Land Bridge

In biogeography, a land bridge is a natural connection—either narrow like an isthmus or considerably broad—linking two otherwise separated landmasses and allowing plants and animals to disperse across them. These connections have played major roles in shaping global biodiversity patterns, enabling faunal and floral exchanges over geological time. Land bridges may arise due to marine regression when sea levels fall, through tectonic uplift creating new land, or by post-glacial rebound in which land formerly depressed by glacial ice rises after melting. The formation and disappearance of land bridges have repeatedly altered migration routes, evolutionary trajectories and ecological distributions across the world.

Formation and Mechanisms

Land bridges typically develop under three primary geological or climatic conditions:

• Marine regression: falling sea levels expose continental shelves, creating temporary connections between landmasses. This process was common during Pleistocene glacial periods, when large volumes of water were locked in ice sheets.
• Tectonic activity: the uplift of crustal blocks or the collision of plates may form new land corridors. The emergence of the Isthmus of Panama is a notable example.
• Post-glacial rebound: areas previously weighted down by ice sheets rise once the ice melts, occasionally elevating sea floors and creating new land surfaces.

These mechanisms demonstrate that land bridges are not static features but part of long-term Earth system dynamics.

Major Examples of Land Bridges

A number of important land bridges have influenced global biological interchange. They may be categorised as former land bridges, which no longer exist, and current ones, which continue to connect major continental or subcontinental regions.

Former Land Bridges

• Bass Strait Land Bridge: once connected mainland Australia with Tasmania, allowing migration of marsupials and other fauna before the region was inundated.
• Antarctic Land Bridge: during the Late Cretaceous and Early Palaeogene, Antarctica was connected to South America and Australia, enabling the exchange of early southern hemisphere biota.
• Beringia: intermittently linked Siberia and Alaska throughout the ice ages; it facilitated the migration of humans, mammals and plant species between Eurasia and North America.
• Greater Antilles–South America Bridge (hypothesised): proposed for the Priabonian or Rupelian eras, possibly explaining some biogeographical affinities.
• Japan–Russia–Korea corridors: multiple land connections existed during glacial periods as sea levels dropped, enabling faunal movement across northeast Asia.
• Thule Land Bridge: proposed former linkage between the British Isles and Greenland.
• Doggerland: the now-submerged landmass in the southern North Sea that connected Great Britain to mainland Europe during the last ice age.
• Torres Strait Land Bridge: linked New Guinea (West Papua) to Cape York Peninsula when lower sea levels combined Sahul’s landmasses.
• Sunda–Sahul connections: vast tracts of Southeast Asia, totalling roughly 1.8 million km², were exposed during periods of low sea level, linking islands and facilitating extensive dispersal.

Current Land Bridges

• Adam’s Bridge (Rama Setu): a chain-like formation connecting India and Sri Lanka, historically significant in mythology and migration.
• Isthmus of Panama: formed around three million years ago, it enabled the Great American Biotic Interchange, in which species migrated between North and South America.
• Sinai Peninsula: forms the land connection between Africa and Eurasia, serving as a major historical migration route for humans and animals.

Biotic Interchange and Evolutionary Impact

Land bridges are central to understanding colonisation and adaptive radiation. The Great American Biotic Interchange, enabled by the formation of the Isthmus of Panama, is a notable example. Through this event, fauna from North America, such as felids, canids and ungulates, migrated southwards, while animals such as xenarthrans (armadillos, ground sloths) moved northward. Similar exchanges occurred in other regions whenever land connections emerged.
When land bridges vanished—through submergence or tectonic separation—isolated populations often evolved independently, contributing to endemism. Their historical presence helps explain modern distribution patterns of species that appear in distant yet ecologically similar regions.

Land Bridge Theory in Nineteenth- and Early Twentieth-Century Science

Before the acceptance of continental drift and plate tectonics, land bridges were widely cited as explanations for puzzling biogeographical distributions. Botanists and zoologists such as Joseph Dalton Hooker noted similarities in flora and fauna between southern continents and proposed vanished land connections. These hypothetical bridges were used to interpret disjunct plant families, fossil evidence and geological affinities.
Jules Marcou was among the first to propose land-bridge hypotheses in geology during the mid-nineteenth century. A range of speculative landmasses was subsequently suggested, including:

• Archatlantis: linking the West Indies and North Africa
• Archhelenis: connecting Brazil with South Africa
• Archiboreis: posited in the North Atlantic
• Archigalenis: stretching from Central America towards Northeast Asia via Hawaii
• Archinotis: linking South America and Antarctica
• Lemuria: a hypothetical Indian Ocean continent invoked to explain distribution of certain species

Supersession by Plate Tectonics

The development of plate tectonic theory in the 1960s replaced speculative land-bridge concepts with a comprehensive model explaining continental movement, seafloor spreading and the historical assembly of landmasses. This scientific shift demonstrated that many similarities between distant biotas stem from the past unity of continents, particularly within Gondwana and Laurasia, rather than from vanished land corridors.
Nevertheless, genuine land bridges—formed by tectonics or sea-level changes—remain critical for understanding historical biogeography. They provide evidence for episodic connectivity between continental and island faunas and continue to inform studies in evolutionary biology, palaeoecology and Earth history.