South American fauna

North and South America were unconnected for millions of years, until the uplifting of the Isthmus of Panama created a land bridge between them. This long isolation permitted the archaic South American fauna to evolve without competition, and helps to account for the extraordinary diversity of South American animals. Though many archaic species vanished, either through inability to compete with immigrants from the north, or in the great Pleistocene extinctions, some survived. The survivors included some of the marsupials otherwise found only in Australasia and the edentates – sloths, armadillos, and anteaters. Many species, both archaic and recent, have diversified to an unusual extent. This is particularly true of the rodents, the bats, and the primates, as well as many birds, fishes, and invertebrates. They exhibit adaptive radiation and evolutionary convergence to a degree and on a scale that is unsurpassed. The result is an unequalled profusion of life in all its forms.

Another factor which allows for exceptional diversity is the South American setting, in which equatorial rainforest and Alpine tundra, lowland Pampas and highland puna, searing deserts and snow-capped mountain ranges lie in close proximity.

Mammals Among the mammals are the capybara, the largest living rodent; three species of tapirs, whose nearest relative is found in Southeast Asia; and the vicuna and guanaco, descendants of the ancient New World camels. Their relatives the llama and the alpaca are wholly domesticated. The primates, all of which are tree-dwellers, range from the vociferous howler monkeys, the long-limbed spider monkeys, and the tiny marmosets and tamarins, to the douroucouli or night monkey Aotus trivirgatus, the only true monkey that is nocturnal. Specialization to life in trees is marked in many species by the development of a prehensile tail, which serves as a fifth limb, and claws. The primates are not alone in having evolved prehensile tails: the kinkajou is one of only two carnivores to have a prehensile tail; there is also a prehensile-tailed porcupine. The five species that make up the sloth family are unique to South America; these animals have become so well adapted to life hanging upside down in trees that movement on the ground is almost impossible. In 1999 a new species of rodent was discovered in Tucumán Province, Argentina. At 7 cm/2.8 in, it is the smallest species in genus Akodon, which are ground dwelling and feed on seeds, berries, and invertebrates. The newly-discovered species has been named A. aliquantulus.

Vampire bats, the world's only parasitic mammals, are found from Mexico to Argentina. Predatory mammals include the grey fox and maned wolf of the temperate grasslands, and the mountain lion, Pampas cat, and jaguar.

Freshwater animals The huge, slow-flowing Amazon and its tributaries have a complex aquatic fauna. The fish include a number of highly specialized forms, among them electric fish, lungfish, the predatory piranha, and the huge, carnivorous arapaima, the world's largest freshwater fish, which can grow to 90 kg/200 lb. The carnivorous river dolphin and plant-eating manatee are marine mammals that have adapted to life in fresh water. Snakes that live in and around the river include the anaconda and the boa constrictor. Another reptile, the caiman, has been extensively hunted for its skin. In the nesting season, Arrau river turtles Podocnemis expansa assemble along the Amazon and Orinoco. In the past their numbers have been so huge that they have impeded the passage of boats, but humans' hunting of the adults for meat, and taking of eggs, have led to their becoming a protected species.

Marine animals Off the west coast, the cold waters of the Peru Current meet nutrient-rich waters rising from deep in the Pacific. This provides ideal conditions for plankton, which in turn provides food for vast shoals of fish, particularly anchovies, that make the area the richest fishery in the world. This biological cornucopia supports seals and sea lions as well as huge flocks of guano birds: cormorants, pelicans, and boobies.

Birds A quarter of all living bird species are to be found in South America. Many of the indigenous forms have no counterpart on any other continent. The birds range from the flightless rhea of the treeless Pampas to the Andean condor, largest of the living birds of prey. In the rainforest live macaws, toucans, and nectar-feeding hummingbirds. The rare harpy eagle Harpia harpyja, the world's largest eagle, lives in remote forest areas; it preys on tree-dwelling mammals such as sloths and monkeys, as well as large birds.

The proliferation of animal life in South America is equalled only by the profligate manner of its exploitation. Fur-bearing animals, above all the marine species, have been particularly severely depleted. The South American fur seals, once numbered in millions, were almost wiped out by commercial hunting. More recently, the hide-hunters have brought the cayman close to extinction. Intensive development of the Pampas for ranching, exploitation of the rainforest, and remorseless hunting pressure are having a dire effect on the native South American fauna.