143-532: Arctodus is an extinct genus of short-faced bear that inhabited North America during the Pleistocene (~2.5 Mya until 12,800 years ago). There are two recognized species : the lesser short-faced bear ( Arctodus pristinus ) and the giant short-faced bear ( Arctodus simus ). Of these species, A. simus was larger, is known from more complete remains, and is considered one of the best known members of North America's extinct Ice Age megafauna . A. pristinus
286-438: 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
429-657: 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
572-415: 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
715-436: 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
858-608: A "gracile" appearance. Although longer, the proportions still overlap with Ursus , and the limb bones are stouter than in the large-bodied felids ( Panthera ). Rather than for running, these elongated limb bones may have evolved for increased locomotor efficiency during prolonged travel. This stiff-legged, swinging gait could have been similar to a polar bear's. Some researchers suggest that proportionally longer limbs may be an adaptation for increased vision over tall ground cover in an open habitat, or were used in tearing and pulling down vegetation. Researchers also disagree when interpreting
1001-474: 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
1144-529: A black bear (Potter Cave). None of the specimens assigned to the larger morph ( A. s. yukonensis ) is from a cave passage, being usually isolated remains from open sites. Furthermore, over 70% of the smaller specimens (once assigned as the A. s. simus subspecies) are from cave deposits where bacula would likely be found if present, suggesting that mostly female individuals of A. simus were using caves. Therefore, in conjunction with ursid sexual dimorphism (e.g. male spectacled bears are 30% - 40% larger than females),
1287-495: 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
1430-429: 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
1573-404: A deep mandible, and large mandibular muscle attachments. Because herbivorous carnivorans lack an efficient digestive tract for breaking down plant matter via microbial action, they must break down plant matter via extensive chewing or grinding, and thus possess features to create a high mechanical advantage of the jaw. This presents the possibility that these traits may be an ancestral condition of
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#17328584038331716-554: A deeper but not a shorter face than most living bears. This characteristic is also shared by the only living tremarctine bear, the omni-herbivorous spectacled bear . Snout deepness could be variable, as specimens from Huntington Reservoir in Utah, and the Hill-Shuler locality , Texas, were noted as being distinctly "short-faced" in comparison with other Arctodus simus individuals. The orbits of Arctodus are proportionally small compared to
1859-399: 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
2002-436: A faunal turnover which extinguished 60–70% of all Eurasian faunal genera, and 70–80% of North American genera. Correspondingly, a 2016 study suggested that the mean divergence dates for Arctotherium , Arctodus and Tremarctos were 4.8 Ma, and between Arctotherium and Tremarctos at 4.1 Ma. A further study calculated the divergence date between Arctodus and Tremarctos at 5.5 Ma. All three genera are first recorded from
2145-543: A higher degree of forelimb dexterity. Originally evolved to facilitate arboreality , other researchers believe that the terrestrial Arctodus (along with Arctotherium and the giant panda ) retained this characteristic to assist in foraging for vegetation. The paws ( metapodials and phalanges ) of Arctodus were characteristically long, slender, and more elongated along the third and fourth digits compared to ursine bears . Arctodus ' paws were therefore more symmetrical than ursine bears, whose feet have axes aligned with
2288-708: 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
2431-489: A hypothesis for the colonization of Vancouver Island by Arctodus simus . Examinations on a mostly full sized young individual of Arctodus simus from an Ozark cave suggest that Arctodus , like other ursids, reached sexual maturity well before full maturity . Comparisons with black bears suggest the Arctodus specimen was either 4–6 years of age if female, or 6–8 years if the specimen was male. Additionally, wear patterns on
2574-482: A large home range and relatively small population size. However, this does not entirely preclude genetic diversity in Arctodus simus , with genetic samples from Chiquihuite Cave , Zacatecas indicating a deep divergence with previously studied specimens of A. simus . Additional specimens from the California Channel Islands and Wyoming have been sequenced, but are unassigned. Below is a cladogram exploring
