Re: Origin of body plans (phyla)
David Campbell (bivalve@mailserv0.isis.unc.edu)
Mon, 19 Oct 1998 11:13:09 -0400
>At 08:53 PM 10/16/98 -0600, Keith wrote:
>This is a point I have been trying to get heard when
>>phyla are claimed to be the unbridgeable categories of life. New
>>discoveries are occurring apace and the origins of several other phyla are
>>close to being able to be reconstructed in manner similar to the
>>arthropods.
>
>But let us not forget that the arthropods proper are already there alive
>and well, and perhaps amused at what future theories will be contrived to
>explain their origin, while all this proposed evolution of the arthropod
>body plan is taking place!
>Art
>http://biology.swau.edu
Descendants of transitional forms that retain the transitional features can
survive after the new form evolves. They generally do not last extremely
long because the new form is generally better at exploiting the niche that
it is partly using, but they may either find their own niche or survive a
while before dying out.
Further study of late Precambrian faunas will probably extend the ranges of
both the arthropods (I have heard rumor of trilobites) and the lobopods (by
identifying the sources of some of the small shelly fossils), so
conclusions about the relative time of appearance are premature.
David C.