Extinction

In biology, extinction is the termination of an organism or of a group of organisms (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point. 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 percent of all species, amounting to over five billion species,[1] that ever lived on Earth are estimated to have died out.[2][3][4] Estimates on the number of Earth's current species range from 10 million to 14 million,[5] of which about 1.2 million have been documented and over 86 percent have not yet been described.[6] In 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described.[7]

Through evolution, species arise through 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.[8] A typical species becomes extinct within 10 million years of its first appearance,[4] although some species, called living fossils, survive with virtually no morphological change for hundreds of millions of years.

Mass extinctions are relatively rare events; however, isolated extinctions are quite common. Only recently have extinctions been recorded and scientists have become alarmed at the current high rate of extinctions.[9][10][11][12] 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.[13] A 2018 report indicated that the phylogenetic diversity of 300 mammalian species erased during the human era since the Late Pleistocene would require 5 to 7 million years to recover.[14]

A dagger symbol (†) placed next to the name of a species or other taxon normally indicates its status as extinct.

Conservation status
Bufo periglenes, the Golden Toad, was last recorded on May 15, 1989
Extinct
Threatened
Lower Risk

Other categories

Related topics

IUCN Red List category abbreviations (version 3.1, 2001)

NatureServe category abbreviations

Definition

LepidodendronOhio
External mold of the extinct Lepidodendron from the Upper Carboniferous of Ohio[15]

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 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 a species (or replacement by a daughter species) plays a key role in the punctuated equilibrium hypothesis of Stephen Jay Gould and Niles Eldredge.[16]

Various dinosaurs
Skeleton of various extinct dinosaurs; some other dinosaur lineages still flourish in the form of birds

In ecology, extinction is often used informally to refer to local extinction, in which a species ceases to exist in the chosen area of study, but may still exist elsewhere. This phenomenon is also known as extirpation. Local extinctions may be followed by a replacement of the species taken from other locations; wolf reintroduction is an example of this. Species which are not extinct are termed extant. Those that are extant but threatened by extinction are referred to as threatened or endangered species.

Edwards' Dodo
The dodo of Mauritius, shown here in a 1626 illustration by Roelant Savery, is an often-cited example of modern extinction[17]

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 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.[18] When possible, modern zoological institutions try to maintain 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".[19] This is especially common with extinction of keystone species.

A 2018 study indicated that the 6th mass extinction started in the Late Pleistocene could take up to 5 to 7 million years to restore 2.5 billion years of unique mammal diversity to what it was before the human era.[14][20]

Pseudoextinction

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,[21] or split into more than one (cladogenesis).[22]

Pseudoextinction 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 a common ancestor with modern horses. Pseudoextinction is much easier to demonstrate for larger taxonomic groups.

Lazarus taxa

The coelacanth, a fish related to lungfish and tetrapods, was considered to have been extinct since the end of the Cretaceous Period until 1938 when a specimen was found, off the Chalumna River (now Tyolomnqa) on the east coast of South Africa.[23] Museum curator Marjorie Courtenay-Latimer discovered the fish among the catch of a local angler, Captain Hendrick Goosen, on December 23, 1938.[23] A local chemistry professor, JLB Smith, confirmed the fish's importance with a famous cable: "MOST IMPORTANT PRESERVE SKELETON AND GILLS = FISH DESCRIBED".[23]

Far more recent possible or presumed extinctions of species which may turn out still to exist 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 ivory-billed woodpecker (Campephilus principalis), last sighted for certain in 1944; and the slender-billed curlew (Numenius tenuirostris), not seen since 2007.[24]

Causes

Ectopistes migratoriusMCN2P28CA
The passenger pigeon, one of hundreds of species of extinct birds, was hunted to extinction over the course of a few decades

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,[25] although this varies widely between taxa. There are a variety of causes that can contribute directly or indirectly to the extinction of 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".[26] 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 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 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.[27] The question of whether more extinctions in the fossil record have been caused by evolution or by catastrophe is a subject of discussion; Mark Newman, the author of Modeling Extinction, argues for a mathematical model that falls between the two positions.[4] 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.

Currently, environmental groups and some governments are concerned with the extinction of species caused by humanity, and they try to prevent further extinctions through a variety of conservation programs.[9] 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 is an essential cause of the extinction crisis.[28] 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.[29]

Genetics and demographic phenomena

If adaptation increasing population fitness is slower than environmental degradation plus the accumulation of slightly deleterious mutations, then a population will go extinct.[30] 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 is the most important determinant of genus extinction at background rates but becomes increasingly irrelevant as mass extinction arises.[31] 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 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.

