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RE: Avian Monophyly (Was Re: Sheesh)... :-)



> Yes, true.  I would even go a little further and say
> that Archie couldn't 
> perch at all.  That's not to say that it wasn't
> arboreal, though.

Leopards spend much of their time loafing in trees but
they can't perch (I'm saying leopards for a reason -
see below). And Archie wouldn't have needed to perch:
it had hands. Not fully functional, but still hands
with discrete fingers.

> I think this alleged non-monophyly of Aves is a
> storm in a teacup.  The 
> Science paper by Mayr et al. (2005) implies that the
> monophyly of Aves is 
> challenged if _Confuciusornis_ is shown to be closer
> to traditional 
> non-avian taxa (like dromaeosaurids) than to
> _Archaeopteryx_.  But Aves, by 
> definition, is monophyletic.  All that happens under
> the proposed cladogram 
> is that some additional taxa (dromaeosaurids &
> troodontids) get scooped up 
> into Aves, which in turn suggests that secondary
> loss of flight occurred in 
> certain taxa close to the base of the Aves.

I'm more comfortable with a multiple-origins-of-flight
scenario than with a secondarily flightless
Caudipteryx, to be sure. To throw out Confuciusornis
from the "main" avian lineage would not really do harm
- it *could* be a more birdlike derivate along the
lines of Archaeopteryx, but the diapsid skull is,
well, *interesting*... Apart from that, I see not much
in Confuciusornis that does not come close to some
Archie-like form elaborating a bit on the theme of
flight - if I interpret the feather impressions
correctly, Confuciusornis wouldn't have made too bad a
glider/soarer in fact. Its wing shape was odd, but
closest to today's albatrosses etc. It was not a
flapping flyer for sure.

As to why I'd prefer multiple flying lineages to "one"
(Microraptor is almost certainly another), I find it a
better way to explain the diversity of modes of flight
that were sort of "tried out".

Basically, I imagine the maniraptoran lineage
branching off ever so often flying clades, flying with
increasing sophistication. Even pygostyles now appear
not to be synapomorphic (i.e. evolving only once). But
from a certain point on, say some 120 mya, it was all
but said and done - the to-and-fro between bird-ness
and non-avian-theropod-ness ended and the flying
lineages either did something completely different (if
they arose anew, a la Microraptor) or had avian flight
a la modern birds (Enantiornithes and ornithurans),
with some losing flight again (Patagopteryx,
Hesperornis). But it is a sort of half-full vs
half-empty thing: if you are half-way on your way to
flying, does that make you a bird? I'd say no. That
Confuciusornis, Liaoningornis and Yanornis (the other
half of "Archaeoraptor" were almost contemporary and
sympatric but as far as anyone can tell not close at
all to each other and differed vastly in flight
adaptation is not easily to reconcile with an "a
common flying ancestor for all birds sensu lato, even
including Microraptor" scenario.

> I'd say Archie was facultatively arboreal and mainly
> terrestrial.

The main problem with that would be competition. It
was not the best of runners. I like a scenario as
outlined by Elzanowski in "Mesozoic Birds": Archie
using its wings to gain successively higher perches,
mainly as an escape mechanism, by a glide assisted by
a few lukewarm downstrokes. As to the "Leopard" from
above, the arrangement of digits and claws in Archie
would enable it to climb vertical trunks as these do:
using either feet or hand claws as anchoring and push
or pull up with the others. The foot morphology as
displayed by the Thermopolis specimen would in fact be
ideal for that. Think of the ecological niche of large
geckos - or the Draco lizards. Archie was certainly
not able to rely upon being able to take off from the
ground in a pinch. Its adaptations to me make most
sense if you imagine it having its "main base" on tree
trunks and lower branches, going up and down from
there as the situation permitted to forage etc.

Add another twist: who says there was much firm ground
to speak of in its habitat? It might have been
something not dissimilar to a Floridan cypress swamp,
only more saline. The preservation state of Archie
fossils at any rate suggests that they died not very
far from where they were buried (i.e. shallow coastal
waters, but not the mud of a nearly-dry lagoon - the
backward-bent necks and tails seem to preclude that).

Regards,

Eike


                
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