Great American Interchange
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2008-07-15T15:55:54Z
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/* Island-hopping ‘waif dispersers’ */ wikilink
[[Image:Americas satellite map.jpg|thumb|right|240px|True-color NASA mosaic of satellite images.]]
The '''Great American Interchange''' was an important [[zoogeography|paleozoogeographic]] event in which land and freshwater [[fauna (animals)|fauna]] migrated from [[North America]] via [[Central America]] to [[South America]] and vice versa, as the volcanic [[Isthmus of Panama]] rose up from the sea floor and bridged the [[continent]]s. The migration peaked dramatically around 3 million years ([[annum|Ma]]) ago (in the [[Piacenzian]], the first half of the Upper [[Pliocene]]).
It resulted in the joining of the [[Neotropic ecozone|Neotropic]] (roughly South America) and [[Nearctic ecozone|Nearctic]] (roughly North America) definitively to form the [[Americas]]. The interchange is visible from observation of both [[stratigraphy]] and nature ([[neontology]]). Its most dramatic effect is on the [[zoogeography]] of [[mammal]]s but it also gave an opportunity for non-flying [[bird]]s, [[arthropod]]s, [[reptile]]s, [[amphibian]]s and even freshwater [[fish]] to migrate.
==South America's endemic fauna==
[[Image:Tylacosmilus DB.jpg|thumb|left|160px|The [[Saber-toothed cat|sabertooth]] marsupial †''[[Thylacosmilus]]'']]
[[Image:Macrauchenia patachonica.jpg|thumb|right|240px|The [[Litopterna|litoptern]] †''[[Macrauchenia|Macrauchenia patagonica]]'']]
After the late [[Mesozoic]] breakup of [[Gondwana]], South America spent most of the [[Cenozoic]] era as an island continent whose "splendid isolation" allowed its fauna to evolve into forms found nowhere else on earth. Its [[Endemic (ecology)|endemic]] mammals initially consisted of [[marsupial]]s, [[xenarthra]]ns (i.e., [[armadillo]]s, [[anteater]]s and [[sloth]]s, like the giant ground sloth ''[[Megatherium]]''), and a diverse group of [[Meridiungulata|native ungulates]]: [[notoungulate]]s (the "southern [[ungulate]]s"), [[litoptern]]s, [[Astrapotheria|astrapotheres]] (e.g. ''[[Trigonostylops]]'', [[Astrapotherium magnum|''Astrapotherium'']]), and [[Pyrotheria|pyrotheres]] (e.g. ''[[Pyrotherium]]'').
Marsupials may have traveled (via [[Gondwana]]n land connections) from South America through [[Antarctica]] to [[Australia (continent)|Australia]] and/or vice versa in the late [[Cretaceous]] or early [[Tertiary]]. One living S. American marsupial, the [[Monito del Monte]], is believed to be more closely related to [[Australidelphia|Australian marsupials]] than to [[Ameridelphia|other South American marsupials]]. A [[Obdurodon #Monotrematum sudamericanum|61-Ma-old platypus-like]] [[monotreme]] fossil from [[Patagonia]] may represent another Australian immigrant. It appears that [[ratite]]s (relatives of S. American [[tinamou]]s) migrated by this route around the same time, more likely in the direction from S. America towards Australia/[[Zealandia (continent)|New Zealand]].<ref name = "Briggs">{{cite journal
| last = Briggs
| first = J. C.
| authorlink =
| coauthors =
| title = Fishes and Birds: Gondwana Life Rafts Reconsidered
| journal = Syst. Biol.
| volume = 52
| issue = 4
| pages = 548–553
| publisher =
| location =
| date = 2003
| url = http://www.jstor.org/sici?sici=1063-5157(200308)52%3A4%3C548%3AFABGLR%3E2.0.CO%3B2-L
| doi = 10.1080/10635150390218385
| id = ISSN: 1063-5157
| accessdate = 2008-04-05
| month = Aug
| year = 2003}}</ref> Other taxa that may have dispersed by the same route (if not by flying or floating) are [[parrot]]s, [[Chelidae|chelid]] turtles and (extinct) [[Meiolaniidae|meiolaniid]] turtles.
The marsupials present in South America included didelphimorphs ([[Didelphimorphia|opossums]] and relatives), but many [[Sparassodonta|larger predatory forms]] also existed, like the [[borhyaenid]]s and the [[saber-toothed cat|sabertooth]] ''[[Thylacosmilus]]''. The marsupials shared the [[ecological niche]]s for large predators with fearsome flightless "terror birds" ([[Phorusrhacidae|phorusrhacids]]), whose closest [[Extant taxon|extant]] relatives are the [[seriema]]s.<ref name = "Naish blog">{{cite web
| last = Naish
| first = Darren
| authorlink =
| coauthors =
| title = Terror birds
| work = Darren Naish: Tetrapod Zoology
| publisher =
| date = 2006-10-27
| url = http://darrennaish.blogspot.com/2006/10/terror-birds.html
| format =
| doi =
| accessdate = 2008-03-29}}</ref><ref name = "Alvarenga and Hofling">{{cite journal
| last = Alvarenga
| first = H. M. F.
| authorlink =
| coauthors = Höfling, E.