Genetic pollution

Purebred wild species evolved to a specific ecology can be threatened with extinction[32] through the process of genetic pollution—i.e., uncontrolled hybridization, introgression genetic swamping which leads to homogenization or out-competition from the introduced (or hybrid) species.[33] 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;[34] interbreeding can swamp the rarer gene pool and create hybrids, depleting the purebred gene pool (for example, 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 evolutionarily process, nevertheless, hybridization (with or without introgression) threatens rare species' existence.[35][36]

The gene pool of 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.[37] Replacing native with alien genes narrows genetic diversity within the original population,[34][38] thereby increasing the chance of extinction.

DirkvdM santa fe scorched
Scorched land resulting from slash-and-burn agriculture

Habitat degradation

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 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 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 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;[13] 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 is the destruction of ocean floors by bottom trawling.[39]

Diminished resources or introduction of new competitor species also often accompany habitat degradation. Global warming has allowed some species to expand their range, bringing unwelcome 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.

Bufo periglenes2
The golden toad was last seen on May 15, 1989. Decline in amphibian populations is ongoing worldwide

Predation, competition, and disease

In 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, inter-species 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 (many people would say premature extinction) of some species, either as 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, 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 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.[40]

Coextinction

Giant Haasts eagle attacking New Zealand moa
The large Haast's eagle and moa from New Zealand

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 a food chain who lose their prey. "Species coextinction is a manifestation of the interconnectedness of organisms in complex ecosystems ... While coextinction may not be the most important cause of species extinctions, it is certainly an insidious one".[41] 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 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.[42]

Climate change

Extinction as a result of climate change has been confirmed by fossil studies.[43] Particularly, the extinction of amphibians during the Carboniferous Rainforest Collapse, 305 million years ago.[43] 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.[44][45] The ecologically rich areas that would potentially suffer 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.[46] Climate change has also been found to be a factor in habitat loss and desertification.[47]

Mass extinctions

CambrianOrdovicianSilurianDevonianCarboniferousPermianTriassicJurassicCretaceousPaleogeneNeogene
Marine extinction intensity during the Phanerozoic
%
Millions of years ago
CambrianOrdovicianSilurianDevonianCarboniferousPermianTriassicJurassicCretaceousPaleogeneNeogene
The blue graph shows the apparent percentage (not the absolute number) of marine animal genera becoming extinct during any given time interval. It does not represent all marine species, just those that are readily fossilized. The labels of the traditional "Big Five" extinction events and the more recently recognised End-Capitanian extinction event are clickable hyperlinks; see Extinction event for more details. (source and image info)

There have been at least five mass extinctions in 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 is considered to be one likely cause of the "Permian–Triassic extinction event" about 250 million years ago,[48] which is estimated to have killed 90% of species then existing.[49] There is also evidence to suggest that this event was preceded by another mass extinction, known as Olson's Extinction.[48] The Cretaceous–Paleogene extinction event (K-Pg) occurred 66 million years ago, at the end of the Cretaceous period, and is best known for having wiped out non-avian dinosaurs, among many other species.

Modern extinctions

According to a 1998 survey of 400 biologists conducted by New York's American Museum of Natural History, nearly 70% believed that the Earth is currently in the early stages of a human-caused mass extinction,[50] 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.[51]

Biologist E. O. Wilson estimated [13] 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.[52] More significantly, the current rate of global species extinctions is estimated as 100 to 1000 times "background" rates (the average extinction rates in the evolutionary time scale of planet Earth),[53][54] while future rates are likely 10,000 times higher.[54] 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 the main drivers of the modern extinction crisis.[55][56][57][58]

History of scientific understanding

Tyrannosaurus-rex-Profile-steveoc86
Tyrannosaurus, one of the many extinct dinosaur genera. The cause of the Cretaceous–Paleogene extinction event is a subject of much debate amongst researchers
Cuvier elephant jaw
Georges Cuvier compared fossil mammoth jaws to those of living elephants, concluding that they were distinct from any known living species.[59]

For much of history, the modern understanding of extinction as the end of a species was incompatible with the prevailing worldview. Through the 18th century, much of Western society adhered to the belief that the world was created by God and as such was complete and perfect.[60] 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 the tiniest microorganism to God, is linked in a continuous chain.[61] 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.[60][61] Thomas Jefferson was a firm supporter of the Great Chain of Being and an opponent of extinction,[60][62] famously denying the extinction of the wooly mammoth on the grounds that nature never allows a race of animals to become extinct.[63]

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 a nautilus to the Royal Society that was more than two feet in diameter,[64] 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.[61] While he contended that it was possible a species could be "lost", he thought this highly unlikely.[61] Similarly, in 1695, Thomas Molyneux published an account of enormous antlers found in Ireland that did not belong to any extant taxa in that area.[65][62] Molyneux reasoned that they came from the North American moose and that the animal had once been common on the British Isles.[65] 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.[65] Using the antlers as evidence for this position, Molyneux described how moose had continued to exist in North America even as they were lost to the British Isles.[62] The antlers were later confirmed to be from the extinct Irish elk Megaloceros.[62] Hooke and Molyneux's line of thinking 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.[66]

