Late Pleistocene extinctions
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The Late Pleistocene to the beginning of the Holocene saw numerous extinctions of predominantly megafaunal (typically defined as having body masses over 44 kilograms (97 lb))[1] animal species (the Pleistocene megafauna), which resulted in a collapse in faunal density and diversity across the globe.[2] The extinctions during the Late Pleistocene are differentiated from previous extinctions by the widespread absence of ecological succession to replace these extinct megafaunal species,[3] and the regime shift of previously established faunal relationships and habitats as a consequence. The timing and severity of the extinctions varied by region and are thought to have been driven by varying combinations of human and climatic factors.[3] Human impact on megafauna populations is thought to have been driven by hunting ("overkill"),[4][5] as well as possibly environmental alteration.[6] The relative importance of human vs climatic factors in the extinctions has been the subject of long-running controversy.[3]
Major extinctions occurred in Australia-New Guinea (Sahul) beginning approximately 50,000 years ago and in the Americas about 13,000 years ago, coinciding in time with the early human migrations into these regions.[7] Extinctions in northern Eurasia were staggered over tens of thousands of years between 50,000 and 10,000 years ago,[2] while extinctions in the Americas were virtually simultaneous, spanning only 3000 years at most.[4][8] Overall, during the Late Pleistocene about 65% of all megafaunal species worldwide became extinct,[9] rising to 72% in North America, 83% in South America and 88% in Australia,[10] with all mammals over 1,000 kilograms (2,200 lb) becoming extinct in Australia and the Americas.[1] Africa, South Asia and Southeast Asia experienced much lower extinctions than other regions.[10]
Extinctions by biogeographic realm
Summary
Biogeographic realm | Giants (over 1,000 kg) |
Very large (400–1,000 kg) |
Large (150–400 kg) |
Moderately large (50–150 kg) |
Medium (10–50 kg) |
Total | Regions included | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Start | Loss | % | Start | Loss | % | Start | Loss | % | Start | Loss | % | Start | Loss | % | Start | Loss | % | ||
Afrotropic | 6 | −1 | 16.6% | 4 | −1 | 25% | 25 | −3 | 12% | 32 | 0 | 0% | 69 | −2 | 2.9% | 136 | -7 | 5.1% | Arabia
|
Indomalaya | 5 | −2 | 40% | 6 | −1 | 16.7% | 10 | −1 | 10% | 20 | −3 | 15% | 56 | −1 | 1.8% | 97 | -8 | 8.2% | Indian subcontinent, Southeast Asia, and southern China |
Palearctic | 8 | −8 | 100% | 10 | −5 | 50% | 14 | −5 | 35.7% | 23 | −3 | 15% | 41 | −1 | 2.4% | 96 | -22 | 22.9% | Eurasia and North Africa |
Nearctic | 5 | −5 | 100% | 10 | −8 | 80% | 26 | −22 | 84.6% | 20 | −13 | 65% | 25 | −9 | 36% | 86 | -57 | 66% | North America |
Neotropic | 9 | −9 | 100% | 12 | −12 | 100% | 17 | −14 | 82% | 20 | −11 | 55% | 35 | −5 | 14.3% | 93 | -51 | 54% | South America, Central America, South Florida, and the Caribbean |
Australasia | 4 | −4 | 100% | 5 | −5 | 100% | 6 | −6 | 100% | 16 | −13 | 81.2% | 25 | −10 | 40% | 56 | -38 | 67% | Australia, New Guinea, New Zealand, and neighbouring islands. |
Global | 33 | −26 | 78.8% | 46 | −31 | 67.4% | 86 | −47 | 54.7% | 113 | −41 | 36.3% | 215 | −23 | 10.1% | 493 | -168 | 34% |
Introduction
The Late Pleistocene saw the extinction of many mammals weighing more than 40 kilograms (88 lb). The proportion of megafauna extinctions is progressively larger the further the human migratory distance from Africa, with the highest extinction rates in Australia, and North and South America.
The increased extent of extinction mirrors the migration pattern of modern humans: the further away from Africa, the more recently humans inhabited the area, the less time those environments (including its megafauna) had to become accustomed to humans (and vice versa).
There are two main hypotheses to explain this extinction:
- ice sheetscausing reduction in favorable habitat.
- Human hunting causing attrition of megafauna populations, commonly known as "overkill".[12]
There are some inconsistencies between the current available data and the prehistoric overkill hypothesis. For instance, there are ambiguities around the timing of Australian megafauna extinctions.[12] Evidence supporting the prehistoric overkill hypothesis includes the persistence of megafauna on some islands for millennia past the disappearance of their continental cousins. For instance, ground sloths survived on the Antilles long after North and South American ground sloths were extinct, woolly mammoths died out on remote Wrangel Island 6,000 years after their extinction on the mainland, while Steller's sea cows persisted off the isolated and uninhabited Commander Islands for thousands of years after they had vanished from the continental shores of the north Pacific.[13] The later disappearance of these island species correlates with the later colonization of these islands by humans.
The original debates as to whether human arrival times or climate change constituted the primary cause of megafaunal extinctions necessarily were based on paleontological evidence coupled with geological dating techniques. Recently, genetic analyses of surviving megafaunal populations have contributed new evidence, leading to the conclusion: "The inability of climate to predict the observed population decline of megafauna, especially during the past 75,000 years, implies that human impact became the main driver of megafauna dynamics around this date."[14]
Recent research indicates that each species responded differently to environmental changes, and no one factor by itself explains the large variety of extinctions. The causes may involve the interplay of
Africa
Although Africa was one of the least affected regions, the region still suffered extinctions, particularly around the Late Pleistocene-Holocene transition. These extinctions were likely predominantly climatically driven by changes to grassland habitats.[16]
- Ungulates
- Even-Toed Ungulates
- Odd-toed Ungulates
- Rhinoceros (Rhinocerotidae).
- Stephanorhinus hemitoechus(North Africa)
- Ceratotherium mauritanicum
- Wild Equus spp.
- Caballine horses
- Equus algericus (North Africa)
- Subgenus Asinus (asses)
- Equus melkiensis (North Africa)
- Zebras
- Equus capensis
- Saharan zebra[17] (Equus mauritanicus)
- Caballine horses
- Rhinoceros (Rhinocerotidae).
- Proboscidea
- Elephantidae (elephants)
- Palaeoloxodon iolensis? (other authors suggest that this taxon went extinct at the end of the Middle Pleistocene)
- Elephantidae (elephants)
- Rodentia
- Paraethomys filfilae?
South Asia and Southeast Asia
The timing of extinctions on the Indian subcontinent is uncertain due to a lack of reliable dating.[18] Similar issues have been reported for Chinese sites, though there is no evidence for any of the megafaunal taxa having survived into the Holocene in that region.[19] Extinctions in Southeast Asia and South China have been proposed to be the result of environmental shift from open to closed forested habitats.[20]
- Ungulates
- Even-Toed Ungulates
- Several Bovidae spp.
