper Olenellus -zone of Virginia (Rome Formation, Mason Creek, Salem; North-East of Roanoke, near Webster; 2 miles South-West of Blue Ridge Springs, 2 miles South of Max Meadows; Mason Creek, 1 mile east of Salem; ½ mile South-East of Indian Rock; 1 mile East of Cleveland, Alabama; 1½ miles North of Montevallo; 1½ miles West of Montevallo). O. terminatus has been collected from
6372-776: The Olenellus -zone of the Yukon Territory, Canada (Unit 6 of the Upper Illtyd Formation, Wernecke Mountains ). O. puertoblancoensis was found in the Botonian/Toyonian Olenellus -zone of the Caborca Region, Mexico (Buelna Formation, Cerro Rajon) O. robsonensis occurs in the ?Middle Olenellus -zone of British Columbia, Canada (?Upper Mahto Formation, drift block on the slope of the Mural Glacier below Mumm Peak, Near Mount Robson). O. roddyi occurs in
6490-537: The Ptychopariida , to which the type species O. thompsoni was originally assigned. The name Olenus refers to a mythological figure who was turned to stone by the gods. The names of the species have the following derivations. Olenellus is the only genus currently recognised in the subfamily Olenellinae. The sister group called the Mesonacinae consists of the genera Mesonacis and Mesolenellus . "Paedeumias"
6608-515: The Quaternary . The Fort Selkirk Volcanic Field in central Yukon is the northernmost Holocene volcanic field in Canada, including the young active cinder cone , Volcano Mountain . A volcanic field in south-central Yukon is called Alligator Lake volcanic complex . It contains two well-preserved cinder cones that caps a small shield volcano . Lava from the cones travelled north and were erupted at
6726-533: The boreal forest ecoregion . Most mountain peaks and higher elevations are characterized by Alpine tundra while the coastal plain is Arctic coastal tundra . More precisely, according to Environment Canada 's ecozone definitions, southern and central Yukon is part of the Boreal Cordillera Ecozone while the northern forest is part of the Taiga Cordillera Ecozone . The Peel River area in
6844-410: The slender-billed curlew ( Numenius tenuirostris ), not seen since 2007. As long as species have been evolving, species have been going extinct. It is estimated that over 99.9% of all species that ever lived are extinct. The average lifespan of a species is 1–10 million years, although this varies widely between taxa. A variety of causes can contribute directly or indirectly to the extinction of
6962-484: The strata of the Paris basin. They saw alternating saltwater and freshwater deposits, as well as patterns of the appearance and disappearance of fossils throughout the record. From these patterns, Cuvier inferred historic cycles of catastrophic flooding, extinction, and repopulation of the earth with new species. Cuvier's fossil evidence showed that very different life forms existed in the past than those that exist today,
7080-539: The wolverine ( Gulo gulo ), Pacific marten ( Martes caurina ), American ermine ( Mustela richardsonii ), least weasel ( Mustela nivalis ), American mink ( Neogale vison ), and the river otter ( Lontra canadensis ). Other small carnivores present are the Canada lynx ( Lynx canadensis ), red fox ( Vulpes vulpes ) and Arctic fox ( Vulpes lagopus ) along the northern coast. More than 250 species of birds have been sighted in Yukon. The common raven ( Corvus corax )
7198-619: The 20 biodiversity goals laid out by the Aichi Biodiversity Targets in 2010, only 6 were "partially achieved" by the deadline of 2020. The report warned that biodiversity will continue to decline if the status quo is not changed, in particular the "currently unsustainable patterns of production and consumption, population growth and technological developments". In a 2021 report published in the journal Frontiers in Conservation Science , some top scientists asserted that even if
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#17328688616557316-409: The 3rd segment. The base of the spine on the 15th thorax segment is almost as wide as the axis itself. This key is based on Lieberman (1999), which describes only part of the species that are recognized today. Extinct Extinction is the termination of a taxon by the death of its last member . A taxon may become functionally extinct before the death of its last member if it loses
7434-451: The Aichi Biodiversity Targets set for 2020 had been achieved, it would not have resulted in a significant mitigation of biodiversity loss. They added that failure of the global community to reach these targets is hardly surprising given that biodiversity loss is "nowhere close to the top of any country's priorities, trailing far behind other concerns such as employment, healthcare, economic growth, or currency stability." For much of history,
7552-455: The Bering Sea to spawning grounds upstream of Whitehorse . There are also land-locked kokanee ( sockeye salmon ) and rainbow trout . chars are represented by lake trout present in most large Yukon lakes, as well as Dolly Varden , bull trout and Arctic char . The Arctic grayling is ubiquitous, while the lakes have various whitefish and inconnu . There are no reptiles in Yukon, but
