# Extinction – Definition, Types, Causes & Examples

> Extinction is a biological condition in which a species is completely lost, with no living individual of that species remaining anywhere in the world. It is...

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Author: Sourav Pan
Last updated: September 19, 2026

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Extinction is a biological condition in which a species is completely lost, with no living individual of that species remaining anywhere in the world. It is the permanent loss of the species. Disappearance from a particular area does not mean that the species has become extinct. When the species is lost from one locality but still survives in other places, this is referred to as local extinction or extirpation.

Determining extinction is not always simple. The death of the last individual is usually not observed, especially in rare species having very small and scattered populations. A species may remain unseen for many years. Because of this, repeated surveys are used to search its known and expected range before it is considered extinct.

Endangered (EN), Critically Endangered (CR), Extinct in the Wild (EW), and Extinct (EX) are different conservation states. They do not indicate the same condition. Endangered species have a very high risk of extinction in the wild, while Critically Endangered species have an extremely high risk. Extinct in the Wild means the species is no longer present in its natural range, but individuals still survive in captivity, cultivation, or as a naturalized population outside its past range. In Extinct (EX), according to IUCN, there is “no reasonable doubt that the last individual has died”. Exhaustive surveys of its known or expected historic range are considered for this category.

Before describing “how many types of extinction are there?”, the basis of classification has to be considered. Extinction can be classified according to the scale or pattern of species loss, whereas the IUCN categories are used for conservation status and extinction risk.

## Types of Extinction

Different terms are used for extinction, but all these terms do not represent the same biological condition. Some are based on geographical loss, while some depend on ecological function and dependence of one species on another. Extinction can also be described according to extinction rate through geological time or by the fate of an evolutionary lineage.

![Classification diagram showing extinction terms grouped by geographic scope, IUCN status, ecological function, species dependence, extinction rate, and evolutionary lineage.](https://biologynotesonline.com/wp-content/uploads/2024/04/Types-of-Extinction-Classification-Framework-1024x576.webp)Classification diagram showing extinction terms grouped by geographic scope, IUCN status, ecological function, species dependence, extinction rate, and evolutionary lineage.

### By Geographic Scope and Survival Status

#### 1. Global Extinction

Global extinction is the complete disappearance of a species from the Earth. No living individual of the species remains anywhere.

Disappearance of a species from a country, island, forest, or any other part of its geographical range is not global extinction.

The dodo (Raphus cucullatus) is an example of global extinction. It was an endemic bird of Mauritius. The species became extinct during the 17th century.

#### 2. Local or Regional Extinction (Extirpation)

Local extinction or extirpation is the disappearance of a species from a particular geographical area while the species is still surviving in other areas. The area may be a small locality or even a larger region. Other populations of the same species remain present.

For regional assessment, IUCN also uses the category Regionally Extinct (RE). It is used when there is no reasonable doubt that the last individual capable of reproduction has disappeared from that particular region, although the taxon is still present outside the region.

#### 3. Extinct in the Wild

Extinct in the Wild (EW) is a formal IUCN Red List category. Species belonging to this category survive only in cultivation, captivity, or as a naturalized population present well outside their past range.

Surveys carried out in the former natural range fail to record any surviving wild individuals. Living individuals are still present. The species, however, no longer occurs within its former natural range.

![Comparison showing a species absent from one region but surviving elsewhere, absent from the wild but surviving under managed conditions, and completely extinct worldwide.](https://biologynotesonline.com/wp-content/uploads/2024/04/Local-Extinction-vs-Extinct-in-the-Wild-vs-Global-Extinction-1024x576.webp)Comparison showing a species absent from one region but surviving elsewhere, absent from the wild but surviving under managed conditions, and completely extinct worldwide.

### By Ecological Function and Species Dependence

#### 1. Functional or Ecological Extinction

Functional extinction or ecological extinction is used when a species is still present, but its population has reduced to such a low level that the former ecological function or important interactions with other species are lost.

For example, a seed disperser may continue to occur within an ecosystem. But if it becomes too rare, its earlier level of seed dispersal is no longer provided.

The term “functional extinction” does not always have exactly the same use in scientific literature. In some studies, it is also used when surviving individuals are unable to reproduce sufficiently for producing another generation. It is not an IUCN Red List category.

#### 2. Coextinction

Coextinction is the loss of one species due to the loss of another species on which it depends. The dependent organisms may be parasites, commensals, mutualists, pollinators, or other species having a close ecological relationship. Extinction effects can pass from one species to another within an ecological network.

The first extinction is referred to as the primary extinction. Loss occurring in a dependent species is called a secondary extinction.

