Re: Prolacerta/Prolacertaform Sources

John Brock wrote:

In article <IqaZf.55805$F_3.37105@xxxxxxxxxxxxxxxxxxxxxxxxxx>,
John Harshman <jharshman.diespamdie@xxxxxxxxxxx> wrote:

Alan Kellogg wrote:


The problem is, apparently having three pairs of limbs is not as
efficient as having two. The extra expenditure in resources during
embryonic development, plus the disadvantages six limbs gives during
life compared to four.


Not that I can tell. Hexapedy doesn't even happen as a mutation in
vertebrates, as far as I know. It's not selection that forbids it, but
the absence of any such mutation. Maybe if it happened selection would
dispose of the mutation, but we never get to that point.


I could swear I've seen photos of frogs from polluted ponds with
an extra set of limbs. Not very well formed or functional limbs,
but limbs nevertheless. I assume this is a developmental thing,
rather than a mutation, but I don't see why a mutation couldn't
have the same effect. Is there any reason to think it really
doesn't happen, rather than simply being to rare for us to have
noticed it? (And is anyone really looking?)

I think we are looking. Developmental anomalies have often been studied
as a guide to developmental processes. I don't know of any duplicated
limbs, only bifurcated ones, i.e. extra fingers, the occasional extra
hand, and perhaps a spare radius and ulna. But never a complete and
separate arm. I could be wrong.
.

Relevant Pages

  • Re: Prolacerta/Prolacertaform Sources
    ... vertebrates, ... Maybe if it happened selection would ... dispose of the mutation, but we never get to that point. ... an extra set of limbs. ...
    (sci.bio.paleontology)
  • Re: Prolacerta/Prolacertaform Sources
    ... Maybe if it happened selection would ... dispose of the mutation, but we never get to that point. ... an extra set of limbs. ... not by any reasonable definition of functional. ...
    (sci.bio.paleontology)
  • Re: Prolacerta/Prolacertaform Sources
    ... dispose of the mutation, but we never get to that point. ... an extra set of limbs. ... is an entire extra pelvic girdle. ... A radical proposition to solve a radical problem, ...
    (sci.bio.paleontology)
  • Re: Prolacerta/Prolacertaform Sources
    ... dispose of the mutation, but we never get to that point. ... an extra set of limbs. ... so we get as far as duplicating the femur. ... is an entire extra pelvic girdle. ...
    (sci.bio.paleontology)
  • Re: Prolacerta/Prolacertaform Sources
    ... The extra expenditure in resources during ... embryonic development, plus the disadvantages six limbs gives during ... dispose of the mutation, but we never get to that point. ... an extra set of limbs. ...
    (sci.bio.paleontology)