Thanks, David. That's a ver nice presentation.

Harry


On 10/26/2011 12:27 PM, David Campbell wrote:
> 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
> Dr. David Campbell
> Collections Assistant
> The Paleontological Research Institution
> 1259 Trumansburg Road
> Ithaca NY 14850

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