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The Antitropical Factor in Cetacean Speciation

J. L. Davies
Evolution
Vol. 17, No. 1 (Mar., 1963), pp. 107-116
DOI: 10.2307/2406339
Stable URL: http://www.jstor.org/stable/2406339
Page Count: 10
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The Antitropical Factor in Cetacean Speciation
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Abstract

Early cetaceans were warm-water animals, and the first cold-water forms probably appeared in mid-Tertiary times in response to an expansion in the cold-water environment. From this time on, the equatorial warm-water belt has acted as an important but variably efficient barrier to dispersal and has given rise to vicarious forms with antitropical distributions. Recurrent cooling of ocean waters in the Pleistocene led to a restriction of many strictly tropical forms to the Indo-Pacific region, but other forms with a wide tropical-temperate distribution have maintained their range. Cold-water cetaceans restricted to one hemisphere are either polar in distribution or archaic types with limited and perhaps relic distributions. In other forms, equatorial transgression and subsequent isolation appears to have been an important factor in speciation and recent oceanic palaeotemperature analysis suggests that, assuming existing temperature associations, equatorial transgression was possible at several times in the Pleistocene.

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