7670-605: The Earth is currently in the early stages of a human-caused mass extinction, known as the Holocene extinction . In that survey, the same proportion of respondents agreed with the prediction that up to 20% of all living populations could become extinct within 30 years (by 2028). A 2014 special edition of Science declared there is widespread consensus on the issue of human-driven mass species extinctions. A 2020 study published in PNAS stated that
7788-570: The North American moose and that the animal had once been common on the British Isles . Rather than suggest that this indicated the possibility of species going extinct, he argued that although organisms could become locally extinct, they could never be entirely lost and would continue to exist in some unknown region of the globe. The antlers were later confirmed to be from the extinct deer Megaloceros . Hooke and Molyneux's line of thinking
7906-710: The Northwest Territories are the Liard River in the southeast and the Peel River and its tributaries in the northeast. Most of Yukon has a subarctic climate ( Köppen climate classification Dfc ), characterized by long cold winters and brief warm summers. The airstrip at Snag , 25 kilometres east of Beaver Creek near the Alaska border, experienced the lowest ever temperature measured in North America, −63.0 °C or −81.4 °F on February 3, 1947. The Arctic Ocean coast has
8024-518: The Paris basin, could be formed by a slow rise and fall of sea levels . The concept of extinction was integral to Charles Darwin 's On the Origin of Species , with less fit lineages disappearing over time. For Darwin, extinction was a constant side effect of competition . Because of the wide reach of On the Origin of Species , it was widely accepted that extinction occurred gradually and evenly (a concept now referred to as background extinction ). It
8142-924: The Saint Elias Mountains contain the highest mountains, there are numerous other mountain ranges, from the British Mountains in the far north and the Richardson Mountains in the northeast, both of which are part of the Brooks Range , to the Selwyn Mountains and Mackenzie Mountains in the east, the Cassiar Mountains in the south-east, the Pelly Mountains in the central Yukon, and the Ogilvie Mountains north of Dawson City and along
8260-448: The Santa Fé Railroad, 100 miles East of Barstow, Mohave Desert, probably Latham Shale; Latham Shale – treated as the Bristolia -zonule – Marble Mountains, ½ mile East of Cadiz, and at the Southern end of the Marble Mountains, near Chambless in the Mohave Desert portion of San Bernardino County , as well as from the Latham Shale, near Summit Springs on the West side of the Providence Mountains , San Bernardino County. In California also from
8378-482: The United States government, to force the removal of Native Americans , many of whom relied on the bison for food. Geography of Yukon#Mountain ranges Yukon is in the northwestern corner of Canada and is bordered by Alaska , British Columbia and the Northwest Territories . The sparsely populated territory abounds with natural scenery, snowmelt lakes and perennial white-capped mountains, including many of Canada's highest mountains. The territory's climate
8496-737: The Upper Olenellus -zone, Bristolia -zonule of California (Carrara Formation, Funeral Mountains and Grapevine Mountains); and from the Latham Shale – treated as the Bristolia -zonule – at the South end of the Marble Mountains, near Chambless in the Mohave Desert portion of San Bernardino County. It also occurs in the Bristolia -zonule, Upper Olenellus -zone of Nevada (Carrara Formation, Desert Range, Locality M-5). O. parvifrontatus has been collected in
8614-429: The accumulation of slightly deleterious mutations , then a population will go extinct. Smaller populations have fewer beneficial mutations entering the population each generation, slowing adaptation. It is also easier for slightly deleterious mutations to fix in small populations; the resulting positive feedback loop between small population size and low fitness can cause mutational meltdown . Limited geographic range
8732-500: The capacity to reproduce and recover. Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena such as Lazarus taxa , where a species presumed extinct abruptly "reappears" (typically in the fossil record ) after a period of apparent absence. More than 99% of all species that ever lived on Earth , amounting to over five billion species, are estimated to have died out. It
8850-600: The consequences can be catastrophic. Invasive alien species can affect native species directly by eating them, competing with them, and introducing pathogens or parasites that sicken or kill them; or indirectly by destroying or degrading their habitat. Human populations may themselves act as invasive predators. According to the "overkill hypothesis", the swift extinction of the megafauna in areas such as Australia (40,000 years before present), North and South America (12,000 years before present), Madagascar , Hawaii (AD 300–1000), and New Zealand (AD 1300–1500), resulted from