2717-405: 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
2860-592: 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
3003-562: A major temperature drop and increased seasonality, and a faunal turnover which extinguished 70–80% of North American genera. Arctodus pristinus was mostly restricted to the more densely forested thermal enclave in eastern North America . A. pristinus has the greatest concentration of fossils in Florida, with the earliest finds being from the Late Blancan Kissimmee River 6 (2.7 - 2.2 Mya) and Santa Fe River 1 sites. During
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#17328584038333146-587: 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
3289-510: A more anterior protocone & extended enamel ridge forming a shearing blade on the maxillary P4 . The molars are also shorter & broader in Arctodus than brown bears. † Hemicyoninae † Ursavinae Ailuropodinae [REDACTED] Ursinae [REDACTED] † Plionarctos † Arctodus Tremarctos [REDACTED] † Arctotherium Arctodus belongs to the subfamily Tremarctinae, which appeared in North America during
3432-456: 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
3575-441: 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,
3718-482: A pace at 8.5 km/h (5.3 mph), and would begin to gallop at 18.5 km/h (11.5 mph), a fairly high speed. Based on other mammals, the optimal pace speed of Arctodus would have been 13.7 km/h (8.5 mph). For comparison, hyenas cross country ~10 km/h (6.2 mph). This mobility would have facilitated travelling across a large home range, which Mattson suggests may have topped 1,000 square miles (2,600 km). Swimming has also been presented as
3861-528: A pan-continental species in the Rancholabrean faunal stage (Late Pleistocene), sharing that distinction with the black bear . Despite Arctodus simus ' large temporal and geographic range, fossil remains are comparatively rare (109 finds as of 2010, in otherwise well-sampled localities). Around the size of grizzly bears , A. pristinus specimens closely overlap the size of Tremarctos floridanus , with some males of A. pristinus overlapping in size with
4004-521: A poor indicator of size in A. simus , as some medium-size individuals have teeth that surpass the size of those with the largest skeletons. Additionally, while A. simus evolved from the smaller A. pristinus , their teeth remained generally the same size. A specimen of A. simus from the Seale Pit of the Hill-Shuler locality, Texas, with only two premolars, crowding of the anterior premolar out of line, and
4147-610: 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
4290-476: A predatory lifestyle- in particular the large canines , the high-crowned lower first molar , and the possible carnassial shear with the upper fourth premolar . However, the wearing of the molars to a relatively flat & blunt loph (suitable as a crushing platform as per modern omnivorous bears), small shear facet, and the flattened cusps across age ranges (unlike carnivores, which instead have carnassial shears) disagrees with this hypothesis. Dentition can be
4433-407: 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
Arctodus - Misplaced Pages Continue
4576-513: A range from Alaska to southernmost Patagonia . All of these forms were extinct by the end of the early Holocene. Around this time, Tremarctos ornatus , otherwise known as the spectacled bear , starts appearing in the South American fossil record. Scholars suggest that the spectacled bear migrated into Central and South America upon the extinction of Arctotherium wingei , if Pleistocene records of Andean Arctotherium sp. aren't confirmed as
4719-540: A reduced or no sagittal crest. Although there are limited samples, the middle ear bones of A. simus are proportionally larger than modern ursine bears, suggesting the species was particularly attuned to low-frequency sounds. Morphologically, Arctodus simus exhibits masticular characteristics common to herbivorous bears. This includes cheek teeth with large, blunt surface areas, a deep mandible, and large mandibular muscle attachments (which are rare in carnivorous mammals). As herbivorous carnivorans such as Arctodus lack
4862-433: A reduced slicing dentition length when compared to A. pristinus . Instead, Arctodus simus was most similar to Arctotherium angustidens- however, both species of Arctodus and Arctotherium angustidens were still comfortably in the "omnivorous" bear cranio-morphotype. The premolars and first molars of Arctodus pristinus are relatively smaller and more widely spaced than those of Arctodus simus . In A. pristinus ,
5005-502: 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
5148-486: 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
