A Wet Route South

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Science  30 Apr 2010:
Vol. 328, Issue 5978, pp. 548
DOI: 10.1126/science.328.5978.548-d

For tens of millions of years, North and South America were mutually isolated and evolved their own flora and fauna. Plate motions gradually consolidated a series of volcanic islands and crustal fragments into a land bridge, the Isthmus of Panama, that finally closed approximately 3.5 million years ago. This closure changed ocean circulation, separated Pacific and Atlantic marine species, and accelerated the exchange of land animals between the formerly isolated continents. Documenting the earlier migrations, before final closure, can enhance understanding of the paleogeography of the region and biotic impacts of the invasions. Campbell et al. resolved the paleomagnetic record of Amazonian sediments containing some of the earliest North American fauna. This record implies that the sediments were deposited about 9 million years ago, consistent with some earlier notions. Thus, some early gomphotheres (similar to elephants), peccaries, and tapirs managed to make it to South America long before the final closure, presumably by swimming between distant islands.

J. South Am. Earth Sci. 29, 619 (2010).

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