brain size and body weight

[Mike Bonham <bonham@jade.ab.ca>]

Michelle Baker sends us this tidbit:

> NOVEMBER 8:    A giant sauropod, such as an Ultrasaurus, had a brain
> that was approximately .001 percent of its' body weight.  For example,
> this is one pound of brain for every 100,000 pounds of body weight.
>

This reminds me of a point I have never seen convincingly explained:
why is the brain mass/body mass ratio always used as a metric of probable
intelligence?  Instead of, perhaps, a component proportional to body
weight (for sensory input and muscular outputs to the entire body),
plus an independent component dependent only on absolute size (for the
`higher' intelligent functions) ?
        eg.
Intelligence = BrainMass / BodyMass
        vs.
Intelligence = (.8 * BrainMass) / BodyMass + (.2 * BrainMass)

Is there really a linear relationship between expressed intelligent
behaviour and the simple brain/body mass ratio in any reasonable
series of variously-sized animals?  (eg. rodents, birds, cephalopods?)

Or, is this only an anthropocentric viewpoint, designed to protect us
from considering that other animals with large absolute-sized brains
but coincidentally having larger bodies (eg. whales, elephants, dolphins)
might have comparable intelligence to our own?

Were dinosaurs really that dumb, just because they had big bodies to
go with their moderate-sized heads & brains?


-- Mike