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113-845: The Pliensbachian ended with the extinction event called the Toarcian turnover . During the Pliensbachian, the middle part of the Lias was deposited in Europe. The Pliensbachian is roughly coeval with the Charmouthian regional stage of North America . The Pliensbachian takes its name from the hamlet of Pliensbach in the community of Zell unter Aichelberg in the Swabian Alb , some 30 km east of Stuttgart in Germany . The name

226-531: A paraphyletic group) by therapsids occurred around the Kungurian / Roadian transition, which is often called Olson's extinction (which may be a slow decline over 20 Ma rather than a dramatic, brief event). Another point of view put forward in the Escalation hypothesis predicts that species in ecological niches with more organism-to-organism conflict will be less likely to survive extinctions. This

339-401: A "collection" (such as a time interval) to assess the relative diversity of that collection. Every time a new species (or other taxon ) enters the sample, it brings over all other fossils belonging to that species in the collection (its " share " of the collection). For example, a skewed collection with half its fossils from one species will immediately reach a sample share of 50% if that species

452-472: A "major" extinction event, and the data chosen to measure past diversity. In a landmark paper published in 1982, Jack Sepkoski and David M. Raup identified five particular geological intervals with excessive diversity loss. They were originally identified as outliers on a general trend of decreasing extinction rates during the Phanerozoic , but as more stringent statistical tests have been applied to

565-425: A Phanerozoic phenomenon, with merely the observable extinction rates appearing low before large complex organisms with hard body parts arose. 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. The Oxygen Catastrophe, which occurred around 2.45 billion years ago in

678-664: A backdrop of decreasing extinction rates through time. Four of these peaks were statistically significant: the Ashgillian ( end-Ordovician ), Late Permian , Norian ( end-Triassic ), and Maastrichtian (end-Cretaceous). The remaining peak was a broad interval of high extinction smeared over the later half of the Devonian , with its apex in the Frasnian stage. Through the 1980s, Raup and Sepkoski continued to elaborate and build upon their extinction and origination data, defining

791-409: A considerable period of time after a mass extinction, and which were reduced to only a few species, are likely to have experienced a rebound effect called the " push of the past ". Darwin was firmly of the opinion that biotic interactions, such as competition for food and space – the 'struggle for existence' – were of considerably greater importance in promoting evolution and extinction than changes in

904-521: A deep loss of ecosystem diversity. On a smaller scale, 57% of genera and at least 75% of species did not survive into the Carboniferous. These latter estimates need to be treated with a degree of caution, as the estimates of species loss depend on surveys of Devonian marine taxa that are perhaps not well enough known to assess their true rate of losses, so it is difficult to estimate the effects of differential preservation and sampling biases during

1017-480: A global cooling event. This oxygen isotope excursion is known from time-equivalent strata in South China and in the western Palaeotethys , suggesting it was a globally synchronous climatic change. The concomitance of the drop in global temperatures and the swift decline of metazoan reefs indicates the blameworthiness of global cooling in precipitating the extinction event. The "greening" of the continents during

1130-505: A global oceanic anoxic event that intruded into epicontinental seas. A positive δ O excursion is observed across the Frasnian-Famennian boundary in brachiopods from North America , Germany, Spain , Morocco , Siberia, and China ; conodont apatite δ O excursions also occurred at this time. A similar positive δ O excursion in phosphates is known from the boundary, corresponding to a removal of atmospheric carbon dioxide and

1243-424: A high-resolution biodiversity curve (the "Sepkoski curve") and successive evolutionary faunas with their own patterns of diversification and extinction. Though these interpretations formed a strong basis for subsequent studies of mass extinctions, Raup and Sepkoski also proposed a more controversial idea in 1984: a 26-million-year periodic pattern to mass extinctions. Two teams of astronomers linked this to

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1356-640: A hugely significant phase of evolution known as the Silurian-Devonian Terrestrial Revolution . Their maximum height went from 30 cm at the start of the Devonian, to 30 m archaeopterids, at the end of the period. This increase in height was made possible by the evolution of advanced vascular systems, which permitted the growth of complex branching and rooting systems, facilitating their ability to colonise drier areas previously off limits to them. In conjunction with this,

1469-425: A hypothetical brown dwarf in the distant reaches of the solar system, inventing the " Nemesis hypothesis " which has been strongly disputed by other astronomers. Around the same time, Sepkoski began to devise a compendium of marine animal genera , which would allow researchers to explore extinction at a finer taxonomic resolution. He began to publish preliminary results of this in-progress study as early as 1986, in

1582-470: A lack of consensus on Late Triassic chronology For much of the 20th century, the study of mass extinctions was hampered by insufficient data. Mass extinctions, though acknowledged, were considered mysterious exceptions to the prevailing gradualistic view of prehistory, where slow evolutionary trends define faunal changes. The first breakthrough was published in 1980 by a team led by Luis Alvarez , who discovered trace metal evidence for an asteroid impact at

1695-440: A long-term stress is compounded by a short-term shock. Over the course of the Phanerozoic , individual taxa appear to have become less likely to suffer extinction, which may reflect more robust food webs, as well as fewer extinction-prone species, and other factors such as continental distribution. However, even after accounting for sampling bias, there does appear to be a gradual decrease in extinction and origination rates during

