animal legs

[Ken Kinman]

    I wasn't going to comment on the question below, but then when I saw
comments about animals evolving legs to walk on land, it is pretty clear
that it is vertebrate legs that pop into people's minds.
      While the origins and evolution of vertebrate legs are relatively well
understood, the legs of invertebrates are a whole different story.  They
almost certainly didn't evolve to walk on land.  And the relationship
between various groups of arthropods is still so poorly known (although some
think they understand it), that there is presently no way to know whether
their legs initially evolved for locomotion (whether crawling or swimming)
or feeding or respiration or possibly even something else.
     Arthropod phylogeny will probably end up looking quite different from
what has been proposed in the 1990's, and until the phylogeny is
established, the origins of those particular "animal" legs will probably
remain a mystery.  So for these types of legs, my answer to Daniel's
question would be that their adaptive values cannot presently be evaluated
and that this will be the case for many years to come.  Of course, the
answer for vertebrate legs is a whole different matter.
                          -------Ken

>From: Daniel Janzen <djanzen at SAS.UPENN.EDU>
>Reply-To: Daniel Janzen <djanzen at SAS.UPENN.EDU>
>To: TAXACOM at USOBI.ORG
>Subject: Selaginaceae are now beyond evolutionary examination
>Date: Wed, 28 Jul 1999 10:22:12 -0600
>
>Animals have had legs for several hundred million years.  Does this put any
>consideration of their original adaptive value effectively out of reach?
>
>Dan Janzen
>
> >X-Sender: jcclark at mail.csupomona.edu
> >Mime-Version: 1.0
> >Date:         Tue, 27 Jul 1999 17:56:32 -0700
> >Reply-To: Curtis Clark <jcclark at CSUPOMONA.EDU>
> >Sender: Taxacom Discussion List <TAXACOM at USOBI.ORG>
> >From: Curtis Clark <jcclark at CSUPOMONA.EDU>
> >Subject:      Re: Help required - Selaginellaceae
> >To: TAXACOM at USOBI.ORG
> >
> >At 05:46 PM 7/27/99 +1200, john steel wrote:
> >>        Any function for the "ligule" which occurs at the base of
> >>        the microsporophyll below the sporangia in Selaginella?
> >
> >The ligule is shared by the major clade that contains the
>Selaginellopsida
> >and Isoetopsida (including the Lepidodendrales), and so goes back maybe
>400
> >million years. That puts any consideration of its original adaptive value
> >effectively out of reach. :-)
> > >----------------------------------------------------------------
> >Curtis Clark                  http://www.csupomona.edu/~jcclark/
> >Biological Sciences Department             Voice: (909) 869-4062
> >California State Polytechnic University      FAX: (909) 869-4078
> >Pomona CA 91768-4032  USA                  jcclark at csupomona.edu
> >


_______________________________________________________________
Get Free Email and Do More On The Web. Visit http://www.msn.com