[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Again: origin of bird flight



An interesting thread has developped in the last 2 days when I didn't have
time to answer...

----- Original Message -----
From: "Tim Williams" <twilliams_alpha@hotmail.com>
To: <kinman@hotmail.com>; <dinosaur@usc.edu>; <twilliams_alpha@hotmail.com>
Sent: Thursday, March 15, 2001 10:14 PM
Subject: Adaptive advantage (was Re: ABSRD BAND on Sinornithosaurus
feathers)


> Let's look at _Archaeopteryx_.  It shows primaries on the manus,
secondaries
> on the ulna, but no remiges on the humerus.  No tertiaries have been
> identified in any _Archaeopteryx_ specimen: the inner arm was devoid of
> flight feathers.

True, but I disagree with the "Pouncing Proavis" hypothesis:
1. It's mantra time: There Were No Trees At Solnhofen. (I don't think 3 m
high bushes are suitable for such pouncing.)
2. *Archaeopteryx* (and *Microraptor*, and even the larger
*Sinornithosaurus* whose skull is only 13 cm long) surely didn't hunt prey
that could be hunted this way. Insects, or, in the case of Archie, fish seem
more probable (and *small* tetrapods in the case of *Sinornithosaurus*).
3. The lack of tertiaries in Archie, and the fact that tertiaries in birds
look like an emergency solution in the first place, is IMHO evidence that
wings were originally used for something else than flight; either pouncing
from above, or, IMHO much more probable, brooding! Have a look at a brooding
oviraptorid; all known specimens have their inner arms closely appressed to
the rib cage, while the forearms and hands are splayed and suggest the
presence of wing feathers, (c) HP Hopp & Orsen 1998.

I'm going to buy that dromaeosaurs may have dragged dead prey up a tree for
safer feeding, like leopards do today and the picture at
http://dinosauricon.com/images/deinonychus-ornithopod-sm.html shows it, but
not much more.

> Also its tail is long and covered in a pairwise
> arrangement of retrices.  Although the tail feathers are asymmetrical, the
> long wide tail is not much good for generating lift.  Excellent for
creating
> drag though.

Or for steering underwater... just like pelicans do today with their stiff
tail feathers. (c) Ebel 1996

The tail feathers of *Archaeopteryx* are symmetrical, unlike its wing
feathers!!!

> Let's look at _Caudipteryx_.  It has primaries on the manus, but no
> pennaceous feathers (remiges) on the forearm or humerus.  It has retrices
> (paired and laterally-splayed as in _Archaeopteryx), but these are
> restricted to the distal half of the tail.  What's more, the symmetrical
> feathers are excellent for producing drag when oriented perpendicular to
the
> air flow (as they would be during leaps to the ground).

AFAIK the wing feathers continued onto the forearms.

> _Protarchaeopteryx_ also has retrices at the end of the tail.  The
forelimbs
> do not show evidence of feathers though (I'm not certain if this is due to
> absence in the living animal, or lack of preservation.)

I attribute this to lack of _preparation_, as seen in the excellent photo HP
Mickey Mortimer shot of it
(http://dinosauricon.com/images/protarchaeopteryx_manus-mm.html, quite large
file, takes time to download).

> The adaptive advantage of stiff, vaned, non-asymmetrical feathers is
clear:
> drag and consequent maneuverability.

Or brooding...
I'm sure symmetry is the plesiomorphy for feathers

> This was the primordial force which
> eventually led to powered flight.  This explains why the incipient flight
> surface (evident in the "proto-wings" of _Caudipteryx_) evolved distally
to
> proximally in both the forelimb and tail.  The incipient flight surface
did
> not first appear close to the body wall (at the armpit) nor equally along
> the entire length of the forelimb+manus - the very arrangements one would
> expect in a glider trying to maximize lift.

Fits underwater flight, too.

> _Caudipteryx_ may not have been at all arboreal, but its ancestors
probably
> were

underwater fliers? :-)

> The obvious terrestriality of
> _Caudipteryx_ and oviraptorids, and troodontids (assuming a monophyletic
> Deinonychosauria) and velociraptorines, would be secondary under this
> scenario.

Just a question here -- is there still anyone on this list who thinks that
the abovementioned groups are not secondarily flightless? :-)

> Chatterjee also suggests that the opisthopubic pelvis and
> semilunate carpal may also be scansorial/arboreal adaptations; both ideas
> deserve further investigation.  (I prefer to regard the semilunate carpal
as
> a pre-adaptation for tree-climbing.)  With this scenario in mind, I would
> like to take a closer look at the claw geometry of _Microvenator_.

Ebel thinks that the semilunate evolved for underwater flight, which is
conceivable, and HP Thomas Hopp thinks it evolved to make tucking the wing
feathers away easier ("brush-odynamic"). It's interesting that the
opisthopubic pelvis is _not_ present in *Archaeopteryx* and *Rahonavis*...

> Anyway, that's my thoughts.  Apologies for the long-winded post -
> considerably more than 2c worth.

Definitely!