5291-465: A short-faced bear clade of Arctodus and Arctotherium . A study of the affinities of bears belonging to Arctotherium indicates that they were more closely related to the spectacled bear than to Arctodus , implying convergent evolution of large size in the two lineages. Tremarctines are occasionally referred to as arctodonts or arctotheres in older scientific literature, although this has fallen out of fashion. The following taxonomy of
5434-479: 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
5577-439: 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
5720-404: 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
5863-518: 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
Arctodus - Misplaced Pages Continue
6006-449: A wide and shortened rostrum , potentially giving Arctodus a more felid -like appearance. Matheus suggested that a broad snout could have housed a highly developed olfactory apparatus , or accommodated a larger throat passage to bolt down large food items, akin to spotted hyenas. However, this apparent shortness is an illusion caused by the deep snouts and short nasal bones of tremarctine bears compared with ursine bears; Arctodus has
6149-549: A wide range across North America for 800,000 years, Arctotherium angustidens appears to be limited to the Southern Cone , in open plains habitat. Furthermore, whereas Arctodus simus varied its diet between quasi-carnivory in Alaska to classic omnivory, Arctotherium angustidens had similar rates of carnivory across specimens, according to isotope studies. Additionally, the much more gracile form of Arctodus , in contrast with
6292-434: A wide range of niches- from small and mostly herbivorous bears inhabiting more forested habitat, such as Arctotherium wingei and Tremarctos ornatus , to the colossal Arctotherium angustidens and Arctodus simus ; plains adapted omnivores with a penchant for large quantities of meat. Although the two giant species appear superficially similar, both species had key, significant differences. While Arctodus simus had
6435-417: A wider and shorter muzzle, was suggested to be an undescribed form of Arctodus . Researchers have differing interpretations on the limb morphology of Arctodus . A comprehensive 2010 study concluded that the legs of Arctodus weren't proportionally longer than modern bears would be expected to have, and that bears in general are long-limbed animals, obscured in life by their girth and fur. The study concluded
6578-517: 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
6721-444: 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
6864-411: Is believed to be one of the largest known terrestrial carnivorans that has ever existed. However, Arctodus , like other bears, was highly sexually dimorphic. Adult A. simus ranged between 300 and 950 kilograms (660 and 2,090 lb), with females clustering at ≤500 kilograms (1,100 lb), and males around 800 kilograms (1,800 lb). The largest males stood at 1.67 metres (5 ft 6 in) at
7007-585: 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
7150-417: 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
7293-417: Is estimated that there are currently around 8.7 million species of eukaryotes globally, and possibly many times more if microorganisms , such as bacteria , are included. Notable extinct animal species include non-avian dinosaurs , saber-toothed cats , dodos , mammoths , ground sloths , thylacines , trilobites , golden toads , and passenger pigeons . Through evolution , species arise through
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#17328584038337436-438: Is much variation in adult size among specimens- the lack of finds, sexual dimorphism , individual variation and potentially ecomorphs could be augmenting the average size of both species of Arctodus . Size differences between specimens of Arctodus simus (such as skull and long bone dimensions) led Kurtén to suggest a larger northern/central subspecies ( A. s. yukonensis ) and a southern subspecies ( A. s. simus ). evolving in
7579-592: 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
7722-525: 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
7865-615: The Americas . Of these short-faced bears, Arctodus was the most widespread in North America. However, the genus was restricted to the Pleistocene. A. pristinus went extinct around 300,000 years ago, with A. simus disappearing ~12,800 years ago in the Late Pleistocene extinctions . The cause behind these extinctions is unclear, but in the case of A. pristinus , this was likely due to climate change and competition with other ursids, such as
8008-587: The Blancan (Pliocene/Pleistocene boundary) of North America. An indeterminate Arctotherium is first recorded from the late Pliocene of El Salvador . In the Early Pleistocene, short-faced bears began to establish themselves more thoroughly in both North and South America. The medium sized Arctodus pristinus inhabited a broad range in the North American continent, with Tremarctos floridanus endemic to
