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Re: Screaming dromaeosaur biplane killers of the air



David Marjanovic (david.marjanovic@gmx.at) wrote:

<Depending on how mobile it was. Why do you think it couldn't have been
(full extension) appressed to the coverts or sunk into them in flight?>

  Because this would create an unaerodynamic position and like all birds,
resettling coverts after flight or any bit of ruffling, as would happen
when the digit would move in and out, would be time consuming and affect
the flight performance, escape, predation, etc.. It seems an easy thing to
consider reduction and loss of the third (minor) digit in birds as a
result of this. It makes sense further than the digit would be embedded in
flesh and feather at all times, rather than mobile through it, save for
the claw which appears to have worked parallel to the second, major digit
if slightly externally.

<In which the 3rd finger is frequently preserved at a right angle to the
other fingers.>

  All the digits tend to be preserved at angles to one another, bent,
dissarticulated, etc.. Often, the first and third digits are close to one
another, and the primary-bearing digit is off at angle, and that cannot be
natural. I cannot see *Confuciusornis* having a very loose hand and still
be a flier, and the finger would still be imparing. Note that in modern
birds, the remnants of the minor digit form a broad plate that ventrally
braces the phalangeal primaries, and this mose likely was true of the
earlier birds which exhibit properties of the manus that do the same, such
as a bowed minor metacarpal or shortened, locked first and second
phalanges of the minor digit and/or close association to the major digit.

<Coverts are present, though.>

  One both sides, apparently, as in birds; thicker on the leg, apparently.
I say apparently because I think it only possible to see the covert
extension on one side of foil, not both. Does not tell us which side was
cambered.

<Ah, sorry.>

  No need. I worked initially in the premise of a glider, because the data
required to look there. With Paul's post, I looked in the premise of a
flapper. My conclusion was that it is a glider-like animal, but I try not
to assume behavior. I have raise display and Tom Hopp raise brooding as
other alternatives to these.

<But then (again if the feathers pointed laterally and were some sort of
airfoil) it becomes difficult to understand why the narrow part of the
asymmetric vanes are distal, not proximal.>

  Indeed. And I think this is why the legs were shown outstretched despite
the lack of evidence that they could (or evidence that shows they
couldn't). But then it becomes problematic to assume that if the feathers
were on the outer and not caudal surface of the metatarsus. The animal is
preserved with the legs partially tucked under its body, and I think no
one has assumed it may have glided this way yet, even closer to the
staggered biplane analogy than the tandem.

<The [*Archaeopteryx*] specimens are 2D... and Middleton (SVP abstract
2002, 88A) uses the degree of torsion of mt I to argue that "the
morphology of the first metatarsal is most consistent with it having been
anteromedially, or at most medially, directed rather than fully reversed.
More derived birds, particularly enantiornithines, possess intermediate
metatarsal I morphologies comparable to those in extant birds with
medially directed halluces.>

  I was not present for Middleton's 2002 talk, but I was there for the
1999 talk at SVP, and this showed an animation of the metatarsal being
twisted, but not evidence of the condition of a torsion of the metatarsal
in articulation to the metatarsus that would support this. Position of the
first metatarsal is as critical as its shape, and hard to prove in
specimens that sometimes show distarticulation of the bone, as in
terrestrial theropods. The close association of MTI would presume that it,
as in birds, had a condition of appression not seen in other theropods
that would relate to stresses borne on it by repeated contact with the
substrate, and this would seem to mean it was reversed or nearly so. I
would need to see Middleton's work when it is published....

<Here I'm only narrow-mindedly concerned with your saying that Archie was
a better flier than *M.* _because of its longer arms_.>

  Not to be obtuse, but I do think I related a list of other features in
that post and the one's in reply to Paul; these include coracoid shape and
features, and furcula shape.

<Looks apomorphic for the latter, doesn't it?>

  Some features of the femora, aside from length, are simialr to
*Archaeopteryx* as well. Yes, though, the lengths of the features in the
legs are considerable apomorphic, if not apomorphic, and I would jump on
this were it not for several of these features present in more terrestrial
maniraptorans, indicating a plesiomorphic condition of the configuration
of the metatarsus and proximal femur that *Archaeopteryx* and other birds
lack.

<To me this looks more like some dietary adaptation than like weight
reduction.>

  I don't think I intended to imply weight reduction, and looking at the
skull of Confuciusornithidae and the jaw of *Jeholornis*, I think the
opposite was true, but those birds also seemed to have developed features
for eating fruits and hard foods. Unlike other maniraptorans, and like
birds, the dentary is straight and the jaw lacks an intramandibular joint.
The joint in ichthyornithids and hesperornithids and the curved jaw of
*Jeholornis* are apomorphic to each as far as I can tell. Comparing other
ornithurines, however, one can certainly tell that the jaw and skull of
*Archaeopteryx* had developed several features of the quadrate, jaw,
snout, and teeth that are lacking in _any_ other maniraptoran but present
in birds. This is something that Feduccia, and Martin and Zhou, are right
in pointing out, but it only shows that there are still a few for taxa
between Archie and the next known dinosaur, wether they were reversals to
dromaeosaurs sensu Paul or acquired only through Archie's lineage
independant of the dromaeosaurid lineage (sensu Gauthier, Holtz, Sereno,
Xu et al., Hwang et al.) [that was not intended as a weight of evidence or
the like, but the idea has been well-supported as a series _to_ flight,
not _from_ it and parsimony plays a part here, Billy Ockham and all that.

[of *Velociraptor*'s furcula]

<Very broad, with thin, straight shafts... pretty different from the
above.>

  Based on the AMNH's new specimens ... in GI 100/25 (fighting dinosaur
specimen) it is less broad and more sigmoid in the shaft curvature, as in
oviraptorids).

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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