- Bos palaesondaicus (ancestor to the banteng)
- Cebu tamaraw (Bubalus cebuensis)
- Bubalus grovesi[21]
- Short-horned water buffalo (Bubalus mephistopheles)
- Bubalus palaeokerabau
- Hippopotamidae
- Hexaprotodon (Indian subcontinent and Southeast Asia)[22]
- Several Bovidae spp.
- Odd-toed Ungulates
- Equus spp.
- Equus namadicus (Indian subcontinent)
- Yunnan horse (Equus yunanensis)
- Giant tapir (Tapirus augustus, Southeast Asia and Southern China)
- Taprus sinensis
- Equus spp.
- Pholidota
- Giant Asian pangolin (Manis palaeojavanica)
- Carnivora
- Caniformia
- Arctoidea
- Bears
- Ailuropoda baconi (ancestor to the giant panda)
- Bears
- Arctoidea
- Caniformia
- Afrotheria
- Afroinsectiphilia
- Orycteropodidae/Tubulidentata
- Aardvark (Orycteropus afer; extirpated in South Asia circa 13,000 BCE)[23][24]
- Orycteropodidae/Tubulidentata
- Paenungulata
- Tethytheria
- Proboscideans
- Stegodontidae
- Stegodon spp. (including Stegodon florensis on Flores, Stegodon orientalis in East and Southeast Asia, and Stegodon sp. in the Indian subcontinent)
- Elephantidae
- Palaeoloxodon spp.
- Palaeoloxodon namadicus (Indian subcontinent, possibly also Southeast Asia)
- Palaeoloxodon spp.
- Stegodontidae
- Proboscideans
- Tethytheria
- Afroinsectiphilia
- Birds
- Japanese flightless duck (Shiriyanetta hasegawai)[25]
- Leptoptilos robustus
- Reptiles
- Crocodilia
- Testudines(turtles and tortoises)
- Primates
- Several simian (Simiiformes) spp.
- Pongo (orangutans)
- Pongo weidenreichi (South China)
- Various Homo spp. (archaic humans)
- Homo erectus soloensis(Java)
- Homo floresiensis (Flores)
- Homo luzonensis (Luzon, Philippines)
- Denisovans(Homo sp.)
- Pongo (
- Several simian (Simiiformes) spp.
Europe, Northern and East Asia
The Palearctic realm spans the entirety of the European continent and stretches into northern Asia, through the Caucasus and central Asia to northern China, Siberia and Beringia. Extinctions were more severe in Northern Eurasia than in Africa or South and Southeast Asia. These extinctions were staggered over tens of thousands of years, spanning from around 50,000 years Before Present (BP) to around 10,000 years BP, with temperate adapted species like the straight-tusked elephant and the narrow-nosed rhinoceros generally going extinct earlier than cold adapted species like the woolly mammoth and woolly rhinoceros. Climate change has been considered a probable major factor in the extinctions, possibly in combination with human hunting.[2]
- Ungulates
- Even-Toed Hoofed Mammals
- Various Bovidae spp.
- Steppe bison (Bison priscus)
- Baikal yak (Bos baikalensis)[26]
- European water buffalo (Bubalus murrensis)
- European tahr (Hemitragus cedrensis)[27][28]
- Giant muskox (Praeovibos priscus)[29]
- Northern saiga antelope (Saiga borealis)[30]
- Twisted-horned antelope (Spirocerus kiakhtensis)[31][32]
- Goat-horned antelope (Parabubalis capricornis)[31][32]
- Bubalus wansijocki (extinct buffalo native to North China)
- Various deer (Cervidae) spp.
- Giant deer(Megaloceros giganteus)
- Cretan deer (Candiacervus spp.)
- Haploidoceros mediterraneus[33][34]
- Sinomegaceros spp. (including Sinomegaceros yabei in Japan, and Sinomegaceros ordosianus and possibly Sinomegaceros pachyosteus in China).[35]
- Dwarf Ryuku deer (Cervus astylodon)
- All native Hippopotamus spp.[36]
- Hippopotamus amphibius(European range, still extant in Africa)
- Maltese dwarf hippopotamus (Hippopotamus melitensis)
- Cyprus dwarf hippopotamus(Hippopotamus minor)
- Sicilian dwarf hippopotamus (Hippopotamus pentlandi)
- Camelus knoblochi[37] and other Camelus spp.
- Various Bovidae spp.
- Odd-Toed Hoofed Mammals
- Various Equus spp. e.g.
- Wild horse (Equus ferus ssp.)
- Equus cf. gallicus[38][39]
- European wild ass (Equus hydruntinus)
- Equus cf. latipes[32][38][40]
- Equus lenensis[32][41]
- Equus cf. uralensis[38]
- All native Rhinoceros(Rhinocerotidae) spp.
- Elasmotherium
- Woolly rhinoceros (Coelodonta antiquitatis)
- Stephanorhinus spp.
- Merck's rhinoceros (Stephanorhinus kirchbergensis)
- Narrow-nosed rhinoceros (Stephanorhinus hemiotoechus)
- Various Equus spp. e.g.
- Even-Toed Hoofed Mammals
- Carnivora
- Caniformia
- Canidae
- Caninae
- Wolves
- Dholes
- European dhole (Cuon alpinus europaeus)
- Sardinian dhole (Cynotherium sardous)
- Caninae
- Arctoidea
- Various Ursus spp.
- Steppe brown bear (Ursus arctos "priscus")[43]
- Gamssulzen cave bear (Ursus ingressus)[44]
- Pleistocene small cave bear (Ursus rossicus)
- Cave bear (Ursus spelaeus)
- Giant polar bear (Ursus maritimus tyrannus)
- Musteloidea
- Mustelidae
- Several otter(Lutrinae) spp.
- Robust Pleistocene European otter (Cyrnaonyx)
- Algarolutra
- Sardinian giant otter(Megalenhydris barbaricina)
- Sardinian dwarf otter (Sardolutra)
- Cretan otter (Lutrogale cretensis)
- Several
- Mustelidae
- Various Ursus spp.
- Canidae
- Feliformia
- Various Felidae spp.
- Herpestoidea
- Cave hyena (Crocuta crocuta spelaea)
- hyaena prisca
- Caniformia
- All native Elephant (Elephantidae) spp.
- Mammoths
- Woolly mammoth (Mammuthus primigenius)
- Dwarf Sardinian mammoth (Mammuthus lamarmorai)
- Straight-tusked elephant (Palaeoloxodon antiquus) (Europe)
- Palaeoloxodon naumanni (Japan, possibly also Korea and northern China)
- Palaeoloxodon huaihoensis (China)
- Dwarf elephant
- Palaeoloxodon creutzburgi (Crete)
- Cyprus dwarf elephant(Palaeoloxodon cypriotes)
- Palaeoloxodon mnaidriensis (Sicily)
- Mammoths
- Rodents
- Allocricetus bursae
- Cricetus major(alternatively Cricetus cricetus major)
- Dicrostonyx gulielmi (ancestor to the Arctic lemming)
- Giant Eurasian porcupine (Hystrix refossa)
- Leithia spp. (Maltese and Sicilian giant dormouse)[46]
- Marmota paleocaucasica
- Microtus grafi
- Mimomys spp.
