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Re: Homing Pigeons? Try Homing Crocodiles...

I remember reading--regarding "magneto-senory apparatus--that bird brains
contain minute traces of ? Was it magnetite? Or simply iron? I used that
tidbit in a long poem entitled "Or Else" back in the mid-80s, of which this
is a short extract:
Recognition: human bones have de ja vu
built in as sure as birds' brains
minced, condensed, melted down make steel..
We are lulled
by the landmarks of sin we think
we have seen before.
We are pulled
by the seductions of magnetic north
to know we are coming home.
----- Original Message ----- 
From: "Mickey Rowe;893-2446" <mrowe@lifesci.ucsb.edu>
To: <dinosaur@usc.edu>
Sent: Friday, September 28, 2007 1:36 PM
Subject: Re: Homing Pigeons? Try Homing Crocodiles...

> Dann Pigdon <dannj@alphalink.com.au> wrote:
> > There's no reason to suspect that the homing abilities of birds and
> > are due to the same physiological adaptations - especially since it's
> > been shown that birds can see magnetic fields via adaptations in the eye
> > itself (not something you'd expect in largely nocturnal crocs).
> Two things of import... first a quasi-philosophical issue... it is
> probably not correct to say that birds "see" magnetic fields.  The
> fact that light receptors in their eyes appear to be involved in
> magnetic field detection doesn't make that detection anything like
> vision and hence seeing.  We have photoreceptors in our eyes that help
> to regulate daily fluctuations in hormone levels... receptors that
> re-set biological clocks as it were.  Since these receptors do not
> appear to play any role in our conscious visual perceptions, it
> wouldn't be correct to say that we see the time of day.  Similarly, if
> birds have any introspective capabilities, it's not likely that
> magnetic field detection is like sight even if the transduction
> process (converting magnetic field strength/orientation into a neural
> signal) takes place in the eye.
> Second, at least some of the relevant magnetosensory apparatus that
> appears to work in birds also works in salamanders.  The basic
> transduction mechanism may thus span a much larger phylogenetic
> bracket than Archosauria.
> > Marine turtles also have phenominal homing abilities, yet I wouldn't
> > suggest that they got them from the common ancestor of turtles and
> > archosaurs.
> I haven't read the latest literature, but based on what I know from a
> few years ago I'd be surprised to find that even within birds there
> was only one magnetic field transduction mechanism.  Marine creatures
> are probably more likely to use a magnetite based mechanism, but even
> that could be conserved between birds and turtles.  I would *not* be
> so quick to discount homologous relationships among various components
> to the homing systems of birds and turtles.
> -- 
> Mickey P. Rowe     (mrowe@lifesci.ucsb.edu)
> P.S. Thanks to all for not pointing out my previous misspelling of the
> word "yolk".  I'm sure you all cringed at it just like I did.