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Re: Psittacosaurus bristles



REPLY: Actually, I read the paper (twice), and have a
print of the photograph of the actual specimen which
Gerald provided me with, after their preliminary
report was published in Naturwissenschaften. I
appreciate your providing an exegesis of my thoughts
on integument morphogenesis in dinosaurs without,
first, discussing them with me, saving me the time of
saying anything. Such are the marvels of psychic
cyberia.  I wrote: "The paper gives one the [or "a"]
likely indication". I see no reason to alter the
formulation. Indeed, further analyses are needed, and
find it intriguing that, perhaps, the "evolutionary
novelty" of feather-like structures were perhaps
present on one ornithischian taxon. However, I would
be quite surprised if theropod feathers (as
capitulated by Dick Prum and Alan Brush in their
paper) were convergent in ornithischian dinosaurs, and
believe (infer) that (again using Prum/Brush as a
paradigm) ornithischians did not have the various
structures (including feathers) discernable among the
theropods.  If, however, it can be shown that
accessory integument structures (with careful
understanding of the diagnoses of the structures
involved) were demonstrably present in non-saurischian
dinosaurs, then another synapomorphy of Dinosauria
would have to be articulated.
--- "Jaime A. Headden" <qilongia@yahoo.com> wrote:
> Stephan Pickering (stefanpickering2002@yahoo.com)
> wrote:
> 
> <A thorough analysis of the structures was
> published, with photographs, by
> Gerald Mayr. Gerald Mayr, D. Stefan Peters, Gerhard
> Plodowski, Olaf Vogel,
> 2002. Bristle-like integumentary structures at the
> tail of the horned
> dinosaur Psittacosaurus. Naturwissenschaften
> 89(8):361-365.>
> 
> ...
> 
> <What do "these things" mean? The paper gives one
> the likely indication.>
> 
>   Actually, Mayr et al. are not very certain what
> these are aside from
> integument, and forward their opinion that these
> have nothing to do with
> avian integumental structures. That some of the
> structures appear to touch
> bone is possible evidence of dermal displacement in
> the carcass, but this
> is not discussed, and the authors sorta ignore the
> possibility of shifting
> of the skin around the carcass during the deposition
> process, which would
> result is a problematic relationship of "bristles"
> to bone. They indicate
> a relationship of bristles to the dorsal line of the
> tail based on
> apparent origins for more elements, and the
> orientation of the tail.
> Histological sections, which would be ideal, have
> not been performed. To
> quote from the paper (pg. 354):
> 
> "If the "bristles" of *Psittacosaurus* can be shown
> to be homologous to
> the filamentous structures of theropod dinosaurs,
> similar structures may
> have already been present in a more comprehensive
> clade including
> ornithischian dinosaurs. At present, however, this
> conclusion would be
> premature and more detailed investigations on the
> microstructure and
> biogeochemistry (Schweitzer et al. 1999; Schweitzer
> 2001) of the
> integumentary structures of Psittacosaurus and
> theropod dinosaurs need to
> be carried out. Without further evidence, there
> remains the possibility
> that the "bristles" of Psittacosaurus are greatly
> modified scales, as has
> been suggested by Reisz and Sues (2000) for the -
> structurally different -
> appendages of the Triassic reptile *Longisquama*."
> 
>   The paper itself, as acknowledged by the authors,
> is a very preliminary
> report offered because of the increased interest and
> debate caused by the
> specimen, despite the fact that ownership was under
> dispute. We may not
> see more if and when the material comes under the
> provenances of the
> Chinese. Junchang Lü has already done work on
> pterosaur integument and it
> is possible he will be able to further research on
> this if it comes to
> China ... soon.
> 
>   Cheers,
> 
> =====
> Jaime A. Headden
> 
>   Little steps are often the hardest to take.  We
> are too used to making leaps in the face of
> adversity, that a simple skip is so hard to do.  We
> should all learn to walk soft, walk small, see the
> world around us rather than zoom by it.
> 
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