Re: AW: Tawa hallae: everything you know about basal saurischians is wrong...

[Tim Williams <tijawi@yahoo.com>]

Evelyn Sobielski <koreke77@yahoo.de> wrote:


> http://www.guardian.co.uk/science/2009/dec/10/tawa-hallae-feathered-
> theropod-mexico
> 
> Is there any evidence for this claim?


I agree with Augusto on this one.  The bipedality and high BMR inferred for 
_Tawa_ and other early saurischians lends support to the presence an insulatory 
body covering.  Also, I know that the homology of these structures has been 
questioned, but the presence of fuzz/down/hair-like integumentary structures in 
representatives of Theropoda, Ornithischia and Pterosauria does at least make 
you wonder how pervasive these structures were.


> (And has anybody ever checked GenBank whether the "feather"
> genes have some sort of viral signature? A "domesticated"
> papillomavirus or similar would explain the structurally
> different but physiologically somehow related - as
> integumental hyperplasies triggered by a fairly simple
> genetic mechanism, essentially - structures phylogenetically
> widespread among archosaurs. But its genetic "footprint"
> would be obvious, and thus this assumption could be
> tested.)


Sorry, I'm having a hard time interpreting what you mean here.


> Nonwithstanding, I find the notion of sticking feathers
> everywhere a bit dubious; eventually it's likely to result
> in major embarrassment and a lot of cheering from BANDits.
> Feathers/fuzz and large-bodied animals living in a tropical
> climate and well on their way to homothermy do not at all
> mix well. Phylogenetic bracketing is also unhelpful with
> such a limited sample of hard evidence; _Elephas_ and
> _Heterocephalus_ for example would provide a nice bracket
> that "proves" all mammals, big and small, are almost nude,
> if we did not know as many mammals as we do.


Doesn't this argue against your point?  Big mammals have secondarily lost their 
extensive hairy body covering.  If the dino-fuzz in _Tianyulong_ is homologous 
to the feathers (and proto-feathers) of theropods, then it is pretty much 
guranteed that this kind of integument is primitive for dinosaurs.


> Absence of quill knobs (and possibly rectrical knobs, which
> are as of yet unknown but might conceivably have evolved as
> alternative to a pygostyle) in a large-bodied non-polar
> non-flying archosaur, I'd presume, is strongly indicative
> that the critter had no integumentary fuzz, feathers or
> bristles to significant extent.


Some modern flying birds lack quill knobs.  _Velociraptor_ has quill knobs, and 
it didn't fly.  So again, sorry, your point escapes me.   


Cheers

Tim