For example, consider a louse that can live only on one particular host bird species. If the host bird becomes extinct first, it is the primary extinction. The host-specific louse disappearing after the loss of this bird represents secondary extinction or coextinction.

![Ecological schematic showing a rare species losing its seed-dispersal function and a host-specific dependent species disappearing after extinction of its host.](https://biologynotesonline.com/wp-content/uploads/2024/04/Functional-Extinction-and-Coextinction-in-Ecological-Networks-1024x576.webp)Ecological schematic showing a rare species losing its seed-dispersal function and a host-specific dependent species disappearing after extinction of its host.

### By Extinction Rate and Scale Through Time

#### 1. Background Extinction

Background extinction is the relatively low and ongoing rate of species extinction occurring through geological time. Species originate and disappear naturally over time. Such losses make up the long-term background against which unusually severe extinction episodes are compared.

It is an extinction-rate pattern. It does not describe whether a species has disappeared locally or globally, or whether living individuals remain in captivity.

Common Drivers & Mechanisms of Background Extinction

The common drivers and mechanisms of background extinction are as follows-

- Gradual environmental change- Changes in climate, temperature, rainfall, sea level, and ocean conditions can make the existing habitat unsuitable. Species unable to shift their range or adapt may gradually disappear.

- Competition and predation- Competition for food and space can reduce a population, while increased predation affects its survival. Such biotic interactions influence extinction and evolutionary turnover, although competition alone does not always result in extinction.

- Disease and parasitism- Pathogens and parasites increase mortality or reduce reproduction of the host population. Their effect can become severe when the population is already small.

- Small population size- Small populations are strongly affected by random births, deaths, reproductive failure, and changes in sex ratio. This is known as demographic stochasticity. Random changes in weather and other environmental conditions produce environmental stochasticity.

- Genetic factors- Genetic drift and inbreeding become more important in small populations. Genetic variation may decrease, reducing the ability of the population to adapt with environmental change.

- Restricted range and specialization- Species restricted to a small geographic area have fewer populations to survive a local disturbance. Highly specialized species may also depend on a narrow habitat or particular environmental condition, making them more vulnerable when it changes.

- Random natural catastrophes- Local floods, fires, storms, volcanic activity, and other rare disturbances can remove small or restricted populations. Their effect depends greatly on population size and distribution.

- Loss of ecological partners- A species may depend on another species for food, pollination, dispersal, or other necessary interaction. Loss of the required partner can then result in coextinction of the dependent species.

#### 2. Mass Extinction

Mass extinction is a large and unusually rapid loss of [biodiversity](/biodiversity/) involving many groups of organisms within a relatively short interval of geological time.

During this process, extinction rates rise far above the ordinary background pattern. Losses occur across a wide range of taxa.

Types of Mass Extinction

The five major mass extinction events in the geological history are commonly referred to as the “Big Five” mass extinctions. They occurred at different geological periods and involved large loss of species within a relatively short geological time.

- Ordovician-Silurian Mass Extinction- It occurred about 444 million years ago, near the end of the Ordovician period. About 85% of marine species were lost. Glaciation, fall in sea level and later changes in ocean circulation and oxygen conditions were associated with this extinction.

- Late Devonian Mass Extinction- This extinction was not a single sudden event. It occurred through a series of extinction pulses, mainly the Kellwasser events (about 372 million years ago) and later Hangenberg event near 359 million years ago. Marine organisms were highly affected. Ocean anoxia and major climatic and environmental changes are associated with these events, while their exact causes are still studied.

- Permian-Triassic Mass Extinction- It occurred about 252 million years ago and was the largest of the Big Five. Around 81-94% of marine species were lost. Massive eruption of the Siberian Traps resulted in severe global warming, ocean anoxia, acidification and other environmental changes.

- Triassic-Jurassic Mass Extinction- It occurred about 201 million years ago. The extinction is closely associated with massive volcanic activity of the Central Atlantic Magmatic Province (CAMP). Large release of CO₂ affected global temperature and ocean chemistry during this period.

- Cretaceous-Paleogene (K-Pg) Mass Extinction- It occurred about 66 million years ago. Around three-fourths of living species disappeared, including the non-avian dinosaurs. The Chicxulub asteroid impact produced dust, soot and sulfate aerosols which blocked sunlight and caused rapid global cooling.

Mechanisms of Mass Extinction

The major mechanisms of mass extinction are as follows-

- Rapid climate change- Rapid increase or decrease in global temperature changes the normal environmental conditions. Volcanic CO₂ causes warming, whereas dust, soot, and sulfate aerosols can produce cooling. Many organisms are unable to tolerate these rapid changes.

- Reduction of sunlight and photosynthesis- Dust, soot, and aerosols present in the atmosphere block the incoming sunlight. Photosynthesis is reduced and the primary productivity falls. This was an important mechanism following the Chicxulub impact.

