Great American Interchange in the context of Biogeography

In biogeography, a land bridge is an isthmus or wider land connection between otherwise separate areas, over which animals and plants are able to cross and colonize new lands. A land bridge can be created by marine regression, in which sea levels fall, exposing shallow, previously submerged sections of continental shelf; or when new land is created by plate tectonics; or occasionally when the sea floor rises due to post-glacial rebound after an ice age.

The Central American Seaway (also known as the Panamanic Seaway, Inter-American Seaway and Proto-Caribbean Seaway) was a prehistoric body of water that once connected the Pacific Ocean to the Atlantic Ocean, separating North America from South America. It formed during the Jurassic (200–154 Ma) during the initial breakup of the supercontinent Pangaea into Laurasia and Gondwana, forming a mediterranean sea between the Panthalassia and Tethys Ocean, and finally closed when the Isthmus of Panama was formed by volcanic activity in the late Pliocene (2.76–2.54 Ma). The modern-day remnants of the seaway are the Gulf of Mexico, Caribbean Sea and the Central Atlantic region around the Sargasso Sea.

The closure of the Central American Seaway had tremendous effects on oceanic circulation and the biogeography of the adjacent seas, isolating many species and triggering speciation and diversification of tropical and sub-tropical marine fauna. The inflow of nutrient-rich water of deep Pacific origin into the Caribbean was blocked and so local species had to adapt to an environment of lower productivity. It had an even larger impact on terrestrial life. The seaway had isolated South America for much of the Cenozoic, which allowed the evolution of a wholly unique diverse mammalian fauna there. When it closed, a faunal exchange with North America ensued and led to the extinction of many of the native South American forms.

Hippidion (meaning "little horse" in Ancient Greek) is an extinct genus of equine that lived in South America from the Late Pliocene to the end of the Late Pleistocene (Lujanian), between 2.5 million and 11,000 years ago. Hippidion arrived in South America along with many other animals of North American origin as part of the Great American Interchange. They were one of two lineages of equines native to South America during the Pleistocene epoch, alongside Equus (Amerhippus) neogeus. Hippidion ranged widely over South America, extending to the far south of Patagonia. Hippidion differs from living equines of the genus Equus in having a long notch separating the nasal bone from the rest of the skull, which may indicate the presence of a prehensile upper lip.

Hippidion became extinct as part of the end-Pleistocene extinction event around 12-11,000 years ago, along with most other large animals native to the Americas. Remains of Hippidion dating to shortly before its extinction have been found with cut marks and associated with human artifacts, such as stone Fishtail points, which may suggest that hunting by recently arrived humans may have been a factor in its extinction.

Xenarthra (/zɛˈnɑːrθrə/; from Ancient Greek ξένος (xénos), meaning "strange, foreign", and ἄρθρον (árthron), meaning "joint") is a superorder and major clade of placental mammals native to the Americas. There are 31 living species: the anteaters, tree sloths, and armadillos. Extinct xenarthrans include the glyptodonts, pampatheres and ground sloths, with some glyptodonts and ground sloths reaching sizes of several tonnes, much larger than any living xenarthran. Xenarthrans originated in South America during the late Paleocene about 60 million years ago. They evolved and diversified extensively in South America during the continent's long period of isolation in the early to mid Cenozoic Era. They spread to the Antilles by the early Miocene and, starting about 3 million years ago, spread to Central and North America as part of the Great American Interchange. Nearly all of the formerly abundant megafaunal xenarthrans became extinct at the end of the Pleistocene as part of the end-Pleistocene extinction event.

Cingulata, part of the superorder Xenarthra, is an order of armored New World placental mammals. The armadillos, whose species are split between the families Dasypodidae and Chlamyphoridae, are the only surviving members of the order. Two groups of cingulates much larger than extant armadillos (maximum body mass of 45 kg (100 lb) in the case of the giant armadillo) existed until recently: pampatheriids, which reached weights of up to 200 kg (440 lb) and chlamyphorid glyptodonts, which attained masses of 2,000 kg (4,400 lb) or more.

The cingulate order originated in South America during the Paleocene epoch about 66 to 56 million years ago, and due to the continent's former isolation remained confined to it during most of the Cenozoic. However, the formation of a land bridge allowed members of all three families to migrate to southern North America during the Pliocene or early Pleistocene as part of the Great American Interchange. After surviving for tens of millions of years, all of the pampatheriids and giant glyptodonts apparently died out during the Quaternary extinction event at the beginning of the Holocene, along with much of the rest of the regional megafauna, shortly after the colonization of the Americas by Paleo-Indians.

Ground sloths are a diverse group of extinct sloths in the mammalian superorder Xenarthra. They varied widely in size; the largest belonged to the genera Lestodon, Eremotherium and Megatherium, and were roughly the size of modern-day elephants. Ground sloths represent a paraphyletic group, as living tree sloths are thought to have evolved from ground sloth ancestors.

