Extinct mammalian biodiversity of the ancient New World tropics.

The origins of mammalian biodiversity in the New World tropics extend back >25 million years, represented by clades that were originally endemic to South America, North America or Africa. Since then, these mammalian clades have been greatly affected by climatic, physiographic and biological changes. The Isthmian land bridge, which formed approximately 4 million years ago between North and South America, resulted in the maximum diversity of 17 New World tropical mammalian orders during the Great American Interchange. This diversity was subsequently reduced to 12 orders as a result of competition, climate change and human impacts. Here, I discuss how the fossil record is now providing a rich archive of past biodiversity, presenting unique evidence of the origins, macroevolution, macro-ecology and extinction of New World tropical mammals.