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Re: feathers, hair and Compsognathus



gpb6845@msu.oscs.montana.edu wrote:

>Paul Davis wrote:
>
>>Actually there is no evidence that pterosaurs are furry
>
>I'm sorry, you are incorrect.  Wellnhofer has identifiied them in quite a 
>large number of Solnhoffen pterosaurs (not just from Sordes, which I know 
>isn't Solnhoffen), AND at this week's SVP he will be presenting a paper on a 
>newly discovered specimen of Pterodactylus that indeed does have pelage on 
>its wings AND on its neck and throat pouch, indicating that pterosaurs were 
>indeed hairy (I can say that right?  Palagey just doesn't sound right).  This 
>pelage canot be explained away as "wing-stiffening" fibers, as Unwin and 
>Bakhurina have done with Sordes' (which I think is a fairly large load of BS, 
>but that's for another time).

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!
 
>> Up to last week all reptiles were not feathered - yet you now believe this
>> to be untrue.
>
>No.... Birds are (unfortunately) Reptiles in the cladistic sense.  Why do you 
>hold so strongly to Linean taxonomic nomenclature that makes up huge doubly 
>paraphyletic taxonomic groupings like the old-style reptiles?

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 ?]


>>> So why not overlapping scales instead?
>Because overlapping scales are a derived Lepidosaur synapomorphy.  _NO_ 
>non-lepidosaur has overlapping scales.  If you found a snake fossil that had 
>overlapping things and said they were feathers, I would say no, they are 
>probably scales because NO non-archosaur (just bear with me) has feathers.  
>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


>You said they look like overlapping *things*.  

Yes but not so overlapping - you can see gaps inbetween the structures

>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 should add that my above answers are not necessarily what my instincts
tell me.  I am quite happy for these structures to be feathers and will
believe when I see a good close -up photo - I only need to see the
branching feather-like morphology to be convinced (and maybe to SEM them to
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!

Paul
-----------------------------------------------
Dr. Paul G. Davis
Division of Vertebrate Palaeontology, National Science Museum, 3-23-1
Hyakunin-cho, Shinjuku-ku, Tokyo 169, Japan.
 
e-mail davis@kahaku.go.jp
Tel + 81 3 3364 2311
Fax. + 81 3 3364 7104
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