page_title: Great American Interchange
section_title: South America's endemic fauna
hierarchical_section_title: Great American Interchange / South America's endemic fauna
caption_attribution_description: English: Anteater at National Zoo.
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: 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 many forms found nowhere else on Earth, most of which are now extinct. Its endemic mammals initially consisted primarily of metatherians (marsupials and sparassodonts), xenarthrans, and a diverse group of native ungulates: notoungulates (the "southern ungulates"), litopterns, astrapotheres, pyrotheres and xenungulates. A few non-therian mammals – monotremes, gondwanatheres, dryolestids and possibly cimolodont multituberculates – were also present in the Paleocene; while none of these diversified significantly and most lineages did not survive long, forms like Necrolestes and Patagonia remained as recently as the Miocene.
  Marsupials appear to have traveled via Gondwanan land connections from South America through Antarctica to Australia in the late Cretaceous or early Tertiary. One living South American marsupial, the monito del monte, has been shown to be more closely related to Australian marsupials than to other South American marsupials; however, it is the most basal australidelphian, meaning that this superorder arose in South America and then colonized Australia after the monito del monte split off. A 61-Ma-old platypus-like monotreme fossil from Patagonia may represent an Australian immigrant. Paleognath birds (ratites and South American tinamous) may made a similar migration around the same time to Australia/New Zealand. Other taxa that may have dispersed by the same route (if not by flying or floating across the ocean) are parrots, chelid turtles, and (extinct) meiolaniid turtles.
  Marsupials present in South America included didelphimorphs (opossums) and several other small groups; larger predatory relatives of these also existed, such as the borhyaenids and the saber-toothed Thylacosmilus (sparassodont metatherians, which are no longer considered to be true marsupials). As the large carnivorous metatherians declined, and before the arrival of most types of carnivorans, predatory opossums such as Thylophorops temporarily attained larger size (about 7 kg).
  Metatherians (and a few xenarthran armadillos such as Macroeuphractus) were the only South American mammals to specialize as carnivores; their relative inefficiency created openings for nonmammalian predators to play more prominent roles than usual (similar to the situation in Australia). Sparassodonts and giant opossums shared the ecological niches for large predators with fearsome flightless "terror birds" (phorusrhacids), whose closest extant relatives are the seriemas. (Similar large terrestrial predatory birds, the bathornithids, were found in North America during the early Cenozoic, but they died out in the Early Miocene, about 20 million years ago.) Through the skies over late Miocene South America (6 Ma ago) soared the largest flying bird known, the teratorn Argentavis, with a wing span of 6 m or more, which may have subsisted in part on the leftovers of Thylacosmilus kills. Terrestrial ziphodont sebecid (metasuchian) crocodyliforms were also present at least through the middle Miocene and maybe to the Miocene-Pliocene boundary. Some of South America's aquatic crocodilians, such as Gryposuchus, Mourasuchus and Purussaurus, reached monstrous sizes, with lengths up to 12 m (comparable to the largest Mesozoic crocodyliforms). They shared their habitat with one of the largest turtles of all time, the 3.3 m (11 ft) Stupendemys.
  Xenarthrans are a curious group of mammals that developed morphological adaptations for specialized diets very early in their history. In addition to those extant today (armadillos, anteaters, and tree sloths), a great diversity of larger types was present, including pampatheres, the ankylosaur-like glyptodonts, predatory euphractines, various ground sloths, some of which reached the size of elephants (e.g. Megatherium), and even semiaquatic to aquatic marine sloths.
  The notoungulates and litopterns had many strange forms, such as Macrauchenia, a camel-like litopter
caption: The giant anteater, Myrmecophaga tridactyla, the largest living descendant of South American's early Cenozoic mammalian fauna
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