8151-481: The Florida spectacled bear ( Tremarctos floridanus ), the North American giant short-faced bears Arctodus ( A. pristinus and A. simus ), the South American giant short-faced bear Arctotherium (including A. angustidens , A. vetustum , A. bonariense , A. wingei , and A. tarijense) as well as Plionarctos (P. edensis and P. harroldorum), which is thought to be ancestral to the other three genera. Of these,
8294-474: 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
8437-478: The La Brea Tar Pits at ~372 kilograms (820 lb), smaller than recovered brown bear remains (~455 kilograms (1,003 lb), although these remains postdate Arctodus ). A 1999 study by Per Christiansen calculated a mean weight of ~770 kilograms (1,700 lb) from seven male A. simus limb bones, suggesting large males weighed between 700 kilograms (1,500 lb) and 800 kilograms (1,800 lb). There
8580-419: 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
8723-544: The Middle Hemphillian (earliest Late Miocene , ~10Ma) of North America; Plionarctos is last recorded in the early Blancan (Early Pliocene, ~3.3Ma). Around the Miocene - Pliocene boundary (~5 Ma), tremarctines, along with other ursids , experienced an explosive radiation in diversity, as C4 vegetation ( grasses ) and open habitats dominated, the world experienced a major temperature drop and increased seasonality, and
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#17328584038338866-498: The black bear and Tremarctos floridanus . A. simus likely went extinct due to ecological collapse disrupting the vegetation and prey it relied on. Arctodus was first described by Joseph Leidy in 1854, with finds of A. pristinus from the Ashley Phosphate Beds , South Carolina. The scientific name of the genus, Arctodus , derives from Greek, and means "bear tooth". The first fossils of Arctodus simus were found in
9009-501: The giant short-faced bears ( Arctodus simus and Arctotherium angustidens ) may have been the largest ever carnivorans in the Americas . The group is thought to have originated in eastern North America, and then invaded South America as part of the Great American Interchange . Most short-faced bears became extinct at the end of the Pleistocene . Tremarctinae originate with their common ancestor, Plionarctos , in
9152-511: The gut microbiota to efficiently break down plant matter, these features created a high mechanical advantage of the jaw to break down plant matter via extensive chewing or grinding. Although the low mandibular condyle relative to the tooth row (and therefore potential wide gape) of Arctodus simus has been inferred as an adaptation for carnivory, it is also present in the omni-herbivorous spectacled bear. However, both Arctodus pristinus and Tremarctos floridanus have condyles raised well above
9295-520: The humerus of Arctodus simus . Sorkin argued that the pronation of the forearm and the flexion of the wrist and digits, and more lightly muscled forelimbs, all of which are crucial to grasping a large prey animal with the forepaws, were probably less powerful in Arctodus than in either the brown bear or in Panthera . This is due to a weak medial epicondyle and reduced development of the pronator teres muscle. The forelimb of Arctodus could have been in
9438-410: 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
9581-484: 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,
9724-477: The trigonid and talonid on the m1 molar , a premasseteric fossa on the mandible , and often an entepicondylar foramen on the humerus of tremarctine bears. Additionally, tremarctine bears' skulls are deeper and more brachycephalic , their zygomatic arches and glenoid fossas are well developed, and they have larger molars in comparison with ursines. Moreover, tremarctine bears' orbits are also bigger, more rounded and lateralized. Tremarctines inhabited
9867-619: 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
10010-451: 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,
10153-605: 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
10296-850: The Eurasian cave bear last shared a common ancestor with the tremarctine Arctodus circa 13.4 million years ago. Fossils of Arctodus pristinus can be confused with the similarly sized, partially contemporaneous short-faced bear , Tremarctos floridanus . Arctodus has higher crowned and considerably larger teeth than its relative Tremarctos . A. pristinus can be distinguished by broader and taller molars on average, but as they are often worn, differentiation can be difficult. Moreover, diagnosing isolated A. simus remains (such as femora, scapulae, certain vertebrae, ribs, podials) from brown bears can be challenging, as some large brown bears overlap in dimensions with small Arctodus simus . Beyond standard differences between tremarctine and ursine bears , A. simus has