- M. pyrenaicus
- M. chandolensis
- Pliomys lenki
- Spermophilus citelloides
- Spermophilus severskensis
- Spermophilus superciliosus
- Trogontherium cuiveri
- Lagomorpha
- Lepus tanaiticus(alternatively Lepus timidus tanaiticus)
- Pika (Ochotona) spp. e.g.
- Giant pika (Ochotona whartoni)
- Tonomochota spp.
- T. khasanensis
- T. sikhotana
- T. major
- Birds
- Asian ostrich (Struthio asiaticus)
- Yakutian goose (Anser djuktaiensis)
- Various European crane spp. (Genus Grus)
- Grus primigenia
- Grus melitensis
- Cretan owl (Athene cretensis)
- Primates
- Homo
- Denisovans (Homo sp.)
- Neanderthals(Homo (sapiens) neanderthalensis; survived until about 40,000 years ago on the Iberian peninsula)
- Homo
- Reptiles
- Solitudo sicula; survived in Sicily until about 12,500 years ago.
- Lacerta siculimelitensis; from Malta.
North America
Extinctions in North America were concentrated at the end of the Late Pleistocene, around 13,800–11,400 years Before Present, which were coincident with the onset of the Younger Dryas cooling period, as well as the emergence of the hunter-gatherer Clovis culture. The relative importance of human and climactic factors in the North American extinctions has been the subject of significant controversy. Extinctions totalled around 35 genera.[4] The radiocarbon record for North America south of the Alaska-Yukon region has been described as "inadequate" to construct a reliable chronology.[47]
North American extinctions (noted as
- Ungulates
- Even-Toed Hoofed Mammals
- Various Bovidae spp.
- Most forms of Pleistocene bison (only Bison bison in North America, and Bison bonasus in Eurasia, survived)
- Ancient bison (Bison antiquus) (H)
- Long-horned/Giant bison (Bison latifrons) (H)
- Steppe bison (Bison priscus) (H)
- Bison occidentalis (H)
- Several members of Caprinae (the muskox survived)
- Giant muskox(Praeovibos priscus) (H)
- Shrub-ox(Euceratherium collinum) (H)
- Harlan's muskox(Bootherium bombifrons) (H)
- Soergel's ox(Soergelia mayfieldi) (H)
- surviving relative) (H)
- Saiga antelope(Saiga tatarica; extirpated) (H)
- Most forms of Pleistocene bison (only Bison bison in North America, and Bison bonasus in Eurasia, survived)
- Deer
- Stag-moose(Cervalces scotti) (H)
- American mountain deer (Odocoileus lucasi) (H)
- Torontoceros hypnogeos (H)
- Various Antilocapridae genera (pronghorns survived)
- Capromeryx(H)
- Stockoceros (H)
- Tetrameryx (H)
- Pacific pronghorn (Antilocapra pacifica) (H)
- Several peccary (Tayassuidae) spp.
- Flat-headed peccary (Platygonus) (H)
- Long-nosed peccary (Mylohyus) (H)
- Collared peccary (Dicotyles tajacu; extirpated, range semi-recolonised) (H) (Muknalia minimus is a junior synonym)
- Various members of Camelidae
- Western camel (Camelops hesternus) (H)
- Stilt legged llamas (Hemiauchenia ssp.) (H)
- Stout legged llamas (Palaeolama ssp.) (H)
- Various Bovidae spp.
- Odd-Toed Hoofed Mammals
- All native forms of Equidae
- Caballine true horses (Equus cf. ferus) from the Late Pleistocene of North America have historically been assigned to many different species, including Equus fraternus, Equus scotti and Equus lambei, but the taxonomy of these horses is unclear, and many of these species may be synonymous with each other, perhaps only representing a single species.[48][49][50]
- Stilt-legged horse (Haringtonhippus francisci / Equus francisci; (H)
- Tapirs (Tapirus; three species)
- California tapir(Tapirus californicus) (H)
- Merriam's tapir (Tapirus merriami) (H)
- Vero tapir (Tapirus veroensis) (H)
- All native forms of Equidae
- †Order Notoungulata
- Even-Toed Hoofed Mammals
- Carnivora
- Feliformia
- Several Felidae spp.
- Saber-Tooths
- North American saber-toothed cat (Smilodon fatalis) (C)
- North American scimitar cat (Homotherium serum) (C)
- American cheetah(Miracinonyx; not true cheetah)
- Miracinonyx trumani(C)
- Cougar (Puma concolor; megafaunal ecomorph extirpated from North America, South American populations recolonised former range) (C)
- Jaguarundi (Herpailurus yagouaroundi; extirpated, range semi-recolonised) (C)
- Margay (Leopardus weidii; extirpated) (C)
- Ocelot (Leopardus pardalis; extirpated, range marginally recolonised) (C)
- Eurasian lynx (Lynx lynx; extirpated)[53] (C)
- Jaguars
- Pleistocene North American jaguar (Panthera onca augusta; range semi-recolonised by other subspecies) (C)
- North America Jaguar
- Panthera balamoides (dubious, suggested to be a junior synonym of the short faced bear Arctotherium)
- Lions
- American lion (Panthera atrox; endemic to North America after 340,000 BP) (C)
- Cave/steppe lion (Panthera spelaea; present only as far as modern day Yukon) (C)
- Saber-Tooths
- Several Felidae spp.
- Caniformia
- Canidae
- Dire wolf (Aenocyon dirus) (C)
- Pleistocene coyote (Canis latrans orcutti) (C)
- Megafaunal wolfe.g.
- Beringian wolf (Canis lupus ssp.) (C)
- Dhole (Cuon alpinus; extirpated) (C)
- Protocyon troglodytes[54](C)
- Arctoidea
- Musteloidea
- Mephitidae
- Short-faced skunk (Brachyprotoma obtusata)[55](C)
- Mustelidae
- Steppe polecat (Mustela eversmanii; extirpated)[56] (C)
- Mephitidae
- Various bear (Ursidae) spp.
- Arctodus simus(C)
- Florida spectacled bear(Tremarctos floridanus) (C)
- South American short-faced bear (Arctotherium wingei)[57][54] (C)
- Giant polar bear (Ursus maritimus tyrannus; a possible inhabitant) (C)
- Musteloidea
- Canidae
- Feliformia
- Afrotheria
- Afroinsectiphilia
- Orycteropodidae/Tubulidentata
- Giant anteater (Myrmecophaga tridactyla; extirpated, range partially recolonised)[58][59] (C)
- Orycteropodidae/Tubulidentata
- Paenungulata
- Tethytheria
- All native spp. of Proboscidea
- Mastodons
- American mastodon(Mammut americanum) (H)
- Pacific mastodon(Mammut pacificus) (H) (validity uncertain)
- Gomphotheriidaespp.
