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Re: MORE FEATHERS & NEKKID MAMMALS



Jeffrey Martz wrote:

>       We may not have huge samples of dinosaur skin, 
> but we have enough to know that scales were present in at least some 
> sauropods, theropods, ceratopsians, and ornithopods.  Yes, for most 
> specimens we do not have either scale or feather impressions.  However, we 
> KNOW that a lot of adult dinosaurs WERE SCALED, that these scales come from 
> dinosaurs were presumably inherited from these scales from
> scaled ancestors.  ANY feathers within dinosaurs at all are known from TWO 
> SMALL THEROPODS to date (possibly three, when the Paleocanimimus paper comes 
> out).  Might juviniles of the known scaley species have had feathers?  
> Perhaps.

Definately.  We have skin impressions of adult Tyrannosaurs that are scaly, 
BUT Tyrannosaurs fall withing the clade of animals that possessed feathers.  It 
would be illogical to assume that since adult tyrannosaurs didn't have 
feathers, their young didn't either, or couldn't have had feathers.  This can 
be used for the whole ornithodira.  Just because you have scales in adults 
you don't necasarily have scales in the young.  This has been shown to be the 
case with Tyrannosaurs (I'm saying Tyrannosaurs had the potential to produce 
feathers, not that they definately did; although they probably did); and it 
can (and probably will) be shown true for the dinosauria as a whole.

> But modern reptile young do not possess them.

All birds are reptiles and all bird young that I know of have feathers.  If 
you are talking about reptiles in the colloquial "all amniotes that aren't 
mammals or birds" sense, then you're right; but they do not possess them 
because they don't have the potential to.  Baby Tyrannosaurs were probably 
faethered, although the adults weren't.  Some sort of insulative covering is 
present in at least two branches of the ornithodira (pterosaurs and 
coelurosaurs), it would be logical to assume that this insulative covering is 
homologous and that all ornithodirans had the potential to covered in 
insulation and probably were insulated for at least part of their life as 
Tyrannosaurs were (probably).

> In summary:  We know that modern reptiles have scales, we know 
> that modern reptile young do not have feathers, we have a phylogenetically 
> broad sampling of scaley dinosaur skin, we have a couple of feather 
> impressions from a phylogenetically confined theropod group.  What PURELY 
> NON-SPECULATIVE reason is there to beleive that feathers were a 
> wide-spread dinosaur trait, or for that matter present in ANY 
> non-coelurosaur, juvinile or adult?  This may change, but for the time 
> being, Occam's Razor says most dinosaurs were scaled.   

Again, you are using the colloquial reptile.  Birds are reptiles whose young 
are insulated.  The non-speculative reason to assume this is that because at 
least 
two branches of the ornithodira have insulative covering, it is more 
parsimonious to assume that it evolved just once and that all ornithodirans 
had the potential to be hairy or feathered.

I know some do not agree that pterosaurs and dinosaurs form an exclusive 
clade.  I use the term ornithodira in this post as a node-based clade (I 
think it's actually stem-based) joining pterosaurs and dinosaurs.  This clade 
might include crocs, it might not include crocs.  I personally think it 
doesn't...
 
> "Let me guess...he's looking for the perfect dozen."
 
Finally someone's got some taste in movies....

Peter Buchholz
gpb6845@msu.oscs.montana.edu