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104-558: Diadectidae is an extinct family of early tetrapods that lived in what is now North America and Europe during the Late Carboniferous and Early Permian , and in Asia during the Late Permian . They were the first herbivorous tetrapods , and also the first fully terrestrial animals to attain large sizes. Footprints indicate that diadectids walked with an erect posture. They were

208-438: A food chain who lose their prey. "Species coextinction is a manifestation of one of the interconnectednesses of organisms in complex ecosystems ... While coextinction may not be the most important cause of species extinctions, it is certainly an insidious one." Coextinction is especially common when a keystone species goes extinct. Models suggest that coextinction is the most common form of biodiversity loss . There may be

312-657: A nautilus to the Royal Society that was more than two feet in diameter, and morphologically distinct from any known living species. Hooke theorized that this was simply because the species lived in the deep ocean and no one had discovered them yet. While he contended that it was possible a species could be "lost", he thought this highly unlikely. Similarly, in 1695, Sir Thomas Molyneux published an account of enormous antlers found in Ireland that did not belong to any extant taxa in that area. Molyneux reasoned that they came from

416-415: A species or a population is the variety of genetic information in its living members. A large gene pool (extensive genetic diversity ) is associated with robust populations that can survive bouts of intense selection . Meanwhile, low genetic diversity (see inbreeding and population bottlenecks ) reduces the range of adaptions possible. Replacing native with alien genes narrows genetic diversity within

520-436: A viable population for species preservation and possible future reintroduction to the wild, through use of carefully planned breeding programs . The extinction of one species' wild population can have knock-on effects, causing further extinctions. These are also called "chains of extinction". This is especially common with extinction of keystone species . A 2018 study indicated that the sixth mass extinction started in

624-417: A 2005 phylogenetic analysis, most species of Diadectes formed a clade with Diasparactus zenos . Two species, Diadectes absitus and Diadectes sanmiguelensis , were placed in more basal positions. These species possess primitive characteristics found in non-diadectid forms, such as Limnoscelis and Tseajaia . Because D. absitus and D. sanmiguelensis were placed far from other species of Diadectes in

728-474: A Lazarus species when extant individuals were described in 2019. Attenborough's long-beaked echidna ( Zaglossus attenboroughi ) is an example of a Lazarus species from Papua New Guinea that had last been sighted in 1962 and believed to be possibly extinct, until it was recorded again in November 2023. Some species currently thought to be extinct have had continued speculation that they may still exist, and in

832-495: A cascade of coextinction across the trophic levels . Such effects are most severe in mutualistic and parasitic relationships. An example of coextinction is the Haast's eagle and the moa : the Haast's eagle was a predator that became extinct because its food source became extinct. The moa were several species of flightless birds that were a food source for the Haast's eagle. Extinction as

936-429: A common ancestor with modern horses. Pseudoextinction is much easier to demonstrate for larger taxonomic groups. A Lazarus taxon or Lazarus species refers to instances where a species or taxon was thought to be extinct, but was later rediscovered. It can also refer to instances where large gaps in the fossil record of a taxon result in fossils reappearing much later, although the taxon may have ultimately become extinct at

1040-399: A fact that was accepted by most scientists. The primary debate focused on whether this turnover caused by extinction was gradual or abrupt in nature. Cuvier understood extinction to be the result of cataclysmic events that wipe out huge numbers of species, as opposed to the gradual decline of a species over time. His catastrophic view of the nature of extinction garnered him many opponents in

1144-708: A higher risk of extinction and die out faster than less sexually dimorphic species, the least sexually dimorphic species surviving for millions of years while the most sexually dimorphic species die out within mere thousands of years. Earlier studies based on counting the number of currently living species in modern taxa have shown a higher number of species in more sexually dimorphic taxa which have been interpreted as higher survival in taxa with more sexual selection, but such studies of modern species only measure indirect effects of extinction and are subject to error sources such as dying and doomed taxa speciating more due to splitting of habitat ranges into more small isolated groups during

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1248-405: A large range, a lack of individuals of both sexes (in sexually reproducing species), or other reasons. Pinpointing the extinction (or pseudoextinction ) of a species requires a clear definition of that species . If it is to be declared extinct, the species in question must be uniquely distinguishable from any ancestor or daughter species, and from any other closely related species. Extinction of

1352-592: A later point. The coelacanth , a fish related to lungfish and tetrapods , is an example of a Lazarus taxon that was known only from the fossil record and was considered to have been extinct since the end of the Cretaceous Period . In 1938, however, a living specimen was found off the Chalumna River (now Tyolomnqa) on the east coast of South Africa. Calliostoma bullatum , a species of deepwater sea snail originally described from fossils in 1844 proved to be

