The Central American Seaway (also known as the Panamanic Seaway, Inter-American Seaway and Proto-Caribbean Seaway) was a body of water that once separated
North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...
from
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...
. It formed during the
Jurassic
The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
(200–154 Ma) during the breakup of the supercontinent
Pangaea
Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million y ...
, and closed when the
Isthmus of Panama
The Isthmus of Panama ( es, Istmo de Panamá), also historically known as the Isthmus of Darien (), is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North and South America. It contains the country ...
was formed by
volcanic
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most often found where tectonic plat ...
activity in the late
Pliocene
The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58
The closure of the Central American Seaway had tremendous effects on oceanic circulation and the
biogeography
Biogeography is the study of the distribution of species and ecosystems in geographic space and through geological time. Organisms and biological communities often vary in a regular fashion along geographic gradients of latitude, elevation, ...
of the adjacent seas, isolating many species and triggering
speciation
Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution withi ...
Caribbean
The Caribbean (, ) ( es, El Caribe; french: la Caraïbe; ht, Karayib; nl, De Caraïben) is a region of the Americas that consists of the Caribbean Sea, its islands (some surrounded by the Caribbean Sea and some bordering both 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
The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configu ...
, 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.
Evidence
The evidence for when the Central American landmass emerged and the closing of the Central American Seaway can be divided into three categories. The first is the direct geologic observation of crustal thickening and submarine deposits in Central America. The second is the
Great American Interchange
The Great American Biotic Interchange (commonly abbreviated as GABI), also known as the Great American Interchange and the Great American Faunal Interchange, was an important late Cenozoic paleozoogeographic biotic interchange event in which lan ...
of
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with ...
s between North and South America which required a continuous land bridge across the two areas for the organisms to travel along with a climate that was very different from the climate today. Lastly is the development of differences in marine assemblages and their isotopic signatures in the Caribbean from those in the Pacific. The Central American Seaway was closed by the elevation of the Central American Isthmus which is proposed to have occurred three and a half to five million years ago. The closing of the Central American Seaway is also supported by the evolution of taxa on different sides of the Central American Isthmus along with the different histories of the oceans on either side of the isthmus.
Consequences
The closing of the seaway allowed a major migration of land mammals between North and South America, known as the Great American Interchange. That allowed species of mammals such as cats, canids, horses, elephants, and camels to migrate from North America to South America, and
porcupine
Porcupines are large rodents with coats of sharp spines, or quills, that protect them against predation. The term covers two families of animals: the Old World porcupines of family Hystricidae, and the New World porcupines of family, Erethiz ...
s,
ground sloth
Ground sloths are a diverse group of extinct sloths in the mammalian superorder Xenarthra. The term is used to refer to all extinct sloths because of the large size of the earliest forms discovered, compared to existing tree sloths. The Caribb ...
s,
glyptodont
Glyptodonts are an extinct subfamily of large, heavily armoured armadillos. They arose in South America around 48 million years ago and spread to southern North America after the continents became connected several million years ago. The best-k ...
s and
terror bird
Phorusrhacids, colloquially known as terror birds, are an extinct clade of large carnivorous flightless birds that were one of the largest species of apex predators in South America during the Cenozoic era; their conventionally accepted temporal ...
s made the reverse migration. There is much controversy about glacial and
interglacial
An interglacial period (or alternatively interglacial, interglaciation) is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age. The current Holocene i ...
climates in South America. Research shows that vegetation in most of the
Amazon basin
The Amazon basin is the part of South America drained by the Amazon River and its tributaries. The Amazon drainage basin covers an area of about , or about 35.5 percent of the South American continent. It is located in the countries of Boli ...
has changed very little since glacial times, but it is believed there was more savanna present during that period. A closed seaway would have led to a very different North Atlantic Ocean circulation, but it impacted the surrounding atmospheric temperatures, which in turn affected the glacial cycle. The emergence of the isthmus caused a reflection of the westward-flowing North Equatorial Current northward and enhanced the northward-flowing
Gulf Stream
The Gulf Stream, together with its northern extension the North Atlantic Drift, is a warm and swift Atlantic ocean current that originates in the Gulf of Mexico and flows through the Straits of Florida and up the eastern coastline of the Unit ...
. The Pacific coast of South America would have cooled as the input of warm water from the Caribbean was cut off. That trend is thought to have caused the extinction of the marine sloths of the area.
The closure of the seaway led to an increased poleward salt and heat transport, which strengthened the North Atlantic thermohaline circulation 2.95–2.82 million years ago. That in turn increased the moisture supply to Arctic latitudes, which contributed to both Arctic continental glaciation and
sea ice
Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice, which has an even lower density). Sea ice covers about 7% of the Earth's surface and about 12% of the world's o ...
formation. Eventually, with the orbitally-paced extension of Gelasian ice sheets, that led to the
Quaternary ice age
The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million ye ...