🚀 go-pugleaf

In article <1704@tdat.teradata.COM> swf@tools3teradata.com 
    (Stan Friesen) writes:

>In article <C0Dt77.Cnn@newcastle.ac.uk>, w.p.coyne@newcastle.ac.uk writes:
>|> --------------------------------------------------------
>|>    Why did mammals evolve large brains 250 Ma?
>|> Reptiles of 300 Ma, dinosaurs and modern reptiles all have the same 
>|> brain size.
>
>Well, right off. you start out with something that is not true.

I was somewhat baffled by the original statement as well.  Peter, are
you sure that you're not mistaken about what the article said?

>|> Reptiles are mainly visual animals and much of the processing of this
>|> data is done at the periphery of their nervous systems - the retina.
>
>Ditto for birds and dinosaurs.  Which is, naturally, why it was the
>optic tecta that enlarged in that lineage.  

I'm not so sure about this.  Yes, the optic tecta are relatively large
in these lineages, but they're also relatively large in fish and
amphibians.  Furthermore, when vision became more important for
mammals, it was cortex that enlarged even though our tectum (superior
colliculus) is still intimately involved with vision.  In cats and
monkeys it's hard to find cortical regions that don't respond to some
sort of visual stimulation...

>(Though I suspect that the auditory tecta might also have enlarged).

If I recall correctly, the inferior colliculus of microchiropteran
bats is hypertrophied, but there isn't much of an "auditory tectum" in
reptiles or birds.  I could easily be wrong about that, though.

>|> They suggest the increase in brain size  was due to 3 reasons, 
>|> the first 2 by Jerison and a 
>|> third by John Allman, though the third is disputed by some.
>|> 
>|> resaon 1 - Mammals had to handle different types of information
>|> reason 2 - Having a centralised processing system meant data from sight
>|>            sound, touch and smell could be integrated to create a more
>|>            detailed mental model of the world

>Though the upper diencephalon (the optic and auditory tecta)

Sorry to pick nits, but you mean mesencephalon.  Diencephalon refers
to thalamic structures.

>Stanley.Friesen@ElSegundoCA.ncr.com

Mickey Rowe     (rowe@pender.ee.upenn.edu)

P.S.  Stan there's a person over in k12.ed.science who works as an
illustrator of paleo-animals and plants.  She (or he, the first name
is Dana) is currently writing a paper about _Allosaurus atrox_ and is
soliciting opinions as to whether or not it could grasp with its
hands.  E-mail me if you'd like me to send you a copy of her article
(the posted one, not the one she's publishing).

P.P.S.  Thanks for bringing the article to our attention, Peter.  I'm
probably going to hunt it down myself.