RE: Pygostyle-like structure from Beipiaosaurus

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Ronald Orenstein
>
> At 10:27 PM 12/10/03 -0400, Nicholas Gardner wrote:
> >--- Ronald Orenstein wrote:
> >>Undoubtedly this will fuel the idea that these critters are secondarily
> >>flightless birds (which will mean, I suppose, that Feduccia et al will
> >>argue that therizinosaurids are not dinosaurs).
> >>
> >
> >And of course, that will only make their argument look more and more
> >ridiculous. ^_^
>
> But - phylogeny aside - what exactly would a pygostyle have been
> for if not
> to support some sort of structure more elaborate than Beipiaosaurus'
> filaments?

One thing to be concerned with, though, is exactly HOW filamentous the
plumage of Beipiaosaurus was.  After all, the type of Sinornithosaurus'
plumage seems to be simply filamentous, but other specimens of the taxon
("Dave") and related taxa (Microraptor) show that dromaeosaurids do have
pennaceous remiges and retrices. I agree that the long shafts along the ulna
of Beipiaosaurus seem too wavy to have been the more rigid rachides (=
plural of rachis) of pennaceous feathers, though.

Also, although I haven't seen Beipiaosaurus' pygostylar structure, that of
Nomingia is by no means as extensive as those of pygostylian birds, at least
basally, so it isn't that likely that it supported a retricial bulb.

>  Might this not be at least suggestive that (like kiwis and
> moas, for example) this animal may have secondarily lost a more
> complex set
> of epidermal tail structures?

Indeed: that is, if it they really weren't present!  (Which they might have
been).


                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
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