1808-399: A new wave of studies into the dynamics of mass extinctions. These papers utilized the compendium to track origination rates (the rate that new species appear or speciate ) parallel to extinction rates in the context of geological stages or substages. A review and re-analysis of Sepkoski's data by Bambach (2006) identified 18 distinct mass extinction intervals, including 4 large extinctions in

1921-813: A paper which identified 29 extinction intervals of note. By 1992, he also updated his 1982 family compendium, finding minimal changes to the diversity curve despite a decade of new data. In 1996, Sepkoski published another paper which tracked marine genera extinction (in terms of net diversity loss) by stage, similar to his previous work on family extinctions. The paper filtered its sample in three ways: all genera (the entire unfiltered sample size), multiple-interval genera (only those found in more than one stage), and "well-preserved" genera (excluding those from groups with poor or understudied fossil records). Diversity trends in marine animal families were also revised based on his 1992 update. Revived interest in mass extinctions led many other authors to re-evaluate geological events in

2034-493: A result, they are likely to cause the climate to oscillate between cooling and warming, but with an overall trend towards warming as the carbon dioxide they emit can stay in the atmosphere for hundreds of years. Kellwasser event The Late Devonian extinction consisted of several extinction events in the Late Devonian Epoch , which collectively represent one of the five largest mass extinction events in

2147-675: A role in conjunction with the Viluy Traps. Bolide impacts can be dramatic triggers of mass extinctions. An asteroid impact was proposed as the prime cause of this faunal turnover. The impact that created the Siljan Ring either was just before the Kellwasser event or coincided with it. Most impact craters, such as the Kellwasser-aged Alamo , cannot generally be dated with sufficient precision to link them to

2260-628: A separate event from the P–T extinction; if so, it would be larger than some of the "Big Five" extinction events.   The End Cretaceous extinction, or the K–Pg extinction (formerly K–T extinction) occurred at the Cretaceous ( Maastrichtian ) – Paleogene ( Danian ) transition. The event was formerly called the Cretaceous-Tertiary or K–T extinction or K–T boundary; it is now officially named

2373-550: A shrubby or tree-like habit by the Late Givetian, including the cladoxylalean ferns , lepidosigillarioid lycopsids , and aneurophyte and archaeopterid progymnosperms . Fish were also undergoing a huge radiation, and tetrapodomorphs, such as the Frasnian-age Tiktaalik , were beginning to evolve leg-like structures. The Kellwasser event and most other Later Devonian pulses primarily affected

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2486-410: A single impact as entirely inconsistent with available evidence, although a multiple impact scenario may still be viable. Near-Earth supernovae have been speculated as possible drivers of mass extinctions due to their ability to cause ozone depletion . A recent explanation suggests that a nearby supernova explosion was the cause for the specific Hangenberg event , which marks the boundary between

2599-508: A species' true extinction must occur after its last fossil, and that origination must occur before its first fossil. Thus, species which appear to die out just prior to an abrupt extinction event may instead be a victim of the event, despite an apparent gradual decline looking at the fossil record alone. A model by Foote (2007) found that many geological stages had artificially inflated extinction rates due to Signor-Lipps "backsmearing" from later stages with extinction events. Other biases include

2712-586: A time interval, and sampling time intervals in sequence, can together be combined into equations to predict extinction and origination with less bias. In subsequent papers, Alroy continued to refine his equations to improve lingering issues with precision and unusual samples. McGhee et al. (2013), a paper which primarily focused on ecological effects of mass extinctions, also published new estimates of extinction severity based on Alroy's methods. Many extinctions were significantly more impactful under these new estimates, though some were less prominent. Stanley (2016)

2825-401: Is also the largest known extinction event for insects . The highly successful marine arthropod, the trilobite , became extinct. The evidence regarding plants is less clear, but new taxa became dominant after the extinction. The "Great Dying" had enormous evolutionary significance: on land, it ended the primacy of early synapsids . The recovery of vertebrates took 30 million years, but

2938-447: Is because the very traits that keep a species numerous and viable under fairly static conditions become a burden once population levels fall among competing organisms during the dynamics of an extinction event. Furthermore, many groups that survive mass extinctions do not recover in numbers or diversity, and many of these go into long-term decline, and these are often referred to as " Dead Clades Walking ". However, clades that survive for

3051-551: Is evidence this shift in reef composition began prior to the Frasnian-Famennian boundary. The collapse of the reef system was so stark that it would take until the Mesozoic for reefs to recover their Middle Devonian extent. Mesozoic and modern reefs are based on scleractinian ("stony") corals, which would not evolve until the Triassic period. Devonian reef-builders are entirely extinct in the modern day: Stromatoporoids died out in

3164-466: Is likely that if a supernova did occur, multiple others also did within a few million years of it. Thus, supernovae have also been speculated to have been responsible for the Kellwasser event, as well as the entire sequence of environmental crises covering several millions of years towards the end of the Devonian period. Detecting either of the long-lived, extra-terrestrial radioisotopes Sm or Pu in one or more end-Devonian extinction strata would confirm

3277-621: Is now the Scottish Highlands and Scandinavia , while the Appalachians rose over America. The biota was also very different. Plants, which had been on land in forms similar to mosses and liverworts since the Ordovician , had just developed roots, seeds, and water transport systems that allowed them to survive away from places that were constantly wet—and so grew huge forests on the highlands. Several clades had developed

3390-464: Is strong evidence supporting periodicity in a variety of records, and additional evidence in the form of coincident periodic variation in nonbiological geochemical variables such as Strontium isotopes, flood basalts, anoxic events, orogenies, and evaporite deposition. One explanation for this proposed cycle is carbon storage and release by oceanic crust, which exchanges carbon between the atmosphere and mantle. Mass extinctions are thought to result when

3503-451: Is the " Pull of the recent ", the fact that the fossil record (and thus known diversity) generally improves closer to the modern day. This means that biodiversity and abundance for older geological periods may be underestimated from raw data alone. Alroy (2010) attempted to circumvent sample size-related biases in diversity estimates using a method he called " shareholder quorum subsampling" (SQS). In this method, fossils are sampled from

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3616-423: Is the first to be sampled. This continues, adding up the sample shares until a "coverage" or " quorum " is reached, referring to a pre-set desired sum of share percentages. At that point, the number of species in the sample are counted. A collection with more species is expected to reach a sample quorum with more species, thus accurately comparing the relative diversity change between two collections without relying on

3729-584: The Cambrian . These fit Sepkoski's definition of extinction, as short substages with large diversity loss and overall high extinction rates relative to their surroundings. Bambach et al. (2004) considered each of the "Big Five" extinction intervals to have a different pattern in the relationship between origination and extinction trends. Moreover, background extinction rates were broadly variable and could be separated into more severe and less severe time intervals. Background extinctions were least severe relative to

3842-520: The Cambrian explosion , five further major mass extinctions have significantly exceeded the background extinction rate. The most recent and best-known, the Cretaceous–Paleogene extinction event , which occurred approximately 66 Ma (million years ago), was a large-scale mass extinction of animal and plant species in a geologically short period of time. In addition to the five major Phanerozoic mass extinctions, there are numerous lesser ones, and

3955-672: The Hangenberg event , also known as the end-Devonian extinction, occurred 359 million years ago, bringing an end to the Famennian and Devonian, as the world transitioned into the Carboniferous Period . Although it is well established that there was a massive loss of biodiversity in the Late Devonian, the timespan of this event is uncertain, with estimates ranging from 500,000 to 25 million years, extending from

4068-538: The Paleoproterozoic , is plausible as the first-ever major extinction event. It was perhaps also the worst-ever, in some sense, but with the Earth's ecology just before that time so poorly understood, and the concept of prokaryote genera so different from genera of complex life, that it would be difficult to meaningfully compare it to any of the "Big Five" even if Paleoproterozoic life were better known. Since

4181-461: The biodiversity on Earth . Such an event is identified by a sharp fall in the diversity and abundance of multicellular organisms . It occurs when the rate of extinction increases with respect to the background extinction rate and 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 disagreement as to what constitutes

4294-649: The biosphere rather than the total diversity and abundance of life. For this reason, well-documented extinction events are confined to the Phanerozoic eon – with the sole exception of the Oxygen Catastrophe in the Proterozoic – since before the Phanerozoic, all living organisms were either microbial, or if multicellular then soft-bodied. Perhaps due to the absence of a robust microbial fossil record, mass extinctions might only seem to be mainly

4407-578: The 40ka Milankovic cycle . The continued drawdown of organic carbon eventually pulled the Earth out of its greenhouse state during the Famennian into the icehouse that continued throughout the Carboniferous and Permian. Magmatism was suggested as a cause of the Late Devonian extinction in 2002. The end of the Devonian Period had extremely widespread trap magmatism and rifting in the Russian and Siberian platforms, which were situated above

4520-480: The Cretaceous–Paleogene (or K–Pg) extinction event. About 17% of all families, 50% of all genera and 75% of all species became extinct. In the seas all the ammonites , plesiosaurs and mosasaurs disappeared and the percentage of sessile animals was reduced to about 33%. All non-avian dinosaurs became extinct during that time. The boundary event was severe with a significant amount of variability in

4633-467: The Devonian and Carboniferous periods. This could offer a possible explanation for the dramatic drop in atmospheric ozone during the Hangenberg event that could have permitted massive ultraviolet damage to the genetic material of lifeforms, triggering a mass extinction. Recent research offers evidence of ultraviolet damage to pollen and spores over many thousands of years during this event as observed in

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4746-465: The Devonian. Extinction rates appear to have been higher than the background rate for an extended interval covering the last 20–25 million years of the Devonian. During this time, about eight to ten distinct events can be seen, of which two, the Kellwasser and the Hangenberg events, stand out as particularly severe. The Kellwasser event was preceded by a longer period of prolonged biodiversity loss . The Kellwasser event, named for its type locality ,

4859-706: The Frasnian / Famennian extinction, with the Kola and Timan-Pechora magmatic provinces being suggested to be related to the Hangenberg event at the Devonian-Carboniferous boundary. Viluy magmatism may have injected enough CO 2 and SO 2 into the atmosphere to have generated a destabilised greenhouse and ecosystem , causing rapid global cooling, sea-level falls, and marine anoxia to occur during Kellwasser black shale deposition. Viluy Traps activity may have also enabled euxinia by fertilising

4972-575: The Frasnian-Famennian boundary, leading other studies to reject volcanism as an explanation for the crisis. Another overlooked contributor to the Kellwasser mass extinction could be the now extinct Cerberean Caldera which was active in the Late Devonian period and thought to have undergone a supereruption approximately 374 million years ago. Remains of this caldera can be found in the modern day state of Victoria, Australia. Eovariscan volcanic activity in present-day Europe may have also played

