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Re: Feathers on Bloody Everything



>No, I'm just arguing an alternative viewpoint to the standard one being 
>advanced by the dinosaurological majority. I never fall into lockstep with 
>everyone else unless there's compelling evidence to do so. Right now, we have 
>>absolutely no idea what protofeathers might have looked like<. The 
>featherlike structures seen on dinosaurs like Sinosauropteryx et al. are 
>>different from< the flight feathers of Archaeopteryx and other birds; that's 
>>all< we know.

No, it isn't quite all we know.  We know that they are also different from
the feathers (or whatever) on Caudipteryx and Protarchaeopteryx.  We also
know that they differ markedly from any known "degenerate" feather, bristle
or filament on any modern bird - not just the flight feathers. This
difference extends to microstructure.  I conclude this based on both Alan
Brush's view (and as I said before, he is intimately familiar with the
feather structure of modern birds) and from the paper by Mary Ellen
Schweitzer at the Ostrom Symposium.

 It is a premature misnomer to call them "protofeathers," since 
>they appear on animals >younger than< Archaeopteryx--which had perfectly 
>good, very modern-looking feathers.

Yes, that may be - and note that Brush et al. are NOT calling them
protofeathers - but it is even worse to call them "feathers".  There is
absolutely nothing about them that makes such an unequivocal diagnosis
possible (and of course as we don't have a diagnosis of a "protofeather");
all we can really say is that they are integumentary structures that COULD
be homologous with feathers (a conclusion that says nothing about
directionality of evolution).  This has nothing to do with phylogeny,
cladistics or whatever.  Calling them "feathers" either forces us to
broaden considerably the definition of a feather, or to assume that they
are degenerate derivatives of the type of structures we see in
Archaeopteryx or Caudipteryx - something for which there is no evidence to
my knowledge.

The time-line argument is meaningless - not just for the reasons I gave
earlier, but because Sinosauropteryx is coeval with Caudipteryx.  This
means that the time-line tells us nothing about which of these two animals
had the more derived integumentary structures.  In fact four possibilities
exist for these two taxa alone:

1.  Their integumentary structures were not present in their common
ancestor, and have been independently derived;

2.  Their common ancestor did have such structures, but either:

a. The structures in the common ancestor share more features with those in
Sinosauropteryx than with those in Caudipteryx;

a. The structures in the common ancestor share more features with those in
Caudipteryx than with those in Sinosauropteryx;

c.  Both forms have diverged to the same extent, but in different
directions, from their common ancestor.

I suspect that of these 2(a) and 2(b) are the most likely a priori.  I
suppose that if 2(a) is true then the structures in Sinosauropteryx could
be called protofeathers, while if 2(b) is true they could be called feathers.

 These integumentary structures could just 
>as easily have been secondarily derived from modern feathers (e.g., down) as 
>they could have been integumentary structures retained unchanged from their 
>protofeather form. Calling them "protofeathers" places an unwarranted bias 
>into the minds of listeners pro the current cladistic rage of "ground-up" 
>avian evolution.

As does calling them feathers, as I hope I have shown.  But I do not think
that is the end of it.  George is stating, really, that of my hypotheses
above 2(b) is just as likely as 2(a).  I think you can marshall some good
arguments that this is not the case.

The chief of these is that there is no structure known to be derived from
(or better, a form of) modern feathers that resembles the integumentary
structures in Sinosauropteryx sufficiently to suggest that the latter
developed in the same manner as the former.  This is despite the presence
in many birds of "degenerate" feather structure and the presence of
unbranched feathers (eg bristles,eyelashes) in most if not all modern birds.

Second, in its skeletal morphology Sinosauropteryx is much more like
"other" theropod dinosaurs, and unlike birds, than is Caudipteryx.  The
only way I see to interpret this is to assume that the common ancestor of
birds and "protobirds" like Caudipteryx on the one hand, and
Sinosauropteryx on the other - an animal I will assume to have been a
theropod dinosaur as opposed to some non-dinosaurian archosaur - was either
more like Sinosauropteryx than Caudipteryx or the reverse.  If it was the
reverse, then we must assume that birdlike dinosaurs actually represent a
primitive character state within at least one complex of theropods, and
that ALL the characters of Sinosauropteryx that resemble other dinosaurs
more than they do those in "protobirds" represent a secondary change - not
just the integumentary structures.  I realize that this might fit in with
George's own views on bird origins, but I do not think one has to be a
cladist to find this the less parsimonious possibility.

In other words:

Given that:

Sinosauropteryx is less birdlike in its overall morphology than
Caudipteryx, Protarchaeopteryx or any "true" bird including known
secondarily flightless forms;

And that:

The integumentary structures of Sinosauropteryx are less featherlike in
their morphology than those in Caudipteryx, Protarchaeopteryx or any "true"
bird including secondarily degenerate feathers in flightless forms;

It is most parsimonious to conclude, in the absence of other hard evidence,
that the structures in Sinosauropteryx are unlikely to represent a
secondarily-degenerate derivation from the feathers in Caudipteryx or in birds.

In other words, barring some pretty amazing future discoveries, I think it
is safe to say that if it doesn't look like a duck, and it doesn't quack
like a duck, chances are it isn't a duck.

--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
1825 Shady Creek Court                 
Mississauga, Ontario, Canada L5L 3W2          mailto:ornstn@home.com