10439-680: The Gulf Coast. The first records of Arctotherium in South America come in the form of the gigantic Arctotherium angustidens , possibly the largest carnivorous land mammal ever, in Argentina circa 1 Ma. What the evolutionary history of Arctotherium in the previous 1.5 million years, and their history in South America, is unclear. In the Middle Pleistocene, both Arctodus and Arctotherium gave way to new forms; Arctodus pristinus gave way to
10582-678: The Irvingtonian and Rancholabrean respectively. However, the discovery of a very large southern Arctodus simus in Florida and New Mexico (deep within the supposed range of A. s. simus ), & possibly Rancho La Brea, and notably small specimens from the Yukon and Vancouver Island , put doubt on this designation. Perceived ecomorphologies are possibly due to the low number of specimens, and sex-biased sampling. For example, only one baculum (penis bone) has been recovered from over 100 giant short-faced bear sites in North America, although it may belong to
10725-734: The Middle Pleistocene of Kansas, with A. simus migrating east in the Late Pleistocene (around the extinction of A. pristinus ). Although both Arctodus species co-inhabited North America for at least half a million years during the Middle Pleistocene ( A. pristinus went extinct ~300,000 BP ), there is no direct evidence of overlap or competition in the fossil record as of yet, as both species established largely separate ranges . Irvingtonian age (1,900,000 BP - 250,000 BP) specimens of Arctodus simus are particularly sparse. Finds are mostly from California, with additional remains from Texas, Kansas, Nebraska, and Montana. However, A. simus became
10868-513: 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
11011-518: 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
11154-541: The Potter Creek Cave, Shasta County , California, by J. A. Richardson in 1878, and were initially described as Arctotherium simum by Edward Drinker Cope in 1879. Historically, all specimens were grouped together under A. pristinus , until a revision by Björn Kurtén in 1967. In the 19th and early 20th centuries, specimens of Arctodus were occasionally referred to Arctotherium , and vice versa. However, today neither genera are considered to have overlapped, with
11297-493: The United States government, to force the removal of Native Americans , many of whom relied on the bison for food. Tremarctinae † Plionarctos † Arctodus † Arctotherium Tremarctos The Tremarctinae or short-faced bears is a subfamily of Ursidae that contains one living representative, the spectacled bear ( Tremarctos ornatus ) of South America , and several extinct species from four genera:
11440-470: The Yukon suggest an extremely low level of genetic diversity among the 23 individuals studied (≤ 44,000 C BP), with only seven haplotypes recovered. Genetic diversity was comparable to modern endangered fauna, such as the brown kiwi and African cheetah. Explanations include a genetic bottleneck before 44,000 C BP, or a low level of genetic diversity being a feature of a species which was primarily solitary, with
11583-429: 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
11726-552: The axis of the foot on either side). The trackways suggest that Arctodus had an oval-shaped, undivided pad on its sole, front paws that were slightly larger than its back paws, possessed long claws, and had its hind foot overstep the forefoot when walking, like modern bears. An additional A. simus paw print measuring 15 cm (5.9 in) long and 19 cm (7.5 in) wide has been recovered from White Sands National Park , New Mexico. Some claw marks attributed to Arctodus simus at Riverbluff Cave (as they were four meters above
11869-597: The closest point of contact being México, with the giant Arctodus simus in Valsequillo , Puebla , and the smaller Arctotherium wingei in the Yucatán Peninsula . Other early researchers believed Arctodus to be a sister lineage of the agriotheriin Indarctos . Sometimes described as the "American cave bear", Arctodus should not be mistaken for the similarly large Eurasian cave bear ( Ursus spelaeus ). As an ursine ,
12012-600: 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
12155-418: 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
12298-541: 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 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
12441-471: 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
