Re: A therizinosauroid dinosaur with integumentary structur

[<TWILLIAMS@canr1.cag.uconn.edu>]

> 
> There's something I don't understand. Given this phylogeny ...
> 
> --+--Compsognathidae (bristles)
>   `--+--+--Therizinosauria (bristles)
>      |  `--+--_Caudipteryx_ (feathers)
>      |     `--Oviraptorosauria (integument unknown)
>      `--+--_Protarchaeopteryx_ (feathers)
>         |--Deinonychosauria (integument unknown)
>         `--Avialae (feathers)
> 
> ... true feathers would have evolved twice.  

I remember hearing on this list that one of the mononykines also 
shows direct evidence of feathers (or some kind of feather-like 
integumentary structure).  Was it _Shuvuuia_?  And then there's 
_Avimimus_ which shows strong, but indirect, evidence of feathers.

I was thinking that maybe "integumentary structures" (bristles/ 
protofeathers, feathers) may not be a very reliable indicator of 
relationships within the Coelurosauria.  Here's why:

Small dinosaurs may have been more likely to have had 
an insulatory body covering because of their high surface-area-to- 
volume ratios (which makes them lose endogenous body heat easier).  
For some species, the juveniles may have had such a body covering, 
but shed it when they reached a certain age (and size) so the adults 
were "naked".  Species with a small adult body size may have been more 
likely to retain their bristles/feathers throughout life.

Even closely related genera may have differed in this respect.  
_Sinosauropteryx_ (a compsognathid) did have a bristly body covering, 
_Compsognathus_ apparently did not.  The presence or absence of such 
an insulatory layer may have also depended on climate, habitat, 
lifestyle.  It may even have been seasonal.  Maybe the two known
_Compsognathus_ specimens died in the summer?  (I've been to Munich 
in July - it can be darn hot!!!)  :-)


Tim