[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: New Jeholornis specimen
HP Jaime Headden wrote...
> >Greg Paul (GSP1954@aol.com) wrote:
> <The shoulder glenoid of dromaeosaurs, troodonts, oviraptorosaurs shares
> about the same degree of lateral orientation as Archaeopteryx, so it
> does not provide evidence of relative grade of flight adaptation.>
> Based on?
> I am quite curious about this as it is not actually possible, given
> the crappy means of preservation or flattening in anterior dorsals of
> most known oviraptorosaurs and dromaeosaurids, not to mention that the
> only complete shoulder for a troodontid is part of a juvenile skeleton
> or is undescribed, this data appears to be presumptuous or based only on
> external morphology of the scapulocoracoid girdle rather than the actual
> nature and position it is in (just like you cannot actually tell what
> orientation the shoulder of *Unenlagia* is in because the vertebrae and
> ribs that allow you to articulate the scapulocoracoids are missing).
There are 3D-preserved articulated specimens of various oviraptorids
and *Velociraptor*, at least one of which is illustrated in DA, and their
glenoids point laterally. When troodontid shoulder girdles -- including
the whole coracoid -- look the same, then I think it's a reasonable
assumption that their glenoids were just as lateral as those of the
> <As for the expanded finger base seen in all Jehol dromaeosaurs, no
> other predator has evolved it. It is such a clear flight adaptation
> that all>
> ... other postulated pre-birds that would be secondarily flightless
> don't have it. Or *Archaeopteryx*. So the thing must be either
> convergent (if *Archaeopteryx* is basal to the dromaeosaurs as Paul
> [1988, 2001] hypothesizes) or does not deal much in the actual nature of
> flight, but ust as a mechanical derivative as was actually considered by
> Tim Williams whose relevance to flight was part of a suite, rather than
> by one or two key features.
I see no problem: it's possible to fly without that feature, as Archie
shows, but it's easier with it. Basal dromies sophisticated their flight
apparatus independently from Archie or short-tailed birds (no matter what
the phylogeny, just judging from the age of *Microraptor*/*Cryptovolans*),
and in doing so evolved that expansion. Flightless dromies lost it because
it was useless to them.
In DA (which is 2002, not 2001) HP GSP argues for
-- and like the basalmost dromies, the basalmost short-tailed bird
(*Sapeornis*) has that flange. So in that case it could easily be a
synapomorphy of (dromies + short-tailed birds). -- If the slightly more
usual idea of
is correct, then, yes, the flange should have evolved twice. Likewise if
the normal idea
is correct. (I ignore the equally parsimonious possibility that Archie
could have secondarily lost it -- what for.) -- I don't think it's likely
that the flange is a mechanical reinforcement in a winged wrestler rather
than a flier. The stresses should be similar (well, weaker, but more
frequent in a flier).
> <other possibilities must be ranked as implausible unless really really
> good evidence shows up indicating otherwise. Since basal dromaeosaurs
> had much greater central finger flattening than Arch, and stiffening
> too, and longer primaries relative to the hand, this is superb evidence
> of more, advanced flight.>
"Superb" may be an exaggeration, but yes, of course it is evidence of more
> Except they didn't have the feathers, as in *Sinornithosaurus* TO fly
Err... uh... ummm... *Microraptor gui* has exactly such feathers, and Dave
has remiges of unknown length.
> much less the sternal size,
As HP GSP shows in DA and elsewhere (beautiful illustration, as usual),
the sterna of *Sinornithosaurus* are comparatively as large as those of a
kiwi -- and a lot larger than those of Archie.
> much less the other "flight-related features" that *Archaeopteryx*
> shares with birds that are not present in *Sinornithosaurus*.
As I mentioned above, Archie and short-tailed birds sophisticated their
flight independently from basal dromies.
And what exactly are those features?
> <To argue otherwise is too dismiss powerful evidence on an arbitrary
> basis and is not really scientific.>
> Let's not argue what is scientific,
In that case, IMHO the scientific thing to do would be to make a great big
analysis in which all these characters (and lots more) are coded, and then
to make a tree of it, and then to interpret that tree.
> when the discussion in Paul, 2001 [sic], as discussed earlier on this
> list, involves a great deal of _a priori_ assumptions of what the
> ürvogel [sic] really is, and what a flight related character really is.
> <There are so many advanced flight features in avepectoran dinosaurs
> that far and away the best explanation is advanced relative to Arch
> flight, it's way beyond mere parsimony.>
I don't think so. (For example, the argument that dromies are closer to
unquestioned birds than [to] Archie is based on a parsimonious
distribution of the character discussed above.) But let's try. Let's take
the data gathered in DA, and shoved them into PAUP*, NONA, Hennig86 or
whatever. Given that data set, I think it's likely that something similar
to the conclusions of DA will emerge.
(Might become my diploma thesis 2 years from now, but I won't
regard it as scooping when someone who, say, has actually seen the
fossils, or at least has enough time, does it in the meantime... :-) )
> I think Williams will agree here, given that this only argues about
> flight performance and ability, not about avian origins, and the
> departure of functional anatomy and phylogeny is one thing that needs
> to be considered.
I don't completely understand this sentence, but probably I agree.
> Birds are not defined, nor should they be, by their ability to fly,
Was anyone talking about that?
> The possible multiple
> origins of flight have not, I believe, ever been discussed in print.
Well, the possibility of this is repeatedly mentioned in DA. I haven't
seen it elsewhere either, though. Wait, once, in a pretty confused paper
that starts from the assumption that FUCHSIA, as originally published, is
Don't ask what you can do for your country.
Ask what you can do for your mother.
-- Author forgotten
+++ GMX - Mail, Messaging & more http://www.gmx.net +++
Bitte lächeln! Fotogalerie online mit GMX ohne eigene Homepage!