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RE: Ah ha! That's where therizinosaurs came from



  Even then, the argument that has been made since the early days of this 
discussion was that regardless of whether *Archaeopteryx lithographica* could 
fly, if it did, it could have descended from a yet earlier form that _could 
not_, thus explaining its features as _convergence_. Even given the phylogeny, 
it is not an _ancestor_, but a sister taxon, or whatever clade it is in. That 
and that point alone eludes those who prefer typological and phenetic phylogeny 
reconstruction over cladistic. So the argument about flight here is a red 
herring. It doesn't matter if _it_ could fly, but that the taxa it is nested 
with could, and that the sister taxon to whatever flying clade might be 
proposed for it could.

  If we follow the phylogeny of Xu et al. (2011), Archie is at the base of a 
group of taxa which have been purported to fly, to varying degrees, or to be 
gliders. They are themselves sister taxa to a group that, for all intents and 
purposes, lack this quality of gliding/arboreality and tend to shorter arms (if 
*Anchiornis huxleyi* is not a troodontid) with weird legs or something, and 
who've also been proposed as _gliders_ (e.g., *Microraptor gui*). The sister 
taxon to this group is *Avialae* in the conventional sense, and we've got 
further purported fliers there, and outside that we've got honest-to-goodness 
cursors in a thread going _waaaay_ down the lineage of *Theropoda*. Since 
flight performance for these taxa has been ambiguous in even the _recent_ 
literature, it is becoming difficult to ensure that Archie is bracketed by 
flight, and thus inferring it is problematic.

  If we choose, instead, to follow other phylogenies analyzed through cladistic 
methods, then Archie is the sister taxon to a long-stem of less-questionably 
flighted forms, and outside that we have gliders, followed by cursors. Flight 
is less of an issue here, since it infers a clinal gradient toward acquisition 
of ever increasing mobility at the shoulder and larger pectoral musculature, 
leverage of the limbs and their rigidity seems to increase while bearing large 
feathers, and the tail is shortening with yet more torsion-resisting fusion 
occurring at the end. These things are generally absent at the base, but 
increase in frequency and emphasize away from Archie, and some of them converge 
in lineages for which their basal members lack (oviraptorosaurs), never have 
(troodontids without *Anchiornis huxleyi* or dromaeosaurids with unenlagiines 
at the base, depending on the position of *Rahonavis ostromi,* although absent 
in *Buitreraptor gonzalezorum*), or are again ambiguous (dromaeosaurids where 
microraptorians are at the base).

Cheers,

  Jaime A. Headden
  The Bite Stuff (site v2)
  http://qilong.wordpress.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 
Backs)


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> Date: Tue, 16 Aug 2011 16:54:47 +1000
> From: tijawi@gmail.com
> To: dinosaur@usc.edu
> Subject: Re: Ah ha! That's where therizinosaurs came from
>
> <GSP1954@aol.com> wrote:
>
> > One reason I realized that dromaeosaurs were likely to be neoflightless
> > was
> > because when I examined the Eichstatt specimen in 81 was it was plain as
> > day that the palate was theropodian not avian in grade, so that did in the
> > argumment that it was a "bird" more derived than dromaeosaurs since Archy
> > does
> > not have a whole lot else indicating it is closer to modern avians than the
> > sickle claws. I also learned on the same trip that dromaeosaurs had
> > ossified
> > uncinates and sternal ribs in addition to the big sternal plates and
> > pterosaur like tail also absent in Archy, plus the folding arms. I figured
> > I would
> > just wait oh about 30 years for the winged dromaeosaur fossils to show up
> > supporting the hypothesis. So it's a mixture of flight adaptations and
> > phylogeny.
>
>
> Assuming that _Archaeopteryx_ is closer to dromaeosaurs than to birds,
> the "neoflightless-ness" of dromaeosaurs only holds if _Archaeopteryx_
> could actually fly. The discovery of winged dromaeosaurs contributes
> little if anything to the "neoflightless" hypothesis, since it only
> shows that a common ancestor of _Archaeopteryx_, dromaeosaurs, and
> birds had wings - not that it was volant.
>
>
> As for "folding arms" being an indication of flight ability (or former
> flight ability).... let's not get carried away. Some
> limited/incipient arm-folding ability, as conferred by a trochlear
> semilunate carpal, is widespread among tetanurans, including
> _Allosaurus_ (Chure, 2001), _Tanycolagreus_ (Carpenter et al., 2005; =
> hand originally referred to _Ornitholestes_), and many, many more.
>
>
>
>
> Cheers
>
> Tim