5085-561: The Givetian-Frasnian boundary and in ones coeval with the Hangenberg event. Because coronene enrichment is only known in association with large igneous province emissions and extraterrestrial impacts and the fact that there is no confirmed evidence of the latter occurring in association with the Kellwasser event, this enrichment strongly suggests a causal relationship between volcanism and the Kellwasser extinction event. However, not all sites show evidence of mercury enrichment across

5198-402: The Kellwasser event, but still experienced some diversity loss. Around half of placoderm families died out, primarily species-poor bottom-feeding groups. More diverse placoderm families survived the event only to succumb in the Hangenberg event at the end of the Devonian. Most lingering agnathan (jawless fish) groups, such as osteostracans , galeaspids , and heterostracans , also went extinct by

5311-412: The Kellwasser extinction, though their fossils are rare until the mid-to-late Famennian. The late Devonian crash in biodiversity was more drastic than the familiar extinction event that closed the Cretaceous . A recent survey (McGhee 1996) estimates that 22% of all the ' families ' of marine animals (largely invertebrates ) were eliminated. The family is a great unit, and to lose so many signifies

5424-654: The Kellwassertal in Lower Saxony , Germany , is the term given to the extinction pulse that occurred near the Frasnian–Famennian boundary (372.2 ± 1.6 Ma). Most references to the "Late Devonian extinction" are in fact referring to the Kellwasser, which was the first event to be detected based on marine invertebrate record and was the most severe of the extinction crises of the Late Devonian. There may in fact have been two closely spaced events here, as shown by

5537-651: The Late Devonian extinction interval ( Givetian , Frasnian, and Famennian stages) to be statistically significant. Regardless, later studies have affirmed the strong ecological impacts of the Kellwasser and Hangenberg Events.   The End Permian extinction or the "Great Dying" occurred at the Permian – Triassic transition. It was the Phanerozoic Eon's largest extinction: 53% of marine families died, 84% of marine genera, about 81% of all marine species and an estimated 70% of terrestrial vertebrate species. This

5650-628: The Late Devonian, the continents were arranged differently from today, with a supercontinent, Gondwana , covering much of the Southern Hemisphere. The continent of Siberia occupied the Northern Hemisphere, while an equatorial continent, Laurussia (formed by the collision of Baltica and Laurentia ), was drifting towards Gondwana, closing the Rheic Ocean . The Caledonian mountains were also growing across what

5763-651: The North American Devonian Seaway. Elevated molybdenum concentrations further support widespread euxinic waters. The timing, magnitude, and causes of Kellwasser anoxia remain poorly understood. Anoxia was not omnipresent across the globe; in some regions, such as South China , the Frasnian-Famennian boundary instead shows evidence of increased oxygenation of the seafloor. Trace metal proxies in black shales from New York state point to anoxic conditions only occurring intermittently, being interrupted by oxic intervals, further indicating that anoxia

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5876-430: The Phanerozoic. This may represent the fact that groups with higher turnover rates are more likely to become extinct by chance; or it may be an artefact of taxonomy: families tend to become more speciose, therefore less prone to extinction, over time; and larger taxonomic groups (by definition) appear earlier in geological time. It has also been suggested that the oceans have gradually become more hospitable to life over

5989-519: The Pliensbachian (the base of the Toarcian Stage) is at the first appearance of ammonite genus Eodactylites . The Pliensbachian contains five ammonite biozones in the boreal domain : In the Tethys domain , the Pliensbachian contains six biozones: Extinction event An extinction event (also known as a mass extinction or biotic crisis ) is a widespread and rapid decrease in

6102-573: The Silurian-Devonian Terrestrial Revolution that led to them being covered with massive photosynthesizing land plants in the first forests reduced CO 2 levels in the atmosphere. Since CO 2 is a greenhouse gas, reduced levels might have helped produce a chillier climate, in contrast to the warm climate of the Middle Devonian. The biological sequestration of carbon dioxide may have ultimately led to

6215-569: The Sun, oscillations in the galactic plane, or passage through the Milky Way's spiral arms. However, other authors have concluded that the data on marine mass extinctions do not fit with the idea that mass extinctions are periodic, or that ecosystems gradually build up to a point at which a mass extinction is inevitable. Many of the proposed correlations have been argued to be spurious or lacking statistical significance. Others have argued that there

6328-415: The accumulating data, it has been established that in the current, Phanerozoic Eon, multicellular animal life has experienced at least five major and many minor mass extinctions. The "Big Five" cannot be so clearly defined, but rather appear to represent the largest (or some of the largest) of a relatively smooth continuum of extinction events. All of the five in the Phanerozoic Eon were anciently preceded by

6441-594: The beginning of the Late Palaeozoic Ice Age during the Famennian, which has been suggested as a cause of the Hangenberg event. The weathering of silicate rocks also draws down CO 2 from the atmosphere, and CO 2 sequestration by mountain building has been suggested as a cause of the decline in greenhouse gases during the Frasnian-Famennian transition. This mountain-building may have also enhanced biological sequestration through an increase in nutrient runoff. The combination of silicate weathering and

6554-400: The biases inherent to sample size. Alroy also elaborated on three-timer algorithms, which are meant to counteract biases in estimates of extinction and origination rates. A given taxon is a "three-timer" if it can be found before, after, and within a given time interval, and a "two-timer" if it overlaps with a time interval on one side. Counting "three-timers" and "two-timers" on either end of

6667-652: The burial of organic matter to decreased atmospheric CO 2 concentrations from about 15 to three times present levels. Carbon in the form of plant matter would be produced on prodigious scales, and given the right conditions, could be stored and buried, eventually producing vast coal measures (e.g. in China) which locked the carbon out of the atmosphere and into the lithosphere . This reduction in atmospheric CO 2 would have caused global cooling and resulted in at least one period of late Devonian glaciation (and subsequent sea level fall), probably fluctuating in intensity alongside

6780-426: The calcite-based reef-builders of the great Devonian reef-systems, including the stromatoporoid sponges and the rugose and tabulate corals . It left communities of beloceratids and manticoceratids devastated. Following the Kellwasser event, reefs of the Famennian were primarily dominated by siliceous sponges and calcifying bacteria, producing structures such as oncolites and stromatolites , although there

6893-413: The context of their effects on life. A 1995 paper by Michael Benton tracked extinction and origination rates among both marine and continental (freshwater & terrestrial) families, identifying 22 extinction intervals and no periodic pattern. Overview books by O.H. Walliser (1996) and A. Hallam and P.B. Wignall (1997) summarized the new extinction research of the previous two decades. One chapter in

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7006-478: The correlation of extinction and origination rates to diversity. High diversity leads to a persistent increase in extinction rate; low diversity to a persistent increase in origination rate. These presumably ecologically controlled relationships likely amplify smaller perturbations (asteroid impacts, etc.) to produce the global effects observed. A good theory for a particular mass extinction should: It may be necessary to consider combinations of causes. For example,

7119-458: The difficulty in assessing taxa with high turnover rates or restricted occurrences, which cannot be directly assessed due to a lack of fine-scale temporal resolution. Many paleontologists opt to assess diversity trends by randomized sampling and rarefaction of fossil abundances rather than raw temporal range data, in order to account for all of these biases. But that solution is influenced by biases related to sample size. One major bias in particular

7232-480: The dominant role in extinction. Evidence exists of a rapid increase in the rate of organic carbon burial and for widespread anoxia in oceanic bottom waters. Signs of anoxia in shallow waters have also been described from a variety of localities. Good evidence has been found for high-frequency sea-level changes around the Frasnian–Famennian Kellwasser event, with one sea-level rise associated with

7345-441: The effect of reducing the estimated severity of the six sampled mass extinction events. This effect was stronger for mass extinctions which occurred in periods with high rates of background extinction, like the Devonian. Because most diversity and biomass on Earth is microbial , and thus difficult to measure via fossils, extinction events placed on-record are those that affect the easily observed, biologically complex component of

7458-513: The end of the Cretaceous period. The Alvarez hypothesis for the end-Cretaceous extinction gave mass extinctions, and catastrophic explanations, newfound popular and scientific attention. Another landmark study came in 1982, when a paper written by David M. Raup and Jack Sepkoski was published in the journal Science . This paper, originating from a compendium of extinct marine animal families developed by Sepkoski, identified five peaks of marine family extinctions which stand out among

7571-537: The end of the Frasnian and were nearly wiped out by the extinctions. The extinction event was accompanied by widespread oceanic anoxia ; that is, a lack of oxygen, prohibiting decay and allowing the preservation of organic matter. This, combined with the ability of porous reef rocks to hold oil, has led to Devonian rocks being an important source of oil, especially in Canada and the United States . During

7684-403: The end of the Frasnian. The jawless thelodonts only barely survived, succumbing early in the Famennian. Among freshwater and shallow marine tetrapodomorph fish, the tetrapod-like elpistostegalians (such as Tiktaalik ) disappeared at the Frasnian-Famennian boundary. True tetrapods (defined as four-limbed vertebrates with digits) survived and experienced an evolutionary radiation following

7797-527: The end of the Middle Devonian ( 382.7 ± 1.6 Ma ), into the Late Devonian ( 382.7 ± 1.6 Ma to 358.9 ± 0.4 Ma ), several environmental changes can be detected from the sedimentary record, which directly affected organisms and caused extinction. What caused these changes is somewhat more open to debate. Possible triggers for the Kellwasser event are as follows: During the Late Silurian and Devonian, land plants, assisted by fungi, underwent

7910-752: The end of the period of pressure. Their statistical analysis of marine extinction rates throughout the Phanerozoic suggested that neither long-term pressure alone nor a catastrophe alone was sufficient to cause a significant increase in the extinction rate. MacLeod (2001) summarized the relationship between mass extinctions and events that are most often cited as causes of mass extinctions, using data from Courtillot, Jaeger & Yang et al. (1996), Hallam (1992) and Grieve & Pesonen (1992): The most commonly suggested causes of mass extinctions are listed below. The formation of large igneous provinces by flood basalt events could have: Flood basalt events occur as pulses of activity punctuated by dormant periods. As

8023-647: The end-Devonian Hangenberg event, while rugose and tabulate corals went extinct at the Permian-Triassic extinction . Further taxa to be starkly affected include the brachiopods , trilobites , ammonites , conodonts , acritarch and graptolites . Cystoids disappeared during this event. The surviving taxa show morphological trends through the event. Atrypid and strophomenid brachiopods became rarer, replaced in many niches by productids , whose spiny shells made them more resistant to predation and environmental disturbances. Trilobites evolved smaller eyes in