| title = Systematic Revision of the Phorusrhacidae (Aves: Ralliformes)
| journal = Papéis Avulsos de Zoologia
| volume = 43
| issue = 4
| pages = 55–91
| publisher = [http://www.usp.br/mz/ Museu de Zoologia da Universidade de São Paulo]
| location = [[São Paulo]]
| date = 2003
| url = http://www.scielo.br/pdf/paz/v43n4/17491.pdf
| doi =
| id = ISSN 0031-1049
| accessdate = 2008-03-29}}</ref>
The notoungulates and litopterns had many strange forms, like ''[[Macrauchenia]]'', a camel-like litoptern with a small [[proboscis]]. They also produced a number of familiar-looking body types that represent examples of [[parallel evolution|parallel]] or [[convergent evolution]]: one-toed ''[[Thoatherium]]'' had legs like those of a horse, ''[[Pachyrukhos]]'' resembled a rabbit, ''[[Homalodotherium]]'' was a semi-bipedal clawed browser like a [[chalicothere]], and horned ''[[Trigodon]]'' looked like a [[Rhinoceros|rhino]]. Both groups started evolving in the Lower [[Paleocene]], possibly from [[condylarth]] stock, diversified, dwindled before the great interchange, and went [[Extinction|extinct]] in the [[Pleistocene]]. The pyrotheres and astrapotheres were also strange but were less diverse and disappeared earlier, well before the interchange.
The North American fauna was a pretty typical [[boreoeutheria]]n one (supplemented with [[Afrotheria]]n [[proboscidea]]ns).
==Island-hopping ‘waif dispersers’==
[[Image:Capibara 2 edit.jpg|thumb|right|160px|''[[Capybara|Hydrochoerus hydrochaeris]]'']]
[[Image:Tamarin portrait edit.jpg|thumb|right|160px|[[Emperor Tamarin|''Saguinus imperator'']]]]
The invasions of South America started at least 31.5 Ma ago (late [[Eocene]]/early [[Oligocene]]), when [[Caviomorpha|cavimorph rodent]]s arrived. This gave rise to – among others – [[capybara]]s, [[chinchilla]]s, [[viscacha]]s, and [[New World porcupine]]s. (The independent development of [[Spine (zoology)|spines]] by New and [[Old World porcupine]]s is another example of parallel evolution.) This invasion most likely came from Africa.<ref>{{cite journal
| title=Recent advances in South American mammalian paleontology
| author= J. J. Flynn, A. R. Wyss
| journal=Trends in Ecology and Evolution
| volume=13
| issue=11
| pages=449–454
| year=1998
|doi= 10.1016/S0169-5347(98)01457-8
}}</ref> The crossing from [[West Africa]] to the northeast corner of [[Brazil]] was much shorter then due to [[continental drift]], and may have been aided by [[island-hopping]] (e.g. via [[St. Paul's Rocks]], if they were an inhabitable island at the time) and westward oceanic currents.<ref>{{cite journal
| title= Low-Latitude Circulation and Mass Transport Pathways in a Model of the Tropical Atlantic Ocean
| last = Fratantoni
| first = D. M.
| authorlink =
| coauthors = Johns, W. E., Townsend, T. L., Hurlburt, H. E.
| journal= Journal of Physical Oceanography
| volume= 30
| issue= 8
| pages= 1944–1966
| date = 2000-08
| url= http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0485(2000)030%3C1944:LLCAMT%3E2.0.CO%3B2&ct=1
|doi= 10.1175/1520-0485(2000)030<1944:LLCAMT>2.0.CO;2
| format= abstract
| year= 2000
}}</ref> Crossings of the ocean were accomplished when at least one fertilised female (more commonly a group of animals) accidentally floated over on [[driftwood]] or [[mangrove]] rafts. ([[Hutia|Island-hopping cavimorphs]] would subsequently colonize the [[Caribbean|West Indies]] as far as the [[Bahamas]]).
A little later (at least 25 Ma ago) [[primate]]s followed. The ancestor of the South American monkeys is believed to have arrived from Africa in a fashion similar to the rodents.
The primates capable of migrating had to be small. These gave rise to the [[New World monkey]]s (Platyrrhini). (Not long after arriving, monkeys apparently most closely related to [[titi]]s island-hopped to [[Cuban monkey|Cuba]], [[Hispaniola Monkey|Hispaniola]] and [[Jamaican Monkey|Jamaica]].) The South American cavimorph rodents and monkeys are both believed to be [[clade]]s (i.e., [[monophyly|monophyletic]]).
Tortoises also arrived in South America in the Oligocene. It was long thought that they had come from N. America, but a recent comparative genetic analysis concludes that S. American members of ''[[Geochelone]]'' are actually most closely related to African [[Kinixys|hingeback tortoises]].<ref name = "Le et al.">{{cite journal
| last = Le
| first = M.
| authorlink =
| coauthors = Raxworthy, C. J., McCord, W. P., Mertz, L.
| title = A molecular phylogeny of tortoises (Testudines: Testudinidae} based on mitochondrial and nuclear genes
| journal = Molecular Phylogenetics and Evolution
| volume = 40
| issue =
| pages = 517-531
| publisher =
| location =
| date = 2006-05-05
| url = http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WNH-4JWFGYC-1&_user=4430&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000059594&_version=1&_urlVersion=0&_userid=4430&md5=17737ababb8f6b572a3a44a520001dc6
| doi = 10.1016/j.ympev.2006.03.003
| id =
| accessdate = }}</ref><ref>N. American [[Gopherus|gopher tortoises]] are most closely related to the Asian genus ''[[Manouria]]''.</ref> Tortoises are aided in oceanic dispersal by their ability to float with their heads up, and to survive up to six months without food or water.<ref name = "Le et al."/> S. American tortoises then went on to colonize the West Indies and [[Galápagos Islands]]. Skinks of genus ''[[Mabuya]]'' apparently floated across the Atlantic from Africa during the last 9 Ma.<ref>{{cite journal
| last = Carranza
| first = S.