The early evolution of ground sloths took place during the late Paleogene and Neogene of South America, while the continent was isolated. At their earliest appearance in the fossil record, they were already distinct at the family level. Sloths dispersed into the Greater Antilles during the Oligocene, and the presence of intervening islands between the American continents in the Miocene allowed a dispersal of some species into North America. They were hardy as evidenced by their high species diversity and their presence in a wide variety of environments, extending from the far south of Patagonia (Cueva del Milodón Natural Monument) to Alaska. Sloths, and xenarthrans as a whole, represent one of the more successful South American groups during the Great American Interchange after the connection of North and South America during the late Pliocene, with a number of ground sloth genera migrating northward. One genus, Thalassocnus, was even adapted to marine life along the Pacific coast of South America during the late Miocene and Pliocene epochs.

Tapirs (/ˈteɪpər/ TAY-pər) are large, herbivorous mammals belonging to the family Tapiridae. They are similar in shape to a pig, with a short, prehensile nose trunk (proboscis). Tapirs inhabit jungle and forest regions of South and Central America and Southeast Asia. They are one of three extant branches of Perissodactyla (odd-toed ungulates), alongside equines and rhinoceroses. Only a single genus, Tapirus, is currently extant. Tapirs migrated into South America during the Pleistocene epoch from North America after the formation of the Isthmus of Panama as part of the Great American Interchange. Tapirs were present across North America, but became extinct in the region at the end of the Late Pleistocene, around 12,000 years ago.

The nine-banded armadillo (Dasypus novemcinctus), also called the nine-banded long-nosed armadillo or common long-nosed armadillo, is a species of armadillo native to North, Central, and South America, making it the most widespread of the armadillos.

Its ancestors originated in South America, and remained there until the formation of the Isthmus of Panama allowed them to enter North America as part of the Great American Interchange.The nine-banded armadillo is a solitary, mainly nocturnal animal, found in many kinds of habitats, from mature and secondary rainforests to grassland and dry scrub. It is an insectivore, feeding chiefly on ants, termites, and other small invertebrates. The armadillo can jump 91–120 cm (3–4 ft) straight in the air if sufficiently frightened, making it a particular danger on roads. It is the state small mammal of Texas.

Opossums (/əˈpɒsəmz/) are members of the marsupial order Didelphimorphia (/daɪˌdɛlfɪˈmɔːrfiə/) endemic to the Americas. The largest order of marsupials in the Western Hemisphere, it comprises 126 species in 18 genera. Opossums originated in South America and entered North America in the Great American Interchange following the connection of North and South America in the late Cenozoic.

The Virginia opossum is the only species found in the United States and Canada. It is often simply referred to as an opossum; in North America, it is commonly referred to as a possum (/ˈpɒsəm/; sometimes rendered as 'possum in written form to indicate the dropped "o"). The Australasian arboreal marsupials of suborder Phalangeriformes are also called possums because of their resemblance to opossums, but they belong to a different order. The opossum is typically a nonaggressive animal and almost never carries the virus that causes rabies.

Sparassodonta (from Greek σπαράσσειν [sparassein], to tear, rend; and ὀδούς, gen. ὀδόντος [odous, odontos], tooth) is an extinct order of carnivorous metatherian mammals native to South America, related to modern marsupials. They were once considered to be true marsupials, but are now thought to be a separate side branch that split before the last common ancestor of all modern marsupials.

A number of these mammalian predators closely resemble placental predators that evolved separately on other continents, and are cited frequently as examples of convergent evolution. They were first described by Florentino Ameghino, from fossils found in the Santa Cruz beds of Patagonia. Sparassodonts were present throughout South America's long period of "splendid isolation" during the Cenozoic; during this time, they shared the niches for large warm-blooded predators with the flightless terror birds. Previously, it was thought that these mammals died out in the face of competition from "more competitive" placental carnivorans during the Pliocene Great American Interchange, but more recent research has shown that sparassodonts died out long before eutherian carnivores arrived in South America (aside from procyonids, which sparassodonts probably did not directly compete with).

Gomphotheres are an extinct group of proboscideans related to modern elephants. First appearing in Africa during the Oligocene, they dispersed into Eurasia and North America during the Miocene and arrived in South America during the Pleistocene as part of the Great American Interchange. Gomphotheres are a paraphyletic group ancestral to Elephantidae, which contains modern elephants, as well as Stegodontidae.

While the most well-known forms like Gomphotherium had long lower jaws with tusks, the ancestral condition for the group, some later members developed shortened (brevirostrine) lower jaws with either vestigial or no lower tusks, which survived considerably later than the long-jawed gomphotheres. This change made them look very similar to modern elephants, an example of parallel evolution. During the Pliocene and Early Pleistocene, the diversity of gomphotheres declined, ultimately becoming extinct outside of the Americas. The last two genera, Cuvieronius ranging from southern North America to northwestern South America, and Notiomastodon ranging over most of South America, continued to exist until the end of the Pleistocene around 12,000 years ago, when they became extinct along with most other American megafauna species following the arrival of humans.