A land bridge, in biogeography, is an isthmus or wider land connection between otherwise separate areas, over which animals and plants are able to cross and colonise 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.
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." The concept was first proposed by Jules Marcou in Lettres sur les roches du Jura et leur distribution géographique dans les deux hémisphères ("Letters on the rocks of the Jura [Mountains] and their geographic distribution in the two hemispheres"), 1857-1860.
The hypothetical land bridges included:
The theory of continental drift provided an alternate explanation that did not require land bridges. However the continental drift theory was not widely accepted until the development of plate tectonics in the early 1960s, which more completely explained the motion of continents over geological time.