8968-418: The contemporary extinction crisis "may be the most serious environmental threat to the persistence of civilization, because it is irreversible." Biologist E. O. Wilson estimated in 2002 that if current rates of human destruction of the biosphere continue, one-half of all plant and animal species of life on earth will be extinct in 100 years. More significantly, the current rate of global species extinctions
9086-421: The deliberate destruction of some species, such as dangerous viruses , and the total destruction of other problematic species has been suggested. Other species were deliberately driven to extinction, or nearly so, due to poaching or because they were "undesirable", or to push for other human agendas. One example was the near extinction of the American bison , which was nearly wiped out by mass hunts sanctioned by
9204-403: The endangered wild water buffalo is most threatened with extinction by genetic pollution from the abundant domestic water buffalo ). Such extinctions are not always apparent from morphological (non-genetic) observations. Some degree of gene flow is a normal evolutionary process; nevertheless, hybridization (with or without introgression) threatens rare species' existence. The gene pool of
9322-575: The event of rediscovery would be considered Lazarus species. Examples include the thylacine , or Tasmanian tiger ( Thylacinus cynocephalus ), the last known example of which died in Hobart Zoo in Tasmania in 1936; the Japanese wolf ( Canis lupus hodophilax ), last sighted over 100 years ago; the American ivory-billed woodpecker ( Campephilus principalis ), with the last universally accepted sighting in 1944; and
9440-443: The extinction crisis. According to the International Union for Conservation of Nature (IUCN), 784 extinctions have been recorded since the year 1500, the arbitrary date selected to define "recent" extinctions, up to the year 2004; with many more likely to have gone unnoticed. Several species have also been listed as extinct since 2004. If adaptation increasing population fitness is slower than environmental degradation plus
9558-475: The extinction of species caused by humanity, and they try to prevent further extinctions through a variety of conservation programs. Humans can cause extinction of a species through overharvesting , pollution , habitat destruction , introduction of invasive species (such as new predators and food competitors ), overhunting, and other influences. Explosive, unsustainable human population growth and increasing per capita consumption are essential drivers of
9676-533: The field of zoology , and biology in general, and has also become an area of concern outside the scientific community. A number of organizations, such as the Worldwide Fund for Nature , have been created with the goal of preserving species from extinction. Governments have attempted, through enacting laws, to avoid habitat destruction, agricultural over-harvesting, and pollution . While many human-caused extinctions have been accidental, humans have also engaged in
9794-429: The final layer of the Upper Olenellus -zone of Nevada (Pioche Formation). O. transitans has been collected from the middle Upper Olenellus -zone of Vermont (Parker Slate, Georgia). As with most early trilobites, Olenellus has an almost flat exoskeleton, that is only thinly calcified, and has crescent-shaped eye ridges. As part of the suborder Olenellina, Olenellus lacks dorsal sutures . Like all other members of
9912-435: The form of a physical destruction of niche habitats. The widespread destruction of tropical rainforests and replacement with open pastureland is widely cited as an example of this; elimination of the dense forest eliminated the infrastructure needed by many species to survive. For example, a fern that depends on dense shade for protection from direct sunlight can no longer survive without forest to shelter it. Another example
10030-580: The habitat retreat of taxa approaching extinction. Possible causes of the higher extinction risk in species with more sexual selection shown by the comprehensive fossil studies that rule out such error sources include expensive sexually selected ornaments having negative effects on the ability to survive natural selection , as well as sexual selection removing a diversity of genes that under current ecological conditions are neutral for natural selection but some of which may be important for surviving climate change. There have been at least five mass extinctions in
10148-660: The heaviest losses include the Cape Floristic Region and the Caribbean Basin . These areas might see a doubling of present carbon dioxide levels and rising temperatures that could eliminate 56,000 plant and 3,700 animal species. Climate change has also been found to be a factor in habitat loss and desertification . Studies of fossils following species from the time they evolved to their extinction show that species with high sexual dimorphism , especially characteristics in males that are used to compete for mating, are at
