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RE: coelophysis



For some background on _Juravenator starki_, see
http://lancelet.blogspot.com/2006/03/juravenator-and-complex-pattern-of.html
http://www.nature.com/nature/journal/v440/n7082/fig_tab/nature04579_ft.html
 
The figures include the feathered theropod cladogram:
http://www.nature.com/nature/journal/v440/n7082/fig_tab/nature04579_F4.html#
figure-title
 
If _Juravenator_ is neither a compsognathid nor a coelurosaur, then the
absence of feathers on parts of the tail and legs would be less surprising.
We don't know whether _Juravenator_ sported feathers elsewhere on its body
that simply weren't preserved.

Regarding whether the absence of feathers in the large theropod,
_Carnotaurus_, represents the secondary loss of feathers due to its size, we
don't know.  The patch of _Tyrannosaurus rex_ skin fossil we have is the
size of a playing card, and we don't know what part of the body it came
from.  _T. rex_ may have retained feathers over much of its body, but not on
the small patch of skin represented by the skin impression fossil.

It is also questionable whether a scaly theropod descended from a fully
feathered theropod would sport fully formed tubercular scales comparable to
those of dinosaurs which had not gone through a feathered stage.  Ostrich
thighs are featherless, but they appear to sport naked skin with sparse
bumps more resembling the skin of a plucked bird than the tubercular scale
pattern of _Carnotaurus_.  Chickens bred in Israel to be virtually
featherless don't look scaly either (aside from the feet).  Of course,
theropod feathers originated a long time ago, so maybe it is too much to ask
that a modern bird be able to retain the ancestral scale texture when it no
longer grows feathers.  But if feathers originated in theropods prior to
their secondary loss in the lineage leading up to _Carnotaurus_, who is to
say if the tubercular scale genes would be functional or activated in
_Carnotaurus_?

If secondarily featherless large theropods sported skin like that on the
ostrich thigh, then _Carnotaurus_ was not a secondarily featherless large
theropod, and the notion that _Coelophysis_ sported feathers would not be
supported.

There are many unknowns here, but I would still guess that _Coelophysis_,
being such an early theropod, was scaly, not fluffy.    

Dino Guy Ralph
Docent at the California Academy of Sciences
Dinosaur and Fossil Education
Member of the Society of Vertebrate Paleontology