| authorlink =
| coauthors = Arnold, N. E.
| title = Investigating the origin of transoceanic distributions: mtDNA shows Mabuya lizards (Reptilia, Scincidae) crossed the Atlantic twice
| journal = Systematics and Biodiversity
| volume = 1
| issue = 2
| pages = 275–282
| publisher = Cambridge University Press
| location =
| date = 2003-08-05
| url = http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=168963
| id =
| doi= 10.1017/S1477200003001099
| accessdate = 2008-04-04}}</ref>
The earliest mammalian arrivals from North America were [[Carnivora|carnivorous]] [[Procyonidae|procyonids]] that island-hopped from Central America prior to the formation of a land bridge, around 7 Ma ago. Some South American procyonids then diversified into forms now extinct (e.g. the "dog-coati" ''[[Cyonasua]]'', which evolved into the [[bear]]-like ''[[Chapalmalania]]''). However, all extant procyonid genera appear to have originated in North America.<ref>{{cite journal
| title=Phylogeny of the Procyonidae (Mammalia: Carvnivora): Molecules, morphology and the Great American Interchange
| author= K.-P. Koepfli, M. E. Gompper, E. Eizirik, C.-C. Ho, L. Linden, J. E. Maldonado, R. K. Wayne
| journal=Molecular Phylogenetics and Evolution
| volume=43
| issue=3
| pages=1076–1095
| year=2007
| doi= 10.1016/j.ympev.2006.10.003
}}</ref> The procyonids were followed to S. America by island-hopping [[Sigmodontinae|sigmodontine rodents]]<ref name = "LGMarshall">{{cite journal
| last = Marshall
| first = L. G.
| authorlink =
| coauthors = Butler, R. F.; Drake, R. E.; Curtis, G. H.; Tedford, R. H.
| title = Calibration of the Great American Interchange
| journal = Science
| volume = 204
| issue = 4390
| pages = 272–279
| publisher = [[American Association for the Advancement of Science|AAAS]]
| location =
| date = 1979-04-20
| url = http://www.sciencemag.org/cgi/content/abstract/204/4390/272
| doi = 10.1126/science.204.4390.272
| id =
| accessdate = 2008-04-15
| format = abstract
| pmid = 17800342}}</ref>, [[Peccary|peccaries]] and [[Hog-nosed skunk|hog-nosed]] [[skunk]]s.<ref name = "SDWebb">{{cite journal
| last = Webb
| first = S. D.
| authorlink =
| coauthors =
| title = Mammalian Faunal Dynamics of the Great American Interchange
| journal = Paleobiology
| volume = 2
| issue = 3
| pages = 220–234
| publisher = [[Paleontological Society]]
| location =
| date = 1976
| url = http://www.jstor.org/stable/2400220
| doi =
| id =
| accessdate = 2008-04-15}}</ref>
Similarly, mylodontid and megalonychid [[ground sloth]]s island-hopped to North America by 9 Ma ago.<ref name = "LGMarshall"/> Megalonychids had colonized the [[Antilles]] previously, by the early [[Miocene]]<ref>{{Citation
| last = Morgan
| first = Gary S.
| editor-last = Emry
| editor-first = Robert J.
| contribution = Late Rancholabrean Mammals from Southernmost Florida, and the Neotropical Influence in Florida Pleistocene Faunas
| title = Cenozoic Mammals of Land and Sea: Tributes to the Career of Clayton E. Ray
| year = 2002
| journal = Smithsonian Contributions to Paleobiology
| publisher = Smithsonian Institution Press
| location = Washington, D.C.
| volume = 93
| pages = 15–38
| url = http://www.sil.si.edu/smithsoniancontributions/Paleobiology/sc_RecordSingle.cfm?filename=SCtP-0093
}}</ref>, and may have reached N. America by that route, since the oldest N. American fossils are from [[Florida]].
==The Great American Biotic Interchange==
[[Image:Titanis07DB.jpg|thumb|right|160px|†''[[Titanis|Titanis walleri]]'', the only known N. American [[Phorusrhacidae|terror bird]].]]
The formation of the Isthmus of Panama led to the last and most conspicuous wave, the great interchange, around 3 Ma ago. This included the immigration of North American ungulates (including [[llama]]s, [[tapir]]s and [[horse]]s), [[proboscidea]]ns (such as [[mastodon]]s), [[carnivora]]ns (including [[felidae|felid]]s like [[cougar]]s and [[Machairodontinae|saber-toothed cats]], [[canid]]s, and [[bear]]s) and a number of types of [[rodent]]s<ref>
Of the 6 families of North American rodents that did not originate in South America, only [[beaver]]s and [[mountain beaver]]s failed to migrate to S. America. (However, introduced beavers have become serious [[Pest (organism)|pests]] in [[Tierra del Fuego]].)</ref>
into South America.