1456-587: A mathematical model that falls in all positions. By contrast, conservation biology uses the extinction vortex model to classify extinctions by cause. When concerns about human extinction have been raised, for example in Sir Martin Rees ' 2003 book Our Final Hour , those concerns lie with the effects of climate change or technological disaster. Human-driven extinction started as humans migrated out of Africa more than 60,000 years ago. Currently, environmental groups and some governments are concerned with

1560-472: A more recent common ancestor with Diadectes than with Tseajaia . Below is a cladogram modified from the 2010 analysis: Limnoscelidae Tseajaiidae Ambedus pusillus ? Oradectes sanmiguelensis Orobates pabsti Desmatodon hesperis Silvadectes absitus Diadectes tenuitectes Diadectes sideropelicus Diasparactus zenos Diadectes is the best known diadectid, with six species named since its initial description. In

1664-456: A natural part of the evolutionary process. Only recently have extinctions been recorded and scientists have become alarmed at the current high rate of extinctions . Most species that become extinct are never scientifically documented. Some scientists estimate that up to half of presently existing plant and animal species may become extinct by 2100. A 2018 report indicated that the phylogenetic diversity of 300 mammalian species erased during

1768-441: A new mega-predator or by transporting animals and plants from one part of the world to another. Such introductions have been occurring for thousands of years, sometimes intentionally (e.g. livestock released by sailors on islands as a future source of food) and sometimes accidentally (e.g. rats escaping from boats). In most cases, the introductions are unsuccessful, but when an invasive alien species does become established,

1872-677: A new species of Diadectes , D. absitus , was described from the Bromacker sandstone quarry of the Tambach Formation in the Thuringian Forest of central Germany. A new genus of diadectid called Orobates was also named from the Bromacker Quarry in 2004. In 2015, the known geographic range of diadectids was expanded with the description of a new genus and species of diadectid from China, Alveusdectes fenestralis . Alveusdectes

1976-610: A population a higher chance in the short term of surviving an adverse change in conditions. Effects that cause or reward a loss in genetic diversity can increase the chances of extinction of a species. Population bottlenecks can dramatically reduce genetic diversity by severely limiting the number of reproducing individuals and make inbreeding more frequent. Extinction sometimes results for species evolved to specific ecologies that are subjected to genetic pollution —i.e., uncontrolled hybridization , introgression and genetic swamping that lead to homogenization or out-competition from

2080-407: A race of animals to become extinct. A series of fossils were discovered in the late 17th century that appeared unlike any living species. As a result, the scientific community embarked on a voyage of creative rationalization, seeking to understand what had happened to these species within a framework that did not account for total extinction. In October 1686, Robert Hooke presented an impression of

2184-502: A reduction in agricultural productivity. Furthermore, increased erosion contributes to poorer water quality by elevating the levels of sediment and pollutants in rivers and streams. Habitat degradation through toxicity can kill off a species very rapidly, by killing all living members through contamination or sterilizing them. It can also occur over longer periods at lower toxicity levels by affecting life span, reproductive capacity, or competitiveness. Habitat degradation can also take

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2288-459: A resemblance in their molar-like morphology to those in Diadectids. There are also a number of other characteristics that distinguish Ambedus from all other Diadectids, such as a shallow rather than deep deep dentary, and relatively high maxillary and dentary tooth counts, among other characteristics that distinguish them from Diadectids. Furthermore, the appearance of Ambedus pusillus so late in

2392-486: A result of climate change has been confirmed by fossil studies. Particularly, the extinction of amphibians during the Carboniferous Rainforest Collapse , 305 million years ago. A 2003 review across 14 biodiversity research centers predicted that, because of climate change, 15–37% of land species would be "committed to extinction" by 2050. The ecologically rich areas that would potentially suffer

2496-479: A species (or replacement by a daughter species) plays a key role in the punctuated equilibrium hypothesis of Stephen Jay Gould and Niles Eldredge . In ecology , extinction is sometimes used informally to refer to local extinction , in which a species ceases to exist in the chosen area of study, despite still existing elsewhere. Local extinctions may be made good by the reintroduction of individuals of that species taken from other locations; wolf reintroduction

2600-439: A species may come suddenly when an otherwise healthy species is wiped out completely, as when toxic pollution renders its entire habitat unliveable; or may occur gradually over thousands or millions of years, such as when a species gradually loses out in competition for food to better adapted competitors. Extinction may occur a long time after the events that set it in motion, a phenomenon known as extinction debt . Assessing

2704-404: A species or group of species. "Just as each species is unique", write Beverly and Stephen C. Stearns , "so is each extinction ... the causes for each are varied—some subtle and complex, others obvious and simple". Most simply, any species that cannot survive and reproduce in its environment and cannot move to a new environment where it can do so, dies out and becomes extinct. Extinction of