10266-447: The history of life on earth, and four in the last 350 million years in which many species have disappeared in a relatively short period of geological time. A massive eruptive event that released large quantities of tephra particles into the atmosphere is considered to be one likely cause of the " Permian–Triassic extinction event " about 250 million years ago, which is estimated to have killed 90% of species then existing. There
10384-475: The human era since the Late Pleistocene would require 5 to 7 million years to recover. According to the 2019 Global Assessment Report on Biodiversity and Ecosystem Services by IPBES , the biomass of wild mammals has fallen by 82%, natural ecosystems have lost about half their area and a million species are at risk of extinction—all largely as a result of human actions. Twenty-five percent of plant and animal species are threatened with extinction. In
10502-431: The introduced ( or hybrid ) species. Endemic populations can face such extinctions when new populations are imported or selectively bred by people, or when habitat modification brings previously isolated species into contact. Extinction is likeliest for rare species coming into contact with more abundant ones; interbreeding can swamp the rarer gene pool and create hybrids, depleting the purebred gene pool (for example,
10620-525: The latter being proposed by Lieberman. O. thompsoni is found in the middle Upper Olenellus -zone of Vermont ( Franklin County , Parker Slate, Georgia). O. agellus is present in the middle Upper Olenellus -zone of Vermont (Parker Slate, Georgia). O. chiefensis has been collected from the final layer of the Upper Olenellus -zone of Nevada ( Pioche Formation ). O. clarki is found in Upper Olenellus -zone of California (Bristol Mountain, near Cadiz, on
10738-485: The main drivers of the modern extinction crisis. In January 2020, the UN's Convention on Biological Diversity drafted a plan to mitigate the contemporary extinction crisis by establishing a deadline of 2030 to protect 30% of the Earth's land and oceans and reduce pollution by 50%, with the goal of allowing for the restoration of ecosystems by 2050. The 2020 United Nations ' Global Biodiversity Outlook report stated that of
10856-421: The modern understanding of extinction as the end of a species was incompatible with the prevailing worldview. Prior to the 19th century, much of Western society adhered to the belief that the world was created by God and as such was complete and perfect. This concept reached its heyday in the 1700s with the peak popularity of a theological concept called the great chain of being , in which all life on earth, from
10974-490: The name of a species or other taxon normally indicates its status as extinct. Examples of species and subspecies that are extinct include: A species is extinct when the last existing member dies. Extinction therefore becomes a certainty when there are no surviving individuals that can reproduce and create a new generation. A species may become functionally extinct when only a handful of individuals survive, which cannot reproduce due to poor health, age, sparse distribution over
11092-469: The natural course of events, species become extinct for a number of reasons, including but not limited to: extinction of a necessary host, prey or pollinator, interspecific competition , inability to deal with evolving diseases and changing environmental conditions (particularly sudden changes) which can act to introduce novel predators, or to remove prey. Recently in geological time, humans have become an additional cause of extinction of some species, either as
11210-410: The newly emerging school of uniformitarianism . Jean-Baptiste Lamarck , a gradualist and colleague of Cuvier, saw the fossils of different life forms as evidence of the mutable character of species. While Lamarck did not deny the possibility of extinction, he believed that it was exceptional and rare and that most of the change in species over time was due to gradual change. Unlike Cuvier, Lamarck
11328-484: The north more than other parts of the world and Yukon is no exception. While residents might welcome warmer temperatures, the ultimate effects are not known. Higher temperatures would mean more evaporation and drying out an already dry climate, resulting in more forest fires and reducing the biological productivity of boreal forests , whose growth is limited more by lack of moisture than temperature. Also glaciers are likely to melt, and permafrost likely to thaw. Yukon
11446-649: The northeast is in the Taiga Plains Ecozone and the Arctic coast is in the Southern Arctic Ecozone . Black spruce ( Picea mariana ), white spruce ( Picea glauca ), quaking aspen ( Populus tremuloides ) and balsam poplar ( Populus balsamifera ) are found throughout much of the territory. Although relatively uncommon, the Alaska birch ( Betula neoalaskana ) is also found in most areas. The lodgepole pine ( Pinus contorta ) reaches its northern extreme in
