Re: [asa] Re: Fossil record was Transitions

From: D. F. Siemens, Jr. <dfsiemensjr@juno.com>
Date: Sat Dec 09 2006 - 13:07:41 EST

On Sat, 09 Dec 2006 10:27:49 -0600 "James Mahaffy" <mahaffy@dordt.edu>
writes:
> I'm aware that there are single-celled creatures that produce tests
> that
> can be traced--if they are distinctive enough. I've heard of the
> White
> Cliffs of Dover and immense deposits of diatomaceous earth. But are
> there
> any fossils of Entamoeba, Volvox, Stentor, Giardia, Paramecium,
> Euglena,
> Myxomycetes, etc., which don't secrete tests, that allow tracing
> their
> evolution?
>
> Softbodied single celled are not abundant in the fossil record,
> unless
> they were algae or blue-greens (cyanobacteria) preserved in
> stromatolites. Some of the earliest preCambrian fossils are in
> these
> two groups.
>
> Parasites like Entamoeba and Giardia are concentrated in the
> intestines
> of their hosts. I don't know their record, but it could be that we
> haven't looked that much. You would have to find good coprolites
> that
> still had lots of organic material. Might well be some around, but
> I am
> not sure they have been looked for (you would waste years looking
> for
> things you might not find - but if you did it would be a great PhD
> these). David Dilcher did his PhD thesis on the fungi growing on
> early
> angiosperm leaves.
>
> Actually Volvox has a zygote that should preserve fairly well, but
> then
> it is a not that common a freshwater alga and the zygotes may even
> be
> missed in fresh water. Now if you want to draw a nice tree in the
> Volvocine algae [which I do not] you would probably use living
> flagellates in the group. You have single celled ones, ones with
> about
> 4 in a colony and others up to the thousand or so in Volvox.
>
> The fungal groups have pretty good records. They have identifiable
> spores and many living on decaying organisms can leave behind some
> vegetative some are distinctive. structures. Mostly it is hard to
> identify from vegetative structures but sometimes you get
> identifiable
> tures on rotting material (good preservation potential)
>
>
>
> Among somewhat larger creatures, are there fossils of
> jellyfish,
>
> Jellyfish have a long but sparce record. Fortunately the fossil
> record
> has localities that occasionally preserve a lot of softbodied chaps.
>
> One of these windows is in the preCambrian Edicarian flora which in
> the
> traditional interpretation (according to Clarkson) has 15 species
> of
> jellyfish (medusa). However, you are right, they generally are not
> preserved (just a few early ones). Another hand chitinous hydrozoan
> are
> more easily preserved and have a fossil record back into the
> Ordovician.
> And of course something like corals have a great record and I
> suspect
> we are pretty sure we know what we had (different types of corals -
> tabulates and horn corals in the Paleozoic - modern corals found
> first
> in the Mesozoic). It is pretty hard not to preserve a coral unless
> it
> dissolves.
>
>
>
> roundworms and flatworms?
>
> Nematodes should be there more often then they are recorded. they
> can
> be found in amber and apparently someone found some in the
> Paleozoic.
> See:
>
http://www.nola.com/living/t-p/index.ssf?/base/living-7/116435034131380.x
ml&coll=1&thispage=2
>
> Sounds like hardly anyone studies them.
>
> I don't think there is much of a record of flatworms (which is to
> be
> expected) but see:
> http://www.sciencedaily.com/releases/1999/03/990322062150.htm
>
>
>
>
> I don't remember any of them with
> calcareous or siliceous parts. I know that there are cephalopods
> with
> shells, which is why I specified octopods. I now understand that
> there
> are fossils of shelled (externally or internally) molluscs from
> which
> they evolved. Any unshelled samples?
>
>
> Actually in the group that includes the octopus and squid it is only
> the
> belemites that had a spearlike internal structure that preserve well
> and
> give us a good record. I am not sure why the chitinous beak is not
> preserved a bit more often but even if they were they would be VERY
> rare
> compared to brachiopods etc and perhaps overlooked.
>
> [snip] There is clearly the
> element of "luck" in encountering fossils.
>
>
> Yes but I have tried to indicate that actually for many groups we
> have a
> very good record that is NOT that spotty. You can usually predict
> which
> ones will not likely to be preserved. It is just not that random.
> And
> now I had better get back to grading, but this has been fun.
>
>
>
>
> James Mahaffy (mahaffy@dordt.edu) Phone: 712 722-6279
> 498 4th Ave NE
> Biology Department FAX : 712
> 722-1198
> Dordt College, Sioux Center IA 51250-1697
>
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>
>

Thanks for the references. However, I note that the flatworms were
tackled with genetic information, not fossils. Also, while Giardia can
cause intestinal problems, they are free living in the highland streams
of Yosemite. The crystalline cold waters have given many unwary hikers a
bellyache. I don't know where else they pursue their nefarious ways, but
I did hear of a problem from the Sierras.

Enjoy the highlight of the professor's year, correcting papers.
Dave

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Received on Sat Dec 9 13:12:58 2006

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