Brain–body mass ratio

A more complex measurement, encephalization quotient, takes into account allometric effects of widely divergent body sizes across several taxa.

[citation needed] Among birds, the highest brain-to-body ratios are found among parrots, crows, magpies, jays and ravens.

Sharks have one of the highest for fish alongside manta rays (although the electrogenic elephantfish has a ratio nearly 80 times higher—about 1/32, which is slightly higher than that for humans).

This phenomenon can be described by an equation of the form E = CSr, where E and S are brain and body weights, r a constant that depends on animal family (but close to 2/3 in many vertebrates[17]), and C is the cephalization factor.

Recent research indicates that, in non-human primates, whole brain size is a better measure of cognitive abilities than brain-to-body mass ratio.

[19] The brain-to-body mass ratio was however found to be an excellent predictor of variation in problem solving abilities among carnivoran mammals.

The bony-eared assfish has the smallest known brain–body mass ratio of all vertebrates ^{[

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