12584-524: The earliest parts of the late Miocene epoch in the form of Plionarctos . The medium-sized Arctodus pristinus, Tremarctos floridanus and Arctotherium sp. evolved from Plionarctos in the Blancan age of North America. The genetic divergence date for Arctodus is ~5 million years ago, around the Miocene - Pliocene boundary, when tremarctine bears, along with other ursids, experienced an explosive radiation in diversity, as C 4 vegetation ( grasses ) and open habitats dominated. The world experienced
12727-507: The early Irvingtonian faunal stage , a western population of A. pristinus evolved into the enormous A. simus, with the earliest confirmed records being at least 780,000 years old from the Irvington type locality in California. Correspondingly, A. simus is most plentiful from western North America, albeit preferring mixed habitat such as temperate open woodlands. Their ranges may have met in
12870-584: The early stages of cursorial evolution, being capable of more efficient and high-speed straight-line locomotion (relative to extant bears), and was possibly more adept at pursuing large prey than polar and brown bears . On the other hand, some researchers argue that the epicondyles were still well developed, with this wide range of ulna rotation suggests that forearms of Arctodus were powerful and could subdue large prey. A 2013 examination of Rancho La Brean specimens found that they did not possess distally elongated limbs, which discredited cursoriality. Furthermore,
13013-403: 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
13156-575: 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
13299-443: 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
13442-475: 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
13585-504: The features of the dentition can be quite variable, particularly the M2 molar. An analysis of the Hunter-Schreger bands from the teeth of A. pristinus and A. simus demonstrated an evolutionary trend towards partially reinforced tooth enamel . This has been convergently evolved with giant pandas, agriotheriin bears, and Hemicyon . The dentition of A. simus has been used as evidence of
13728-407: The females of A. simus. Floridan A. pristinus individuals were calculated to an average of ~140 kilograms (310 lb). However, the dimensions of some individuals from Port Kennedy Bone Cave and Aguascalientes suggest that northern and western A. pristinus may have been larger than Floridan A. pristinus , being up to 400 kilograms (880 lb). Some A. simus individuals might have been
13871-533: 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
14014-563: The floor of the cave) were nearly 20 cm in width. The presence of a partial false thumb in Arctodus simus is a characteristic shared with Tremarctos floridanus and the spectacled bear, and is possibly an ancestral trait. Absent in ursine bears , the false thumb of the spectacled bear has been suggested to assist in herbivorous food manipulation (such as bromeliads , leaves, berries, tree bark & fruits, cactus fruits & pulp, palm hearts & fronds), or arboreality . Beyond carbohydrate-associated dental pathologies present in
14157-435: 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
14300-464: The genus, extensive pathologies have been preserved on the most nearly complete skeleton of Arctodus . The leading hypothesis suggests the Fulton County Arctodus specimen suffered from a syphilis -like ( treponemal ) disease, or yaws , based on the various lesions present. The same individual records a pathological growth distorting the right humerus , with abscesses are noted between
14443-428: The group, if not an indication of their preferred dietary habits. † Hemicyoninae † Ursavinae † Agriotheriinae Ailuropodinae [REDACTED] Ursinae [REDACTED] † Plionarctos † Arctodus Tremarctos [REDACTED] † Arctotherium Traditionally, analyses of the phylogenetic inner relationships of tremarctines had Plionarctos and Tremarctos as basal groups with respect to
14586-580: 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
14729-660: 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
14872-447: 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
15015-399: The huge Arctodus simus , which inhabited a pan-continental range, from Alaska to Mexico . Arctotherium angustidens , on the other hand, was replaced by a series of smaller, medium-sized species- Arctotherium vetustum , then shortly thereafter by Arctotherium bonariense , and Arctotherium tarijense . Although the smaller Arctotherium wingei is only known from Late Pleistocene records,
15158-475: 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
15301-476: The individual's teeth are similar to a 4-6 year old Ursus americanus . Fused sutures , epiphyses , and epiphyseal plates , along with tooth eruption , have been used to determine adulthood in Arctodus. Legend: [REDACTED] Main mitochondrial haplogroup of A. simus (haplotypes A, B, C, D, E, F, G) [REDACTED] Chiquihuite Cave A.simus An examination of mitochondrial DNA sequenced from specimens of Arctodus simus from Alaska, Alberta, Ohio and
