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Re: Where did birds come from in their evolutional process?



Matsunari Takahiro wrote:

> ..."But I heard that a
> fossil of Ornithischia which has traces of feathers (parrot-dinosaur ?) was
> found in China.

There is an article in Volume 2 of _DinoPress_ magazine (a Japanese publication;
see <www.dinopress.com>) by Ryuchi Kaneko which covers the 5th Society of Avian
Paleontology and Evolution that took place in Beijing in May and June 2000.
According to the report, a Liaoning _Psittacosaurus_ specimen was exhibited at
the Yizhou Fossil Museum in Yi, which attendees visited.  _Psittacosaurus_ means
"parrot lizard," and is said to be the most common dinosaur found in the
Liaoning region (according to the Kaneko paper).

On page 87 of the article are two views of a _Psittacosaurus_ specimen, which I
suppose is the same one mentioned in the text.  The lower photograph, labeled
"_Psittacosaurus_ (skin impression)," shows a large patch of skin texture along
one of its forelimbs (along the humerus).  It is tubercular, that is, composed
of a pattern of polygonal nonoverlapping scales, much like the texture on the
side of a crocodile.  This is the typical dinosaur tubercle texture, nothing
like the filaments that adorn the feathered non-avian coelurosaurian theropods
of the Yixian Formation.  I have not seen the specimen in person, but it
certainly appears to contradict your statement.

I don't know where you got the information that there is a feathered
_Psittacosaurus_ specimen.  Perhaps there was a misunderstanding.  I am unaware
of any feathered ornithischian dinosaurs.  So far as I know, as far as dinosaurs
are concerned, there is only evidence for feathers and filaments among the
theropods (including birds).  A number of ornithischian skin patterns have been
fossilized, but no ornithischian feathers or filaments.

Even among theropods, _Carnotaurus_ sported tubercular scales, but _Carnotaurus_
was not a coelurosaur, so it is less closely related to birds and less bird-like
than those theropods found with feathers or filaments.  Very small skin
impressions have been reported for tyrannosaurs, again with a tubercular
pattern, which is somewhat surprising.  Even so, the finding of a large patch of
scale impressions along the _Psittacosaurus_ humerus appears to me to be
somewhat more telling, as the forelimbs of birds and feathered non-avian
theropods tend to be generously covered in feathers or filaments.
Unfortunately, I cannot judge from the photograph whether the specimen exhibits
skin impressions elsewhere on the body.

-- Ralph W. Miller III   ralph.miller@alumni.usc.edu