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Brain Evolution and Dinosaur Brains

Harry J. Jerison
The American Naturalist
Vol. 103, No. 934 (Nov. - Dec., 1969), pp. 575-588
Stable URL: http://www.jstor.org/stable/2459034
Page Count: 14
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Brain Evolution and Dinosaur Brains
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Abstract

Dinosaur brains were typically reptilian in size relative to body size. Living and fossil reptiles, amphibians, and fish are "lower" vertebrates with respect to brain evolution and may be described collectively by a single set of brain: body relationships. Their brains evolved conservatively: selection pressures apparently did not require gross changes of the brain: body function in these classes. Birds and mammals, on the other hand, may be considered to be "higher" vertebrates with respect to brain evolution. The size of their brains relative to body size increased in successive geological eras, presumably in response to selection pressures on higher vertebrates for increased neural control and information processing. Within the several vertebrate classes there are, of course, neural specializations reflected in enlargement of different brain structures in different species. These are adaptations to niches which require different kinds of information processing and neural control. Changes in total brain size, however, are associated with gross increments in total information processing capacity, and major changes have apparently not occurred in the evolution of the lower vertebrates.

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