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Re: Screaming dromaeosaur biplane killers of the air



----- Original Message -----
From: "Jaime A. Headden" <qilongia@yahoo.com>
Sent: Monday, January 27, 2003 1:01 AM

> 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,

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?

> 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*, [...]

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

> <_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

Sure.

> and that may only be
> acheivable by longitudinal extension of the leg.

I'll try to reconstruct this and put it online. :-)

> And we still don't know which, is ay, side is cambered.

Coverts are present, though.

>   I don't presume the thing glided, either.

Ah, sorry.

> The legs, however, may very
> easily have extended posteriorly, [...]

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.

> 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.

Ah, metatarsus. Here I agree that that of Archie is more avian -- or
plesiomorphic, what is the same in this case -- than that of *Microraptor*
and *Sinornithosaurus*.

>   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,

The 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."

> <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,

Monotreme relatives, not marsupials. :-)

> the case is not closed, if Rich et al. are to be believed at all.

The case is not closed, but Rich et al. are IMHO not to be believed, as
their JVP paper is only concerned with the teeth and doesn't even try to
discuss away the trough in the lower jaw that outside crown-group mammals
supported the middle ear. In a eutherian this feature would be a very funky
reversal.

> <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.>

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

>   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: [...]

Looks apomorphic for the latter, doesn't it?

>   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.

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

> <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.

Hm. The picture in http://www.dinosauria.com/jdp/archie/furcula.html is
pretty similar to the furcula of *Confuciusornis*. The latter is more
strongly bent, thicker and rounder, though, but the ventral apex in whatever
oviraptorid it is seems to be composed only of the hypocleidium.

> In *Velociraptor*, it is broad and V-shaped,

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