The Great American Biotic Interchange


South America broke from Antartica and Australia about 60 million years ago and became an island continent where its fauna evolved in isolation.  The most common mammals were marsupials, edentates, and primitive hooved animals unfamiliar to most non-paleontologists.  Circa 30 million years ago, caviomorph rodents and monkeys arrived from Africa via clumps of floating vegetation originating from that continent.  During this time Africa and South America were closer together than they presently are.  Floods in African rivers must have carried these little islands of vegetation with their clinging inhabitants  far into the sea where favorable currents brought the lucky animals to South America.  These new colonizers diversified into many species.  South America remained an isolated continent until 9 million years ago when volcanic islands began emerging  below North America.  Although there was not yet a landbridge between the 2 continents, the fossil record shows there was an early exchange of species. …

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About George Crawford

archaeologist, archer, primitive technologist, and wannabee musician ... mostly
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