- Cuvieronius[60] (H)
- Mammoth (Mammuthus) spp.
- Columbian mammoth (Mammuthus columbi) (H)
- Pygmy mammoth (Mammuthus exilis) (H)
- Woolly mammoth (Mammuthus primigenius) (H)
- Mastodons
- Sirenia
- Dugongidae
- Steller's sea cow (Hydrodamalis gigas; extirpated from North America, survived in Beringia into 18th century) (H)
- Dugongidae
- All native spp. of Proboscidea
- Tethytheria
- Afroinsectiphilia
- Euarchontoglires
- Bats
- Stock's vampire bat (Desmodus stocki) (C)
- Pristine mustached bat (Pteronotus (Phyllodia) pristinus) (C)
- Rodents
- Giant beaver (Castoroides) spp.
- Klein's porcupine (Erethizon kleini)[61] (H)
- Giant island deer mouse (Peromyscus nesodytes) (C)
- Neochoerus spp. e.g.
- Pinckney's capybara (Neochoerus pinckneyi) (H)
- Neochoerus aesopi (H)
- Neotoma findleyi
- Neotoma pygmaea
- Synaptomys australis
- All giant hutia(Heptaxodontidae) spp.
- Blunt-toothed giant hutia (Amblyrhiza inundata; could grow as large as an American black bear) (H)
- Plate-toothed giant hutia (Elasmodontomys obliquus) (H)
- Twisted-toothed mouse (Quemisia gravis) (H)
- Osborn's key mouse (Clidomys osborn's) (H)
- Xaymaca fulvopulvis (H)
- Lagomorphs
- Aztlan rabbit (Aztlanolagus sp.) (H)
- Giant pika (Ochotona whartoni) (H)
- Bats
- Eulipotyphla
- Xenarthrana
- All remaining ground sloth spp.
- Eremotherium (megatheriid giant ground sloth) (H)
- Nothrotheriops (nothrotheriid ground sloth) (H)
- Megalonychid ground sloth spp.
- Megalonyx (H)
- Nohochichak[62][63] (H)
- Xibalbaonyx[64][65] (H)
- Meizonyx
- Mylodontid ground sloth spp.
- Paramylodon (H)
- All members of Glyptodontidae
- Glyptotherium[66] (H)
- (H)
- Beautiful armadillo (Dasypus bellus)[67] (H)
- Pachyarmatherium
- All Pampatheriidae spp.
- Holmesina (H)
- Pampatherium (H)
- All remaining ground sloth spp.
- Birds
- Water Fowl
- Ducks
- Bermuda flightless duck (Anas pachyscelus) (H)
- Californian flightless sea duck (Chendytes lawi) (C)
- Mexican stiff-tailed duck (Oxyura zapatima)[57] (H)
- Ducks
- Turkey (Meleagris) spp.
- Californian turkey (Meleagris californica) (H)
- Meleagris crassipes[57] (H)
- Various Gruiformes spp.
- All cave rail (Nesotrochis) spp. e.g.
- Antillean cave rail (Nesotrochis debooyi) (C)
- Barbados rail (Incertae sedis) (C)
- Cuban flightless crane(Antigone cubensis) (H)
- La Brea crane (Grus pagei) (H)
- All cave rail (Nesotrochis) spp. e.g.
- Various flamingo (Phoenicopteridae) spp.
- Dow's puffin (Fratercula dowi) (C)
- Pleistocene Mexican diver spp.
- Storks
- La Brea/Asphalt stork (Ciconia maltha)[57] (C)
- Wetmore's stork (Mycteria wetmorei)[57] (C)
- Pleistocene Mexican cormorants spp. (genus Phalacrocorax)[57]
- Phalacrocorax goletensis (C)
- Phalacrocorax chapalensis (C)
- All remaining teratorn (Teratornithidae) spp.
- Several New World vultures(Cathartidae) spp.
- Pleistocene black vulture (Coragyps occidentalis ssp.) (C)
- Megafaunal Californian condor (Gymnogyps amplus) (C)
- Clark's condor(Breagyps clarki) (C)
- Cuban condor (Gymnogyps varonai) (C)
- Several Accipitridae spp.
- (C)
- Woodward's eagle (Amplibuteo woodwardi) (C)
- Cuban great hawk (Buteogallus borrasi) (C)
- Daggett's eagle (Buteogallus daggetti) (C)
- Fragile eagle(Buteogallus fragilis) (C)
- Cuban giant hawk (Gigantohierax suarezi)[71][72] (C)
- Errant eagle(Neogyps errans) (C)
- Grinnell's crested eagle (Spizaetus grinnelli)[57] (C)
- Willett's hawk-eagle (Spizaetus willetti)[57] (C)
- Caribbean titan hawk (Titanohierax) (C)
- Several owl (Strigiformes) spp.
- Brea miniature owl(Asphaltoglaux) (C)
- Kurochkin's pygmy owl(Glaucidium kurochkini) (C)
- Brea owl (Oraristix brea) (C)
- Cuban giant owl (Ornimegalonyx) (C)
- Bermuda flicker (Colaptes oceanicus) (C)
- Several caracara (Caracarinae) spp.
- Bahaman terrestrial caracara (Caracara sp.) (C)
- Puerto Rican terrestrial caracara (Caracara sp.) (C)
- Jamaican caracara (Carcara tellustris) (C)
- Cuban caracara (Milvago sp.) (C)
- Hispaniolan caracara (Milvago sp.) (C)
- Psittacopasserae
- Psittaciformes
- Mexican thick-billed parrot (Rhynchopsitta phillipsi)[57] (H)
- Psittaciformes
- Water Fowl
- Several giant tortoise spp.
- Hesperotestudo (H)
- Gopherus spp.
- Chelonoidis spp.
The survivors are in some ways as significant as the losses:
The culture that has been connected with the wave of extinctions in North America is the paleo-American culture associated with the
South America
South America suffered among the worst losses of the continents, with around 83% of its megafauna going extinct.[10] These extinctions postdate the arrival of modern humans in South America around 15,000 years ago. Both human and climatic factors have been attributed as factors in the extinctions by various authors.[79] Although some megafauna has been historically suggested to have survived into the early Holocene based on radiocarbon dates this may be the result of dating errors due to contamination.[80] The extinctions are coincident with the end of the Antarctic Cold Reversal (a cooling period earlier and less severe than the Northern Hemisphere Younger Dryas) and the emergence of Fishtail projectile points, which became widespread across South America. Fishtail projectile points are thought to have been used in big game hunting, though direct evidence of exploitation of extinct megafauna by humans is rare,[79] though megafauna exploitation has been documented at a number of sites.[80][81] Fishtail points rapidly disappeared after the extinction of the megafauna, and were replaced by other styles more suited to hunting smaller prey.[79] Some authors have proposed the "Broken Zig-Zag" model, where human hunting and climate change causing a reduction in open habitats preferred by megafauna were synergistic factors in megafauna extinction in South America.[82]
- Ungulates
- Even-Toed Hoofed Mammals
- Several Cervidaespp.