2808-518: A subsequent report, IPBES listed unsustainable fishing, hunting and logging as being some of the primary drivers of the global extinction crisis. In June 2019, one million species of plants and animals were at risk of extinction. At least 571 plant species have been lost since 1750, but likely many more. The main cause of the extinctions is the destruction of natural habitats by human activities, such as cutting down forests and converting land into fields for farming. A dagger symbol (†) placed next to

2912-517: Is also evidence to suggest that this event was preceded by another mass extinction, known as Olson's Extinction . The Cretaceous–Paleogene extinction event (K–Pg) occurred 66 million years ago, at the end of the Cretaceous period; it is best known for having wiped out non-avian dinosaurs , among many other species. According to a 1998 survey of 400 biologists conducted by New York 's American Museum of Natural History , nearly 70% believed that

3016-555: Is also the youngest known diadectid by 16 million years, coming from a unit of the Late Permian Shangshihezi Formation that dates to about 256 million years. Diadectids have long been considered close relatives of the amniotes , tetrapods that lay eggs on land or retain the fertilized egg within the mother. In 1987, the paleontologist D.M.S. Watson placed the family in the larger group Diadectomorpha , which includes another family of large-bodied diadectomorphs,

3120-444: Is an example of this. Species that are not globally extinct are termed extant . Those species that are extant, yet are threatened with extinction, are referred to as threatened or endangered species . Currently, an important aspect of extinction is human attempts to preserve critically endangered species. These are reflected by the creation of the conservation status "extinct in the wild" (EW) . Species listed under this status by

3224-585: Is difficult to demonstrate unless one has a strong chain of evidence linking a living species to members of a pre-existing species. For example, it is sometimes claimed that the extinct Hyracotherium , which was an early horse that shares a common ancestor with the modern horse , is pseudoextinct, rather than extinct, because there are several extant species of Equus , including zebra and donkey ; however, as fossil species typically leave no genetic material behind, one cannot say whether Hyracotherium evolved into more modern horse species or merely evolved from

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3328-417: Is estimated as 100 to 1,000 times "background" rates (the average extinction rates in the evolutionary time scale of planet Earth), faster than at any other time in human history, while future rates are likely 10,000 times higher. However, some groups are going extinct much faster. Biologists Paul R. Ehrlich and Stuart Pimm , among others, contend that human population growth and overconsumption are

3432-642: Is highly unlikely according to Berman. Diadectids were some of the first tetrapods, or four-legged vertebrates, to attain large sizes. Diadectids first appear in the Late Carboniferous with the genus Desmatodon , although recently described bones from Tennessee suggest that they may have appeared even earlier in the Early Carboniferous. They underwent a small evolutionary radiation in the Late Carboniferous and Early Permian, diversifying into thirteen species and outnumbering other diadectomorphs, such as

3536-674: Is known from a broken lower jaw and several teeth found in Mississippian-age ( Chesterian ) strata that are likely part of the Bangor Formation . In a detailed review of Diadectidae, paleontologist E.C. Olson placed three North American genera within the family: Diadectes , Diasparactus , and Desmatodon . Chilonyx , Empedias , Diadectoides , and Animasaurus were synonymized with Diadectes , and four species of Diadectes ( D. sideropelicus , D. tenuitectes , D. lentus , and D. carinatus ) were recognized. A fourth genus, Ambedus ,

3640-412: Is no longer recognized and Diadectomorpha is placed as the sister taxon of Amniota . However, while the majority of analyses now place diadectids outside Amniota, some have found them to be true amniotes. Most phylogenetic studies of the three diadectomorph families – Diadectidae, Limnoscelidae, and Tseajaiidae – have found diadectids and limnoscelids to be more closely related to each other than either

3744-497: Is not valid. Because the names "Oradectes" and "Silvadectes" have not yet been formally erected in a published paper, they were not, as of 2010, considered valid. In a 2013 study, David Berman argued that there wasn't enough evidence to justify Ambedus being in Diadectidae. He stated in his paper that its assignment to Diadectidae is based only on several isolated maxillae and dentaries containing cheek teeth that only exhibited

3848-623: Is now China until the Middle Permian because, prior to that time, the Tethys Sea separated it from the rest of Laurasia. The group does not seem to have diversified to the same extent in the east as they did in the west given that no diadectids are known from Russia, which has an extensive fossil record of Early and Middle Permian tetrapod assemblages. Diadectids were the first fully herbivorous tetrapods. Although several other groups of early tetrapods independently acquired herbivory, diadectids were

3952-592: Is the destruction of ocean floors by bottom trawling . Diminished resources or introduction of new competitor species also often accompany habitat degradation. Global warming has allowed some species to expand their range, bringing competition to other species that previously occupied that area. Sometimes these new competitors are predators and directly affect prey species, while at other times they may merely outcompete vulnerable species for limited resources. Vital resources including water and food can also be limited during habitat degradation, leading to extinction. In