Georges Cuvier is credited with establishing the modern conception of extinction in a 1796 lecture to the French Institute,[63][59] though he would spend most of his career trying to convince the wider scientific community of his theory.[67] Cuvier was a well-regarded geologist, lauded for his ability to reconstruct the anatomy of an unknown species from a few fragments of bone.[59] His primary evidence for extinction came from mammoth skulls found in the Paris basin.[59] 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.[59] In 1812, Cuvier, along with Alexandre Bronigniart & Geoffroy Saint-Hilaire, mapped the strata of the Paris basin.[61] They saw alternating saltwater and freshwater deposits, as well as patterns of the appearance and disappearance of fossils throughout the record.[62][67] From these patterns, Cuvier inferred historic cycles of catastrophic flooding, extinction, and repopulation of the earth with new species.[62][67]

Cuvier's fossil evidence showed that very different life forms existed in the past than those that exist today, a fact that was accepted by most scientists.[60] The primary debate focused whether this turnover caused by extinction was gradual or abrupt in nature.[67] 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.[68] His catastrophic view of the nature of extinction garnered him many opponents in the newly emerging school of uniformitarianism.[68]

Jean-Baptist Lamarck, a gradualist and colleague of Cuvier, saw the fossils of different life forms as evidence of the mutable character of species.[67] 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.[67] Unlike Cuvier, Lamarck 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.[67][69]

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 the total extinction of the dodo and the extirpation of indigenous horses to the British Isles.[61] He similarly argued against mass extinctions, believing that any extinction must be a gradual process.[59][63] 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 the Paris basin, could be formed by a slow rise and fall of sea levels.[62]

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.[70] Because of the wide reach of On the Origin of Species, it was widely accepted that extinction occurred gradually and evenly (a concept we now refer to as background extinction).[63] It 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.

Human attitudes and interests

Extinction is an important research topic in 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 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 the United States government, to force the removal of Native Americans, many of whom relied on the bison for food.[71]

Biologist Bruce Walsh of the University of Arizona states three reasons for scientific interest in the preservation of species: genetic resources, ecosystem stability, and ethics;[72] and today the scientific community "stress[es] the importance" of maintaining biodiversity.[72][73]

In modern times, commercial and industrial interests often have to contend with the effects of production on plant and animal life. However, some technologies with minimal, or no, proven harmful effects on Homo sapiens can be devastating to wildlife (for example, DDT).[74] Biogeographer Jared Diamond notes that while big business may label environmental concerns as "exaggerated", and often cause "devastating damage", some corporations find it in their interest to adopt good conservation practices, and even engage in preservation efforts that surpass those taken by national parks.[75]

Governments sometimes see the loss of native species as a loss to ecotourism,[76] and can enact laws with severe punishment against the trade in native species in an effort to prevent extinction in the wild. Nature preserves are created by governments as a means to provide continuing habitats to species crowded by human expansion. The 1992 Convention on Biological Diversity has resulted in international Biodiversity Action Plan programmes, which attempt to provide comprehensive guidelines for government biodiversity conservation. Advocacy groups, such as The Wildlands Project[77] and the Alliance for Zero Extinctions,[78] work to educate the public and pressure governments into action.

People who live close to nature can be dependent on the survival of all the species in their environment, leaving them highly exposed to extinction risks. However, people prioritize day-to-day survival over species conservation; with human overpopulation in tropical developing countries, there has been enormous pressure on forests due to subsistence agriculture, including slash-and-burn agricultural techniques that can reduce endangered species's habitats.[79]

Antinatalist philosopher David Benatar concludes that any popular concern about non-human species extinction usually arises out of concern about how the loss of a species will impact human wants and needs, that "we shall live in a world impoverished by the loss of one aspect of faunal diversity, that we shall no longer be able to behold or use that species of animal." He notes that typical concerns about possible human extinction, such as the loss of individual members, are not considered in regards to non-human species extinction.[80]

Planned extinction

Completed

  • The smallpox virus is now extinct in the wild,[81] although samples are retained in laboratory settings.
  • The rinderpest virus, which infected domestic cattle, is now extinct in the wild.[82]

Proposed

The poliovirus is now confined to small parts of the world due to extermination efforts.[83]

Dracunculus medinensis, a parasitic worm which causes the disease dracunculiasis, is now close to eradication thanks to efforts led by the Carter Center.[84]

Treponema pallidum pertenue, a bacterium which causes the disease yaws, is in the process of being eradicated.

