Re: Paedomorphosis ( Re: BARYONYX' CLAWS )

[Ronald Orenstein <ornstn@inforamp.net>]

GO writes:
><< Thus, unless a fossil shows up that is both a clearly and considerably
>specialized volant or near-volant form and obviously represents an
ancestor to
>both birds and at least some theropods, the "difference" between BCF and BADD
>may be minimal, unimportant or impossible to distinguish. >>
>
>We already have such a fossil, although it is somewhat later in the fossil
>record than I'm comfortable with, namely, _Rahona_, the flying
dromaeosauroid.
>I'd like to see a _Rahona_-like dinosaur in the Middle Jurassic (lotsa
luck!).

I think it would take such a fossil to make the case - and again, I suggest
that Rahona may only show that, as I have said, in reality there may have been
a broad range of intergrades between birdlike dinosaurs, dinosaurlike birds
etc
following a number of evolutionary pathways, rather than any sort of clear-cut
division between BADD and BCF.  And I still think it would be hard to tell
what
is really going on from a fossil.

>
>If you pin its advocates down, they will aver that BADD makes no statement
>about the lifestyle of the common ancestors of birds and theropods. 

I think the point is that although proponents of BADD may have their notions
about the lifestyles of bird ancestors, these notions are really sidebars -
proving them wrong would not invalidate the central cladistic hypothesis. 
Again, there could have been many small dinosaurs equally at home in trees and
on the ground (as are many living birds), and a slight preference for one over
the other might have very little expression in the skeletal structure.
--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
1825 Shady Creek Court                 
Mississauga, Ontario, Canada L5L 3W2          mailto:ornstn@inforamp.net