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Re: Screaming dromaeosaur biplane killers of the air



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

<In the right wing of the holotype (Fig. 1 of the Nature paper), the
longest feather (3rd primary?) is very similar in length to the bony arm,
isn't it? (Probably it is a little shorter, but its base is prepared away
to expose the 3rd finger.)>

  The longest wing feather, at 86mm, measures to the distale end of the
first phalanx of the second digit, is 81% the length of the articulated
arm, using humeral, radial, and manual lengths (with carpus included).

<Depending on what a primitive flier is. Confuciusornithids have pretty
long wings, so that IIRC Rayner in the Ostrom Symposium volume concluded
they must have flown like swifts, at constant high speeds. Apparently
unlike *M. gui* they lack alulae.>

  Indeed, all the preserved specimens lack such a structure, and that in
*Microraptor* may not be an aerodynamic alula, but rather integument
covering the digit itself, perhaps for streamlining a protuberance.
Incidentally, this brings up the streamlinign function of coverts: if
these were present, and the under coverts of the wing were covering only
the secondaries, then presumably the third digit was completely free of
these, and would have been such an oblique protuberance, and rather
un-aerodynamic for all the presence of streamlinging coverts. Whatever the
digital mobility from articular surfaces, inferred differently among
observers, the digit may have been embedded in the wing and not really
mobile at the base, in order to account for aerodynamics. This would be
true of *Confuciusornis*, *Archaeopteryx* and *Microraptor*.

<[*Caudipteryx*, w]hose wings are much shorter.>

  The feather to arm ratio in *Caudipteryx* is identical to that of
*Microraptor* gui and the preserved length of the feathers in the
Eichstätt specimen of *Archaeopteryx*, which though conforming to a wing
shape may be missing the distal ends. In the London *Archaeopteryx*, the
ratio is 60%, and in Paul's restoration, it is 71%. Otherwise, a stable
ratio of shorter feather than to arm is seen other birds, but not high
speed fliers, in which, as in *Confuciurornis*, the feather is longer than
the arm. In a columbid, for instance (not a high-speed flyer but a low
speed aerialist), the ratio is 97%, nearly equal, and shortens in soarers.
Another low-speed flyer, the swan, has a shorter, near 75% ratio. In
hummingbirds (low speed flyer), the arm and feather are nearly equal (as
in the columbid), though the feather is a tad shorter, contra my earlier
claim of slightly longer. 

<_If_ the metatarsal remiges pointed laterally instead of (as preserved,
in 2D specimens and with the feather bases ?preserved away) caudally, and
if *M.* flew in a squatting position, then it is imaginable that the
metatarsal remiges formed an airfoil below that that was formed by the arm
feathers.>

  A special circumstance, squatting, does not support the claim. This
would still require the metatarsus to be horizontal and that may only be
acheivable by longitudinal extension of the leg. And we still don't know
which, is ay, side is cambered. So far, no one has -- except to summarily
dismiss it -- suggested that these structures were for display, however
unusual it may be.

<Above you write that *M. gui* had narrow arm wings, below you write that
it had no ability to sprawl -- should make gliding difficult, except
perhaps in the pose I imagine above, which would produce a bit much drag
for a glider, right?>

  I don't presume the thing glided, either. The legs, however, may very
easily have extended posteriorly, but others, including Xu et al. and
Paul, are supporting the _lateral_ splay of the leg, without suggesting
the _posterior_ splay of the leg. This may because of an idea that the
caudal surface (facing dorsally in a lateral splay as reconstructed in the
paper) of the metatarsal foils were dorsally cambered, instead of the
posterior splay in which the reverse would be true. Then again, there may
be no camber, and they would have still served to induce a good deal of
drag. The idea that they were fully developed airfoils has sorta caught on
too fast.

  Paul also reported on the so-called indicativeness of body flattening on
side or top/bottom as support for the leg sprawl theory of hip design.
*Confuciusornis* is preserved in both positions, and I see no reason to
suspect that the hip may not be disarticulated to a varying degree
depending on the taxon.

I wrote:

<<*Archaeopteryx* has a more avian tarsus and foot, with a reversed hallux
and...>>

and David replied:

<A more avian tarsus? Why? What about Middleton's doubts about the
reverted hallux?>

  The metatarsals are not mediolaterally compressed, and are to some
degree proportioned as in birds. As explained in an earlier post, the
subarctometatarsal pes of *Microraptor* and other "sinornithosaurs" is a
terrestrial adaptation, used to resist longitudinal stress along the
metatarsus (though it may also resist torsional stresses, as supported by
recent work including Holtz's 1994 paper).

  As for the hallux, I presume the articulation of the halluces, though
doubted by some few, are present in the Eichstätt, Solnhofen, and
Aktien-Verein specimens, as fully reverted halluces, whereas the trend in
other Liaoning animals with halluces tend to show the opposite when
supported by intact, 3D specimens of relatives. Thus, I do think the
evidence is for *Archaeopteryx* with a reversed hallux, and *Microraptor*
without.