Biologist Olivia Judson has advocated the deliberate extinction of certain disease-carrying mosquito species. In a September 25, 2003 article in The New York Times, she advocated "specicide" of thirty mosquito species by introducing a genetic element which can insert itself into another crucial gene, to create recessive "knockout genes".[85] She says that the Anopheles mosquitoes (which spread malaria) and Aedes mosquitoes (which spread dengue fever, yellow fever, elephantiasis, and other diseases) represent only 30 species; eradicating these would save at least one million human lives per annum, at a cost of reducing the genetic diversity of the family Culicidae by only 1%. She further argues that since species become extinct "all the time" the disappearance of a few more will not destroy the ecosystem: "We're not left with a wasteland every time a species vanishes. Removing one species sometimes causes shifts in the populations of other species—but different need not mean worse." In addition, anti-malarial and mosquito control programs offer little realistic hope to the 300 million people in developing nations who will be infected with acute illnesses this year. Although trials are ongoing, she writes that if they fail: "We should consider the ultimate swatting."[85]

Biologist E. O. Wilson has advocated the eradication of several species of mosquito, including malaria vector Anopheles gambiae. Wilson stated, "I'm talking about a very small number of species that have co-evolved with us and are preying on humans, so it would certainly be acceptable to remove them. I believe it's just common sense."[86]

Cloning

Some, such as Harvard geneticist George M. Church, believe that ongoing technological advances will let us "bring back to life" an extinct species by cloning, using DNA from the remains of that species. Proposed targets for cloning include the mammoth, the thylacine, and the Pyrenean ibex. For this to succeed, enough individuals would have to be cloned, from the DNA of different individuals (in the case of sexually reproducing organisms) to create a viable population. Though bioethical and philosophical objections have been raised,[87] the cloning of extinct creatures seems theoretically possible.[88]

In 2003, scientists tried to clone the extinct Pyrenean ibex (C. p. pyrenaica). This attempt failed: of the 285 embryos reconstructed, 54 were transferred to 12 mountain goats and mountain goat-domestic goat hybrids, but only two survived the initial two months of gestation before they too died.[89] In 2009, a second attempt was made to clone the Pyrenean ibex: one clone was born alive, but died seven minutes later, due to physical defects in the lungs.[90]

See also

References

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External links

Chicxulub crater

The Chicxulub crater (; Mayan: [tʃʼikʃuluɓ]) is an impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is located near the town of Chicxulub, after which the crater is named. It was formed by a large asteroid or comet about 11 to 81 kilometres (6.8 to 50.3 miles) in diameter, the Chicxulub impactor, striking the Earth. The date of the impact coincides precisely with the Cretaceous–Paleogene boundary (K–Pg boundary), slightly less than 66 million years ago, and a widely accepted theory is that worldwide climate disruption from the event was the cause of the Cretaceous–Paleogene extinction event, a mass extinction in which 75% of plant and animal species on Earth became extinct, including all non-avian dinosaurs.

The crater is estimated to be 150 kilometres (93 miles) in diameter and 20 km (12 mi) in depth, well into the continental crust of the region of about 10–30 km (6.2–18.6 mi) depth. It is the second largest confirmed impact structure on Earth and the only one whose peak ring is intact and directly accessible for scientific research.The crater was discovered by Antonio Camargo and Glen Penfield, geophysicists who had been looking for petroleum in the Yucatán during the late 1970s. Penfield was initially unable to obtain evidence that the geological feature was a crater and gave up his search. Later, through contact with Alan Hildebrand in 1990, Penfield obtained samples that suggested it was an impact feature. Evidence for the impact origin of the crater includes shocked quartz, a gravity anomaly, and tektites in surrounding areas.

In 2016, a scientific drilling project drilled deep into the peak ring of the impact crater, hundreds of meters below the current sea floor, to obtain rock core samples from the impact itself. The discoveries were widely seen as confirming current theories related to both the crater impact and its effects.

Cretaceous

The Cretaceous ( , kri-TAY-shəs) is a geologic period and system that spans 79 million years from the end of the Jurassic Period 145 million years ago (mya) to the beginning of the Paleogene Period 66 mya. It is the last period of the Mesozoic Era, and the longest period of the Phanerozoic Eon. The Cretaceous Period is usually abbreviated K, for its German translation Kreide (chalk, creta in Latin).

The Cretaceous was a period with a relatively 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, while dinosaurs continued to dominate on land. During this time, new groups of mammals and birds, as well as flowering plants, appeared.

The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs and large marine reptiles died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary (K–Pg boundary), a geologic signature associated with the mass extinction which lies between the Mesozoic and Cenozoic eras.

Cretaceous–Paleogene extinction event

The Cretaceous–Paleogene (K–Pg) extinction event, also known as the Cretaceous–Tertiary (K–T) extinction, was a sudden mass extinction of some three-quarters of the plant and animal species on Earth, approximately 66 million years ago. With the exception of some ectothermic species such as the leatherback sea turtle and crocodiles, no tetrapods weighing more than 25 kilograms (55 lb) survived. It marked the end of the Cretaceous period and with it, the entire Mesozoic Era, opening the Cenozoic Era that continues today.

