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Re: feathers, hair and Compsognathus



Paul Davis Wrote:

> All the available evidence for the Solnhofen pterosaurs is equivocal to say
> the least.  Unfortunately I do not know about this new specimen so I may be
> wrong.  Other evidence comes from Santana specimens where the skin of
> pterosaurs (at least 3 specimens to my knowledge) has been preserved in  3D
> allowing histological sections to be cut. There are no traces of pelage and
> no traces of epidermal folicles which could be interpretted as 'pelage
> roots'.  However there are sub-cutaneous bundles of fibres.  These bundles
> represent small diameter structures (of unknown composition) rather like
> when hemp/nylon fibres that are twisted together to make ropes.  It has
> been suggested that pelage structures that are observed in Solnhofen and
> elsewhere represent the decay of the skin and these 'bundles' which then
> unravel into their constituent fibres giving the impression that the skin
> was hairy.  Solnhofen isn't the perfect preservation that people assume
> (hence the long standing debate about the wing planiformin pterosaurs).  So
> like I said before the evidence points to unpelageous pterosaurs - so get
> the erasers out!

Why would these sub-cutaneous "wing-stiffening" fibres be present sticking
out of the skin of the neck?  Also, how exactly would they be stiffening the
wing?  From Unwin and Bukharina's less than convincing description, I would
think they would produce a lot of drag and not srengthen the wing at all.  I
would think that an explanation that fits the facts better is that pterosaurs
were indeed covered by some sort of pelage that looked like twisted hemp up
close, but from far away looked like hair, and that on the wing surface of
the wing membrane they created a LOT of drag and evolved to be actually a
kind of "in-grown" hair structure that would have less drag, but still some
drag.  Also something that is thuroughly
unconvincing in Unwin and Bukharina's discription is their insistance that
the legs were indeed in the wings.  I have seen photographs of specimens of
Rhamphorhynchus with it's leg COMPLETELY free of the otherwise perfectly
preserved wing membrane that attatches near the hip.  I unfortunately don't
know how this specimen is identified, but it can be seen in "Ranger Rick's
Dinosaur Book" in the pterosaur section.  If anyone knows any more on this
specimen I'd love to hear about it.

> Because it is useful to do so!  'Birds' must be treated as a derived
> monophyletic clade of dinosaurs with the key synapomorphy of the prescence
> of feathers (it is the only distinguishing synapomorphy that we have
> left!).  IF this specimen of Compsognathid from China does have feathers (I
> am quite happy for it to do so but I want to see the proof first) then
> there are two possible alternatives if you take the ultracladist most
> parsimonious line. 1) All dinosaur above the compognathid node on the
> theropod cladogram are by definition 'birds' or even more extreme but less
> parsimonious 2) All dinosaurs are birds (following ICZN notes on priority
> of names) [Mickey does this list then become Birds.usc.edu ?]

It is ABSOLUTELY NOT useful to stick to the Linnean taxonomic rank of
"Reptile."  It is Doubly paraphyletic.  It is an awful example of Linnean
taxonomy.  Also, birds are defined cladistically as "All the descendants of
the most recent common ancestor of both Archaeopteryx and Corvis", and since
Sinosauropteryx does not fall within that clade, it is not a bird.

> >Same thing.  You are pulling features from groups that aren't that
>related and
> >can't have these features in common (I know they CAN, but you get what I'm
> >saying....).
>
> I just need to say convergence

Convergence could also produce anteorbital fenestrae in turtles, but it's not
very likely, just like it's not very likely that dinosaurs had overlapping
scales.

> >Based on the evidence that NO non-lepidosaur has overlapping scales,
> >AND the fact that birds are theropods, AND this fossil is of a
> >theropod, AND birds have feathers, AND feathers had to start
> >evolving sometime or another; it is more logical to assume that
> >these overlapping things are in fact feathers AND NOT overlapping
> >scales
>
> Logical and parsimonious but is it correct?

I would hope that the most parsimonious assumptions turn out to be correct.

> look at the taphonomy if the above is not equivocal).  In the mean time I
> am going to continue to play Devils Advocate -'cos i enjoy it!

You just wanna ruin our fun : )

Peter Buchholz
gpb6845@msu.oscs.montana.edu

Los Angeles loves love.