11564-399: The original population, thereby increasing the chance of extinction. Habitat degradation is currently the main anthropogenic cause of species extinctions. The main cause of habitat degradation worldwide is agriculture, with urban sprawl , logging, mining, and some fishing practices close behind. The degradation of a species' habitat may alter the fitness landscape to such an extent that
11682-412: The other two genera in the family, Mesolenellus and Mesonacis , because the angle in the back rim of the cephalon is less than 15°, making the head approximately semi-circular. The genal spines are reaching back no further than the 6th thorax segment, making them 4-5 times as long as the most backward lobe of the glabella (occipital ring or L0)1. The thorax is 4-4½ times wider that the axis, measured at
11800-535: The population of most Yukon communities . Note that the Census data represents those people who lived within the community boundaries, while the Yukon Bureau of Statistics (YBS) includes everyone with a postal address in the community. Typically, many people live immediately outside the community boundaries, hence the larger YBS numbers. Notes: Part of Whitehorse Census Agglomeration Includes
11918-466: The population; the second largest is Dawson City , (pop. 1800) which was the capital until 1952. Traditionally, Yukon was inhabited by nomadic Athapaskan -speaking First Nations people who had established extensive trading networks with the Pacific Coast Tlingit . The interior people traded copper , furs and meat for coastal products such as eulachon oil. About 20% of the Yukon population
12036-530: The previous (2002–2011) Yukon Party government led by Dennis Fentie has suspended the application of the Protected Areas Strategy (established by a previous Yukon New Democratic Party government) and has indicated its intention of not creating additional protected areas or parks. The Gwichʼin people of Old Crow are dependent on the Porcupine caribou herd for food and clothing, as are others in
12154-702: The process of speciation —where new varieties of organisms arise and thrive when they are able to find and exploit an ecological niche —and species become extinct when they are no longer able to survive in changing conditions or against superior competition . The relationship between animals and their ecological niches has been firmly established. A typical species becomes extinct within 10 million years of its first appearance, although some species, called living fossils , survive with little to no morphological change for hundreds of millions of years. Mass extinctions are relatively rare events; however, isolated extinctions of species and clades are quite common, and are
12272-410: The relative importance of genetic factors compared to environmental ones as the causes of extinction has been compared to the debate on nature and nurture . The question of whether more extinctions in the fossil record have been caused by evolution or by competition or by predation or by disease or by catastrophe is a subject of discussion; Mark Newman, the author of Modeling Extinction , argues for
12390-712: The same time. Volcanoes in south-western Yukon are part of the Wrangle Volcanic Field , which is related to the subduction of the Pacific Plate beneath the North American Plate at the easternmost end of the Avalanche Trench . Yukon volcanoes include: The Saint Elias mountains are part of the Coast Mountains which range from southern British Columbia to Alaska and cover the southwestern Yukon. While
12508-644: The south, Rocky Mountain goat ( Oreamnos americanus ). Polar bears ( Ursus maritimus ) are found on the Arctic coast. The mule deer ( Odocoileus hermionus ) and its predator, the cougar ( Puma concolor ), are becoming increasingly common in the south, and coyotes ( Canis latrans ) are increasing their range to the northern Yukon. Elk ( Cervus canadensis ) and wood bison ( Bison bison athabascae ) are also present. There are many species of rodents , including squirrels , ground squirrels , lemmings , pikas , beavers , various voles , porcupines , muskrats , etc. Mustelids are also well represented and include
12626-543: The south-central part of the territory, while tamarack ( Larix laricina ) is found in the southeast and the subalpine fir ( Abies lasiocarpa ) is found at higher elevations in the southern part of the territory. The large mammals found throughout the territory include caribou ( Rangifer tarandus , both barren-ground and woodland), moose ( Alces alces ), wolves ( Canis lupus ), grizzly bears ( Ursus arctos horribilis ) and American black bears ( Ursus americanus ). Higher elevation have Dall sheep ( Ovis dalli ) and, in