4056-525: Is the most important determinant of genus extinction at background rates but becomes increasingly irrelevant as mass extinction arises. Limited geographic range is a cause both of small population size and of greater vulnerability to local environmental catastrophes. Extinction rates can be affected not just by population size, but by any factor that affects evolvability , including balancing selection , cryptic genetic variation , phenotypic plasticity , and robustness . A diverse or deep gene pool gives

4160-457: Is the termination of a taxon by the death of its last member . A taxon may become functionally extinct before the death of its last member if it loses the capacity to reproduce and recover. Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena such as Lazarus taxa , where a species presumed extinct abruptly "reappears" (typically in

4264-489: Is to Tseajaia . In other words, Diadectidae and Limnoscelidae form a clade within Diadectomorpha and Tseajaia is excluded from the clade. In a 2010 phylogenetic analysis, Diadectidae formed a clade that was characterized by wide cheek teeth with cusps on either side. Unlike previous studies, it was found to be more closely related to Tseajaiidae than Limnoscelidae. The family was defined as Diadectes and all taxa sharing

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4368-881: The American Journal of Science only five days before Cope described Diadectes in Proceedings of the American Philosophical Society . Under rules of the International Code of Zoological Nomenclature , the name Nothodon would have priority over Diadectes , but because the name Diadectes has been in use since Case and Williston first synonymized the genera, Diadectes remains the accepted name. In North America, diadectids are known from Texas, Colorado , Utah , New Mexico , Oklahoma , Ohio , West Virginia , Pennsylvania , and Prince Edward Island . A possible diadectid has also been found from Tennessee. It

4472-474: The International Union for Conservation of Nature (IUCN) are not known to have any living specimens in the wild and are maintained only in zoos or other artificial environments. Some of these species are functionally extinct, as they are no longer part of their natural habitat and it is unlikely the species will ever be restored to the wild. When possible, modern zoological institutions try to maintain

4576-579: The Late Pennsylvanian , fragmentary remains of possible diadectids are known from much earlier deposits, including a piece of lower jaw found in Mississippian strata from Tennessee . Diadectids have large bodies with relatively short limbs. The rib cage is barrel-shaped to accommodate a large digestive tract necessary for the digestion of cellulose in plants. The skulls of diadectids are wide and deep with blunt snouts. The internal nares (holes for

4680-477: The Late Pleistocene could take up to 5 to 7 million years to restore mammal diversity to what it was before the human era. Extinction of a parent species where daughter species or subspecies are still extant is called pseudoextinction or phyletic extinction. Effectively, the old taxon vanishes, transformed ( anagenesis ) into a successor, or split into more than one ( cladogenesis ). Pseudoextinction

4784-619: The Limnoscelidae , as well as the monotypic diadectomorph family Tseajaiidae, represented by the genus Tseajaia . Throughout the twentieth century, amniotes and diadectomorphs were often grouped together using the old name Cotylosauria , a name originally used for the most basal grade of what was then thought to be reptiles. In the early part of the century, many paleontologists regarded diadectids, along with other cotylosaurs (such as placodonts ), to be close relatives of turtles . In most recent studies of early tetrapod phylogeny , Cotylosauria

4888-555: The dentary bone of the lower jaw may have provided a surface for chewing or even supported a beak. The first diadectid to be described was Diadectes . American paleontologist Edward Drinker Cope named the genus in 1878 on the basis of several vertebrae and teeth from the Early Permian of Texas . Cope erected the family Diadectidae in 1880 to include Diadectes and Empedocles , a genus he named two years earlier. Nothodon , named by Cope's rival Othniel Charles Marsh in 1878,

4992-619: The fossil record ) after a period of apparent absence. More than 99% of all species that ever lived on Earth , amounting to over five billion species, are estimated to have died out. It is estimated that there are currently around 8.7 million species of eukaryotes globally, and possibly many times more if microorganisms , such as bacteria , are included. Notable extinct animal species include non-avian dinosaurs , saber-toothed cats , dodos , mammoths , ground sloths , thylacines , trilobites , golden toads , and passenger pigeons . Through evolution , species arise through

5096-410: The slender-billed curlew ( Numenius tenuirostris ), not seen since 2007. As long as species have been evolving, species have been going extinct. It is estimated that over 99.9% of all species that ever lived are extinct. The average lifespan of a species is 1–10 million years, although this varies widely between taxa. A variety of causes can contribute directly or indirectly to the extinction of

5200-484: The strata of the Paris basin. They saw alternating saltwater and freshwater deposits, as well as patterns of the appearance and disappearance of fossils throughout the record. From these patterns, Cuvier inferred historic cycles of catastrophic flooding, extinction, and repopulation of the earth with new species. Cuvier's fossil evidence showed that very different life forms existed in the past than those that exist today,

5304-619: The 20 biodiversity goals laid out by the Aichi Biodiversity Targets in 2010, only 6 were "partially achieved" by the deadline of 2020. The report warned that biodiversity will continue to decline if the status quo is not changed, in particular the "currently unsustainable patterns of production and consumption, population growth and technological developments". In a 2021 report published in the journal Frontiers in Conservation Science , some top scientists asserted that even if

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5408-451: The Aichi Biodiversity Targets set for 2020 had been achieved, it would not have resulted in a significant mitigation of biodiversity loss. They added that failure of the global community to reach these targets is hardly surprising given that biodiversity loss is "nowhere close to the top of any country's priorities, trailing far behind other concerns such as employment, healthcare, economic growth, or currency stability." For much of history,

5512-605: The Earth is currently in the early stages of a human-caused mass extinction, known as the Holocene extinction . In that survey, the same proportion of respondents agreed with the prediction that up to 20% of all living populations could become extinct within 30 years (by 2028). A 2014 special edition of Science declared there is widespread consensus on the issue of human-driven mass species extinctions. A 2020 study published in PNAS stated that

5616-570: The North American moose and that the animal had once been common on the British Isles . Rather than suggest that this indicated the possibility of species going extinct, he argued that although organisms could become locally extinct, they could never be entirely lost and would continue to exist in some unknown region of the globe. The antlers were later confirmed to be from the extinct deer Megaloceros . Hooke and Molyneux's line of thinking

5720-518: The Paris basin, could be formed by a slow rise and fall of sea levels . The concept of extinction was integral to Charles Darwin 's On the Origin of Species , with less fit lineages disappearing over time. For Darwin, extinction was a constant side effect of competition . Because of the wide reach of On the Origin of Species , it was widely accepted that extinction occurred gradually and evenly (a concept now referred to as background extinction ). It

5824-491: The Tambach Formation in central Germany. A 2007 study identified two different ichnospecies , Ichniotherium cottae and I. sphaerodactylum , as footprints of the diadectids Silvadectes absitus and Orobates pabsti , respectively. This was the first species-level identification of trackmakers of Paleozoic -era trackways, making the footprints the oldest yet associated with specific animal species. The close positioning of

5928-464: The United States government, to force the removal of Native Americans , many of whom relied on the bison for food. American Journal of Science In early years, the journal was often referred to as "Silliman's Journal", and the publication became associated with Yale University due to his long tenure there (1804–1853). The editorship long remained in the family of Professor Silliman, as he

6032-429: The accumulation of slightly deleterious mutations , then a population will go extinct. Smaller populations have fewer beneficial mutations entering the population each generation, slowing adaptation. It is also easier for slightly deleterious mutations to fix in small populations; the resulting positive feedback loop between small population size and low fitness can cause mutational meltdown . Limited geographic range

6136-480: The analysis, their assignment to the genus was questioned. The same results were found in the 2010 analysis. Two new genera were erected in the study to include D. abstus and D. sanmiguelensis . D. sanmiguelensis , the more basal of the two forms, was placed in the new genus "Oradectes". D. abstus was renamed "Silvadectes". However, according to the ICZN, a name presented in an initially unpublished thesis such as Kissel's

6240-430: The ankle structure of diadectids bears a closer resemblance to those of advanced terrestrial vertebrates like mammals and reptiles than those of earlier tetrapods. Since diadectids are the only diadectomorphs with astragali, they likely developed the structure independent of amniotes. Although they bear similarities to those of amniotes, the tarsal bones of diadectids are poorly ossified and loosely connected. The digits of

6344-600: The consequences can be catastrophic. Invasive alien species can affect native species directly by eating them, competing with them, and introducing pathogens or parasites that sicken or kill them; or indirectly by destroying or degrading their habitat. Human populations may themselves act as invasive predators. According to the "overkill hypothesis", the swift extinction of the megafauna in areas such as Australia (40,000 years before present), North and South America (12,000 years before present), Madagascar , Hawaii (AD 300–1000), and New Zealand (AD 1300–1500), resulted from

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6448-418: The contemporary extinction crisis "may be the most serious environmental threat to the persistence of civilization, because it is irreversible." Biologist E. O. Wilson estimated in 2002 that if current rates of human destruction of the biosphere continue, one-half of all plant and animal species of life on earth will be extinct in 100 years. More significantly, the current rate of global species extinctions

6552-471: 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

6656-403: The endangered wild water buffalo is most threatened with extinction by genetic pollution from the abundant domestic water buffalo ). Such extinctions are not always apparent from morphological (non-genetic) observations. Some degree of gene flow is a normal evolutionary process; nevertheless, hybridization (with or without introgression) threatens rare species' existence. The gene pool of

6760-575: The event of rediscovery would be considered Lazarus species. Examples include the thylacine , or Tasmanian tiger ( Thylacinus cynocephalus ), the last known example of which died in Hobart Zoo in Tasmania in 1936; the Japanese wolf ( Canis lupus hodophilax ), last sighted over 100 years ago; the American ivory-billed woodpecker ( Campephilus principalis ), with the last universally accepted sighting in 1944; and

