Brain/Body Weight

[Ralph Chapman <MNHAD002@SIVM.SI.EDU>]

All statistics like the one given for the sauropod for brain/body
weight ratios are bogus. The relationship is distinctly allometric and
not intelligently described by a single ratio but, instead, needs to
be plotted loagirthmically and the proper lines fit to it. The larger
the organism gets, the relatively smaller brain it needs to do the same stuff,
regardless of the group. The differences in the groups are in the positions
and slopes of the line. Mammals have big brains because their line is
higher in the plot of brain (y) vs body (x) than the reptile line is. Birds
I think are intermediate. Therefore, for the same body size, the average mammal
has a larger size than the average reptile. Humans have large brains because
they are way above the line - that is - their residual is high and positive.
Dinos tend to plot like reptiles, except that some theropods tend to, not
surprisingly, encroach into the bird region.

To put it as simply as possible - as you get bigger, you are not doing that
much more than a smaller animal, except you have a few more muscles to
coordinate. That's why you get nerve groupings in the butt end of many
larger forms, including us, I believe. They help coordinate the mass
of muscles toward the back (no sonnets being thought of back there).
So, as animals get bigger, they don't need to get a proportionately bigger
brain - it is not isometric by any means. That's why humans have relativelyt
big heads that seem to get smaller with age (size) (except perhaps Nancy
Reagan who always seemed to have a big head), and other beasts as well
ontogenetically, and why you seem similar trends across taxa.

Single ratios just are used by popularizers to be sensationalistic, but
they betray their lack of understanding of the subject matter.

I'll get off my soapbox now   - Ralph Chapman