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Re: MORE ON SAUROPOD FEEDING HIGH & LOW



On Wed, 27 Mar 1996, King, Norm wrote:

> Relative to sauropods, Nicholas Longrich wrote (03/27/96; 3:55p):
> 
> [snip]
> 
> >The skulls and necks have been reduced down to the bare minimum
> >necessary, so that the amount of bone, muscle and brain supported by
> >the skeletal and circulatory systems is minimized. Sauropods
> >actually evolved smaller brains to reduce the amount of blood needed
> >in the head.
> 
> [snip]
> 
> 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"?)?  This is the first place I've ever seen a 
> discussion of selection pressure for _small_ brains--I mean, pressure to 
> _decrease_ brain size.  It sounds like selection pressure to be stupid.  
> 
> 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?  Are we sure this is WHY sauropod brains are small?

        I saw a lecture Bakker gave on exactly this topic. He said that 
advanced sauropods actually had smaller brains than the more primitive ones, 
(I'll assume that he considered that brain does not increase
directly with body weight) and that this trend is paralelled by stegosaurs.
This would be in answer to the question posed of how sauropods supplied blood 
to their heads 50 feet in the trees: reduce brain size, reduce facial 
musculature and bone, and you've reduced blood demands. Note that the 
general trend is an increase in brain size. 
        The pressure to develop longer necks must have been enormous. It 
may be that the pressure to develop more reach could not have been 
entirely met by developing longer necks, hence other strategies like 
rearing and elongate forelimbs. These two strategies would increase 
reach, perhaps without increasing work done by the heart quite so much as 
extra neck- the heart was being taken up towards the trees.
        I wonder, are hearts in giraffes more dorsally located than in 
other animals?

        -nick L.