8136-462: The entire Phanerozoic. As data continued to accumulate, some authors began to re-evaluate Sepkoski's sample using methods meant to account for sampling biases . As early as 1982, a paper by Phillip W. Signor and Jere H. Lipps noted that the true sharpness of extinctions was diluted by the incompleteness of the fossil record. This phenomenon, later called the Signor-Lipps effect , notes that

8249-412: The event; others dated precisely are not contemporaneous with the extinction. Although some evidence of meteoric impact have been observed in places, including iridium anomalies and microspherules, these were probably caused by other factors. Some lines of evidence suggest that the meteorite impact and its associated geochemical signals postdate the extinction event. Modelling studies have ruled out

8362-483: The evolution of seeds permitted reproduction and dispersal in areas which were not waterlogged, allowing plants to colonise previously inhospitable inland and upland areas. The two factors combined to greatly magnify the role of plants on the global scale. In particular, Archaeopteris forests expanded rapidly during the closing ages of the Devonian. These tall trees required deep rooting systems to acquire water and nutrients, and provide anchorage. These systems broke up

8475-472: The first volcanic phase is in agreement with the age of 372.2 ± 3.2  Ma proposed for the Kellwasser event. However, the second volcanic phase is slightly older than Hangenberg event, which is dated to around 358.9 ± 1.2  Ma. Coronene and mercury enrichment has been found in deposits dating back to the Kellwasser event, with similar enrichments found in deposits coeval with the Frasnes event at

8588-556: The following section. The "Big Five" mass extinctions are bolded. Graphed but not discussed by Sepkoski (1996), considered continuous with the Late Devonian mass extinction At the time considered continuous with the end-Permian mass extinction Includes late Norian time slices Diversity loss of both pulses calculated together Pulses extend over adjacent time slices, calculated separately Considered ecologically significant, but not analyzed directly Excluded due to

8701-429: The former source lists over 60 geological events which could conceivably be considered global extinctions of varying sizes. These texts, and other widely circulated publications in the 1990s, helped to establish the popular image of mass extinctions as a "big five" alongside many smaller extinctions through prehistory. Though Sepkoski died in 1999, his marine genera compendium was formally published in 2002. This prompted

8814-424: The fossil record and that, in turn, points to a possible long-term destruction of the ozone layer. A supernova explosion is an alternative explanation to global temperature rise, that could account for the drop in atmospheric ozone. Because very high mass stars, required to produce a supernova, tend to form in dense star-forming regions of space and have short lifespans lasting only at most tens of millions of years, it

8927-465: The geological record.   The largest extinction was the Kellwasser Event ( Frasnian - Famennian , or F-F, 372 Ma), an extinction event at the end of the Frasnian, about midway through the Late Devonian. This extinction annihilated coral reefs and numerous tropical benthic (seabed-living) animals such as jawless fish, brachiopods , and trilobites . The other major extinction

9040-591: The history of life on Earth. The term primarily refers to a major extinction, the Kellwasser event , also known as the Frasnian-Famennian extinction , which occurred around 372 million years ago, at the boundary between the Frasnian age and the Famennian age, the last age in the Devonian Period. Overall, 19% of all families and 50% of all genera became extinct. A second mass extinction called

9153-675: The hot mantle plumes and suggested as a cause of the Frasnian / Famennian and end-Devonian extinctions. The Viluy Large igneous province, located in the Vilyuysk region on the Siberian Craton , covers most of the present day north-eastern margin of the Siberian Platform. The triple-junction rift system was formed during the Devonian Period; the Viluy rift is the western remaining branch of the system and two other branches form

9266-456: The large terrestrial vertebrate niches. The dinosaurs themselves had been beneficiaries of a previous mass extinction, the end-Triassic , which eliminated most of their chief rivals, the crurotarsans . Similarly, within Synapsida , the replacement of taxa that originated in the earliest, Pennsylvanian and Cisuralian evolutionary radiation (often still called " pelycosaurs ", though this is

9379-422: The last 500 million years, and thus less vulnerable to mass extinctions, but susceptibility to extinction at a taxonomic level does not appear to make mass extinctions more or less probable. There is still debate about the causes of all mass extinctions. In general, large extinctions may result when a biosphere under long-term stress undergoes a short-term shock. An underlying mechanism appears to be present in

9492-460: The latter almost completely disappeared. The causes of these extinctions are unclear. Leading hypotheses include changes in sea level and ocean anoxia , possibly triggered by global cooling or oceanic volcanism. The impact of a comet or another extraterrestrial body has also been suggested, such as the Siljan Ring event in Sweden. Some statistical analysis suggests that the decrease in diversity

9605-430: The marine aspect of the end-Cretaceous extinction appears to have been caused by several processes that partially overlapped in time and may have had different levels of significance in different parts of the world. Arens and West (2006) proposed a "press / pulse" model in which mass extinctions generally require two types of cause: long-term pressure on the eco-system ("press") and a sudden catastrophe ("pulse") towards

9718-419: The marine community, and had a greater effect on shallow warm-water organisms than on cool-water organisms. The Kellwasser event's effects were also stronger at low latitudes than high ones. Large differences are observed between the biotas before and after the Frasnian-Famennian boundary, demonstrating the extinction event's magnitude. The most hard-hit biological category affected by the Kellwasser event were