- Ocean anoxia and euxinia- Warming decreases the amount of dissolved oxygen present in seawater. Severe depletion of oxygen produces anoxic condition. Under euxinic condition, hydrogen sulfide-rich water may develop, highly affecting the marine organisms.

- Ocean acidification- A large amount of atmospheric CO₂ is absorbed by the oceans, which decreases the pH of seawater. Organisms having calcium carbonate shells and skeletons are more affected by this change.

- Acid rain and ozone depletion- Volcanic SO₂ and halogen compounds can alter the atmospheric chemistry. Acid rain affects the terrestrial and freshwater habitats. Ozone depletion increases the amount of ultraviolet radiation reaching the Earth.

- Food-web collapse- Loss of primary producers or other important species affects those organisms which depend on them. The effect then passes through different trophic levels of the food web. Complex food webs may require millions of years for recovery following a severe mass extinction.

- Multiple environmental stresses- Several mechanisms may occur at the same time during a mass extinction. During the Permian-Triassic extinction, global warming, ocean anoxia, acidification, and other environmental stresses occurred together.

![Geological timeline showing a low background extinction rate interrupted by five major extinction-rate spikes corresponding to the Big Five mass-extinction events.](https://biologynotesonline.com/wp-content/uploads/2024/04/Background-Extinction-vs-Mass-Extinction-Through-Geologic-Time-1024x427.png)Geological timeline showing a low background extinction rate interrupted by five major extinction-rate spikes corresponding to the Big Five mass-extinction events.

### By Evolutionary Lineage Outcome

#### 1. Pseudoextinction

Pseudoextinction is mainly a paleontological and evolutionary term. It can occur when an ancestral morphospecies disappears as the lineage gradually changes into a different descendant form, as observed in [anagenetic change](/evolution-definition-types-advantages-examples/).

The earlier species name disappears from the fossil record. The evolutionary lineage itself, however, has not terminated.

Pseudoextinction differs from genuine lineage termination. Paleontologists make this distinction because considering every morphological replacement as a true extinction can change the estimates of species turnover. It is not a standard conservation-status category.

![Evolutionary lineage comparison showing true extinction as complete lineage termination and pseudoextinction as disappearance of an ancestral morphospecies while the lineage continues into a descendant form.](https://biologynotesonline.com/wp-content/uploads/2024/04/Pseudoextinction-vs-True-Extinction-in-Evolutionary-Lineages-1024x683.webp)Evolutionary lineage comparison showing true extinction as complete lineage termination and pseudoextinction as disappearance of an ancestral morphospecies while the lineage continues into a descendant form.

TermWhat disappears?Does the species survive elsewhere?Classification dimensionExampleGlobal extinctionEntire speciesNoGeographic scope and survivalDodo (Raphus cucullatus)Local or regional extinctionPopulation from a defined areaYesGeographic scopeA regional population disappears while populations remain elsewhereExtinct in the Wild (EW)Wild populations within the former natural rangeYes, in captivity, cultivation, or certain populations outside the past rangeIUCN survival statusCaptive or cultivated survival onlyFunctional or ecological extinctionEcological function becomes absent or greatly reducedThe species itself may still be presentEcological functionA seed disperser becomes too rare to perform its former roleCoextinctionA dependent species following loss of its ecological partnerNot if the dependency is obligate and no alternative partner is availableSpecies dependenceHost extinction followed by loss of its host-specific parasiteBackground extinctionIndividual species at the ordinary long-term geological rateNo for each species that becomes extinctExtinction rate through timeScattered species losses between major extinction crisesMass extinctionMany species and groups within a geologically short intervalMany other species survive, but biodiversity falls sharplyRate and scale through timeThe “Big Five” eventsPseudoextinctionAn ancestral morphospecies or taxonomic formThe evolutionary lineage continues as a descendant formEvolutionary lineage outcomeAnagenetic replacement of one morphospecies by another

## Causes of Extinction

![Causal diagram showing habitat change, overexploitation, invasive species, climate change, pollution, disease, small populations, partner loss, and catastrophes converging on population decline and extinction.](https://biologynotesonline.com/wp-content/uploads/2024/04/Major-Causes-and-Pathways-Leading-to-Species-Extinction-1024x512.webp)Causal diagram showing habitat change, overexploitation, invasive species, climate change, pollution, disease, small populations, partner loss, and catastrophes converging on population decline and extinction.

The major causes of extinction are as follows-

- Habitat loss and degradation- Destruction of natural habitats causes loss of food, shelter, breeding sites, and the living space required by species. Agriculture, urbanization, forest clearing, and other changes in land use also break continuous habitats into small and isolated populations.

