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AW: New feather-like fossil from the Jurassic of Kazakhstan, Dzik et al 2010
> not merely additional plumes. All in all a rather unusual
> and surprising paper, what do the fossil feather experts on
> the list think of it?
I'm not a feather expert (though I do handle a lot of the stuff), but I think
place (E shore of Turgai Strait) and time (Kimmeridgian?) make this a most
Needs utmost scrutiny.
As regards the "mainstream model of feather evolution", I wouldn't bet on it if
it were a horse. Not as long as the evo-devo geneticists are still pipetting
stuff together. It may be correct, it may be utter bollocks; I am not aware of
any data that resolves this at the moment. Though it seems to me that more data
weights towards the latter.
The "type I to type V" transition scheme (if that's what you mean by mainstream
model) still assumes genetics hasn't progressed since the model's inception (in
other word, it has not accomodated a lot of crucial facts that were established
since its inception) and does not seem to map well on the fossil record.
Evolution of the final complex branching structure seems to have occured in an
evolutionary blink of an eye, and quirttre likely repeatedly so, after or
coincident with prolonged stasis of "protofuzz". Undisputable evidence of
stages III and IV has not, I think, been found yet, and these stages would
quite likely be the least advantageous (don't keep you warm well, can't
flutter-hop with them, maintenance is a nightmare and energy expenditure
considerable), killing hopes of progress to stage V dead. But stage V has been
realized at least once and quite possibly more often, perhaps far more often.
We know that avian foot scales can be induced to grow into feather-like
structures. Very ugly stuff, but pigeons and chicken with properly feathered
tmt have been bred within one person's lifespan from unfeathered progenitors;
too bad nobody has recorded any transitional stages.
Fractal theory might give some hints what happened. Plant genetics is a bit
further in this regard, but need not apply; in any case, the evolution of
complex branching structures does not seem to require many intermediates. As
long as the original metabolic pathway for an initial branching is established,
it simply needs to acquire an iterative loop, which can in theory happen within
one generation. That such loops are possible and may actually be quite common
easily evolved is shown by the repeating color patterns of bird feathers, which
is mathematically rather trivial to model:
I'd rather think that the "mainstream model" starts off all wrong. "Reptile"
scales in the proper sense do not seem to transform into feathers easily. I'd
rather use normal archosaurian skin as the starting point, or actually the more
or less amorphous deposits of beta-keratin that make it tough (think croc skin,
not the osteoderms but the irregular scale- or knob-like keratin accumulations
on the softer parts or in young individuals - or think Musophagidae eyerings
such as in this guy: http://www.biolib.cz/IMG/GAL/10485.jpg). Whether by a
papillomavirus or similar external factor, or by an endogenous mutation, such
structures could be transformed into the half-scale-half-feathers that can be
induced at will in chicken legs these days. Ugly as hell, but evolution is a
fecundity contest, not a beauty pageant (though these may be related, they
probably were not in this case). Then, it only takes natural selection to pick
a good pattern-generating
"algorithm", i.,e. biochemical/genetical pathway, and you go from normal
archosaurian skin to a "stage V" feather in one-and-a-half steps (one step with
a somewhat pathological and unstable intermediate). "Protofuzz" might be a
parallel development rather than an ancestor of vaned feathers; it is as it
seems not as similar to avian down in structure as it ought to be.
This approach has the advantage of providing a reason why a "proto-rhachis" or
"vane-without-rhachis" is so peskily elusive in the fossil record: because
there never was one. A modern-type rhachis may be produced by the same process
that produces vanes, and acquired in the same evolutionary step or with minmal
transition. As I said, this is a problem for evo-devo genetics to look into;
until we know wether rhachis and vanes are produced by the same mechanism or by
two different pathways, any speculation is liable to be not very well founded.
What could be worthwhile to consider is Tetraorninae (grouse) leg "feathers".
They appear to be a purpose-adapted version of the stuff that can be induced in
chickens. I would not call them "feathers", but they are something similar...
microscopically probably similar to vaned feathers, but macroscopically they
resemble scales. If you get a chance to handle a grouse specimen, do check out
the tmt. If you have not seen it before, you'll be in for quite an intriguing
surprise. At a cursory glance, the stuff looks like feathers; touch it, and
you'll be reminded of a handling a phrynosomatid. The haptics are decidedly
unpleasant compared to handling the body plumage (which is very nice and soft
in grouse, as it needs to be in these "pheasants in Arctic gear" that they
are); grouse tmt "feathers" are tough things indeed. And these different
variations on the feather theme are produced by the very same individuals,
presumably utilizing genetical mechanisms
that are for the largest part identical.
Other aberrant feathers might also provide insight here, as they illustrate the
plasticity of the normal avian feather pathway. _Pteroglossus bailloni_ head
plumage is definitely a thing no discerning zoologist should miss. (Could
actually make a superior biodegradable plastic, from the looks of it. Reminds
me of nothing more than extremely tough strips of video tape, only thicker,
that have been exposed to a little too much heat)