6864-443: The extinction crisis. According to the International Union for Conservation of Nature (IUCN), 784 extinctions have been recorded since the year 1500, the arbitrary date selected to define "recent" extinctions, up to the year 2004; with many more likely to have gone unnoticed. Several species have also been listed as extinct since 2004. If adaptation increasing population fitness is slower than environmental degradation plus

6968-475: The extinction of species caused by humanity, and they try to prevent further extinctions through a variety of conservation programs. Humans can cause extinction of a species through overharvesting , pollution , habitat destruction , introduction of invasive species (such as new predators and food competitors ), overhunting, and other influences. Explosive, unsustainable human population growth and increasing per capita consumption are essential drivers of

7072-533: The field of zoology , and biology in general, and has also become an area of concern outside the scientific community. A number of organizations, such as the Worldwide Fund for Nature , have been created with the goal of preserving species from extinction. Governments have attempted, through enacting laws, to avoid habitat destruction, agricultural over-harvesting, and pollution . While many human-caused extinctions have been accidental, humans have also engaged in

7176-473: The first to exploit plant material in terrestrial food chains, making their appearance an important stage in both vertebrate evolution and the development of terrestrial ecosystems . The best known and largest representative of the family is Diadectes , a heavily built animal that attained a maximum length of several metres. Several other genera and various fragmentary fossil remains are also known. Although well known genera like Diadectes first appear in

7280-477: The foot connect only to the fourth distal tarsal, providing a wide range of movement in the foot. This flexibility enabled diadectids to rotate their feet in a forward position while walking, providing greater force when pushing off. The feet could also be placed closer to the midline of the body to give diadectids an erect stance. Evidence for an erect stance can be found in trackways attributed to diadectids. The most well-preserved of these trackways are present in

7384-413: The footprints attributed to the more advanced diadectides suggests that the animals held their feet almost underneath their bodies, giving them a more efficient gait and to some degree paralleling the stance of mammals more than that of the sprawling amphibians and most reptiles. [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Extinct Extinction

7488-435: The form of a physical destruction of niche habitats. The widespread destruction of tropical rainforests and replacement with open pastureland is widely cited as an example of this; elimination of the dense forest eliminated the infrastructure needed by many species to survive. For example, a fern that depends on dense shade for protection from direct sunlight can no longer survive without forest to shelter it. Another example

7592-594: The fossil record also casts a doubt on the fact that it is supposed to represent the basalmost member of the Diadectid lineage. In contrast, the first Diadectids from the Upper Pennsylvanian were far more developed and had the characteristic dentary and maxillary features of the Diadectid lineage. This implies that there should be a ghost lineage that goes back all the way back to the Middle Pennsylvanian , which

7696-580: The habitat retreat of taxa approaching extinction. Possible causes of the higher extinction risk in species with more sexual selection shown by the comprehensive fossil studies that rule out such error sources include expensive sexually selected ornaments having negative effects on the ability to survive natural selection , as well as sexual selection removing a diversity of genes that under current ecological conditions are neutral for natural selection but some of which may be important for surviving climate change. There have been at least five mass extinctions in

7800-660: The heaviest losses include the Cape Floristic Region and the Caribbean Basin . These areas might see a doubling of present carbon dioxide levels and rising temperatures that could eliminate 56,000 plant and 3,700 animal species. Climate change has also been found to be a factor in habitat loss and desertification . Studies of fossils following species from the time they evolved to their extinction show that species with high sexual dimorphism , especially characteristics in males that are used to compete for mating, are at

7904-447: The history of life on earth, and four in the last 350 million years in which many species have disappeared in a relatively short period of geological time. A massive eruptive event that released large quantities of tephra particles into the atmosphere is considered to be one likely cause of the " Permian–Triassic extinction event " about 250 million years ago, which is estimated to have killed 90% of species then existing. There

8008-475: The human era since the Late Pleistocene would require 5 to 7 million years to recover. According to the 2019 Global Assessment Report on Biodiversity and Ecosystem Services by IPBES , the biomass of wild mammals has fallen by 82%, natural ecosystems have lost about half their area and a million species are at risk of extinction—all largely as a result of human actions. Twenty-five percent of plant and animal species are threatened with extinction. In

8112-431: The introduced ( or hybrid ) species. Endemic populations can face such extinctions when new populations are imported or selectively bred by people, or when habitat modification brings previously isolated species into contact. Extinction is likeliest for rare species coming into contact with more abundant ones; interbreeding can swamp the rarer gene pool and create hybrids, depleting the purebred gene pool (for example,

8216-411: The jaw joints above or below the level of the occlusal plane (the plane at which the teeth come together) would have given diadectid jaws mechanical advantage . The joints themselves give the jaws a complex range of movement suitable for consuming plants. Large holes and cavities in the skull called adductor chambers and temporal openings would have provided room for large jaw-closing muscles. A ridge on

