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RE: Senter 2006, Confuciusornis, and humeral mobility



> >   An abstract "hypertrophy" term is meaningless to
> me. I suspect it is to
> > everyone else. It is only meaningful to use as a
> referent from another
> > condition.

Not necessarily, given that in evolution the referred condition must be the 
ancestral one. Strictly speaking, one would have to distinguish between 
"hypertrophied" as an absolute term (meaning an element that has evolved to be 
larger by comparison to the rest of its functional unit, e.g. a forelimb, as 
well as larger by comparison to the ancestral condition) and "relatively 
hypertrophied" (only larger in relation to the rest of the functional unit, but 
in absolute terms smaller than in the ancestor).

Because generally, a trait evolves in two respects - on one hand, it evolves as 
such. But on the other hand, the freedom to evolve is constrained by the 
trait's functional unit. This is not the case when there is loss-of-function, 
e.g. secondary flightlessness. But otherwise, functional units (limbs etc.) 
evolve need to maintain their function, and thus cannot become larger if the 
overall body size becomes smaller. Likewise, a part of such a unit can hardly 
evolve to become *absolutely* larger if the unit itself becomes smaller.

So we have two different ands sometimes contradictory evolutionary 
trajectories: one affecting a specific trait, and the other affecting the unit 
of which this trait is part of or even the whole organism.


Regards,

Eike