In the geologic record, the K–Pg event is marked by a thin layer of sediment called the K–Pg boundary, which can be found throughout the world in marine and terrestrial rocks. The boundary clay shows high levels of the metal iridium, which is rare in the Earth's crust, but abundant in asteroids.As originally proposed in 1980 by a team of scientists led by Luis Alvarez and his son Walter Alvarez, it is now generally thought that the K–Pg extinction was caused by the impact of a massive comet or asteroid 10 to 15 km (6 to 9 mi) wide, 66 million years ago, which devastated the global environment, mainly through a lingering impact winter which halted photosynthesis in plants and plankton. The impact hypothesis, also known as the Alvarez hypothesis, was bolstered by the discovery of the 180-kilometer-wide (112 mi) Chicxulub crater in the Gulf of Mexico's Yucatán Peninsula in the early 1990s, which provided conclusive evidence that the K–Pg boundary clay represented debris from an asteroid impact. The fact that the extinctions occurred simultaneously provides strong evidence that they were caused by the asteroid. A 2016 drilling project into the Chicxulub peak ring, confirmed that the peak ring comprised granite ejected within minutes from deep in the earth, but contained hardly any gypsum, the usual sulfate-containing sea floor rock in the region: the gypsum would have vaporized and dispersed as an aerosol into the atmosphere, causing longer-term effects on the climate and food chain.

Other causal or contributing factors to the extinction may have been the Deccan Traps and other volcanic eruptions, climate change, and sea level change.

A wide range of species perished in the K–Pg extinction, the best-known being the non-avian dinosaurs. It also destroyed a plethora of other terrestrial organisms, including certain mammals, pterosaurs, birds, lizards, insects, and plants. In the oceans, the K–Pg extinction killed off plesiosaurs and the giant marine lizards (Mosasauridae) and devastated fish, sharks, mollusks (especially ammonites, which became extinct), and many species of plankton. It is estimated that 75% or more of all species on Earth vanished. Yet the extinction also provided evolutionary opportunities: in its wake, many groups underwent remarkable adaptive radiation—sudden and prolific divergence into new forms and species within the disrupted and emptied ecological niches. Mammals in particular diversified in the Paleogene, evolving new forms such as horses, whales, bats, and primates. Birds, fish, and perhaps lizards also radiated.

Extinction event

An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. It occurs when the rate of extinction increases with respect to the rate of speciation. Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty. These differences stem from the threshold chosen for describing an extinction event as "major", and the data chosen to measure past diversity.

Because most diversity and biomass on Earth is microbial, and thus difficult to measure, recorded extinction events affect the easily observed, biologically complex component of the biosphere rather than the total diversity and abundance of life. Extinction occurs at an uneven rate. Based on the fossil record, the background rate of extinctions on Earth is about two to five taxonomic families of marine animals every million years. Marine fossils are mostly used to measure extinction rates because of their superior fossil record and stratigraphic range compared to land animals.

The Great Oxygenation Event, which occurred around 2.45 billion years ago, was probably the first major extinction event. Since the Cambrian explosion five further major mass extinctions have significantly exceeded the background extinction rate. The most recent and arguably best-known, the Cretaceous–Paleogene extinction event, which occurred approximately 66 million years ago (Ma), was a large-scale mass extinction of animal and plant species in a geologically short period of time. In addition to the five major mass extinctions, there are numerous minor ones as well, and the ongoing mass extinction caused by human activity is sometimes called the sixth extinction. Mass extinctions seem to be a mainly Phanerozoic phenomenon, with extinction rates low before large complex organisms arose.

Global catastrophic risk

A global catastrophic risk is a hypothetical future event which could damage human well-being on a global scale, even crippling or destroying modern civilization. An event that could cause human extinction or permanently and drastically curtail humanity's potential is known as an existential risk.Potential global catastrophic risks include anthropogenic risks, caused by humans (technology, governance, climate change), and non-anthropogenic or external risks. Examples of technology risks are hostile artificial intelligence and destructive biotechnology or nanotechnology. Insufficient or malign global governance creates risks in the social and political domain, such as a global war, including nuclear holocaust, bioterrorism using genetically modified organisms, cyberterrorism destroying critical infrastructure like the electrical grid; or the failure to manage a natural pandemic. Problems and risks in the domain of earth system governance include global warming, environmental degradation, including extinction of species, famine as a result of non-equitable resource distribution, human overpopulation, crop failures and non-sustainable agriculture.

Examples of non-anthropogenic risks are an asteroid impact event, a supervolcanic eruption, a lethal gamma-ray burst, a geomagnetic storm destroying electronic equipment, natural long-term climate change, hostile extraterrestrial life, or the predictable Sun transforming into a red giant star engulfing the Earth.