- Morenelaphus
- Antifer
- Odocoileus salinae[85][86]
- Various Camelidae spp.
- Eulamaops
- Stilt legged llama Hemiauchenia
- Stout legged llama Palaeolama
- Several
- Odd-Toed Hoofed Mammals
- All remaining Meridiungulatagenera
- Even-Toed Hoofed Mammals
- Carnivora
- Feliformia
- Several Felidae spp.
- Saber-toothed cat (Smilodon) spp.[93]
- North American saber-toothed cat(Smilodon fatalis)
- South American saber-toothed cat(Smilodon populator)
- Patagonian jaguar (Panthera onca mesembrina) (some authors have suggested that these remains actually belong to the American lion instead[94])
- Several Felidae spp.
- Caniformia
- Canidae
- Dire wolf (Aenocyon dirus)
- Nehring's wolf (Canis nehringi)
- Protocyon spp.[95]
- Dusicyon avus
- Pleistocene bush dog (Speothos pacivorus)
- Arctoidea
- South American short-faced bear (Arctotherium spp.)
- Arctotherium bonairense
- Arctotherium tarijense
- Arctotherium wingei
- South American short-faced bear (Arctotherium spp.)
- Canidae
- Feliformia
- Rodents
- Bats
- Giant vampire bat (Desmodus draculae)
- All remaining Gomphotheridaespp.
- Xenarthrans
- All remaining ground sloth genera
- All remaining Glyptodontinaespp.
- Several Dasypodidae spp.
- Beautiful armadillo (Dasypus bellus)
- Eutatus
- Pachyarmatherium
- Propaopus[36][86]
- All Pampatheriidae spp.
- Holmesina (et 'Chlamytherium occidentale')[104][105]
- Pampatherium[106]
- Tonnicinctus[106]
- Birds
- Psilopterus (small terror bird remains dated to the Late Pleistocene,[107][108] but these are disputed)[109]
- Various Caracarinaespp.
- Venezuelan caracara (Caracara major)[110]
- Seymour's caracara (Caracara seymouri)[111]
- Peruvian caracara (Milvago brodkorbi)[112]
- Various Cathartidaespp.
- Pampagyps imperator
- Geronogyps reliquus
- Wingegyps cartellei
- Pleistovultur nevesi
- Crocs & Gators
- Testudines
- Chelonoidis lutzae (Argentina)
- Peltocephalus maturin[113]
Sahul (Australia-New Guinea) and the Pacific
A scarcity of reliably dated megafaunal bone deposits has made it difficult to construct timelines for megafaunal extinctions in certain areas, leading to a divide among researches about when and how megafaunal species went extinct.[114][115]
There are at least three hypotheses regarding the extinction of the Australian megafauna:
- that they went extinct with the arrival of the Aboriginal Australians on the continent,
- that they went extinct due to natural climate change.
This theory is based on evidence of megafauna surviving until 40,000 years ago, a full 30,000 years after homo sapiens first landed in Australia, and thus that the two groups coexisted for a long time. Evidence of these animals existing at that time come from fossil records and ocean sediment. To begin with, sediment core drilled in the Indian Ocean off the SW coast of Australia indicate the existence of a fungus called Sporormiella, which survived off the dung of plant-eating mammals. The abundance of these spores in the sediment prior to 45,000 years ago indicates that many large mammals existed in the southwest Australian landscape until that point. The sediment data also indicates that the megafauna population collapsed within a few thousand years, around the 45,000 years ago, suggesting a rapid extinction event.[116] In addition, fossils found at South Walker Creek, which is the youngest megafauna site in northern Australia, indicate that at least 16 species of megafauna survived there until 40,000 years ago. Furthermore, there is no firm evidence of homo sapiens living at South Walker Creek 40,000 years ago, therefore no human cause can be attributed to the extinction of these megafauna. However, there is evidence of major environmental deterioration of South Water Creek 40,000 years ago, which may have caused the extinct event. These changes include increased fire, reduction in grasslands, and the loss of fresh water.[117] The same environmental deterioration is seen across Australia at the time, further strengthening the climate change argument. Australia's climate at the time could best be described as an overall drying of the landscape due to lower precipitation, resulting in less fresh water availability and more drought conditions. Overall, this led to changes in vegetation, increased fires, overall reduction in grasslands, and a greater competition for already scarce fresh water.[118] These environmental changes proved to be too much for the Australian megafauna to cope with, causing the extinction of 90% of megafauna species.
- The third hypothesis shared by some scientists is that human impacts and natural climate changes led to the extinction of Australian megafauna. About 75% of Australia is semi-arid or arid, so it makes sense that megafauna species used the same fresh water resources as humans. This competition could have led to more hunting of megafauna.[119] Furthermore, Homo sapiens used fire agriculture[clarification needed] to burn impassable[clarification needed] land. This further diminished the already disappearing grassland which contained plants that were a key dietary component of herbivorous megafauna. While there is no scientific consensus on this, it is plausible that homo sapiens and natural climate change had a combined impact. Overall, there is a great deal of evidence for humans being the culprit, but by ruling out climate change completely as a cause of the Australian megafauna extinction we are not getting the whole picture. The climate change in Australia 45,000 years ago destabilized the ecosystem, making it particularly vulnerable to hunting and fire agriculture by humans; this is probably what led to the extinction of the Australian megafauna.
Several studies provide evidence that climate change caused megafaunal extinction during the Pleistocene in Australia. One group of researchers analyzed fossilized teeth found at
In Sahul (a former continent composed of Australia and New Guinea), the sudden and extensive spate of extinctions occurred earlier than in the rest of the world.[121][122][123][124] Most evidence points to a 20,000 year period after human arrival circa 63,000 BCE,[125] but scientific argument continues as to the exact date range.[126] In the rest of the Pacific (other Australasian islands such as New Caledonia, and Oceania) although in some respects far later, endemic fauna also usually perished quickly upon the arrival of humans in the late Pleistocene and early Holocene.
- Marsupials
- Various members of Diprotodontidae
- Diprotodon (largest known marsupial)
- Hulitherium tomasetti
- Maokopia ronaldi
- Zygomaturus
- Palorchestes ("marsupial tapir")
- Various members of Vombatidae
- Lasiorhinus angustidens (giant wombat)
- Phascolonus (giant wombat)
- Ramasayiamagna (giant wombat)
- Vombatus hacketti (Hackett's wombat)
- Warendja wakefieldi (dwarf wombat)
- Sedophascolomys (giant wombat)
- Phascolarctos stirtoni (giant koala)
- Marsupial lion(Thylacoleo carnifex)
- Various members of Macropodidae
- Procoptodon (short-faced kangaroos) e.g.
