Thursday, November 8, 2012

The Great American Interchange

According to Larry G. Marshall, R. F. Butler, R. E. Drake, G. H. Curtis, and R. H. Tedford, the emergence of the Panamanian land bridge that connected North and South America, permitted the mingling of the long-separated faunas of previously separated areas. F. Stehli and S. Webb also weighed in on the biotic interchange once the isthmus raised up and formed a land bridge from Central to South America. Also in A. Coates and J. Obando, “The geologic evolution of the Central American isthmus,” is covered in Evolution and Environment in Tropical America. Numerous other scientists have written about their work in tracing the mammalian evolution and the great American interchange in such works as Science, Molecular Ecology, Proceedings of the Royal Society, and numerous biological and other journals.
In fact, Marshall has stated that “there is no convincing geological evidence to indicate that South America had a continuous land connection with any other continent until the Bolivar Trough marine barrier disappeared and the Americas were united by the emergence of the Panamanian land bridge.” This connection resulted in “an intermingling that has come to be known as the Great American Interchange” which resulted in “different groups of plants and animals moving between the two biotic provinces.”
This raising of the land bridge—the Panamanian Isthmus—connecting North and South America, was an important paleozoogeographic (the study of the geographic distribution of fossil organisms) event in which land and freshwater fauna migrated from North America via Central America to South America and vice versa, as the volcanic Isthmus of Panama rose up from the sea floor and bridged the formerly separated continents
When the Isthmus of Panama rose up, it created the Panamanian land bridge over which isolated animals and plants were able to migrate north and south  

This connection resulted in the joining of the Neotropic (roughly South America) and Nearctic (roughly North America) ecozones definitively to form the Americas. The interchange is visible from observation of both stratigraphy and nature (neontology). Its most dramatic effect is on the zoogeography of mammals but it also gave an opportunity for weak-flying or flightless birds, reptiles, amphibians, arthropods and even freshwater fish to migrate.
According to Marshall, the total surface area of North America and Central America (15 million square miles) is greater than that of South America (11 million square miles) which, along with the known fossil record, explains why North America had an average of 60% greater generic diversity and hence more potential dispersants than South America during the time of the interchange, thus more species dispersed into South America from North America than the other way around. However, later explosive diversification of true dispersants in South America as opposed to North America is unique and asymmetrical (that is, unbalanced). Thus, though scientific belief felt more species migrated southward than northward, the opposite was found to be true and scientists are at a loss as to explain this phenomenon. Perhaps it is because the animals brought to the Western Hemisphere after the flood arrived in South America with the Jaredites, and eventually worked their way northward.
The occurrence of this raising of the Panamanian Isthmus, or land bridge, and the biologic interchange was first discussed in 1876 by the "father of biogeography," Alfred Russel Wallace. Others who made significant contributions to understanding the event in the century that followed include Florentino Ameghino, W.D. Matthew, W.B. Scott, Bryan Patterson, George Gaylord Simpson  and S. David Webb.
Animals from South America migrated over the newly created Panamanian land bridge into Central and North America 

According to Phillip Hershkovitz regarding the land bridge and Latin America faunal interchange, the formation of the Isthmus of Panama led to the last and most conspicuous wave, the great interchange, which included the immigration of ungulates (including camelids, tapirs, deer and horses), proboscids (gomphotheres), carnivorans (including felids like cougars and cats, canids, mustelids, and a number of types of rodents.
In addition, the effect of formation of the isthmus on the marine biota of the area was the inverse of its effect on terrestrial organisms, a development that has been termed the "Great American Schism." The connections between the east Pacific Ocean and the Caribbean were severed, setting now-separated populations on divergent evolutionary paths. Caribbean species also had to adapt to an environment of lower productivity after the inflow of nutrient-rich water of deep Pacific origin was blocked.
George Gaylord Simpson in Splendid Isolation: the Curious History of South American Mammals, agrees with Marshall’s work published in Science and the American Scientist, and numerous other scientists have discussed, written about, studied, and researched the importance of the rising of the Panamanian Isthmus and its effect on movement of animals between South and North America.
It should also be noted that “the Great American Interchange resulted in a major restructuring—nearly half of the families and genera now on the South American continent belong to groups that emigrated.” Might not this emigration have come from the Jaredites bringing to the Land of Promise “flocks, both male and female, of every kind; and also of the seed of the earth of every kind” and “fowls of the air; and they did also prepare a vessel, in which they did carry with them the fish of the waters. And they did also carry with them deseret, which, by interpretation, is a honey bee,” and Lehi brought “seed of every kind that we might carry into the wilderness” and “we did put all our seeds into the earth, which we had brought from the land of Jerusalem.”
While scientists of every kind struggle to make sense out of what they find, and labor to develop theories to explain away their findings, the Lord has given to us the very knowledge of how and when the Western Hemisphere was re-peopled and what animals and plants they brought with them, and how the Americas were replenished with fauna and flora after the destruction of the Great Flood, and how “after the waters had receded from off the face of this land it became a choice land above all other lands, a chosen land of the Lord.”
We even know, where scientists struggle to place the time frame, of when the Panamanian Isthmus was raised and created the Land Bridge over which the Great American Interchange took place—all after the settling of the Land of Promise, after the Jaredites and the Lehi Colony brought animals and plants to the New World, and after the raising of the Andes, “whose height is great,” took place. There are no mysteries to the Lord—only to man, who for the most part, have no idea of His workings among them.

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