15444-431: 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,
15587-514: The large body size, taller front legs, high shoulders, short and sloping back, and long legs of Arctodus also compounded locomotive efficiency, as these traits swelled the amount of usable elastic strain energy in the tendons, and increased stride length, making Arctodus built more for endurance than for great speed. His calculations suggested that Arctodus likely had a top speed of 40–45 kilometres per hour (25–28 mph), and based on hyaenid proportions, would shift from singlefoot locomotion to
15730-470: The larger, massive Arctodus individuals are often considered male, particularly older males, with the smaller, more lightly built individuals being females. Sexual dimorphism may also explain A. simus teeth (from multiple individuals at the same site) generally clustering into two sizes. The two species of Arctodus are differentiated not only by size, but also by the shorter snout, greater prognathism , more robust teeth and longer limbs of A. simus, and
15873-430: The largest land-dwelling specimens of Carnivora that ever lived in North America. Standing up on its hind legs, A. simus stood 2.4–3.4 m (8–11 ft), with a maximum vertical arm reach of 4.3 metres (14 ft). When walking on all fours, A. simus stood 1–1.67 m (3.3–5.5 ft) high at the shoulder, with the largest males being tall enough to look an adult human in the eye. The average weight of A. simus
16016-485: 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
16159-421: 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
16302-501: The molars and on both ulna . Hypotheses include syphilis, osteoarthritis , a fungal infection in addition to long term syphilis, or an infected wound. Several specimens from Fairbanks , Alaska, also exhibit either pathological growths or periodontal disease , along with a healed toe bone from Big Bear Cave, Missouri. Paul Matheus proposed that Arctodus simus may have moved in a highly efficient, moderate-speed pacing gait, more specialized than modern bears. His research concluded that
16445-453: The most lateral (fifth) digit. Also, the first digit of Arctodus was positioned more closely and parallel to the other four digits (i.e. with straight toes, Arctodus had less lateral splaying). However this is potentially contradicted by possible Arctodus simus trackways from near Lakeview , Oregon, with strong toe splaying, three centrally aligned & evenly spaced toes at the front, and two almost perpendicular lateral toes (80° from
16588-490: 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
16731-469: 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
16874-410: 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
17017-399: 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
17160-416: The plane of the teeth. The purpose of the highly vaulted calvarium and straight cheek bones of Arctodus simus have been similarly disputed. A 2009 analysis of the mandibular morphology of tremarctine bears found notable differences between Arctodus pristinus and Arctodus simus , with A. simus specimens possessing a concave jaw, large masseter and temporalis muscles, deeper horizontal ramus and
17303-702: 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
17446-406: The relationships between the mitochondrial haplogroups of Arctodus simus . Other than the specimen from Chiquihuite Cave, all haplotypes form a single clade . Tremarctos [REDACTED] Arctotherium Chiquihuite Cave A B C D E Extinct Extinction is the termination of a taxon by the death of its last member . A taxon may become functionally extinct before
17589-410: 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
17732-527: The relative proportions of each species' molars and premolars. Arctodus pristinus is distinguished from A. simus smaller, narrower, and less crowded teeth. However, the morphologies of both species are otherwise very similar. As a result, differentiating Arctodus simus from Arctodus pristinus can be difficult, as male individuals of Arctodus pristinus can overlap in size with female individuals of Arctodus simus . Arctodus simus superficially resembled living hyaenids in skull shape and relative lengths of
17875-443: The relatively broad humeral & femoral epicondyles were characteristic of diggers and polar bears, and suggested Arctodus simus could have foraged for roots, tubers and ground squirrels and/or had developed forelimb muscles to immobilze moving prey. The shape of the elbow joint , along with an well-developed medial epicondyle which forms an angle with the condyle , and shallower olecranon fossa , would have given Arctodus
