Re: synapomorphies not created equal

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

Dinogeorge wrote:

> Incidentally, any clade is united not by a list of synapomorphies but only 
> by
> a single synapomorphy; in any list of synapomorphies, some must inevitably 
> be
> synapomorphies of nested groups contained in the clade, and others must be
> plesiomorphies of clades that contain it. This is because it is extremely
> unlikely that a set of apomorphies would all evolve at exactly the same 
> time.

Not necessarily.  Certain apomorphies may be developmentally or functionally 
linked.  Some dental characters in mammals may fall into both or either 
category.  The enlargement and aerodynamic refinement of wing and tail 
feathers may be both developmentally and functionally correlated.

It has been suggested that the appearance of forward-shifted neural arches 
in the caudal vertebrae of titanosaurs might be a correlate of extreme 
procoely of the caudal centra.  (I would dispute this, however, on the basis 
of sauropod taxa that show one of these apomorphies, but not the other.)



Tim



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