THE ANTITROPICAL FACTOR IN CETACEAN SPECIATION

作者：J. L. Davies · 发表于：Evolution · 年份：1963 · DOI：10.1111/j.1558-5646.1963.tb03258.x · 被引用次数：91 · 研究领域：Cephalopods and Marine Biology、Evolution and Paleontology Studies、Paleontology and Evolutionary Biology

It is well known that several cetacean genera, and possibly even some species, are discontinuously distributed on either side of the equator.Such distributions, often described as "bipolar," have been widely discussed for other marine animals-notably by Berg (1933) and by Ekman (1953)--but no one has attempted a systematic examination of the phenomenon in regard to the whales and dolphins.Because most so-called "bipolar" marine distributions are actually "bitemperate" or even "bisubtropical," Hubbs (1952) suggested the term "antitropical" as more appropriate and all-inclusive.An attempt is made here to review the nature of antitropical distributions in the Cetacea, to account for them, and to suggest something of their evolutionary significance.Present evidence, both specific and circumstantial, suggests that the earlier cetaceans lived in a warm-water environment.Thus the earliest known forms are zeuglodonts from the Middle Eocene of Egypt, Nigeria, and Texas and the distribution of existing species still suggests an aversion to cold: only three genera (Ba- laena, Delphinapterus, and M onodon) breed in polar waters, none breeds in Antarctic polar waters, and the majority of species frequenting cold water appear to move equatorward to breed.By the end of the Eocene, zeuglodonts had spread north to British Columbia, England, and Germany and probably south to Australia and New Zealand; at any rate they were certainly in southern waters by the Oligocene.Toward the end of the Eoc...