18018-597: The robust Arctotherium angustidens , has puzzled researchers. However, it has been posited that the Pliocene extinctions of scavenger-niche mega-carnivores, such as the procyonid Chapalmalania in South America, and both Borophagus and Agriotherium in North America, was a shared impetus for gigantism in Arctodus and Arctotherium . Arctodus and Tremarctos share characteristics common to herbivorous bears. This includes cheek teeth with large surface areas,
18161-490: The shoulder, and up to 3.4 metres (11 ft) tall on their rear legs. Studies suggest that Arctodus simus browsed on C 3 vegetation and consumed browsing herbivores such as deer , camelids , and tapir . A. simus preferred temperate open woodlands but was an adaptable species, taking advantage of many habitats and feeding opportunities. Arctodus belongs to the Tremarctinae subfamily of bears, which are endemic to
18304-484: The size of the skull, and somewhat laterally orientated (a characteristic of tremarctine bears), more so than actively predatory carnivorans or even the brown bear , suggesting that stereoscopic vision was not a priority. The optic canal and other sphenoidal openings crowd together more in A. simus than in Ursus . As with Tremarctos ornatus , specimens with a large sagittal crest were likely male, whereas females had
18447-460: 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
18590-485: The species' more archaic position in the Arctotherium family tree also suggests an origin in the Middle Pleistocene. Arctotherium wingei was the only known species of Arctotherium to principally inhabit a range north of the Southern Cone , and to reinvade Central America . By the terminal Pleistocene, Arctodus simus , Tremarctos floridanus , Arctotherium tarijense and Arctotherium wingei collectively occupied
18733-471: The spectacled bear. Tremarctinae appear to have a disproportionately shorter snouts compared with most modern bears, giving them the name "short-faced." This apparent shortness is an illusion caused by the deep snouts and short nasal bones of tremarctine bears compared with ursine bears; Tremarctinae had a deeper but not a shorter face than most living bears. Osteological differences between tremarctine and ursine bears include an extra lateral cusp between
18876-430: 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
19019-416: The supposed "long-legged" appearance of the bear is largely an illusion created by the animal's relatively shorter back and torso. In fact, Arctodus probably had an even shorter back than other bears, due the necessary ratio between body length and body mass of the huge bear. However, other researchers argue that the limb bones of Arctodus simus are proportionally longer than those of other bears, leading to
19162-412: 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
19305-555: 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
19448-538: The trunk, back and limbs. The most nearly complete skeleton of A. simus found in the United States was unearthed in Fulton County , Indiana; the original bones are in the Field Museum of Natural History , Chicago. Members of the Tremarctinae subfamily of bears appear to have a disproportionately short snout compared with most modern bears, giving them the name "short-faced". Arctodus has also been argued to exhibit
19591-577: 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
19734-421: Was between 957 kg and 317 kg (699 lb). Hypothetically, the largest individuals of A. simus may have approached 1,000 kilograms (2,200 lb), or even 1,200 kg (2,600 lb). However, a 2006 study argued that the maximum size of Arctodus was ~555 kilograms (1,224 lb), based on the largest known skull. Additionally, a 1998 study calculated the average weight of Arctodus specimens from
19877-483: 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
20020-428: Was largely restricted to the Early Pleistocene of the eastern United States , whereas A. simus had a broader range, with most finds being from the Late Pleistocene of the United States, Mexico and Canada. A. simus evolved from A. pristinus , but both species likely overlapped in the Middle Pleistocene. Both species are relatively rare in the fossil record. Today considered to be an enormous omnivore, Arctodus simus
20163-430: 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
20306-571: 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
20449-526: Was ~625 kilograms (1,378 lb), with the maximum recorded at 957 kilograms (2,110 lb). In a 2010 study, the mass of six A. simus specimens was estimated; half of the specimens weighed between 740 kg (1,631 lb) and 957 kg (2,110 lb), with a mean weight of ~850 kg, suggesting larger specimens were probably more common than previously thought. However, the other specimens were calculated to be less than 500 kg (1,100 lb). The weight range calculated from all examined specimens
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