8320-504: The late Carboniferous and Permian these regions formed a single landmass called Laurasia , which comprised the northern portion of the supercontinent Pangea . For most of their evolutionary history, diadectids were likely limited to the western half of Laurasia, which is now North America and Europe. The presence of the late-surviving Alveusdectes in China suggests that diadectids radiated eastward across Laurasia. They could not have reached what

8424-399: The length of the jaws. The teeth are wide and bear many cusps or projections, an indication that diadectids ate tough plants. Some teeth are leaf-shaped and laterally compressed, another indication that diadectids were able to shred plant material. The procumbent front teeth of the lower jaw project forward. Diadectids likely had strong jaw muscles for processing plant material; the placement of

8528-494: The limnoscelids. This radiation was likely the result of diadectids' expansion into a new herbivorous ecological niche that was previously unfilled. Diadectids had a much wider geographic distribution than their relatives; while the distribution of limnoscelids is limited to parts of North America and Tseajaia is restricted to just the southwestern United States, diadectids are present in North America, Europe, and Asia. During

8632-485: The main drivers of the modern extinction crisis. In January 2020, the UN's Convention on Biological Diversity drafted a plan to mitigate the contemporary extinction crisis by establishing a deadline of 2030 to protect 30% of the Earth's land and oceans and reduce pollution by 50%, with the goal of allowing for the restoration of ecosystems by 2050. The 2020 United Nations ' Global Biodiversity Outlook report stated that of

8736-421: The modern understanding of extinction as the end of a species was incompatible with the prevailing worldview. Prior to the 19th century, much of Western society adhered to the belief that the world was created by God and as such was complete and perfect. This concept reached its heyday in the 1700s with the peak popularity of a theological concept called the great chain of being , in which all life on earth, from

8840-490: The name of a species or other taxon normally indicates its status as extinct. Examples of species and subspecies that are extinct include: A species is extinct when the last existing member dies. Extinction therefore becomes a certainty when there are no surviving individuals that can reproduce and create a new generation. A species may become functionally extinct when only a handful of individuals survive, which cannot reproduce due to poor health, age, sparse distribution over

8944-469: The natural course of events, species become extinct for a number of reasons, including but not limited to: extinction of a necessary host, prey or pollinator, interspecific competition , inability to deal with evolving diseases and changing environmental conditions (particularly sudden changes) which can act to introduce novel predators, or to remove prey. Recently in geological time, humans have become an additional cause of extinction of some species, either as

9048-410: The newly emerging school of uniformitarianism . Jean-Baptiste Lamarck , a gradualist and colleague of Cuvier, saw the fossils of different life forms as evidence of the mutable character of species. While Lamarck did not deny the possibility of extinction, he believed that it was exceptional and rare and that most of the change in species over time was due to gradual change. Unlike Cuvier, Lamarck

9152-425: The nostrils) are also short. Paleontologist E.C. Case compared diadectids to turtles in 1907, noting their large pectoral girdles, short, strong limbs, and robust skulls. Case described them as "lowly, sluggish, inoffensive herbivorous reptiles, clad in an armor of plate to protect them from the fiercely carnivorous pelycosaurs ." Diadectids have a heterodont dentition, meaning that their teeth vary in shape along

9256-562: The only Carboniferous tetrapods that were able to process high-fiber terrestrial plants. Diadectids were also the most diverse group of herbivores, representing the first radiation of plant-eating tetrapods. Both Cope and Marsh recognized that diadectids were herbivores in 1878 when they studied their distinctively broad, cusped teeth (in his description of Diadectes , Cope mentioned, "animals belonging to this genus were, in all probability, herbivorous"). Diadectids were once thought to be sprawling animals with their short, robust legs positioned to

9360-399: The original population, thereby increasing the chance of extinction. Habitat degradation is currently the main anthropogenic cause of species extinctions. The main cause of habitat degradation worldwide is agriculture, with urban sprawl , logging, mining, and some fishing practices close behind. The degradation of a species' habitat may alter the fitness landscape to such an extent that

9464-702: The process of speciation —where new varieties of organisms arise and thrive when they are able to find and exploit an ecological niche —and species become extinct when they are no longer able to survive in changing conditions or against superior competition . The relationship between animals and their ecological niches has been firmly established. A typical species becomes extinct within 10 million years of its first appearance, although some species, called living fossils , survive with little to no morphological change for hundreds of millions of years. Mass extinctions are relatively rare events; however, isolated extinctions of species and clades are quite common, and are

9568-410: The relative importance of genetic factors compared to environmental ones as the causes of extinction has been compared to the debate on nature and nurture . The question of whether more extinctions in the fossil record have been caused by evolution or by competition or by predation or by disease or by catastrophe is a subject of discussion; Mark Newman, the author of Modeling Extinction , argues for

