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Re: Removing segnosaurs from ...



At 11:42 PM 8/30/95, Dinogeorge@aol.com wrote:
>In a message dated 95-08-30 23:08:26 EDT, Thomas_R_HOLTZ@umail.umd.edu (th81)
>writes:
>
>>Reversals do occur sometimes in nature: there are apparent reversals in
>>sacral numbers in the evolution of horses (granted, a simpler situation than
>>the metatarsals.)
>>
>
>THOSE kinds of reversals I have no problem with. Indeed, such reversals
>probably occurred more often than we guess, much to the consternation of
>taxonomists(!). The kinds of reversals I have a very hard time accepting are
>ones in which a substantial anatomical feature purportedly reappears after
>vanishing entirely.

        But with the prosauropod/therizinosaur problem, the fourth
(actually, the first) digit never really disappeared!  You claimed that the
functionally tetradactyl pedes of therizinosauroids could never be derived
from that of a theropod pes because theropods are tridactyl.  Untrue:  most
are _functionally_ tridactyl, but are in reality tetradactyl.  The reversal
in question would come from re-enlarging that first digit and making it
functional once again.  This is far, far easier to believe, it is true,
than having the toe reappear if it had originally disappeared
entirely...but, of course, that never happened.



Jerry D. Harris
Shuler Museum of Paleontology
Southern Methodist University
Box 750395
Dallas  TX  75275-0395
(214) 768-2750
FAX:  (214) 768-2701
jdharris@lust.isem.smu.edu
        (Compuserve:  73132,3372)

---------/O\------*     --->|:|:|>     w___/^^^\--o

"If it looks like a duck, walks like a duck, and
quacks like a duck, then it is the sister taxon to,
but cannot parsimoniously be, the direct ancestor
to all other ducks."

                                --  _not_ W. Hennig

---------/O\------*     --->|:|:|>     w___/^^^\--o