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The Evolutionary Strategy of the Equidae and the Origins of Rumen and Cecal Digestion

Christine Janis
Evolution
Vol. 30, No. 4 (Dec., 1976), pp. 757-774
DOI: 10.2307/2407816
Stable URL: http://www.jstor.org/stable/2407816
Page Count: 18
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The Evolutionary Strategy of the Equidae and the Origins of Rumen and Cecal Digestion
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Abstract

The so-called 'inefficiency' of the perissodactyls, resulting from the evolution of a cecal site of fermentation, arises because the strategy of selecting fibrous herbage was developed early in their evolution. The ruminant artiodactyls did not adopt this sort of diet until they were of a sufficiently large body size for a rumen fermentation site to be physiologically possible. It appears that body size at the time of the adoption of a fibrous diet is the critical factor in determining the type of digestive system that will be evolved. Cecal digestion is in fact the superior adaptation for dealing with high fiber content herbage, provided that intake is not limited by the actual quantity of herbage available. The Equidae continued to be successful in the face of the radiation of ruminant artiodactyls because they could maintain themselves on herbage more fibrous than could be tolerated by a ruminant of similar body size.

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