In general, the initial net migration was symmetrical. Later on, however, the Neotropic species proved far less successful than the Nearctic. This "bad luck" happened both ways. Northwardly migrating animals often were not able to compete for resources as well as the North American species already occupying the same ecological niches; even when they became established, they usually did not diversify much. Southwardly migrating Nearctic species diversified more, and are thought to have caused the [[extinction]] of much of the South American fauna. (There were no extinctions in N. America obviously attributable to S. American immigrants.) Although terror birds were initially able to invade N. America, this success was temporary; all of the large Neotropic avian and marsupial predators ultimately disappeared. South America's [[Meridiungulata|native ungulates]] also fared very poorly, with only several of the largest forms, ''[[Macrauchenia]]'' and a few [[Toxodonta|toxodont]]s, withstanding the northern onslaught. (Among the notoungulates, the [[Mesotheriidae|mesotheriids]] and [[Hegetotheriidae|hegetotheriids]] did manage to survive into the Pleistocene.) Its [[Ameridelphia|small marsupials]] fared better, while the [[Primitive (biology)|primitive]]-looking [[xenarthra]]ns proved to be surprisingly competitive. The African immigrants, the cavimorph rodents and platyrrhine monkeys, generally held their own during the interchange, although the largest rodents (e.g. the [[Dinomyidae|dinomyids]]) seem to have disappeared. With the exception of the [[North American porcupine]] and several extinct porcupines and capybaras, however, they did not migrate past [[Central America]].<ref>
Of the 11 extant families of South American cavimorph rodents, 5 are present in Central America; only 2 of these, [[New World porcupine|Erethizontidae]] and [[Caviidae]], ever reached N. America. (The [[Coypu|nutria/coypu]] has been introduced to a number of N. American locales.) </ref>
The presence of armadillos, opossums, and porcupines in the [[United States]] today is explained by the Great American Interchange. Opossums and porcupines were among most successful northward migrants, reaching as far as [[Canada]]. While only one example each of xenarthrans, marsupials and cavimorph rodents currently lives in North America, 32 species from these [[taxon|taxa]] are [[Lists of mammals by region #Central America|present in tropical Central America]]. Prior to the end-[[Pleistocene]] [[New World Pleistocene extinctions|extinctions]], most major groups of xenarthrans were established in Central or North America. Among the [[megafauna]], ground sloths were notably successful invaders of North America; [[Ground sloth|''Megalonyx'']] spread as far north as [[Alaska]].
Generally speaking, however, the dispersal and subsequent explosive [[adaptive radiation]] of [[Sigmodontinae|sigmodontine rodents]] through South America was much more successful (both spatially and by number of species) than any northward migration of S. American mammals. Other examples of N. American mammal groups that diversified conspicuously in S. America include canids and [[cervid]]s, both of which currently have [[Talk:Great American Interchange #Canid and cervid species/genera listings by continent|4 genera in N. America, 2 or 3 in Central America, and 6 in S. America]]. Although ''[[Canis]]'' currently ranges only as far south as Panama, S. America still has more extant canid genera than any other continent.
==Reasons for success or failure==
[[Image:Americas Koppen Map.png|thumb|right|240px|A north-south climatic asymmetry in the Americas. Tropical climate zones, which are warm year-round and moist at least part of the year (blue zones Af, Am and Aw) cover nearly all of Central America and much of South America, but very little of North America.]]
The eventual triumph of the Nearctic migrants was ultimately based on [[geography]], which played into the hands of the northern invaders in two crucial respects. The first was a matter of [[climate]]. Obviously, any species that reached [[Panama]] from either direction had to be able to tolerate [[Köppen climate classification #GROUP A: Tropical/megathermal climates|moist tropical conditions]]. Those migrating southward would then be able to occupy much of South America without encountering climates that were markedly different. However, northward migrants would begin to encounter drier and/or cooler conditions as soon as they reached the doorstep of North America. The challenge this climatic asymmetry (see map) presented was particularly acute for Neotropic species specialized for [[tropical rainforest]] environments, who had little prospect of penetrating beyond Central America.
The second and more important advantage geography gave to the northerners is related to the land area available for their ancestors to evolve in. During the Cenozoic, North America was periodically connected to [[Eurasia]] via [[Beringia]], allowing multiple migrations back and forth to unite the faunas of the two continents. Eurasia was [[Afro-Eurasia|connected in turn to Africa]], which contributed further to the species that made their way to North America. South America, on the other hand, was connected to Antarctica and Australia, two much smaller continents, only in the earliest part of the Cenozoic, and this land connection does not seem to have carried much traffic (apparently no mammals other than marsupials and perhaps a few monotremes ever migrated by this route). Effectively, this means that northern hemisphere species arose over a land area roughly six times larger than was available to S. American species. This calculation may not be entirely fair, in that migrations between continents would have been more difficult and less frequent than migrations within S. America. Nevertheless, it is clear that N. American species were products of a larger and more competitive arena, where [[evolution]] would have proceeded more rapidly. They tended to be more efficient and [[brain]]ier, generally able to outrun and outwit their S. American counterparts. These advantages can be clearly seen in the cases of ungulates and their predators, where S. American forms were replaced wholesale by the invaders.
