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Re: MORE ON SAUROPOD FEEDING HIGH & LOW



From: "King, Norm" <nking.ucs@smtp.usi.edu>
 > 
 > Are sauropod brains really smaller than those of their ancestors with 
 > shorter necks?  How do we equate brain size vs. body size here (is that 
 > called "encephalization"?)? 

The brain size is measure relative to body size using an allometric
equation - a non-linear one.  The result is called the encephalization
quotient, or EQ for short.


Sauropods have, by a good margin, the lowest average EQ of any
dinosaur group. (And maniraptors and their kin have the highest
EQ of any (non-avian) dinosaur - approaching the avian range).

 > If sauropod brains were twice the size (or so) they actually are, would 
 > that have made the amount of blood needed in the head prohibitively 
 > great? 

It would increase maintenance costs more than you would imagine.

First, to support that larger brain, you need a larger skull. Now,
since strength of a support structure tend to increase as the square
of the linear dimension, and the weight increases by the cube, this
menas that the enlarged skull must be *relatively* thicker to support
its own weight.

Now, since the skull is larger, and substantially heavier, the
neck must be strengthened to support the added weight.  Oops, that
weight is at the end of the *long* side of a lever (the side with
the "mechanical advantage").  This means the torque increases by a
larger proportion than the weight.  Guess what?  The *neck* is now
substantially larger in diameter.

So, doubling the weight of the brain has probably at *least* doubled
the weight of the whole neck.  Boy that was an expensive increase.
[The exact allometry depends on acceptable safety margins, the sorts
of support structures used, and the exact distribution of the added
weight].

 > Are we sure this is WHY sauropod brains are small?

Not really.

But given that they have the smallest EQ, and the longest necks,
it seems reasonable that the two are related!

swf@elsegundoca.attgis.com              sarima@netcom.com

The peace of God be with you.