page_title: Great American Interchange
section_title: Late Pleistocene extinctions
hierarchical_section_title: Great American Interchange / Late Pleistocene extinctions
caption_attribution_description: Tapirus bairdii English: Baird's Tapir at Franklin Park Zoo, Massachusetts, USA.
context_page_description: The Great American Biotic Interchange, also known as the Great American Interchange or Great American Faunal Interchange, was an important late Cenozoic paleozoogeographic event in which land and freshwater 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 formerly separated continents. Although earlier dispersals have occurred, probably over water, the migration accelerated dramatically about 2.7 million years ago during the Piacenzian age. It resulted in the joining of the Neotropic and Nearctic biogeographic realms definitively to form the Americas. The interchange is visible from observation of both biostratigraphy and nature. Its most dramatic effect is on the zoogeography of mammals, but it also gave an opportunity for reptiles, amphibians, arthropods, weak-flying or flightless birds, and even freshwater fish to migrate.
  The occurrence of the interchange was first discussed in 1876 by the "father of biogeography", Alfred Russel Wallace. Wallace had spent 1848–1852 exploring and collecting specimens in the Amazon basin.
context_section_description: At the end of the Pleistocene epoch, about 12,000 years ago, three dramatic developments occurred in the Americas at roughly the same time (geologically speaking). Paleoindians invaded and occupied the New World, the last glacial period came to an end, and a large fraction of the megafauna of both North and South America went extinct. This wave of extinctions swept off the face of the Earth many of the successful participants of the GABI, as well as other species that had not migrated.
  All the pampatheres, glyptodonts, ground sloths, equids, proboscids, giant short-faced bears, dire wolves, and machairodont species of both continents disappeared. The last of the South and Central American notoungulates and litopterns died out, as well as North America's giant beavers, lions, dholes, cheetahs, and many of its antilocaprid, bovid, cervid, tapirid and tayassuid ungulates. Some groups disappeared over most or all of their original range, but survived in their adopted homes, e.g. South American tapirs, camelids, and tremarctine bears (cougars and jaguars may have been temporarily reduced to South American refugia also). Others, such as capybaras, survived in their original range, but died out in areas to which they had migrated. Notably, this extinction pulse eliminated all Neotropic migrants to North America larger than about 15 kg (the size of a big porcupine), and all native South American mammals larger than about 65 kg (the size of a big capybara or giant anteater). In contrast, the largest surviving native North American mammal, the wood bison, can exceed 900 kg, and the largest surviving Nearctic migrant to South America, Baird's tapir, can reach 400 kg.
  The near-simultaneity of the megafaunal extinctions with the glacial retreat and the peopling of the Americas has led to proposals that both climate change and human hunting played a role. Although the subject is contentious, 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 no plausible general climate-based megafauna-killing mechanism could explain the continent-wide extinctions. The climate change took place worldwide, but had little effect on the megafauna in Africa and southern Asia, where megafaunal species had coevolved with humans. Numerous very similar glacial retreats had occurred previously within the ice age of the last several million years without ever producing comparable waves of extinction in the Americas or anywhere else.
  Similar megafaunal extinctions have occurred on other recently populated land masses (e.g. Australia, Japan, Madagascar, New Zealand, and many smaller islands around the world, such as Cyprus, Crete, Tilos and New Caledonia) at different times that correspond closely to the first arrival of humans at each location. These extinction pulses invariably swept rapidly over the full extent of a contiguous land mass, regardless of whether it was an island or a hemisphere-spanning set of connected continents. This was true despite the fact that all the larger land masses involved (as well as many of the smaller ones) contained multiple climatic zones that would have been affected differently by any climate changes occurring at the time. However, on sizable islands far enough offshore from newly occupied territory to escape immediate human colonization, megafaunal species sometimes survived for many thousands of years after they or related species became extinct on the mainland; examples include giant kangaroos in Tasmania, giant Chelonoidis tortoises of the Galápagos Islands (formerly also of South America), giant Dipsochelys tortoises of the Seychelles (formerly also of Madagascar), giant meiolaniid turtles on Lord Howe Island, New Caledonia and Vanuatu (previously also of Australia), ground sloths on the Antilles, Steller's sea cows off the Commander Islands and woolly mammoths on Wrangel Island and Saint Paul Island.
  The glacial retreat may have played a primarily indirect role in the extinction
caption: Baird's tapir, Tapirus bairdii, the largest surviving Nearctic migrant to South America
exif: {"Image Make": "NIKON CORPORATION", "Image Model": "NIKON D300S", "Image Orientation": "Horizontal (normal)", "Image XResolution": "240", "Image YResolution": "240", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Adobe Photoshop CS4 Windows", "Image DateTime": "2010:07:18 20:10:21", "Image ExifOffset": "216", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "914", "Thumbnail JPEGInterchangeFormatLength": "6037", "EXIF ExposureTime": "1/100", "EXIF FNumber": "9/2", "EXIF ExposureProgram": "Aperture Priority", "EXIF ISOSpeedRatings": "800", "EXIF ExifVersion": "0221", "EXIF DateTimeOriginal": "2010:06:27 15:31:49", "EXIF DateTimeDigitized": "2010:06:27 15:31:49", "EXIF ShutterSpeedValue": "415241/62500", "EXIF ApertureValue": "86797/20000", "EXIF ExposureBiasValue": "0", "EXIF MaxApertureValue": "43/10", "EXIF SubjectDistance": "631/100", "EXIF MeteringMode": "Pattern", "EXIF LightSource": "Unknown", "EXIF Flash": "Flash did not fire", "EXIF FocalLength": "70", "EXIF SubSecTime": "50", "EXIF SubSecTimeOriginal": "50", "EXIF SubSecTimeDigitized": "50", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "3051", "EXIF ExifImageLength": "2100", "EXIF SensingMethod": "One-chip color area", "EXIF FileSource": "Digital Camera", "EXIF SceneType": "Directly Photographed", "EXIF CVAPattern": "[2, 0, 2, 0, 0, 1, 1, 2]", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Auto", "EXIF DigitalZoomRatio": "1", "EXIF FocalLengthIn35mmFilm": "105", "EXIF SceneCaptureType": "Standard", "EXIF GainControl": "Low gain up", "EXIF Contrast": "Normal", "EXIF Saturation": "Normal", "EXIF Sharpness": "Normal", "EXIF SubjectDistanceRange": "0"}