Against this backdrop, the ability of S. America's [[xenarthra]]ns to compete effectively against the northerners represents a special case. The explanation for the xenarthrans' success lies in their idiosyncratic approach to defending against [[predation]], based on possession of [[Animal shell|body armor]] and/or formidable [[claw]]s. The xenarthrans did not need to be fleet-footed or quick-witted to survive. Such a strategy may have been forced on them by their low [[Basal metabolic rate|metabolic rate]] (the lowest among the [[theria]]ns).<ref>{{cite journal
| last = Elgar
| first = M. A.
| authorlink =
| coauthors = Harvey, P. H.
| title = Basal Metabolic Rates in Mammals: Allometry, Phylogeny and Ecology
| journal = Functional Ecology
| volume = 1
| issue = 1
| pages = 25–36
| publisher = [[British Ecological Society]]
| location =
| date = 1987
| url = http://www.jstor.org/stable/2389354
| doi = 10.2307/2389354
| id =
| accessdate = 2008-04-18}}</ref><ref>{{cite journal
| last = Lovegrove
| first = B. G.
| authorlink =
| coauthors =
| title = The Zoogeography of Mammalian Basal Metabolic Rate
| journal = The American Naturalist
| volume = 156
| issue = 2
| pages = 201–219
| publisher = [[The University of Chicago Press]]
| location =
| date = 2000-08
| url = http://www.jstor.org/stable/3079219
| doi = 10.1086/303383
| id =
| accessdate = 2008-04-19}}</ref> Their low metabolic rate may in turn have been advantageous in allowing them to specialize on less abundant and/or less nutritious food sources.
==End-Pleistocene extinctions==
[[Image:Glyptodon old drawing.jpg|thumb|right|200px|''[[Human|Homo sapiens]]'' and †''[[Glyptodon]]'']]
At the end of the [[Pleistocene|Pleistocene epoch]], about 12,000 years ago, three dramatic developments occurred in the Americas at roughly the same time (geologically speaking). [[Indigenous peoples of the Americas|Paleoindians]] invaded and occupied the [[New World]], the [[last glacial period]] came to an end, and a large fraction of the [[megafauna]] of both [[List of North American megafauna|North]] and [[List of Central and South American megafauna|South America]] went extinct. This [[Pleistocene extinctions|wave of extinctions]] swept off the face of the [[Earth]] many of the successful participants of the Great American Interchange, as well as other species that had not migrated. All the proboscideans, equids, lions, ''[[Smilodon]]'' species, dire wolves, ground sloths, glyptodonts, and pampatheres of both continents disappeared. The last of the South and Central American notoungulates and litopterns died out, as well as North America's [[American cheetah|native cheetahs]], [[Homotherium|scimitar cats]], [[Giant Beaver|giant beavers]] and many of its [[Shrub-ox|bovid]], [[Stag-moose|cervid]], [[Platygonus|tayassuid]] and [[Capromeryx minor|antilocaprid]] ungulates. Some groups survived in their adopted homes but disappeared over most or all of their original range, e.g. South American camelids, tapirs and tremarctine bears (cougars and jaguars may have been temporarily reduced to S. American ranges also). Others, such as capybaras, survived in their original range but died out in areas they had migrated to.
The near simultaneity of the megafaunal extinctions with the glacial retreat and the [[Models of migration to the New World|peopling of the Americas]] has led to proposals that both climate change and human hunting played a role. However, a number of considerations suggest that human activities were pivotal. The extinctions did not occur selectively in the climatic zones that would have been most affected by the warming trend, and there is no plausible general climate-based megafauna-killing mechanism that could explain the continent-wide extinctions. The climate change took place worldwide, but had little effect on the megafauna in areas like [[List of African megafauna|Africa]] and [[List of Eurasian megafauna|South Asia]], where megafaunal species had coevolved with [[Homo (genus)|humans]]. Numerous [http://en.wikipedia.org/wiki/Image:Five_Myr_Climate_Change.png very similar] [http://en.wikipedia.org/wiki/Image:Atmospheric_CO2_with_glaciers_cycles.gif glacial retreats] had occurred previously within the [[ice age]] of the last several Ma without ever producing <includeonly></includeonly>comparable waves of extinction in the Americas or anywhere else. Similar megafaunal extinctions have occurred on other recently populated land masses (e.g. [[Australian megafauna|Australia]], [[Holocene extinction event|Madagascar, New Zealand]], and many smaller islands around the world, such as [[Prehistoric Cyprus|Cyprus]]) at different times that correspond closely to the first arrival of humans at each location. Additionally, on sizable islands far enough offshore from newly occupied territory to escape immediate human colonization, megafaunal species sometimes survived for thousands of years after they became extinct on the mainland; examples include [[wooly mammoth]]s on [[Wrangel Island]] and [[Saint Paul Island (Alaska)|Saint Paul Island]], [[Megalocnus|ground sloths]] on the [[Antilles]], [[Steller's Sea Cow|Steller's sea cows]] off the [[Commander Islands]], and [[Meiolania|meiolaniid turtles]] on [[Lord Howe Island]] and [[Biodiversity of New Caledonia|New Caledonia]]. The glacial retreat may have played a primarily indirect role in the extinctions by simply facilitating the movement of humans southeastward from [[Beringia]] down to N. America. The reason that a number of groups went extinct in N. America but lived on in S. America (while there are no notable examples of the opposite pattern) appears to be that the dense rain forests of the [[Amazon Basin|Amazon basin]] and the high peaks of the [[Andes]] provided environments that afforded a degree of protection from human predation.
