Date: Tue, 4 Jan 2000 10:05:25 -0500
Reply-To: Conchologists of America List <CONCH-L@LISTSERV.UGA.EDU>
Sender: Conchologists of America List <CONCH-L@LISTSERV.UGA.EDU>
From: Art Weil <artweil@FUSE.NET>
Subject: Re: Developmental History
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I would agree that mollusks are probably just "worms with shells".
Cincinnati rocks go back to the Ordivician and have many casts of
mollusks---although Brachiopods are much more common. I understand that they are
found back to the Cambrian as well. I wonder if they had developed colorful
shells back then.
Kurt Auffenberg wrote:
> Perhaps one of our more informed can expound on these more thoroughly, but
> since you've had no response......
> Mollusks are found as far back as the fossil record extends for
> macro-creatures...not one-celled critters. They apparently were pretty
> much fully diversified by the time they show up as fossils....So we are
> lacking a big chunk of their evolution....
> We don't know from which group they arose, but annelids (worms) seem to be
> the best fit for their closest relative.....however, many questions persist.
> I'm not sure on who or what shows up first in the fossil record, but as I
> said above, mollusks seem to have been fully diversified by the time they
> do show up. To give you an idea of how old these animals really
> are.....I'll use the Paleozoic land snails of North America (A. Solem and
> E. L. Yochelson. 1979. North American Paleozoic Land Snails, with a Summary
> of other Paleozoic Nonmarine Snails. Geological Survey Professional
> Papers, no. 1072:1-42, 10 plates)...."Representatives of three orders and
> five families of land snails appear essentially simultaneously in the
> fossil record of the Pennsylvanian. These families persist today, thus
> demonstrating that in the early late Carboniferous, the land snails had
> achieved a high and stable level of diversity (pg. 1)." I find this
> amazing....and when you think that these little babies probably arose from
> an already diverse marine fauna....well, it boggles the mind. All those
> vertebrates are cool, but they are short-lived, minor groups when you
> compare them to mollusks.
> We don't know what, if anything, evolved from mollusks......
> Perhaps someone with access to the Treatise on Invertebrate Paleontology
> will further enlighten you and yours....
> At 09:06 PM 1/3/2000 -0500, you wrote:
> >Dear Conch-l,
> >I was wondering... what the current thought is as to when molluscs first
> >appeared in history? What did molluscs descend from? What order did
> >molluscs appear? What descended from molluscs?
> >My father asked me the first question recently during a meal we were
> >sharing. I couldn't answer his question and spent a few days pondering
> >with no resolution.
> >Lori Schroeder