9672-445: The sides of their large bodies. Despite this, several lines of evidence, including trackways and limb morphology, suggest that diadectids moved in a more erect posture. While earlier tetrapods possess several simple tarsal bones in their ankles, diadectids have a more complex astragalus formed from the fusion of these bones. Astragali are present in terrestrial amniotes and are identical in structure to those of diadectids. Therefore,

9776-460: The species is no longer able to survive and becomes extinct. This may occur by direct effects, such as the environment becoming toxic , or indirectly, by limiting a species' ability to compete effectively for diminished resources or against new competitor species. Habitat destruction, particularly the removal of vegetation that stabilizes soil, enhances erosion and diminishes nutrient availability in terrestrial ecosystems. This degradation can lead to

9880-430: The sudden introduction of human beings to environments full of animals that had never seen them before and were therefore completely unadapted to their predation techniques. Coextinction refers to the loss of a species due to the extinction of another; for example, the extinction of parasitic insects following the loss of their hosts. Coextinction can also occur when a species loses its pollinator , or to predators in

9984-412: The tiniest microorganism to God, is linked in a continuous chain. The extinction of a species was impossible under this model, as it would create gaps or missing links in the chain and destroy the natural order. Thomas Jefferson was a firm supporter of the great chain of being and an opponent of extinction, famously denying the extinction of the woolly mammoth on the grounds that nature never allows

10088-555: The total extinction of the dodo and the extirpation of indigenous horses to the British Isles. He similarly argued against mass extinctions , believing that any extinction must be a gradual process. Lyell also showed that Cuvier's original interpretation of the Parisian strata was incorrect. Instead of the catastrophic floods inferred by Cuvier, Lyell demonstrated that patterns of saltwater and freshwater deposits , like those seen in

10192-577: The wider scientific community of his theory. Cuvier was a well-regarded geologist, lauded for his ability to reconstruct the anatomy of an unknown species from a few fragments of bone. His primary evidence for extinction came from mammoth skulls found in the Paris basin . Cuvier recognized them as distinct from any known living species of elephant, and argued that it was highly unlikely such an enormous animal would go undiscovered. In 1812, Cuvier, along with Alexandre Brongniart and Geoffroy Saint-Hilaire , mapped

10296-549: Was assisted by his son, Benjamin Silliman Jr. , from 1838. On the death of the elder Silliman in 1864, he was succeeded as chief editor by his son-in-law, James Dwight Dana , and then from 1895 till 1926 by Dana's son Edward Salisbury Dana . Associate editors included the botanist Asa Gray and the zoologist Louis Agassiz . The current editors are Mark T. Brandon, professor at Yale University , and C. Page Chamberlain, professor at Stanford University . This article about

10400-483: Was difficult to disprove. When parts of the world had not been thoroughly examined and charted, scientists could not rule out that animals found only in the fossil record were not simply "hiding" in unexplored regions of the Earth. Georges Cuvier is credited with establishing the modern conception of extinction in a 1796 lecture to the French Institute , though he would spend most of his career trying to convince

10504-457: Was named in 2004 from the Early Permian of Ohio. Diadectids are also known from Germany . Phanerosaurus was described from several vertebrae near Zwickau by German paleontologist Christian Erich Hermann von Meyer in 1860, but was not recognized as a diadectid until 1925. A second species of Phanerosaurus was identified from some vertebrae and a fragmentary skull in 1882, and was given its own genus, Stephanospondylus , in 1905. In 1998,

10608-430: Was not until 1982, when David Raup and Jack Sepkoski published their seminal paper on mass extinctions, that Cuvier was vindicated and catastrophic extinction was accepted as an important mechanism . The current understanding of extinction is a synthesis of the cataclysmic extinction events proposed by Cuvier, and the background extinction events proposed by Lyell and Darwin. Extinction is an important research topic in

10712-571: Was skeptical that catastrophic events of a scale large enough to cause total extinction were possible. In his geological history of the earth titled Hydrogeologie, Lamarck instead argued that the surface of the earth was shaped by gradual erosion and deposition by water, and that species changed over time in response to the changing environment. Charles Lyell , a noted geologist and founder of uniformitarianism , believed that past processes should be understood using present day processes. Like Lamarck, Lyell acknowledged that extinction could occur, noting

10816-512: Was soon placed in the family. Cope named several other diadectids, including Helodectes in 1880, Chilonyx and Empedias in 1883, and Bolbodon in 1896. Paleontologist E.C. Case named four other diadectids: Desmatodon in 1908, Diasparactus in 1910, Diadectoides in 1911, and Animasaurus along with paleontologist Samuel Wendell Williston in 1912. Case and Williston considered Marsh's Nothodon and Cope's Bolbodon to be synonymous with Diadectes . Marsh named Nothodon in

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