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Re: Digit Loss

On Fri, 8 Jun 2001 10:27:33   
 William.BONNET wrote:
>First of all, please forgive me for using terms which may not be the
>accurate  "technical terms/words", or which are french :) I'm not a
>professional, just an amateur unlurking.
>> Digit loss is something commonly seen, so it must have been an
>> evolutionary response to a commonly recurring pressure.  The answer is out
>> there...somewhere.
>I do not fully agree with the point that "it must have been an evolutionary
>response". I tend to agree with Daniel Bensen who said that 
>       "evolution is driven by random mutation"

I surely don't disagree with that point!  Mutations drive evolution; that is 
one of the basic principles and concepts of the theory of evolution.  

>Digit loss can also be explained by genetic mutation. This reminds me of
>Jean Rostand's work on frogs. Frogs (Bufo bufo) can show a loss of digits,
>which is an herited mutation (non-dominant), and which is not lethal.

Well, I'm sure that digit loss in dinosaurs can be explained by genetic 
mutation.  I don't disagree with this.  I have been talking about the why, not 
the how.  The "how," by this I mean what proteins do what and which genes are 
responsible, is becoming better understood every year.  However, the why is 

>So i would say that a possible answer to explain the theropods loss of digit
>could be genetic mutation. 
>As long as this mutation is not lethal, or at least as long as it is not an
>evolutionnary handicap (a complete lack of digit would not be necessarily
>lethal, but would be a heavy handicap) theropods having this mutation can
>fully compete with others theropods (which do not have the same mutation). 

Oh, sure.  But, why don't digits reevolve?  Tyrannosaurus and other large 
theropods may have become better predators if they re-evolved larger arms and 
more digits.  Why does this not happen?  That is a mystery to me.  I doubt that 
it is impossible to re-evolve digits,


Steve Brusatte
Dino Land Paleontology

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