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Re: Polish find in Nature
How reliable is the trackway dating?
How reliable is the dating of tiktaalik?
It seems odd to me that tiktaalik would exist in the presence of fishapods with
better developed limbs, but that may just be my inability to conceive of a
niche that would favor the development of stubby leg like fins over "true"
limbs or "true" fins.
Or is it possible that Tiktaalik is a "degenerate" tetrapod, in the process of
returning to a more aquatic life style from more terrestrial ancestors?
I assume that transitioning back and forth was a lot easier when the transition
to land was first occurring:
No special blood chemistry like whales have for oxygen storage, no special skin
that they breath through (like amphibians - particularly a species of "lungless
frog"): they'd still have gills, their limbs would still be very fin like, and
their bodies would still be hydrodynamic.
Likewise the relative vacancy of land, and their muscular stubby fin-legs would
allow them to go on land and (evolutionarily speaking) not be too far behind
other terrestrial vertebrates, and of course they already had basic lungs.
The evidence for a tidal marine origin over a swampy freshwater origin is
interesting - although I think that fits in well with extant tetrapods
producing Urea (or Uric acid), whereas extant freshwater fish have lost that
ability (or am I mistaken on this point?).
Wasn't part of Urea's original function to bring internal salt concentration
closer to that of the sea?
Freshwater fish can simply let ammonia/nitrogen waste diffuse through their
I had previously thought it was merely fortuitous that Sarcopterygians made it
onto land where Urea production was beneficial, before loosing the ability to
make urea in favor of the simpler system of diffusion of Ammonia waste through
the gills in freshwater fish.
--- On Wed, 1/6/10, Dawid Mazurek <email@example.com> wrote:
> From: Dawid Mazurek <firstname.lastname@example.org>
> Subject: Polish find in Nature
> To: email@example.com
> Date: Wednesday, January 6, 2010, 11:51 AM
> Check out th
latest issue cover.
> There's of course a paper inside. Plus
> an accompanying movie:
> BiaÅe szaleÅstwo trwa!
> DokÄd w tym roku?
> SprawdÅ trasy, wyciÄgi, oferty: