Re: Young Allosaur feathers?

["Tim Williams" <twilliams_alpha@hotmail.com>]

T. Michael Keesey <mightyodinn@yahoo.com> wrote:

> 1) Feathery integument first evolved in some tetanuran ancestor of the
> aforementioned unnamed clade.
> 2) Feathery integument evolved even earlier, and _Carnotaurus_ is 
> secondarily "feather"less.

I think (1) is more likely to be correct - though I'd be quite happy to be 
proved wrong (feathered eoraptors, for example).  However the presence or 
absence of a feathery integument in a given taxon may also depend on other, 
non-phylogenetic factors.  After all, _Sinosauropteryx_ has a feathery 
integument; but its kissing cousin _Compsognathus_ does not.  In 
_Compsognathus_, the absence of feathers (especially in a specimen preserved 
in the same depositional environment as _Archaeopteryx_) is likely due to 
secondary loss.

Geographical, seasonal, ontogenetic and size-related factors almost 
certainly impacted upon whether a theropod exhibited the feathery body 
covering of its ancestors.  For example, baby tyrannosaurs may have been 
clothed in down; but they shed their coats by the time they reached 
maturity.  Ditto for allosaurs.  Phylogenetic bracketing has its limitatons.



Tim

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