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Re: Science feather strength debate



Hey Jason,

Thank you, I appreciate the compliment on the manuscript.  When the
2007 paper was written the investigation into the soft tissue
impressions was at an earlier stage, and I dare say the emphasis was
on the osteological description.  Particular emphasis was placed on
clearing up previously controversial and/or mistaken interpretations
that the Thermopolis specimen could shed light on.  Later
investigation of the imprints around the humerus made it clear that
they could not represent veined feathers.  The fact that something is
in fact preserved but it is not the more durable flight feathers
indicates they really are absent, rather than simply failing to make
an imprint.  There are three possibilities to explain this:

1) Archaeopteryx lacked tertials and the imprints are "dinofuzz"
material from the body; I favor this interpretation.

2) Archaeopteryx lacked terials but had dinofuzz-like soft tissue
growing from the arm, possibly with a significant distance covered
from the posterior edge.  This is certainly possible, but for other
reasons (including other traces of the same non-rachis imprints from
other parts of the body) I think it's less likely.

3) Archaeopteryx had terials, but they are missing in all of the
specimens, and the imprints are thus body "dinofuzz" that is leaving
an impression where the tertials should be.

Obviously all three are conceivable, but given the extremely
low-energy depositional environment and the complete lack of
disturbance of the other feathers (and that includes the tail
feathers...it's not clear that pre-pygostyle tail fans such as that in
Archaeopteryx should be any better attached than tertials) it seems
the least likely explanation to assume that the tertials have always
detached, even when the rest of the animal appears to be in a pristine
level of preservation.

I sympathize with your concerns about inferring from a lack of
evidence.  Indeed, it was the positive evidence of non-rachis bearing
epidermal structures that caused me to pursue the issue.  Still, I
think it has to be addressed because without fail every published
estimation on the flight and gliding capabilities of Archaeopteryx
assume a priori that it had a derived wing; that falsely reduces the
actual range of error (and I would argue introduces significant
additional error) into attempts to model the aerodynamic properties of
Archaeopteryx.

As for the Longipteryx specimen you mention; I agree that you are on
good ground here in assuming primaries and secondaries.  That said,
there are two significant differences between Longipteryx and
Archaeopteryx.  First, it's not like there are otherwise undisturbed
feathers preserved with only one subset missing (in contrast, that IS
the case in Confusciousornis where the lack of a preserved tail fan in
specimens with excellent wing feathers and/or two elongate
ribbon-style feathers is inferred to demonstrate a lack of a tail
fan).  Second, phylogenetically we already know that primaries and
secondaries evolve further down in the tree than Longipteryx, making
it the default inference that would require positive evidence to
refute. With Archaopteryx we have no such situation.  Almost all
consensus trees show that wing feathers originate distally (e.g. in
oviraptors), so a wing that is contiguous with the body is a derived
condition.  Since we don't actually know at what point on the tree
such a wing evolved, that fact that Archaeopteryx retains the
plesiomorphic condition really shouldn't be controversial.

Indeed, I don't believe it would be except that we're stuck with a
century of protobirds-as-flying-squirrel-analogs (and a litany of
accompanying illustrations) as conceptual baggage.

Best wishes,

-Scott


-- 
Scott Hartman
Scientific Advisor/Technical Illustrator
(307) 921-9750
www.skeletaldrawing.com