==South American species that migrated to North America==
[[Image:Glyptodon (Riha2000).jpg|thumb|right|200px|†''[[Glyptotherium texanum|Glyptotherium]]'']]
[[Image:Megatherium.jpg|thumb|right|200px|The [[ground sloth]] †''[[Megatherium]]''.]]
[[Extant taxon|Extant]] or [[Extinction|extinct]] North American [[taxon|taxa]] whose ancestors migrated out of South America during the last 10 [[Annum|Ma]]<ref name=qualifier>
This listing currently has fairly complete coverage of nonflying mammals. but only spotty coverage of other groups. Crossings may have been made before 10 Ma ago by some fish, waif-dispersing amphibians and reptiles, and flying bats and birds.</ref>:
*[[Cichlids]] (e.g. ''[[Texas cichlid|Herichthys cyanoguttatus]]'') [[freshwater fish]] that often tolerate [[Brackish water|brackish]] conditions
*[[Virginia Opossum]] (''Didelphis virginiana'')
*[[Nine-banded Armadillo]] (''Dasypus novemcinctus'')
*other [[Armadillo]]s (e.g. †''[[Beautiful Armadillo|Dasypus bellus]]'', †''Pachyarmatherium leiseyi'')
*[[Pampatheriidae|Pampatheres]] (†''Holmesina'', giant armadillo-like animals)
*[[Glyptodontidae|Glyptodont]]s (†''[[Glyptotherium texanum|Glyptotherium]]'')
*[[Ground Sloth]]s (†Mylodontidae, †Megatheriidae, Megalonychidae<ref>
While all megalonychid ground sloths are extinct, extant [[Two-toed sloth|two-toed tree sloths]] are from the same family. [[Three-toed sloth|Three-toed tree sloths]], in contrast, are not closely related to any of the groups of extinct ground sloths.</ref>)
*[[North American Porcupine]] (''Erethizon dorsatum'')
*other [[New World porcupine]]s (e.g. †''[[Erethizon poyeri]]'', †''[[Erethizon kleini|E. kleini]]'')
*[[Capybara]]s (e.g. †''[[Neochoerus pinckneyi]]'', †''[[Hydrochaeris holmesi]]'')
*[[Vampire Bat]]s (e.g. †''[[Desmodus stocki]]'', †''D. archaeodaptes'')
*[[Dire Wolf #Evolution and extinction|Dire Wolf]] (†''Canis dirus'', which evolved from earlier N. American migrants)
*[[Cougar]] (returning from a S. American [[Refugium (population biology)|refugium]] after N. American cougars were [[Local extinction|extirpated]] in the [[New World Pleistocene extinctions|Pleistocene extinctions]])<ref>{{cite journal
| title=Genomic Ancestry of the American Puma (Puma concolor)
| author= M. Culver, W. E. Johnson, J. Pecon-Slattery, S. J. O'Brien
| journal=Journal of Heredity
| volume=91
| issue=3
| pages=186–197
| year=2000
| doi=10.1093/jhered/91.3.186
| url=http://www.coryi.org/Florida_panther/Miscellaneous_Panther_Material/Genomic%20ancestry%20of%20the%20American%20puma.pdf
| format = PDF
| pmid=10833043
}}</ref>
*[[Phorusrhacidae|"Terror Birds"]] (†Phorusrhacidae: †''[[Titanis walleri]]'') <!-- extinct by [[Late Pliocene]] <- these should replace "...for a time" -->
*[[King Vulture]]s (''Sarcoramphus'': †''S. kernensis'') <!-- extinct by [[Late Pliocene]] -->
*[[Hummingbird]]s
*[[Tanager]]s
*[[Tyrant flycatcher|Tyrant Flycatcher]]s
*[[Parrot]]s (†[[Carolina Parakeet|''Conuropsis carolinensis'']], [[Thick-billed Parrot|''Rhynchopsitta pachyrhyncha'']])
==South American species that migrated only as far as Central America==
[[Image:Dendrobates pumilio.jpg|thumb|right|160px|''[[Strawberry Poison-dart Frog|Oophaga pumilio]]'']]
[[Image:Toxodon.jpg|thumb|right|160px|The [[Notoungulata|notoungulate]] †''[[Toxodon]]''.]]
Extant or extinct Central American taxa whose ancestors migrated out of South America during the last 10 [[Annum|Ma]]<ref name=qualifier/>:
*[[Gymnotiformes|Electric knifefishes]]
*[[Caeciliidae|Caeciliid]] [[Caecilian]]s (snake-like amphibians)<ref name="early amphibians">{{cite journal
| title = Molecular Evidence for the Early History of Living Amphibians
| author = Feller, A. E. and [http://evo.bio.psu.edu/hedgeslab/People/sbh.htm Hedges, S. B.]
| journal = Molecular Phylogenetics and Evolution
| volume = 9
| issue = 3
| pages = 509–516
| year = June 1998
| doi = 10.1006/mpev.1998.0500
}}</ref> of genera ''[[Caecilia]]'', ''[[Dermophis]]'', ''[[Gymnopis]]'' and ''[[Oscaecilia]]''
*Dendrobatid [[Poison dart frog|Poison Dart Frogs]]
*[[Boidae|Boa]]s (snakes of the subfamily [[Boa #Boinae subfamiliy|Boinae]])
*other [[Opossum]]s (12 additional extant species, listed on [[Talk:Great American Interchange #Central American opossum species|discussion page]])
*[[Northern Naked-tailed Armadillo]] (''Cabassous centralis'')
*[[Hoffmann's Two-toed Sloth|Hoffmann's]] [[Two-toed sloth|Two-toed Sloth]] (''Choloepus hoffmanni'')
*[[Three-toed sloth|Three-toed Sloths]] ([[Brown-throated Three-toed Sloth|''Bradypus variegatus'']] and [[Pygmy Three-toed Sloth|''B. pygmaeus'']])
*[[Silky Anteater|Silky]] and [[Giant Anteater|Giant]] [[Anteater]]s, and [[Tamandua|Northern Tamandua]]
*[[Toxodonta|Toxodonts]] (†''[[Mixotoxodon]]'', a rhino-like [[Notoungulata|notoungulate]])
*[[Rothschild's Porcupine|Rothschild's]] and [[Mexican Hairy Dwarf Porcupine|Mexican Hairy Dwarf]] [[New World porcupine|Porcupines]] (''Coendou rothschildi'' and ''Sphiggurus mexicanus'')
*other [[Caviomorpha|Caviomorph Rodents]] (9 additional extant species, listed on [[Talk:Great American Interchange #Central American cavimorph rodent species|discussion page]])
*[[New World monkey|Platyrrhine Monkeys]] (up to 10 extant species, listed on [[Talk:Great American Interchange #Central American platyrrhine monkey species|discussion page]])
*other [[Vampire Bat]]s (all 3 extant species)
*[[Toucan]]s
*[[Tinamou]]s
==North American species that migrated to South America==
[[Image:BlankMastodon.jpg|thumb|right|200px|The [[mastodon]] †''[[American mastodon|Mammut americanum]]''.]]
[[Image:Coati roux Amiens 4.jpg|thumb|right|200px|The [[coati]] ''[[Coatimundi|Nasua nasua]]''.]]
[[Image:Smilodon.jpg|thumb|right|200px|The [[saber-toothed cat]] †''[[Smilodon]]''.]]
Extant or extinct South American taxa whose ancestors migrated out of North or Central America during the last 10 [[Annum|Ma]]<ref name=qualifier/>:
*[[Lungless salamander|Lungless Salamanders]]<ref>
Salamanders may have dispersed to South America more than 10 Ma ago. Nevertheless, the salamander fauna of S. America, which is restricted to the tropical region, consists of only 2 clades, and has fewer species and is far less diverse than that of much smaller Central America. S. America hosts the world's only [[southern hemisphere]] [[salamander]]s - see the [http://en.wikipedia.org/wiki/Image:Distribution.caudata.1.png world salamander distribution map].
</ref><ref name="early amphibians"/> of genera ''[[Bolitoglossa]]''<ref>{{cite journal
| title= Molecular diversification of salamanders of the tropical American genus ''Bolitoglossa'' (Caudata: Plethodontidae) and its evolutionary and biogeographical implications
| author = Parra-Olea, G., Garcia-Paris, M. and [[David B. Wake|Wake, D. B.]]
| journal = Biological Journal of the Linnean Society
| volume = 81
| issue = 3
| pages= 325–346
| year= 2004
| url= http://repositories.cdlib.org/postprints/159/
| accessdate = 2008-01-11
| doi= 10.1111/j.1095-8312.2003.00303.x
}}</ref> and ''[[Oedipina]]''
*[[Coral snake|Coral Snakes]]<ref>{{cite journal
| title= Phylogenetic Relationships of Elapid Snakes Based on Cytochrome b mtDNA Sequences
| author = [[Joseph Bruno Slowinski|Slowinski, J. B.]] and [http://www.anu.edu.au/BoZo/keogh.html Keogh J. S.]
| journal = Molecular Phylogenetics and Evolution
| volume = 15
| issue= 1
| pages= 157–164
| year= April 2000
| url= http://www.ingentaconnect.com/content/ap/fy/2000/00000015/00000001/art00725
| doi = 10.1006/mpev.1999.0725
| accessdate = 2007-12-29
}}</ref><ref>{{cite journal
| title= The Phylogenetic Relationships of Asian Coral Snakes (Elapidae: Calliophis and Maticora) Based on Morphological and Molecular Characters
| author = [[Joseph Bruno Slowinski|Slowinski, J. B.]], Boundy, J. and Lawson, R.
| journal = Herpetologica
| volume = 57
| issue= 2
| pages= 233–245
| year= June 2001
| url= http://www.jstor.org/stable/3893186
| accessdate = 2007-12-29
| doi=
| format= abstract
}}</ref>
*[[Rattlesnake]]s<ref>{{cite journal
| title= A Quantitative Analysis of the Ancestral Area of Rattlesnakes
| author = Place, A. J., Abramson, C. I.
| journal = Journal of Herpetology
| volume = 38
| issue= 1
| pages= 152–156
| year= 2004
| doi = 10.1670/103-03N}}</ref>
*other [[Crotalinae|Pit Vipers]] (e.g., ancestors of [[Lachesis (genus)|bushmasters]] and [[Bothrops|lanceheads]])<ref>{{cite journal
| title= Molecular Systematics and Biogeographical History of Pit Vipers as Determined by Mitochondrial Ribosomal DNA Sequences
| author = Parkinson, C. L.