- Procoptodon goliah
- Sthenurus (giant kangaroo)
- Simosthenurus (giant kangaroo)
- Various Macropus (giant kangaroo) spp. e.g.
- Protemnodon (giant wallaby)
- Troposodon (wallaby)[121][122][127][128][129][130]
- tree kangaroo)
- Propleopus oscillans (omnivorous, giant musky rat-kangaroo)
- Nombe
- Congruus
- Procoptodon (short-faced kangaroos) e.g.
- Various forms of Sarcophilus (Tasmanian devil)
- Sarcophilus laniarius (25% larger than modern species, unclear if it is actually a distinct species from living Tasmanian devil[131])
- Sarcophilus moornaensis
- Various members of Diprotodontidae
- Monotremes: egg-laying mammals.
- Echidna
- Murrayglossus hacketti(giant echidna)
- Megalibgwilia ramsayi
- Echidna
- Birds
- Pygmy Cassowary (Casuarius lydekkeri)
- Genyornis (a two-meter-tall (6.6 ft) dromornithid
- Giant malleefowl (Progura gallinacea)
- Cryptogyps lacertosus
- Dynatoaetus gaffae
- Several Phoenicopteridaespp.
- Xenorhynchopsis spp. (Australian flamingo)[132]
- Xenorhynchopsis minor
- Xenorhynchopsis tibialis
- Reptiles
- Crocs & Gators
- Ikanogavialis (the last fully marine crocodilian)
- mekosuchinecrocodiian)
- Quinkana (Australian terrestrial mekosuchine crocodilian, apex predator)
- Volia (a two-to-three meter long mekosuchine crocodylian, apex predator of Pleistocene Fiji)
- Mekosuchus
- Mekosuchus inexpectatus(New Caledonian land crocodile)
- Mekosuchus kalpokasi (Vanuatu land crocodile)
- Varanussp. (Pleistocene and Holocene New Caledonia)
- Megalania (Varanus pricus) (a giant predatory monitor lizard comparable or larger than the Komodo dragon)
- Snakes
- Several spp. of Meiolaniidae (giant armoured turtles)
- Crocs & Gators
Causes
History of research
During the 19th century, a number of scientists remarked on topic of megafaunal extinction:[133][134]
It is impossible to reflect without the deepest astonishment, on the changed state of [South America]. Formerly it must have swarmed with great monsters, like the southern parts of Africa, but now we find only the tapir, guanaco, armadillo, capybara; mere pigmies compared to antecedents races... Since their loss, no very great physical changes can have taken place in the nature of the Country. What then has exterminated so many living creatures?
— Charles Darwin, The Voyage of the Beagle (1834)
It is clear, therefore, that we are now in an altogether exceptional period of the earth's history. We live in a zoologically impoverished world, from which all the hugest, and fiercest, and strangest forms have recently disappeared; and it is, no doubt, a much better world for us now they have gone. Yet it is surely a marvellous fact, and one that has hardly been sufficiently dwelt upon, this sudden dying out of so many large mammalia, not in one place only but over half the land surface of the globe. We cannot but believe that there must have been some physical cause for this great change; and it must have been a cause capable of acting almost simultaneously over large portions of the earth's surface, and one which, as far as the Tertiary period at least is concerned, was of an exceptional character.
— Alfred Russel Wallace, The geographical distribution of animals; with a study of the relations of living and extinct faunas as elucidating the past changes of the Earth's surface (1876)
Discussion of the topic became more widespread during the 20th century, particularly following the proposal of the "overkill hypothesis" by Paul Schultz Martin during the 1960s. By the end of the 20th century, two "camps" of researchers had emerged on the topic, one supporting climate change, the other supporting human hunting as the primary cause of the extinctions.[134]
Human Activity - Hunting
The hunting hypothesis suggests that humans hunted
Circumstantially, the close correlation in time between the appearance of humans in an area and extinction there provides weight for this scenario.[140][9][3] Radiocarbon dating has supported the plausibility of this correlation being reflective of causation.[141] The megafaunal extinctions covered a vast period of time and highly variable climatic situations. The earliest extinctions in Australia were complete approximately 50,000 BP, well before the Last Glacial Maximum and before rises in temperature. The most recent extinction in New Zealand was complete no earlier than 500 BP and during a period of cooling. In between these extremes megafaunal extinctions have occurred progressively in such places as North America, South America and Madagascar with no climatic commonality. The only common factor that can be ascertained is the arrival of humans.[142][143] This phenomenon appears even within regions. The mammal extinction wave in Australia about 50,000 years ago coincides not with known climatic changes, but with the arrival of humans. In addition, large mammal species like the giant kangaroo Protemnodon appear to have succumbed sooner on the Australian mainland than on Tasmania, which was colonised by humans a few thousand years later.[144][145] A study published in 2015 supported the hypothesis further by running several thousand scenarios that correlated the time windows in which each species is known to have become extinct with the arrival of humans on different continents or islands. This was compared against climate reconstructions for the last 90,000 years. The researchers found correlations of human spread and species extinction indicating that the human impact was the main cause of the extinction, while climate change exacerbated the frequency of extinctions. The study, however, found an apparently low extinction rate in the fossil record of mainland Asia.[146][147] A 2020 study published in Science Advances found that human population size and/or specific human activities, not climate change, caused rapidly rising global mammal extinction rates during the past 126,000 years. Around 96% of all mammalian extinctions over this time period are attributable to human impacts. According to Tobias Andermann, lead author of the study, "these extinctions did not happen continuously and at constant pace. Instead, bursts of extinctions are detected across different continents at times when humans first reached them. More recently, the magnitude of human driven extinctions has picked up the pace again, this time on a global scale."[148][149] On a related note, the population declines of still extant megafauna during the Pleistocene have also been shown to correlate with human expansion rather than climate change.[14]
The extinction's extreme bias towards larger animals further supports a relationship with human activity rather than climate change.[150] There is evidence that the average size of mammalian fauna declined over the course of the Quaternary,[151] a phenomenon that was likely linked to disproportionate hunting of large animals by humans.[5]
Extinction through human hunting has been supported by archaeological finds of
Major objections have been raised regarding the hunting hypothesis. Notable among them is the sparsity of evidence of human hunting of megafauna.[158][159][160] There is no archeological evidence that in North America megafauna other than mammoths, mastodons, gomphotheres and bison were hunted, despite the fact that, for example, camels and horses are very frequently reported in fossil history.[161] Overkill proponents, however, say this is due to the fast extinction process in North America and the low probability of animals with signs of butchery to be preserved.[162] The majority of North American taxa have too sparse a fossil record to accurately assess the frequency of human hunting of them.[10] A study by Surovell and Grund concluded "archaeological sites dating to the time of the coexistence of humans and extinct fauna are rare. Those that preserve bone are considerably more rare, and of those, only a very few show unambiguous evidence of human hunting of any type of prey whatsoever."[163] Eugene S. Hunn points out that the birthrate in hunter-gatherer societies is generally too low, that too much effort is involved in the bringing down of a large animal by a hunting party, and that in order for hunter-gatherers to have brought about the extinction of megafauna simply by hunting them to death, an extraordinary amount of meat would have had to have been wasted.[164]
Second-order predation
The scenario is as follows:
- After the arrival of H. sapiens in the New World, existing predators must share the prey populations with this new predator. Because of this competition, populations of original, or first-order, predators cannot find enough food; they are in direct competition with humans.
