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Advanced Features of Birds
At 01:48 PM 9/25/96 -0500, Betty C. wrote:
> And further, how does Confuci-etc's muscle development compare to
Better question: Can we really reconstruct these muscles well
enough to tell?
>similar in both; is Archie more developed than Confuc-etc; or is
>Confuc-etc more developed (and thus, supposedly a better flier) than
Devlepod? You mean closer to modern birds? Yes. Does that make it
a better flier? If we could determine this, we wouldn't be having these
discussions. See rant below.
>Is there enough of Protoavis to determine if HE was better or
>worse than either?
No. There isn't enough to prove it was a bird, by some people's
reckoning. The most convincing bits of it, so I understand, the most
important, and further, the most diagnostic, are in the braincase, which
won't tell you much about flight capability.
> Since Archie is now only one of several types of early birds, is there
>enough to compare them to each other, as opposed to modern birds? How do
Oh yes, it's all the rage!
>the pub[e]s compare to each other? Can we tell if at rest, some were
They seem to get progressively smaller and more backtrned in
more modern-looking specimens (I haven't read Confusciornis, maybe
>setters (like ducks) and some were perchers (like song birds)?
I don't see how this would matter, but one of the
early-bird-of-the-month-club, Sinornis, I believe, was billed as the
earliest "perching bird". As for "setting", if I understand correcly, that
is probably a more modern adaptation that isn't going to be very relevant to
early bird evolution.
>How do the lengths of the tails compare to each other?
Archy: long. Sinornis: shorter. One thing that does come up is
that early birds apparently developed the adaptions required for powered
flight *without* the development of the pygostyle [sic].
>Are some of these early bird types more developed in this tail
>region (and thus muscular) than others?
I guess this correlates inversely with tail reduction. More samples
might give some sort of variation, and I'm not really sure what you mean by
"developed". We just have so few species of these *really* primitive birds
that it's hard to really say what was going on (but we have enough
Confusciornises that they can be smuggled out of China and sold here).
>Are these the earlier forms or not?
With long tails? It seems so, although it sounds to me like some of
the more "primitive" birds were still cruising around when more "modern"
birds showed up.
>How does one tell if a change is an 'advanced characteristic' if it's a
>transition between two distinct types?
If you mean for phylogeny, you find an "outgroup", an animal closely
related to the taxa you are analysing and see what the state is in that
animal, and you do this again, and the state which prevails in the outgroups
is the primitive state (this is a very simplified explanation). the other
state is the "advaced" state. A state in between might be coded as a
multi-state character, or as two characters, where those with the
intermediate show one derived character, ad those with the full state show
two. Of course, if you're doing phylogeny, you don't call it "advanced",
you call it "derived".
To apply this to the discussion of bird flight, I would point out
that the features we commonly identify as "advanced" are simply derived
features of successive clades leading to modern birds. Pygostyle, ossified
keeled sternum, furcula, reversed hallux, possibly feathers, etc, most
everything people have sworn up and down is required for flight, all seem to
have come about at one point or another as an innovation of one or more
groups of flying or unflighted theropods.
The only character which we can positively and undeniably correlate
with flight, flight feathers, starts at Archaeopteryx and work their way
down. The "advanced characteristics" may be refinements which may have made
subsequent members of the clade better flyers, or they may have happened for
other reasons (weight economy, developmental economy, etc). We cannot prove
that their absence made these "primitive" forms less flightworthy.
I don't know what you mean about the transition. The idea of
transition probably will not come into play in a fossil. The animal in
question is using that feature to some effect, and that is all. Maybe later
it will be refined. Think of it this way, to Sinornis, or whomever it was,
that half-pygostyle *WAS* "advanced". It somehow represented an improvement
in one of Sinornis' ancestors' lives. Once again, gross oversimplification.
>Only by the end results? If
Still depends on what you're looking for. It seems that many of the
people who study bird origins, at least those on one side of the fence,
haven't really kept up with current evolutionary and paleontologic thought,
and some of the stuff that comes down the pike isn't exactly cutting edge.
If you're looking for an answer to "how do I rate my fossil bird on the
scala natura", just look at how many features it shares with modern birds. :)
>having a well-developed butt is advanced in therapods but not in birds,
>is losing it advanced or not?
Losing a derived characteristic is going to result in a state more
derived than never having developed it. Once again, "advanced" is a
different question, and you'll have to ask an evolutionary systematicist.
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