The Isthmus of Panama is a land bridge whose appearance 3 million years ago allowed the Great American Interchange.

A land bridge, in biogeography, is an isthmus or wider land connection between otherwise separate areas, which allows terrestrial animals and plants to cross over and colonise new lands. Land bridges 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.

[edit] Prominent examples

• The Bering land bridge, which intermittently connected Asia with North America as sea levels rose and fell under the effect of ice ages;
• The Isthmus of Panama, whose appearance 3 mya allowed the Great American Interchange;
• The Sinai Peninsula, linking Africa and Eurasia;
• Doggerland, a former landmass in the southern North Sea which connected the island of Great Britain to mainland Europe during the last ice age.

[edit] Land bridge theory

In the 19th century a number of scientists noted puzzling geological and zoological similarities between widely separated areas. To solve these problems, "…whenever geologists and paleontologists were at a loss to explain the obvious transoceanic similarities of life that they deduced from the fossil records, they sharpened their pencils and sketched land bridges between appropriate continents."^[1] The concept was first proposed by Jules Marcou in Lettres sur les roches du Jura.^[2]

These hypothetical land bridges included:^[3]

• Lemuria in the Indian Ocean
• Archiboreis in the North Atlantic
• Archatlantis from the West Indies to North Africa
• Archhelenis from Brazil to South Africa
• Archigalenis from Central America thru Hawaii to Northeast Asia
• Archinotis from South America to Antarctica

All of these became obsolete with the gradual acceptance of continental drift and the development of plate tectonics by the mid-20th century.

[edit] See also

• Habitat fragmentation
• Sea level rise

[edit] Notes