9831-434: The mass extinction were global warming , related to volcanism , and anoxia , and not, as considered earlier, cooling and glaciation . However, this is at odds with numerous previous studies, which have indicated global cooling as the primary driver. Most recently, the deposition of volcanic ash has been suggested to be the trigger for reductions in atmospheric carbon dioxide leading to the glaciation and anoxia observed in

9944-675: The mid-Givetian to the end-Famennian. Some consider the extinction to be as many as seven distinct events, spread over about 25 million years, with notable extinctions at the ends of the Givetian , Frasnian , and Famennian ages. By the Late Devonian, the land had been colonized by plants and insects . In the oceans, massive reefs were built by corals and stromatoporoids . Euramerica and Gondwana were beginning to converge into what would become Pangaea . The extinction seems to have only affected marine life . Hard-hit groups include brachiopods , trilobites , and reef-building organisms ;

10057-411: The modern margin of the Siberian Platform. Volcanic rocks are covered with post Late Devonian–Early Carboniferous sediments. Volcanic rocks, dyke belts , and sills that cover more than 320,000 km , and a gigantic amount of magmatic material (more than 1 million km ) formed in the Viluy branch. The Viluy and Pripyat-Dnieper-Donets large igneous provinces were suggested to correlate with

10170-457: The oceans with sulphate, increasing rates of microbial sulphate reduction. Recent studies have confirmed a correlation between Viluy traps in the Vilyuysk region on the Siberian Craton and the Kellwasser extinction by Ar/ Ar dating. Ages show that the two volcanic phase hypotheses are well supported and the weighted mean ages of each volcanic phase are 376.7 ± 3.4 and 364.4 ± 3.4  Ma, or 373.4 ± 2.1 and 363.2 ± 2.0  Ma, which

10283-426: The old, dominant group and makes way for the new one, a process known as adaptive radiation . For example, mammaliaformes ("almost mammals") and then mammals existed throughout the reign of the dinosaurs , but could not compete in the large terrestrial vertebrate niches that dinosaurs monopolized. The end-Cretaceous mass extinction removed the non-avian dinosaurs and made it possible for mammals to expand into

10396-400: The ongoing mass extinction caused by human activity is sometimes called the sixth mass extinction . Mass extinctions have sometimes accelerated the evolution of life on Earth . When dominance of particular ecological niches passes from one group of organisms to another, it is rarely because the newly dominant group is "superior" to the old but usually because an extinction event eliminates

10509-485: The onset of anoxic deposits; marine transgressions likely helped spread deoxygenated waters. Evidence exists for the modulation of the intensity of anoxia by Milankovitch cycles as well. Negative δ U excursions concomitant with both the Lower and Upper Kellwasser events provide direct evidence for an increase in anoxia. Photic zone euxinia , documented by concurrent negative ∆ Hg and positive δ Hg excursions, occurred in

10622-565: The origination rate in the middle Ordovician-early Silurian, late Carboniferous-Permian, and Jurassic-recent. This argues that the Late Ordovician, end-Permian, and end-Cretaceous extinctions were statistically significant outliers in biodiversity trends, while the Late Devonian and end-Triassic extinctions occurred in time periods which were already stressed by relatively high extinction and low origination. Computer models run by Foote (2005) determined that abrupt pulses of extinction fit

10735-425: The oxygen isotope ratio , and thus with the sea water temperature; this may relate to their occupying different trophic levels as nutrient input changed. As with most extinction events, specialist taxa occupying small niches were harder hit than generalists. Marine invertebrates that lived in warmer ecoregions were devastated more compared to those living in colder biomes. Vertebrates were not strongly affected by

10848-686: The pattern of prehistoric biodiversity much better than a gradual and continuous background extinction rate with smooth peaks and troughs. This strongly supports the utility of rapid, frequent mass extinctions as a major driver of diversity changes. Pulsed origination events are also supported, though to a lesser degree which is largely dependent on pulsed extinctions. Similarly, Stanley (2007) used extinction and origination data to investigate turnover rates and extinction responses among different evolutionary faunas and taxonomic groups. In contrast to previous authors, his diversity simulations show support for an overall exponential rate of biodiversity growth through

10961-480: The physical environment. He expressed this in The Origin of Species : Various authors have suggested that extinction events occurred periodically, every 26 to 30 million years, or that diversity fluctuates episodically about every 62 million years. Various ideas, mostly regarding astronomical influences, attempt to explain the supposed pattern, including the presence of a hypothetical companion star to

11074-499: The presence of two distinct anoxic shale layers. There is evidence that the Kellwasser event was a two-pulsed event, with the two extinction pulses being separated by an interval of approximately 800,000 years. The second pulse was more severe than the first. Since the Kellwasser-related extinctions occurred over such a long time, it is difficult to assign a single cause, and indeed to separate cause from effect. From

11187-596: The presumed far more extensive mass extinction of microbial life during the Great Oxidation Event (a.k.a. Oxygen Catastrophe) early in the Proterozoic Eon . At the end of the Ediacaran and just before the Cambrian explosion , yet another Proterozoic extinction event (of unknown magnitude) is speculated to have ushered in the Phanerozoic. In May 2020, studies suggested that the causes of

