Re: Pteromimus and pterosaur origins

[Nick Pharris <npharris@umich.edu>]

Quoting David Marjanovic <david.marjanovic@gmx.at>:

> > For instance, note that all of the sister and predecessor taxa of  
> > pterosaurs in Atanassov's phylogeny have a vestigial or absent  
> > pedal digit V. Pterosaurs don't. That's a red flag that should tell  
> > any reasonable person, evolution doesn't work that way
>
> Wait, wait, wait, wait, wait. Be very careful with this kind of  
> assumptions. Natural selection is not constrained by history; if a  
> population with a reduced 5th toe that only consists of 2 phalanges  
> anymore finds itself under selective pressure for elongation of that  
> toe, that's what's going to happen. Even lost phalanges can come  
> back; how many phalanges a digit contains depends on the way it  
> grows in the embryo -- a metapodial and its phalanges start as a  
> cartilaginous rod that grows from proximal to distal and segments as  
> it grows --, and, according to an SVP presentation I saw last year,  
> the basal anomodont *Suminia* did reverse from 2-3-3-3-3 to 2-3-4-5-3.

You guys would know better than I, but last I looked, pedal digit V in  
basal pterosaurs may be long, but it still only consists of two  
phalanges.  That certainly suggests to me that it's been re-elongated  
secondarily.

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Nicholas J. Pharris