- Second-order predation begins as humans begin to kill predators.
- Prey populations are no longer well controlled by predation. Killing of nonhuman predators by H. sapiens reduces their numbers to a point where these predators no longer regulate the size of the prey populations.
- Lack of regulation by first-order predators triggers boom-and-bustcycles in prey populations. Prey populations expand and consequently overgraze and over-browse the land. Soon the environment is no longer able to support them. As a result, many herbivores starve. Species that rely on the slowest recruiting food become extinct, followed by species that cannot extract the maximum benefit from every bit of their food.
- Boom-bust cycles in herbivore populations change the nature of the vegetative environment, with consequent climatic impacts on relative humidity and continentality. Through overgrazing and overbrowsing, mixed parkland becomes grassland, and climatic continentalityincreases.
The second-order predation hypothesis has been supported by a computer model, the Pleistocene extinction model (PEM), which, using the same assumptions and values for all variables (herbivore population, herbivore recruitment rates, food needed per human, herbivore hunting rates, etc.) other than those for hunting of predators. It compares the overkill hypothesis (predator hunting = 0) with second-order predation (predator hunting varied between 0.01 and 0.05 for different runs). The findings are that second-order predation is more consistent with extinction than is overkill[165][166] (results graph at left). The Pleistocene extinction model is the only test of multiple hypotheses and is the only model to specifically test combination hypotheses by artificially introducing sufficient climate change to cause extinction. When overkill and climate change are combined they balance each other out. Climate change reduces the number of plants, overkill removes animals, therefore fewer plants are eaten. Second-order predation combined with climate change exacerbates the effect of climate change.[167] (results graph at right). The second-order predation hypothesis is further supported by the observation above that there was a massive increase in bison populations.[168]
However, this hypothesis has been criticised on the grounds that the multispecies model produces a mass extinction through indirect competition between herbivore species: small species with high reproductive rates subsidize predation on large species with low reproductive rates.[157] All prey species are lumped in the Pleistocene extinction model. Also, the control of population sizes by predators is not fully supported by observations of modern ecosystems.[169] The hypothesis further assumes decreases in vegetation due to climate change, but deglaciation doubled the habitable area of North America. Any vegetational changes that did occur failed to cause almost any extinctions of small vertebrates, and they are more narrowly distributed on average, which detractors cite as evidence against the hypothesis.
Competition for water
In southeastern Australia, the scarcity of water during the interval in which humans arrived in Australia suggests that human competition with megafauna for precious water sources may have played a role in the extinction of the latter.[119]
Landscape alteration
One consequence of the colonisation by humans of lands previously uninhabited by them may have been the introduction of new fire regimes because of extensive fire use by humans.[7] There is evidence that anthropogenic fire use had major impacts on the local environments in both Australia[6] and North America.[170]
Climate change
At the end of the 19th and beginning of the 20th centuries, when scientists first realized that there had been glacial and interglacial ages, and that they were somehow associated with the prevalence or disappearance of certain animals, they surmised that the termination of the Pleistocene ice age might be an explanation for the extinctions.
The most obvious change associated with the termination of an ice age is the increase in temperature. Between 15,000
Other scientists have proposed that increasingly extreme weather—hotter summers and colder winters—referred to as "
Evidence in Southeast Asia, in contrast to Europe, Australia, and the Americas, suggests that climate change and an increasing sea level were significant factors in the extinction of several herbivorous species. Alterations in vegetation growth and new access routes for early humans and mammals to previously isolated, localized ecosystems were detrimental to select groups of fauna.[184]
Some evidence from Europe also suggests climatic changes were responsible for extinctions there, as the individuals extinctions tended to occur during times of environmental change and did not correlate particularly well with human migrations.[2]
In Australia, some studies have suggested that extinctions of megafauna began before the peopling of the continent, favouring climate change as the driver.[185]
In Beringia, megafauna may have gone extinct because of particularly intense paludification and because the land connection between Eurasia and North America flooded before the Cordilleran Ice Sheet retreated far enough to reopen the corridor between Beringia and the remainder of North America.[186] Woolly mammoths became extirpated from Beringia because of climatic factors, although human activity also played a synergistic role in their decline.[187] In North America, a Radiocarbon-dated Event-Count (REC) modelling study found that megafaunal declines in North America correlated with climatic changes instead of human population expansion.[188]
In the North American Great Lakes region, the population declines of mastodons and mammoths have been found to correlate with climatic fluctuations during the Younger Dryas rather than human activity.[189]
In the Argentine Pampas, the flooding of vast swathes of the once much larger Pampas grasslands may have played a role in the extinctions of its megafaunal assemblages.[8]
Critics object that since there were multiple glacial advances and withdrawals in the evolutionary history of many of the megafauna, it is rather implausible that only after the last glacial maximum would there be such extinctions. Proponents of climate change as the extinction event's cause like David J. Meltzer suggest that the last deglaciation may have been markedly different from previous ones.[190] Also, one study suggests that the Pleistocene megafaunal composition may have differed markedly from that of earlier interglacials, making the Pleistocene populations particularly vulnerable to changes in their environment.[191]
Studies propose that the annual mean temperature of the current interglacial that we have seen for the last 10,000 years is no higher than that of previous interglacials, yet most of the same large mammals survived similar temperature increases.