11300-566: The rate of extinction between and among different clades . Mammals , descended from the synapsids , and birds , a side-branch of the theropod dinosaurs, emerged as the two predominant clades of terrestrial tetrapods. Despite the common presentation focusing only on these five events, no measure of extinction shows any definite line separating them from the many other Phanerozoic extinction events that appear only slightly lesser catastrophes; further, using different methods of calculating an extinction's impact can lead to other events featuring in

11413-588: The rock exposure of Western Europe indicates that many of the minor events for which a biological explanation has been sought are most readily explained by sampling bias . Research completed after the seminal 1982 paper (Sepkoski and Raup) has concluded that a sixth mass extinction event due to human activities is currently under way: Extinction events can be tracked by several methods, including geological change, ecological impact, extinction vs. origination ( speciation ) rates, and most commonly diversity loss among taxonomic units. Most early papers used families as

11526-478: The run-up to the Kellwasser event, with eye size increasing again afterwards. This suggests vision was less important around the event, perhaps due to increasing water depth or turbidity. The brims of trilobites (i.e. the rims of their heads) also expanded across this period. The brims are thought to have served a respiratory purpose, and the increasing anoxia of waters led to an increase in their brim area in response. The shape of conodonts' feeding apparatus varied with

11639-639: The same short time interval. To circumvent this issue, background rates of diversity change (extinction/origination) were estimated for stages or substages without mass extinctions, and then assumed to apply to subsequent stages with mass extinctions. For example, the Santonian and Campanian stages were each used to estimate diversity changes in the Maastrichtian prior to the K-Pg mass extinction. Subtracting background extinctions from extinction tallies had

11752-530: The surface can sink at such a rate that decomposition of dead organisms uses up all available oxygen, creating anoxic conditions and suffocating bottom-dwelling fish. The fossil reefs of the Frasnian were dominated by stromatoporoids and (to a lesser degree) corals—organisms which only thrive in low-nutrient conditions. Therefore, the postulated influx of high levels of nutrients may have caused an extinction. Anoxic conditions correlate better with biotic crises than phases of cooling, suggesting anoxia may have played

11865-602: The top five. Fossil records of older events are more difficult to interpret. This is because: It has been suggested that the apparent variations in marine biodiversity may actually be an artifact, with abundance estimates directly related to quantity of rock available for sampling from different time periods. However, statistical analysis shows that this can only account for 50% of the observed pattern, and other evidence such as fungal spikes (geologically rapid increase in fungal abundance) provides reassurance that most widely accepted extinction events are real. A quantification of

11978-453: The unit of taxonomy, based on compendiums of marine animal families by Sepkoski (1982, 1992). Later papers by Sepkoski and other authors switched to genera , which are more precise than families and less prone to taxonomic bias or incomplete sampling relative to species. These are several major papers estimating loss or ecological impact from fifteen commonly-discussed extinction events. Different methods used by these papers are described in

12091-645: The upper layers of bedrock and stabilized a deep layer of soil, which would have been of the order of metres thick. In contrast, early Devonian plants bore only rhizoids and rhizomes that could penetrate no more than a few centimeters. The mobilization of a large portion of soil had a huge effect: soil promotes weathering , the chemical breakdown of rocks, releasing ions which are nutrients for plants and algae. The relatively sudden input of nutrients into river water as rooted plants expanded into upland regions may have caused eutrophication and subsequent anoxia. For example, during an algal bloom, organic material formed at

12204-494: The vacant niches created the opportunity for archosaurs to become ascendant . In the seas, the percentage of animals that were sessile (unable to move about) dropped from 67% to 50%. The whole late Permian was a difficult time, at least for marine life, even before the P–T boundary extinction. More recent research has indicated that the End-Capitanian extinction event that preceded the "Great Dying" likely constitutes

12317-457: Was another paper which attempted to remove two common errors in previous estimates of extinction severity. The first error was the unjustified removal of "singletons", genera unique to only a single time slice. Their removal would mask the influence of groups with high turnover rates or lineages cut short early in their diversification. The second error was the difficulty in distinguishing background extinctions from brief mass extinction events within

12430-400: Was caused more by a decrease in speciation than by an increase in extinctions. This might have been caused by invasions of cosmopolitan species, rather than by any single event. Placoderms were hit hard by the Kellwasser event and completely died out in the Hangenberg event, but most other jawed vertebrates were less strongly impacted. Agnathans (jawless fish) were in decline long before

12543-456: Was introduced into scientific literature by German palaeontologist Albert Oppel in 1858. The base of the Pliensbachian is at the first appearances of the ammonite species Bifericeras donovani and genera Apoderoceras and Gleviceras . The Wine Haven profile near Robin Hood's Bay ( Yorkshire , England ) has been appointed as global reference profile for the base ( GSSP ). The top of

12656-473: Was not globally synchronous, a finding also supported by the prevalence of cyanobacterial mats in the Holy Cross Mountains in the time period around the Kellwasser event. Evidence from various European sections reveals that Kellwasser anoxia was relegated to epicontinental seas and developed as a result of upwelling of poorly oxygenated waters within ocean basins into shallow waters rather than

12769-514: Was the Hangenberg Event (Devonian-Carboniferous, or D-C, 359 Ma), which brought an end to the Devonian as a whole. This extinction wiped out the armored placoderm fish and nearly led to the extinction of the newly evolved ammonoids . These two closely spaced extinction events collectively eliminated about 19% of all families, 50% of all genera and at least 70% of all species. Sepkoski and Raup (1982) did not initially consider

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