Holocene extinction

The Holocene extinction, otherwise referred to as the Sixth extinction or Anthropocene extinction, is a current event, and is one of the most significant extinction events in the history of the Earth. This ongoing extinction of species coincides with the present Holocene epoch (approx. 11,700 years), and is a result of human activity. This large number of extinctions spans numerous families of plants and animals, including mammals, birds, amphibians, reptiles and arthropods. With widespread degradation of highly biodiverse habitats such as coral reefs and rainforests, as well as other areas, the vast majority of these extinctions are thought to be undocumented, as no one is even aware of the existence of the species before they go extinct, or no one has yet discovered their extinction. The current rate of extinction of species is estimated at 100 to 1,000 times higher than natural background rates.The Holocene extinction includes the disappearance of large land animals known as megafauna, starting at the end of the last Ice Age. Megafauna outside of the African continent, which did not evolve alongside humans, proved highly sensitive to the introduction of new predation, and many died out shortly after early humans began spreading and hunting across the Earth (additionally, many African species have also gone extinct in the Holocene). These extinctions, occurring near the Pleistocene–Holocene boundary, are sometimes referred to as the Quaternary extinction event.

The most popular theory is that human overhunting of species added to existing stress conditions as the extinction coincides with human emergence. Although there is debate regarding how much human predation affected their decline, certain population declines have been directly correlated with human activity, such as the extinction events of New Zealand and Hawaii. Aside from humans, climate change may have been a driving factor in the megafaunal extinctions, especially at the end of the Pleistocene.

Ecologically, humanity has been noted as an unprecedented "global superpredator" that consistently preys on the adults of other apex predators, and has worldwide effects on food webs. There have been extinctions of species on every land mass and in every ocean: there are many famous examples within Africa, Asia, Europe, Australia, North and South America, and on smaller islands. Overall, the Holocene extinction can be linked to the human impact on the environment. The Holocene extinction continues into the 21st century, with meat consumption, overfishing, ocean acidification and the decline in amphibian populations being a few broader examples of an almost universal, cosmopolitan decline in biodiversity. Human overpopulation (and continued population growth) along with profligate consumption are considered to be the primary drivers of this rapid decline.

Hominidae

The Hominidae (), whose members are known as great apes or hominids, are a taxonomic family of primates that includes eight extant species in four genera: Pongo, the Bornean, Sumatran and Tapanuli orangutan; Gorilla, the eastern and western gorilla; Pan, the common chimpanzee and the bonobo; and Homo, which includes modern humans and their extinct relatives (e.g., the Neanderthal), and ancestors, such as Homo erectus.Several revisions in classifying the great apes have caused the use of the term "hominid" to vary over time. Its original meaning referred only to humans (Homo) and their closest extinct relatives. That restrictive meaning has now been largely assumed by the term "hominin", which comprises all members of the human clade after the split from the chimpanzees (Pan). The current, 21st-century meaning of "hominid" includes all the great apes including humans. Usage still varies, however, and some scientists and laypersons still use "hominid" in the original restrictive sense; the scholarly literature generally shows the traditional usage until around the turn of the 21st century.Within the taxon Hominidae, a number of extant and known extinct, that is, fossil, genera are grouped with the humans, chimpanzees, and gorillas in the subfamily Homininae; others with orangutans in the subfamily Ponginae (see classification graphic below). The most recent common ancestor of all Hominidae lived roughly 14 million years ago, when the ancestors of the orangutans speciated from the ancestral line of the other three genera. Those ancestors of the family Hominidae had already speciated from the family Hylobatidae (the gibbons), perhaps 15 million to 20 million years ago.

Human extinction

In futures studies, human extinction is the hypothetical end of the human species. This may result from natural causes or it may be the result of human action. The likelihood of human extinction in the future by wholly natural scenarios, such as a meteorite impact or large-scale volcanism, is generally considered to be extremely low.For anthropogenic extinction, many possible scenarios have been proposed: human global nuclear annihilation, biological warfare or the release of a pandemic-causing agent, overpopulation, ecological collapse, and climate change; in addition, emerging technologies could bring about new extinction scenarios, such as advanced artificial intelligence, biotechnology or self-replicating nanobots. The probability of anthropogenic human extinction within the next hundred years is the topic of an active debate.

Human extinction needs to be differentiated from the extinction of all life on Earth (see also future of Earth) and from the extinction of major components of human culture (e.g., through a global catastrophe leaving only small, scattered human populations, which might evolve in isolation).

IUCN Red List

The IUCN Red List of Threatened Species (also known as the IUCN Red List or Red Data List), founded in 1965, has evolved to become the world's most comprehensive inventory of the global conservation status of biological species. It uses a set of criteria to evaluate the extinction risk of thousands of species and subspecies. These criteria are relevant to all species and all regions of the world, With its strong scientific base, the IUCN Red List is recognized as the most authoritative guide to the status of biological diversity. A series of Regional Red List are produced by countries or organizations, which assess the risk of extinction to species within a political management unit.

