Re: Journal of Negative Results -- Ecology & Evolutionary Biology

[evelyn sobielski <koreke77@yahoo.de>]

--- "T. Michael Keesey" <keesey@gmail.com> schrieb:

> On 1/28/07, evelyn sobielski <koreke77@yahoo.de>
> wrote:
> >
> > The lack of anything avian from the
> > Morrison Fm.
> 
> First of all, which definition of "Aves"? I assume
> sensu Chiappe (=
> clade(Archaeopteryx + Aves sensu stricto))? Or sensu
> Marjanovic (:=
> clade(Vultur <-- Velociraptor, Troodon, Oviraptor,
> and a buttload of
> other traditionally non-avian specifiers))? (Clearly
> not sensu
> Gauthier, i.e., the crown group.)

OK, got myself tangled up here. Meant "bird". I.e. =
the old definition = the form "taxon" = sensu Chiappe
but only volant (or secondarily flightless) forms.
Basically the questionable conception of birds as a
monophyletic lineage "starting" with Archie.
Regardless of the actual phylogeny, any such critter
would shed some light on the problem.

> Second of all, as I recall there's undiagnostic
> eumaniraptoran
> material from the Brushy Basin Member that could be
> avian sensu
> Chiappe or sensu Marjanovic (please correct me if
> I'm wrong).

Aha! Any reference?

> Its position seems about as volatile as that of
> Archie, but anyway, it
> occurs far too late to tell us anything geographic
> about the origins
> of flight.

Not necessarily so. If my assumptions are correct, it
is simply a Johnny-come-lately. Confuciusornis seems
uniquely and peculiarly advanced; clearly, an
aerodynamic shape most similar (but not very similar)
to swifts does not drop out of thin air. So that
lineage seems to have quite some evolutionary history
behind it. And if Mayr et al's assumptions about a
closer relationship between C. and Microraptor are
correct... M. might represent a primitive
morphotype/flight adaptation of the same lineage, but
how to get from something where the tail seems to play
a major role in flight, long, bony and feathered as it
was, to something where the tail's only significant
role in flight *might* have been that of a vortex
generator similar to its role in needletails today is
beyond wht I'd want to imagine.

Suffice to say that it *appears* as if tree-down vs
ground-up (with all their modifications, such as
cliff-jumping etc) today seems a fair bit of
oversimplification. It has been shown that either is
entirely conceivable, and I wouldn't be dumbfounded if
both general approaches were in fact realized.
Rahonavis, despite its outward similarity to Archie at
first glance, seems a much better candidate for
ground-up than Archie for the simple reason that long
stretches of open ground seem to have been scarce in
Tithonian Solnhofen, judging from the biota, the
sediment, and the fact that Archie specimens are in
association (meaning that death cannot have occurred
far from the deposit site) which all point at some
sort of "mangrove"/archipelago/shore ecosystem. But
this is tentative; I'd have to look closer into the
taphonomy of the Maevarano Fm. The proposed
unenlagiine affiliarion of R. would also tentatively
support a ground-up scenario (the possibility of
undiscovered unenlagiines from Africa, small enough to
climb, must be taken into account however).

> It's also not a given that Archie was capable of
> powered flight.

Ah, the eternal question... I'd put it "active" rather
than "powered", because it was capable of a downstroke
which near-certainly could generate significant lift.
So there seems to have been a powered component to its
flight, but how large that was is debatable.

Regards,

Eike


                
___________________________________________________________ 
Telefonate ohne weitere Kosten vom PC zum PC: http://messenger.yahoo.de