Evolution

A Northerly Migration

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Science  17 May 2002:
Vol. 296, Issue 5571, pp. 1203
DOI: 10.1126/science.296.5571.1203c

Many groups of organisms have members in both Africa and South America. These disjunct distributions are commonly attributed either to an origin on the Gondwanan supercontinent before its breakup around 100 million years ago (Ma) or to long-distance dispersal across the widening Atlantic Ocean.

In a molecular phylogenetic analysis of the plant family Malpighiaceae, Davis et al. provide evidence for a new scenario. The Malpighiaceae are a family of trees, shrubs, and lianas occurring throughout the tropics, with a peak of diversity in the New World. Their analysis indicates that the family originated in what is now northern South America about 64 Ma, well after the breakup of Gondwana; at least six separate transoceanic dispersal events would have to have taken place to produce the current distribution, which seems unlikely. Instead, Davis et al. propose that the early Malpighiaceae spread mostly overland across the Northern Hemisphere Laurasian supercontinent, during the climatically favorable thermal maxima in the Eocene and Miocene epochs.—AMS

Proc. Natl. Acad. Sci.U.S.A. 10.1073/pnas.102175899 (2002).

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