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*Archaeopteryx* Bros.



----- Original Message -----
From: "Tim Williams" <twilliams_alpha@hotmail.com>
To: <Dinogeorge@aol.com>; <dinosaur@usc.edu>
Sent: Thursday, March 15, 2001 11:31 PM
Subject: Re: ABSRD BAND on Sinornithosaurus feathers


> (_Sinornithosaurus_'s ancestors, if semi-arboreal, may have
> used their feathers for drag as well.  But I like the idea that
> _Sinornithosaurus_ may have been partly arboreal too - those long arms,
with
> a trailing edge of feathers, may have been excellent for co-ordinated
> branch-to-ground leaping).

In this case, not "Mantra: Give me more fossils", but I always wonder why
Liáoníng fossils are so incompletely prepared. At present, it is really
possible (though improbable IMHO) that *Sinornithosaurus* had substantial
wings.

> Unlike _Archaeopteryx_, the early evolution of modern birds focussed on
> increased locomotive efficiency in the air.  The tail got shorter.  The
> manus lost its prehensile and raptorial function - manipulation of prey
> might sully the wings, and protecting the integrity of the wing became of
> paramount importance to metornithines.

Pygostylians.

> The teeth were lost (to reduce weight?).

This came late, and 3 times independently (Confuciusornithidae,
Enantiornithiformes or so, Neornithes). All other pygostylians had teeth.
BTW, mammal teeth are really heavy, but bird teeth... hm...

> [...] Archie's mosaic morphology is best
> explained by the fact that it was adaptively advantageous to retain the
> predatory and cursorial abilities of its maniraptoran ancestors.
> Maniraptorans were the consummate predators of the Mesozoic.  Why mess
with
> success?

Never change a running system!!! "Stabilising selection" in action.

> Keep the enhanced predatory capabilities of maniraptorans, and
> evolve flight to increase the animal's versatility as a predator (e.g. to
> swoop down from the trees onto prey below; increase the theropod's hunting
> range; escape from larger predators by flying away.)

Sounds like a good idea on the ecological niche of *Rahonavis*.

BTW, I have copied the Nature article "An Early Cretaceous pellet" which was
mentioned onlist some weeks ago. "Bird 1" has a very large claw on its 2nd
toes (larger than those of confuciusornithids); it is only seen in dorsal
view, so I can't say whether it was curved or straight, but it looks a lot
like a sickle claw. (The foot _is_ avian, as the long, retroverted hallux
unambiguously shows.)

> The success of the _Archaeopteryx_ "grade" of evolution is shown by the
> record of very similar birds in the Cretaceous - _Proornis_ and
_Rahonavis_
> (which lived close to the end of the Mesozoic).  Basal avialans didn't go
> kaput at the end of the Jurassic; in the Cretaceous they lived alongside
> metornithine (non-basal) avians that sacrificed certain features (retained
> in Archie and kin) for improved aerodynamic efficiency.  Metornithines
took
> a punt that clawed hands, a long tail and long legs could all be dispensed
> with for the sake of improved flight performance - and it paid off.
> _Archaeopteryx_ / _Proornis_ / _Rahonavis_ took a different route.

Does this mean you know what *Proornis* looks like? How... when... where...
:-9

Anyway, this is a case of "give me more fossils"...