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Re: SARCOPTERYGIANS



"Matthew Troutman" <m_troutman@hotmail.com> wrote:

> Sorry to nitpick but instead of "crossopterygian" the term should have been 
> osteolepiform (Osteolepiformes).

D'oh!  I used Crossopterygia because David (not "Ross") Schwimmer used
it on the dinosaur list a few years back.  IIRC I did verify that his
usage was accurate, and I've been using it for a while.  However, I
see that the Tree of Life web pages use Sarcopterygia as you
indirectly suggest.  I will use it until somebody tells me that that
usage has also been superseded :-)

> Out of curiosity, since I believe that something relating dipnoans
> to tetrapods based on cone classes was written up in Nature a few
> years ago,

The presence in a dipnoan of colored oil droplets filtering the light
which reaches the light-sensitive part of some of the photoreceptors
is most probably what you are recollecting (it was in _Nature_).  That
too was in my talk and will be in the paper when I get around to
writing it.

> are eye characters shared between the groups primitive for
> sarcopteygians (if found in actinistians)

I wouldn't say for sure, but I suspect that for some characters that
is the case and for others it's not.  Even the colored oil droplets
may not be shared derived characters.  Oil droplets such as are found
in Sarcopterygians are unknown in Actinopterygians, but there are some
similar structures (called "ellipsosomes" in the literature).  It is
possible that the oil droplets of all animals that have them derive
from similar biochemical pathways, but that their expression in some
of the different lineages are parallelisms.  Colored oil droplets are
distributed a bit haphazardly among the Tetrapoda so it's not clear
whether the distribution is due to independent developments or
secondary losses.  On topics like this we have a lot more questions
than answers...  However, I'm pretty confident that dinosaurs had them
because the oil droplets in turtles look like the oil droplets in
birds.

--
Mickey Rowe     (mrowe@indiana.edu)