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Comparisons of the Contemporary Mammalian Faunas of the Southern Continents

Allen Keast
The Quarterly Review of Biology
Vol. 44, No. 2 (Jun., 1969), pp. 121-167
Stable URL: http://www.jstor.org/stable/2819437
Page Count: 47
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Comparisons of the Contemporary Mammalian Faunas of the Southern Continents
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Abstract

A group of papers on the mammalian faunas of Africa, the Neotropical region, and Australia (Quart. Rev. Biol., 43: 265-300; 373-408, 1968; 1-70, 1969) is reviewed from a comparative standpoint and certain general concepts relative to faunal evolution and distribution on those continents are developed. On the basis of current taxonomic information Africa has 51 families and 756 species of mammals, Neotropica 50 and 810, and Australia 18 and 364. If the section of Africa that has a rainfall of less than 5 inches per annum be excluded (the Sahara Desert covers almost one-third of the continent) the number of families and species per 100,000 square miles are comparable: Africa, 0.63 (9.39); Neotropica, 0.70 (11.3); Australia, 0.55 (11.03). Africa has the most diversified fauna. Neotropica owes its numerical richness to large faunas of rodents and bats. Stemming from their different basal stocks and different histories of isolation and faunistic interchange with adjacent continents, the three continents differ fundamentally in their faunal compositions, levels of endemism and dominant groups. Differences in rainfall and degree of development of different vegetation types (present and former) explain the predominantly savannah nature of the Africa fauna and the prominence of rain forest elements in Neotropica. The impoverishment of the Neotropical large mammal fauna, however, must be explained partly on historic grounds (extinction without replacement). Factors affecting faunistic richness include continental area, latitudinal position, percentage of the continent lying within the tropics, relative amounts of tropical rain forest, savannah, and desert, degree of biotic and physiographic diversity, past opportunities for acquiring new species from outside, and for evolving new ones within the continent. Although the continents differ greatly in these factors, some degree of balance is discernible in the number of species occupying the various major adaptive zones or ways of life. Thus, small terrestrial omnivores and rabbit-sized terrestrial herbivores make up about the same percentages of the total fauna of each continent. One of the most striking events in the evolution of Southern Hemisphere faunas was the colonization of South America by North American mammals in the late Tertiary. Authorities disagree about the time this colonization began. On the basis of fossil evidence, paleontologists Simpson, Patterson, and Pascual date the formation of the land-bridge as late Pliocene and the major interchange as Pleistocene. Neontologist Hershkovitz, on the other hand, arguing from the degree of differentiation achieved by many of the northern groups in Neotropica, suggests widespread colonization before the land-bridge and a somewhat earlier date for its completion.

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