- Overexploitation- Excessive hunting, fishing, harvesting, collecting, and wildlife trade can decrease the population of a species faster than it can reproduce. Species having slow growth and low reproductive rate are more severely affected.

- Invasive species- Introduced species may act as predators or competitors of native organisms. Some also carry diseases. Native species are sometimes unable to survive these new interactions, particularly the species present on islands.

- Climate change- Changes in temperature, rainfall, sea level, and seasonal conditions alter the suitable habitats available for species. It can also affect their reproduction, distribution, and availability of food.

- Pollution- Pesticides, heavy metals, plastics, toxic chemicals, and excess nutrients can damage both terrestrial and aquatic habitats. The survival and reproduction of organisms may be reduced by these pollutants.

- Diseases and pathogens- Infectious diseases can rapidly decrease susceptible populations. Chytridiomycosis caused by Batrachochytrium fungi is an important example occurring in amphibians.

- Small population size and loss of genetic variation- Small populations are more affected by inbreeding and [genetic drift](/population-genetics-unitary-and-modular-population-hardy-weinberg-law/). Demographic changes and random environmental events also have greater effects on them. Their ability to adapt with environmental changes may decrease.

- Loss of ecological partners- Some organisms depend on a particular host, prey, pollinator, or mutualist for their survival. Loss of such an organism can lead to the extinction of the species dependent on it. This is referred to as coextinction.

- Natural catastrophes and environmental changes- Asteroid impacts, extensive volcanic eruptions, major climatic shifts, and changes in ocean chemistry have caused extinctions throughout geological history. The Chicxulub impact is associated with the Cretaceous-Paleogene (K-Pg) mass extinction. Extensive volcanism is strongly linked with the Permian-Triassic mass extinction.

## Examples of Extinction

Some of the important examples of extinct species are as follows-

- Dodo (Raphus cucullatus)- Dodo was a flightless bird found in Mauritius. It became extinct during the late 17th century. Human activities and introduced mammals were responsible for its extinction.

- Passenger pigeon (Ectopistes migratorius)- It was once present in very large numbers in North America. Commercial hunting greatly reduced its population and habitat loss also affected the species. The last known passenger pigeon died in captivity in 1914.

- Great auk (Pinguinus impennis)- Great auk was a large flightless seabird of the North Atlantic. It was extensively hunted for meat, feathers, eggs, and specimens. The last reliably recorded breeding pair was killed in Iceland in 1844.

- Thylacine (Thylacinus cynocephalus)- Also known as the “Tasmanian tiger”, it was a marsupial predator of Australia. The animals were heavily killed in Tasmania and bounties were also given for their killing. Its last known captive individual died in 1936.

- Steller’s sea cow (Hydrodamalis gigas)- It was a large marine mammal found around the Commander Islands. After its discovery by Europeans in 1741, heavy hunting rapidly reduced the population. The species became extinct by 1768.

- Moa (Dinornithiformes)- Moa were large flightless birds endemic to New Zealand. Hunting and habitat removal after Polynesian settlement resulted in their rapid decline. They became extinct during the early to mid-15th century.

## Extinction At a Glance – Key Summary Table for Exam

TopicKey PointsExtinctionComplete and permanent disappearance of a species from the Earth. No living individual remains.Local extinction (Extirpation)Species disappears from a particular area but survives in other regions.Extinct in the Wild (EW)Species survives only in captivity, cultivation, or outside its former natural range.Global extinctionComplete loss of the species throughout the world.Functional extinctionSpecies is still present, but its population becomes too low to perform its normal ecological function.CoextinctionExtinction of one species following the loss of another species on which it depends.Background extinctionNormal and relatively low rate of extinction occurring through geological time.Mass extinctionLarge and rapid loss of many species and groups within a short geological period.PseudoextinctionAn ancestral form disappears by changing into a descendant form, while the evolutionary lineage continues.Major causesHabitat loss, overexploitation, invasive species, climate change, pollution, diseases, small population size, coextinction, and natural catastrophes.DodoRaphus cucullatus. Flightless bird of Mauritius. Became extinct during the late 17th century.Passenger pigeonEctopistes migratorius. Last known individual died in 1914.Great aukPinguinus impennis. Last reliably recorded breeding pair was killed in 1844.ThylacineThylacinus cynocephalus. Last known captive individual died in 1936.Steller’s sea cowHydrodamalis gigas. Became extinct by 1768 mainly due to heavy hunting.MoaLarge flightless birds of New Zealand. Became extinct during the early to mid-15th century.IUCN Extinct (EX)Used when there is “no reasonable doubt that the last individual has died”.Big FiveFive major mass extinction events, not five types of extinction.

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