Critics have also identified a number of problems with the continentality hypotheses. Megaherbivores have prospered at other times of continental climate. For example, megaherbivores thrived in Pleistocene Siberia, which had and has a more continental climate than Pleistocene or modern (post-Pleistocene, interglacial) North America.[196][197][198] The animals that became extinct actually should have prospered during the shift from mixed woodland-parkland to prairie, because their primary food source, grass, was increasing rather than decreasing.[199][198][200] Although the vegetation did become more spatially specialized, the amount of prairie and grass available increased, which would have been good for horses and for mammoths, and yet they became extinct. This criticism ignores the increased abundance and broad geographic extent of Pleistocene bison at the end of the Pleistocene, which would have increased competition for these resources in a manner not seen in any earlier interglacials.[191] Although horses became extinct in the New World, they were successfully reintroduced by the Spanish in the 16th century—into a modern post-Pleistocene, interglacial climate. Today there are feral horses still living in those same environments. They find a sufficient mix of food to avoid toxins, they extract enough nutrition from forage to reproduce effectively and the timing of their gestation is not an issue. Of course, this criticism ignores the obvious fact that present-day horses are not competing for resources with ground sloths, mammoths, mastodons, camels, llamas, and bison. Similarly, mammoths survived the Pleistocene Holocene transition on isolated, uninhabited islands in the Mediterranean Sea until 4,000 to 7,000 years ago,[201] as well as on Wrangel Island in the Siberian Arctic.[202] Additionally, large mammals should have been able to migrate, permanently or seasonally, if they found the temperature too extreme, the breeding season too short, or the rainfall too sparse or unpredictable.[203] Seasons vary geographically. By migrating away from the equator, herbivores could have found areas with growing seasons more favorable for finding food and breeding successfully. Modern-day African elephants migrate during periods of drought to places where there is apt to be water.[204] Large animals also store more fat in their bodies than do medium-sized animals and this should have allowed them to compensate for extreme seasonal fluctuations in food availability.[205]
Some evidence weighs against climate change as a valid hypothesis as applied to Australia. It has been shown that the prevailing climate at the time of extinction (40,000–50,000 BP) was similar to that of today, and that the extinct animals were strongly adapted to an arid climate. The evidence indicates that all of the extinctions took place in the same short time period, which was the time when humans entered the landscape. The main mechanism for extinction was probably fire (started by humans) in a then much less fire-adapted landscape. Isotopic evidence shows sudden changes in the diet of surviving species, which could correspond to the stress they experienced before extinction.[206][207][208]
Some evidence obtained from analysis of the tusks of
It may be observed that neither the overkill nor the climate change hypotheses can fully explain events:
Disease
The hyperdisease hypothesis, as advanced by Ross D. E. MacFee and Preston A. Marx, attributes the extinction of large mammals during the late Pleistocene to indirect effects of the newly arrived
If a disease was indeed responsible for the end-Pleistocene extinctions, then there are several criteria it must satisfy (see Table 7.3 in MacPhee & Marx 1997). First, the pathogen must have a stable carrier state in a reservoir species. That is, it must be able to sustain itself in the environment when there are no susceptible hosts available to infect. Second, the pathogen must have a high infection rate, such that it is able to infect virtually all individuals of all ages and sexes encountered. Third, it must be extremely lethal, with a mortality rate of c. 50–75%. Finally, it must have the ability to infect multiple host species without posing a serious threat to humans. Humans may be infected, but the disease must not be highly lethal or able to cause an epidemic.[citation needed]
As with other hypotheses, a number of counterarguments to the hyperdisease hypothesis have been put forth. Generally speaking, disease has to be very virulent to kill off all the individuals in a
Extraterrestrial impact
An extraterrestrial impact, which has occasionally been proposed as a cause of the Younger Dryas,[219] has been suggested by some authors as a potential cause of the extinction of North America's megafauna due to the temporal proximity between a proposed date for such an impact and the following megafaunal extinctions.[220][4] However, the Younger Dryas impact hypothesis lacks widespread support among scholars due to various inconsistencies in the hypothesis.[221][222][223]
Geomagnetic field weakening
Around 41,500 years ago, the
Effects
The extinction of the megafauna has been argued by some authors to be disappearance of the mammoth steppe rather than the other way around. Alaska now has low nutrient soil unable to support bison, mammoths, and horses. R. Dale Guthrie has claimed this as a cause of the extinction of the megafauna there; however, he may be interpreting it backwards. The loss of large herbivores to break up the permafrost allows the cold soils that are unable to support large herbivores today. Today, in the arctic, where trucks have broken the permafrost grasses and diverse flora and fauna can be supported.[227][228] In addition, Chapin (Chapin 1980) showed that simply adding fertilizer to the soil in Alaska could make grasses grow again like they did in the era of the mammoth steppe. Possibly, the extinction of the megafauna and the corresponding loss of dung is what led to low nutrient levels in modern-day soil and therefore is why the landscape can no longer support megafauna.
However, more recent authors have viewed it as more likely that the collapse of the mammoth steppe was driven by climatic warming, which in turn impacted the megafauna, rather than the other way around.[229]
Megafauna play a significant role in the lateral transport of mineral nutrients in an ecosystem, tending to translocate them from areas of high to those of lower abundance. They do so by their movement between the time they consume the nutrient and the time they release it through elimination (or, to a much lesser extent, through decomposition after death).
Large populations of megaherbivores have the potential to contribute greatly to the atmospheric concentration of
Recent studies have indicated that the extinction of megafaunal herbivores may have caused a reduction in atmospheric methane. One study examined the methane emissions from the bison that occupied the Great Plains of North America before contact with European settlers. The study estimated that the removal of the bison caused a decrease of as much as 2.2 million tons per year.[238] Another study examined the change in the methane concentration in the atmosphere at the end of the Pleistocene epoch after the extinction of megafauna in the Americas. After early humans migrated to the Americas about 13,000 BP, their hunting and other associated ecological impacts led to the extinction of many megafaunal species there. Calculations suggest that this extinction decreased methane production by about 9.6 million tons per year. This suggests that the absence of megafaunal methane emissions may have contributed to the abrupt climatic cooling at the onset of the Younger Dryas. The decrease in atmospheric methane that occurred at that time, as recorded in ice cores, was 2–4 times more rapid than any other decrease in the last half million years, suggesting that an unusual mechanism was at work.[239]
The extermination of megafauna left many niches vacant, which has been cited as an explanation for the vulnerability and fragility of many ecosystems to destruction in the later Holocene extinction. The comparative lack of megafauna in modern ecosystems has reduced high-order interactions among surviving species, reducing ecological complexity.
Relationship to later extinctions
There is no general agreement on where the Quaternary extinction event ends, and the Holocene, or anthropogenic, extinction begins, or if they should be considered separate events at all.[244][245] Some authors have argued that the activities of earlier archaic humans have also resulted in extinctions, though the evidence for this is equivocal.[246]
This hypothesis is supported by rapid megafaunal extinction following recent human colonisation in
See also
- Australian megafauna – Large animals in Australia, past and present era
- Holocene extinction – Ongoing extinction event caused by human activity
- Late Quaternary prehistoric birds– Extinct bird species
- List of Ice Age species preserved as permafrost mummies
- List of quaternary mammalian fauna of China
- Megafauna – Large animals
- Pleistocene megafauna– Extinctions of large mammals in the Late Pleistocene
- Pleistocene rewilding – Ecological practice
- Toba catastrophe theory – Supereruption 74,000 years ago that may have caused a global volcanic winter
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External links
Hyperdisease hypothesis
- MacFee RD, Marx PA (1998). "Lightning Strikes Twice: Blitzkrieg, Hyperdisease, and Global Explanations of the Late Quaternary Catastrophic Extinctions". American Museum of Natural History. Archived from the original on 3 September 2011.
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Second-order predation
- Elin Whitney-Smith. "Quaternary.Net". Archived from the original on 3 December 2020. Retrieved 9 August 2008.
Other links
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