12744-460: The species is no longer able to survive and becomes extinct. This may occur by direct effects, such as the environment becoming toxic , or indirectly, by limiting a species' ability to compete effectively for diminished resources or against new competitor species. Habitat destruction, particularly the removal of vegetation that stabilizes soil, enhances erosion and diminishes nutrient availability in terrestrial ecosystems. This degradation can lead to
12862-430: The sudden introduction of human beings to environments full of animals that had never seen them before and were therefore completely unadapted to their predation techniques. Coextinction refers to the loss of a species due to the extinction of another; for example, the extinction of parasitic insects following the loss of their hosts. Coextinction can also occur when a species loses its pollinator , or to predators in
12980-403: The superfamily Olenelloide, the eye-ridges emerge from the back of the frontal lobe (L4) of the central area of the cephalon , that is called glabella . Olenellus also shares the typical character of whole family Olenellidae that the frontal (L3) and middle pair (L2) of lateral lobes of the glabella are partially merged. This creates two very typical, isolated slits. It can be distinguished from
13098-412: The tiniest microorganism to God, is linked in a continuous chain. The extinction of a species was impossible under this model, as it would create gaps or missing links in the chain and destroy the natural order. Thomas Jefferson was a firm supporter of the great chain of being and an opponent of extinction, famously denying the extinction of the woolly mammoth on the grounds that nature never allows
13216-555: The total extinction of the dodo and the extirpation of indigenous horses to the British Isles. He similarly argued against mass extinctions , believing that any extinction must be a gradual process. Lyell also showed that Cuvier's original interpretation of the Parisian strata was incorrect. Instead of the catastrophic floods inferred by Cuvier, Lyell demonstrated that patterns of saltwater and freshwater deposits , like those seen in
13334-459: The town and adjoining First Nations settlements of Upper Liard and Two and One-Half Mile Village. Includes both the Village of Teslin and the adjoining reserve Includes both the settlement and the adjoining Reserve Yukon has abundant mineral resources and mining was the mainstay of the economy until recently. Abundant gold was found in the Klondike region leading to
13452-577: The wider scientific community of his theory. Cuvier was a well-regarded geologist, lauded for his ability to reconstruct the anatomy of an unknown species from a few fragments of bone. His primary evidence for extinction came from mammoth skulls found in the Paris basin . Cuvier recognized them as distinct from any known living species of elephant, and argued that it was highly unlikely such an enormous animal would go undiscovered. In 1812, Cuvier, along with Alexandre Brongniart and Geoffroy Saint-Hilaire , mapped
13570-483: Was difficult to disprove. When parts of the world had not been thoroughly examined and charted, scientists could not rule out that animals found only in the fossil record were not simply "hiding" in unexplored regions of the Earth. Georges Cuvier is credited with establishing the modern conception of extinction in a 1796 lecture to the French Institute , though he would spend most of his career trying to convince
13688-430: Was not until 1982, when David Raup and Jack Sepkoski published their seminal paper on mass extinctions, that Cuvier was vindicated and catastrophic extinction was accepted as an important mechanism . The current understanding of extinction is a synthesis of the cataclysmic extinction events proposed by Cuvier, and the background extinction events proposed by Lyell and Darwin. Extinction is an important research topic in
13806-618: Was previously regarded as a genus related to Olenellus or a subgenus being part of Olenellus . Recent analysis shows that there is a group of species formerly assigned to Olenellus (Paedeumias) nested within Olenellus ( O. clarki , O. nevadensis , O. parvofrontatus , O. roddyi and O. transitans ). However, this group is more closely related to the majority of the remainder of Olenellus species than to O. agellus and O. romensis . This implies that either two new monophyletic subgenera need to be erected, or Olenellus (Paedeumias) and Olenellus (Olenellus) need to be dropped as subgenera,
13924-571: Was skeptical that catastrophic events of a scale large enough to cause total extinction were possible. In his geological history of the earth titled Hydrogeologie, Lamarck instead argued that the surface of the earth was shaped by gradual erosion and deposition by water, and that species changed over time in response to the changing environment. Charles Lyell , a noted geologist and founder of uniformitarianism , believed that past processes should be understood using present day processes. Like Lamarck, Lyell acknowledged that extinction could occur, noting
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