The suggestion of chemosymbiosis in inoceramids is based largely on
their ability to survive in relatively low oxygen habitats.  However,
they are not limited to such facies, and they have no close living
relatives.

It seems likely that isotopic studies would be informative, but I
don't think they have been done.  Many elements have multiple stable
isotopes, as well as radioactive ones.  As a rule, the variation
between the isotopes doesn't make much difference, but there is a
slight tendency for the lighter isotope to be more reactive, more
easily evaporated, etc.  (The difference is bigger for lighter atoms.)
 In complex series of reactions, such as those involved in many
biological processes, the end product can get very enriched in the
lighter isotope.  Photosynthesis and chemosynthesis tend to leave very
distinct isotopic ratios.  However, there's a problem in that the
aminal may be making the calcium carbonate for the shell largely from
dissolved carbonate in seawater while making its tissues from carbon
compounds derived from symbionts.

Similar adjustment of the ratio of different isotopes is important if
you want to make a uranium atomic bomb.

On Tue, Oct 25, 2011 at 6:01 PM, Harry G. Lee <[log in to unmask]> wrote:
> Dear Listers,
>
> Our local science and history museum has been featuring a traveling exhibit
> entitled "Savage Ancient Seas" for a couple of months, and I took a look at
> it today. Basically it focuses on top-level marine predators and features
> several large and menacing marine reptiles and fish. There are a couple of
> giant sea turtles in the mix. All the biota seems to be Upper Cretaceous -
> and, get this: no dinosaurs!
>
> Literally overshadowed in the gallery dominated by the remains of the
> fearsome vertebrates is an artificial cast of a very well-preserved three
> foot-long bivalve identified as the inoceramid, Magadiceramus
> subquadratus (Schlüter 1887). In characteristic hyperbole the signage
> indicates that this rather deepwater clam lived symbiotically with bacteria
> that metabolized "deadly hydrogen sulfide gas."
>
> I was greatly relieved to see this confirmation of my pretty much
> stab-in-the-dark hypothesis that the giant sedentary pelecypods of this
> family hosted mutualist microbes. I was actually beginning to have
> my doubts.
>
> I wonder how paleontologists figured this symbiosis out? Chemical, physical,
> or morphological footprints in the remains? Inference from the Recent fauna?
>
> Harry
>
> --
> Harry G. Lee MD
> 4132 Ortega Forest Drive
> Jacksonville, FL 32210-5813
> USA
> (904) 389 4049
> [log in to unmask]
> [log in to unmask]



--
Dr. David Campbell
Collections Assistant
The Paleontological Research Institution
1259 Trumansburg Road
Ithaca NY 14850

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