| journal = Copeia
| volume = 3
| pages= 576–586
| year= 1999
| url = http://www.jstor.org/sici?sici=0045-8511%2819990802%293%3A1999%3A3%3C576%3AMSABHO%3E2.0.CO%3B2-Z&origin=crossref
| doi= 10.2307/1447591
| format=
}}</ref>
*[[Small-eared shrew|Small-eared Shrews]] (genus ''Cryptotis''; only present in NW S. America - [[Colombia]], [[Venezuela]], [[Ecuador]], [[Peru]])
*[[Pocket gopher|Geomyid Pocket Gophers]] (one species, ''[[Thaeler's Pocket Gopher|Orthogeomys thaeleri]]'', in [[Colombia]])
*[[Heteromyidae|Heteromyid Mice]] (genus ''[[Heteromys]]''; only present in NW S. America - [[Colombia]], [[Venezuela]], [[Ecuador]]])
*[[New World rats and mice|Cricetid ]] (primarily [[Sigmodontinae|Sigmodontine]]) Rats and Mice
*Tree [[Sciuridae|Squirrel]]s of genera ''[[Sciurus]]'', ''[[Microsciurus]]'', and ''[[Neotropical Pygmy Squirrel|Sciurillus]]''
*[[Cottontail rabbit|Cottontail]] [[Rabbit]]s ([[Tapeti|''Sylvilagus brasiliensis'']], [[Eastern Cottontail|''S. floridanus'']] and [[Lagomorphs discovered in the 2000s|''S. varynaensis]])
*[[Tapir]]s
*[[Equidae|Equid]]s (†''[[Evolution of the horse #Plesippus|Plesippus]]'', †''[[Hippidion]]'')
*[[Peccary|Peccaries]]
*[[Deer]] of genera [[White-tailed deer|''Odocoileus'']], [[Marsh Deer|''Blastocerus'']], [[Pampas deer|''Ozotoceros'']], [[Brocket deer|''Mazama'']], [[Pudú|''Pudu'']], and ''[[Hippocamelus]]''
*[[Camelid]]s
*[[Mastodon|American Mastodon]] (†''Mammut americanum'')
*[[Gomphothere]]s (†''[[Cuvieronius]]'', elephant relatives)
*[[Otter]]s of genera ''[[Lontra]]'' and ''[[Giant Otter|Pteronura]]''
*other [[Mustelidae|Mustelids]], from subfamily [[Mustelinae]], of genera ''[[Tayra|Eira]]'', ''[[Galictis]]'', ''[[Patagonian Weasel|Lyncodon]]'' and ''[[Weasel|Mustela]]''
*[[Hog-nosed skunk|Hog-Nosed]] [[Skunk]]s (''[[Molina's Hog-nosed Skunk|Conepatus chinga]]'', ''[[Humboldt's Hog-nosed Skunk|C. humboldtii]]'' and ''[[Striped Hog-nosed Skunk|C. semistriatus]]'')
*[[Procyonidae|Procyonid]]s ([[Procyon (genus)|raccoons]], [[coati]]s, [[kinkajou]]s and [[olingo]]s)
*[[Spectacled Bear]] (''Tremarctos ornatus'')
*other [[Arctodus|Short-Faced Bear]]s of subfamily [[Bear #Classification|Tremarctinae]] (†''Arctotherium brasilense'', †''Arctotherium latidens'')
*[[Dire Wolf #Evolution and extinction|Wolves]] (e.g. †''[[Dire Wolf|Canis dirus]]'', †''[[Canis ambrusteri|C. ambrusteri]]'')
*[[Gray Fox]]<ref>Not to be confused with the [[South American Gray Fox|South American gray fox]].</ref> (''Urocyon cinereoargenteus'', only present in NW S. America - [[Colombia]], [[Venezuela]])
*other [[Canids]] (genera [[Short-eared Dog|''Atelocynus'']], [[Crab-eating Fox|''Cerdocyon'']], ''[[Pseudalopex]]'', [[Maned Wolf|''Chrysocyon'']], and [[Bush Dog|''Speothos'']])
*[[Cougar]] (''Puma concolor'') and [[jaguarundi]] (''P. yaguarondi)''
*[[Jaguar]] (''Panthera onca'')
*[[Smilodon|Saber-Toothed Cats]] (†''[[Smilodon gracilis]]'', †''[[Smilodon fatalis|S. fatalis]]'', †''[[Smilodon populator|S. populator]]'')
*[[American Lion]] (†''Panthera leo atrox'')
*all members of ''[[Leopardus]]'' (small [[Felidae|Felid]]s such as the [[ocelot]] and [[margay]])
==References and Notes==
{{reflist|2}}
==External links==
*[http://www.wku.edu/~smithch/biogeog/SIMP1950.htm History of the Fauna of Latin America by George Gaylord Simpson (1950)]
[[Category:Biogeography]]
[[Category:Natural history of Central America]]
[[Category:Natural history of North America]]
[[Category:Natural history of South America]]
[[Category:Natural history of the Americas]]
[[ca:Gran intercanvi americà]]
[[fr:Grand échange inter-américain]]
[[it:Grande scambio americano]]
[[hu:Nagy amerikai faunacsere]]
[[fi:Suuri Amerikan eläimistövaihto]]
[[uk:Великий міжамериканський обмін]]
[[zh:南北美洲生物大遷徙]]