<And indeed, mammalogists' predictions were right, the oldest
australosphenidans are a lot older than the oldest metatherians. (Crown
group marsupials are still unknown from the Mesozoic.)>

  There are still doubts as to wether australosphenidans are marsupials,
the case is not closed, if Rich et al. are to be believed at all.

<while *M. gui* has arms that are only as long as those of...
confuciusornithids. Okay, the latter appear to have a bit longer hands,
and considerably longer remiges.>

  And a carpometacarpus ... and a largus carpus ... and a shorter, robust
humerus ... and a more reverted coracoid ... and an acrocoracoid process
... and longer feathers than arm ... and a shorter trunk ... and a bigger
sternum ... and a keeled sternum....

<In the holotype of *M. gui*, the right wrist is maximally flexed,
therefore the primary fan is maximally folded, and its appearance in a
more extended position hard to judge (from Fig. 1 and 2 of the Nature
paper). The left wing is incomplete.>

  Given the sharp decline in feather lengths, the wing, whether folded
(and it is not maximally folded) sports a narrow taper, not a broad,
Archie-like fan. This is true of *Confuciusornis* as well. Note that in
most modern birds, except those where all carpal feathers are fanned, a
narrow fan is present in speed-flyers where the primaries are all parallel
at wing extension. The issue is equivocal on fan shape during extension,
though the shapes of the feathers do in fact show a strict taper.

<In comparison to what? The trunk-leg ratio looks very similar in *M. gui*
and *Archaeopteryx*.>

  An example, with length of the femur increasing in length relative to
the leg in "sinornithosaurs", shows that the femur in some forms is
distinctly different between the two:

femur:trunk length (humeral glenoid to acetabulum length, drawn from the
middle of each):

Archaeopteryx
  (Solnhofen)  0.59
  (Eichstätt) 0.68
  (London)  0.61
Confuciusornis
  (3 specimens)  0.53, 0.58, 0.62
Microraptor
  (IVPP V13352)  0.66
  (CAGS 20-8-001)  0.67
Caudipteryx sp.
  (BPM 0001)  0.7
Sinornithosaurus? sp.
  (NGMC 91)  0.85

  Whereas total limb length to trunk length is different:

Archaeopteryx
  (Solnhofen)  2.15
  (Eichstätt) 2.7
  (London)  2.25
Confuciusornis
  (3 specimens)  1.77, 1.83, 2
Microraptor
  (IVPP V13352)  2.38
  (CAGS 20-8-001)  2.29
Caudipteryx sp.
  (BPM 0001)  2.56
Sinornithosaurus? sp.
  (NGMC 91)  2.83

  *Microraptor* has a long leg and femur ro trunk length than does
*Archaeopteryx*, though admittedly not by very much.

<Please elaborate. I only see a small snout there; the size of the
antorbital fenestra of *M. gui* appears to be unknown. (If it's large then
the snout can be as light as Archie's, I assume, while being as high as
preserved.)>

  The dentary of CAGS 20-8-001 is about 60% the skull length, as in
*Archaeopteryx*, when scaled to IVPP V12330, type of *M. zhaoianus*.
However, the jaw is curved and deeper to length than is *Archaeopteryx*',
with larger teeth, and relatively longer maxilla to maxillary height. The
anterior snout also appears to be deeper in *Microraptor*, as well.

<Can you see this from the figures in the Nature paper? :-/>

  I can see the coracoid shape and the position of the glenoid. However,
these conclusions are based on *M. zhaoianus*, whose shoulder is not as
advanced as *Archaeoptreryx*'. The problem here may also be that
*Microraptor* has a broader, larger sternum, dorsal/medial/cranial edge of
the coracoid is concave, as in *Bambiraptor*, but the coracoid tubercle is
not as close to the scapula as it is in *Archaeopteryx*. This indicates,
as  I wrote, a less advanced humeral elevator system, and a lack fo a true
flapping mechanic, unlike which seems to be incipient in some way in
*Archaeopteryx* and in *Confuciusornis*.

<And oviraptorids, and *Bambiraptor*...>

  In *Bambiraptor*, yes, but not any oviraptorid where the rami are more
V-shaped, coming to a ventral apex even though the rami curve along their
length. In *Velociraptor*, it is broad and V-shaped, whereas in CAGS
20-7-004, it is also V-shaped, and has a small hypocleidial process, but
in CAGS 20-8-001 it is apparently viewed from a different angle and is
U-shaped without the hypocleidial process apparent. It also seems to be
preserved on its caudodorsal surface rather than the ventrocranial surface
as in CAGS 20-7-004, and this may distort the perspective.

  I had written that Archie and confuciusornithids were advanced in the
brevity of the pelvis in general, and David replied:

<Not of the pubis, though.>

  In *Conficiusornis*, the symphyseal region of the pubis is protracted
posteriorly, but subhorizontally as in *Microraptor gui*, but not as in
*Sinornithosaurus*. The point is that the pubis of *Confuciusornis* is of
a different morphology than the much shorter relative pubis in
*Archaeopteryx* and *Jeholornis*.

  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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