The IUCN Red List is set upon precise criteria to evaluate the extinction risk of thousands of species and subspecies. These criteria are relevant to all species and all regions of the world. The aim is to convey the urgency of conservation issues to the public and policy makers, as well as help the international community to try to reduce species extinction. According to the International Union for Conservation of Nature (IUCN) (1996), the formally stated goals of the Red List are (1) to provide scientifically based information on the status of species and subspecies at a global level, (2) to draw attention to the magnitude and importance of threatened biodiversity, (3) to influence national and international policy and decision-making, and (4) to provide information to guide actions to conserve biological diversity.Major species assessors include BirdLife International, the Institute of Zoology (the research division of the Zoological Society of London), the World Conservation Monitoring Centre, and many Specialist Groups within the IUCN Species Survival Commission (SSC). Collectively, assessments by these organizations and groups account for nearly half the species on the Red List.

The IUCN aims to have the category of every species re-evaluated every five years if possible, or at least every ten years. This is done in a peer reviewed manner through IUCN Species Survival Commission (SSC) Specialist Groups, which are Red List Authorities responsible for a species, group of species or specific geographic area, or in the case of BirdLife International, an entire class (Aves).As of 2018, 26,197 species are now classified as vulnerable, critical or endangered.

Language death

In linguistics, language death occurs when a language loses its last native speaker. By extension, language extinction is when the language is no longer known, including by second-language speakers. Other similar terms include linguicide, the death of a language from natural or political causes, and rarely glottophagy, the absorption or replacement of a minor language by a major language.

Language death is a process in which the level of a speech community's linguistic competence in their language variety decreases, eventually resulting in no native or fluent speakers of the variety. Language death can affect any language form, including dialects. Language death should not be confused with language attrition (also called language loss), which describes the loss of proficiency in a first language of an individual.In the modern period (c. 1500 CE–present; following the rise of colonialism), language death has typically resulted from the process of cultural assimilation leading to language shift and the gradual abandonment of a native language in favour of a foreign lingua franca, largely those of European countries.As of the 2000s, a total of roughly 7,000 natively spoken languages existed worldwide. Most of these are minor languages in danger of extinction; one estimate published in 2004 expected that some 90% of the currently spoken languages will have become extinct by 2050.

Local extinction

Local extinction or extirpation is the condition of a species (or other taxon) that ceases to exist in the chosen geographic area of study, though it still exists elsewhere. Local extinctions are contrasted with global extinctions.

Local extinctions may be followed by a replacement of the species taken from other locations; wolf reintroduction is an example of this.

Mammoth

A mammoth is any species of the extinct genus Mammuthus, one of the many genera that make up the order of trunked mammals called proboscideans. The various species of mammoth were commonly equipped with long, curved tusks and, in northern species, a covering of long hair. They lived from the Pliocene epoch (from around 5 million years ago) into the Holocene at about 4,000 years ago, and various species existed in Africa, Europe, Asia, and North America. They were members of the family Elephantidae, which also contains the two genera of modern elephants and their ancestors.

The oldest representative of Mammuthus, the South African mammoth (M. subplanifrons), appeared around 5 million years ago during the early Pliocene in what is now southern and eastern Africa. Descendant species of these mammoths moved north and continued to propagate into numerous subsequent species, eventually covering most of Eurasia before extending into the Americas at least 600,000 years ago. The last species to emerge, the woolly mammoth (M. primigenius), developed about 400,000 years ago in East Asia, with some surviving on Russia's Wrangel Island in the Arctic Ocean until as recently as roughly 3,700 to 4,000 years ago, still extant during the construction of the Great Pyramid of ancient Egypt.

Mesozoic

The Mesozoic Era ( or ) is an interval of geological time from about 252 to 66 million years ago. It is also called the Age of Reptiles and the Age of Conifers.The Mesozoic ("middle life") is one of three geologic eras of the Phanerozoic Eon, preceded by the Paleozoic ("ancient life") and succeeded by the Cenozoic ("new life"). The era is subdivided into three major periods: the Triassic, Jurassic, and Cretaceous, which are further subdivided into a number of epochs and stages.

The era began in the wake of the Permian–Triassic extinction event, the largest well-documented mass extinction in Earth's history, and ended with the Cretaceous–Paleogene extinction event, another mass extinction whose victims included the non-avian dinosaurs. The Mesozoic was a time of significant tectonic, climate and evolutionary activity. The era witnessed the gradual rifting of the supercontinent Pangaea into separate landmasses that would move into their current positions during the next era. The climate of the Mesozoic was varied, alternating between warming and cooling periods. Overall, however, the Earth was hotter than it is today. Dinosaurs first appeared in the Mid-Triassic, and became the dominant terrestrial vertebrates in the Late Triassic or Early Jurassic, occupying this position for about 150 or 135 million years until their demise at the end of the Cretaceous. Birds first appeared in the Jurassic (however, true toothless birds appeared first in the Cretaceous), having evolved from a branch of theropod dinosaurs. The first mammals also appeared during the Mesozoic, but would remain small—less than 15 kg (33 lb)—until the Cenozoic. The flowering plants (angiosperms) arose in the Triassic or Jurassic and came to prominence in the late Cretaceous when they replaced the conifers and other gymnosperms as the dominant trees.

Permian

The Permian is a geologic period and system which spans 47 million years from the end of the Carboniferous Period 298.9 million years ago (Mya), to the beginning of the Triassic period 251.902 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 ancestral groups of the mammals, turtles, lepidosaurs, and archosaurs. The world at the time was dominated by two continents 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 (along with the Paleozoic) ended with the Permian–Triassic extinction event, the largest mass extinction in Earth's history, in which nearly 96% of marine species and 70% of terrestrial species died out. 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, ecosystems took 30 million years to recover.

Permian–Triassic extinction event

The Permian–Triassic (P–Tr or P–T) extinction event, colloquially known as the Great Dying, the End-Permian Extinction or the Great Permian Extinction, occurred about 252 Ma (million years) ago, forming the boundary between the Permian and Triassic geologic periods, as well as between the Paleozoic and Mesozoic eras. It is the Earth's most severe known extinction event, with up to 96% of all marine species and 70% of terrestrial vertebrate species becoming extinct. It was the largest known mass extinction of insects. Some 57% of all biological families and 83% of all genera became extinct. Because so much biodiversity was lost, the recovery of land-dwelling life took significantly longer than after any other extinction event, possibly up to 10 million years. Studies in Bear Lake County, near Paris, Idaho, showed a relatively quick rebound in a localized marine ecosystem, taking around 2 million years to recover, suggesting that the impact of the extinction may have been felt less severely in some areas than others.

There is evidence for one to three distinct pulses, or phases, of extinction. Suggested mechanisms for the latter include one or more large meteor impact events, massive volcanism such as that of the Siberian Traps, and the ensuing coal or gas fires and explosions, and a runaway greenhouse effect triggered by sudden release of methane from the sea floor due to methane clathrate dissociation according to the clathrate gun hypothesis or methane-producing microbes known as methanogens. Possible contributing gradual changes include sea-level change, increasing anoxia, increasing aridity, and a shift in ocean circulation driven by climate change.

Resident Evil (film series)

Resident Evil is an action horror science fiction film series loosely based on the Capcom survival horror video game series of the same name. German studio Constantin Film bought the rights to adapt the series to film in January 1997. In 2001, Screen Gems acquired distribution rights and hired Paul W. S. Anderson as writer and director for Resident Evil (2002). Anderson continued as writer and producer for Resident Evil: Apocalypse (2004) and Resident Evil: Extinction (2007), and returned as the director for Resident Evil: Afterlife (2010), Resident Evil: Retribution (2012), and Resident Evil: The Final Chapter (2016).

The films follow Alice (Milla Jovovich), a character created for the films, who battles the Umbrella Corporation, whose bioweapons have triggered a zombie apocalypse. Characters from the games also appear, including Jill Valentine, Carlos Olivera, Claire Redfield, Albert Wesker, Chris Redfield, Barry Burton, Leon S. Kennedy, Ada Wong and James Marcus.

The Resident Evil film series is the highest-grossing film series based on a video game, having grossed over $1.2 billion worldwide.

Triassic

The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.9 million years ago (Mya), to the beginning of the Jurassic Period 201.3 Mya. The Triassic is the first and shortest period of the Mesozoic Era. Both the start and end of the period are marked by major extinction events.Triassic began in the wake of the Permian–Triassic extinction event, which left the Earth's biosphere impoverished; it was well into the middle of the Triassic before life recovered its former diversity. Therapsids and archosaurs were the chief terrestrial vertebrates during this time. A specialized subgroup of archosaurs, called dinosaurs, first appeared in the Late Triassic but did not become dominant until the succeeding Jurassic Period.The first true mammals, themselves a specialized subgroup of therapsids, also evolved during this period, as well as the first flying vertebrates, the pterosaurs, who, like the dinosaurs, were a specialized subgroup of archosaurs. 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, with deserts spanning much of Pangaea's interior. However, the climate shifted and became more humid as Pangaea began to drift apart. The end of the period was marked by yet another major mass extinction, the Triassic–Jurassic extinction event, that wiped out many groups and allowed dinosaurs to assume dominance in the Jurassic.

The Triassic was named in 1834 by Friedrich von Alberti, after the three distinct rock layers (tri meaning "three") that are found throughout Germany and northwestern Europe—red beds, capped by marine limestone, followed by a series of terrestrial mud- and sandstones—called the "Trias".

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