Re: [asa] Transitions

From: James Mahaffy <>
Date: Fri Dec 08 2006 - 07:53:46 EST

James Mahaffy ( Phone: 712 722-6279
498 4th Ave NE
Biology Department FAX : 712
Dordt College, Sioux Center IA 51250-1697
>>> "D. F. Siemens, Jr." <> 12/07/06 1:14 PM >>>

I'm not a paleontologist, but I'm going to stick my neck out. I expect
that there are virtually no fossils from amoebae, ciliates and
flagellates, for they do not produce tests.

*** me ***
Of course fossils are much more apt to be fossilized if they have hard
but many invertebrates do. Actually a number of "amoebae like" chaps
have hard parts
an fossilize very well. One group is the foraminiferins that have
carbonate shells. The
white chalks of Dover and most Cretaceous chalks are made up mainly of
shells of these
and coccoliths (part of the cell wall of some algae). Another group that
is often fossilized
is radiolarians (glass shells). When you have small invertebrate fossils
that originally in
the plankton they often are abundant enough and widely enough deposited
to become
good biostratigraphic tools.

Diatoms and foramins have
many fossil representatives. Many sponges have spicules that identify
them, Coelenterates like corals and gorgonians leave many fossils, but I
doubt that there are many from jellyfish. Some annelids produce
elements, but most helminths leave behind nothing but burrows--if they
burrow. I recall reading that, if every living thing except roundworms
were suddenly eliminated, their ghostly forms would remain in the
ubiquitous roundworms. Has anyone reported finding their traces in other
fossils that presumably would have harbored the tiny rascals? We've got
lots of molluscs fossilized (acres of clams), but I doubt that many of
these are octopods.

no but the squid has a pen that is fossilized and there is an excellent
of nautiloids and ammonoids both of which were octopus like chaps with
The ammonoids were quite abundant in the Cretaceous and again found
enough to be used for biostratigraphy.

I believe that there are relatively few invertebrate
sequences because there are few that readily fossilize, not because they
never existed. Can somebody familiar with the range of fossils confirm
logic or tell me I'm all wet?

Not really the case. Some don't fossilize well but others do and if they
were invertebrates of
the ocean we often have a much better record than that of vertebrates.
Terrestrial chaps
are usually buried in sediment that is eroding and being buried. Yes we
do occasionally
get old rocks with terrestrial sediments preserved (like coal), but
except for recent rocks it is usually
marine shales and limestones that are preserved. Trilobites, crinoids
and brachipods and
many other invertebrates have a great chance of being preserved in these
rocks. Some
of the best fossils records belong to some of the invertebrates.

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Received on Fri Dec 8 07:54:36 2006

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