Andrew,

In a more contemporary framework, one may add to these taphonomic anomalies
the transport by mollusk-eating fish.  This is inferred from our getting an
occasional bathyl species in the bycatch of scallopboats trawling well onto
the continental shelf off northeast Florida.

Harry


At 03:35 PM 8/18/2003, you wrote:
>>On the other
>>hand, dead shells generally give a pretty good idea of the
>>local fauna.  Folks have noted the risk of some extraneous
>>shell turning up, and there is some degree of transport
>>between habitats as well, but the common dead shells
>>almost certainly give a good picture of the local live fauna.
>
>Er... well. Fossils can weather out and become mixed into Recent
>faunas... such as a South American scallop, Austrochlamys natans,
>which I dredged at about 600m depth in a Dunedin canyon.
>
>Sealevels can rise and crust tectonically subside, resulting in
>shallow or even land and fluvial shells and the surface they lie upon
>becoming deeply submerged.
>
>Also land and fluvial shells can be washed out to sea, at least in
>part by unstable slopes.
>
>I have found landsnails (Charopa and close relatives eg Mocella)
>washed-up in windrows with what I think was a rain/storm kill, with
>scissurellids and billions of tiny Gaimardia plus over 60 other spp.
>
>The example which really brings this to attention is that I have
>dredged Potamopyrgus (3 specimens) in a haul in which the dredge ran
>upslope from 300-600m. I cannot tell whether these are the fluvial
>P. antipodarum or the marginal-estuarine P. estuarinus, but it
>matters little. Also the umboniine Antiosolarium egenum,
>superabundant in the shallows close to the coast, is common in the
>haul... though the shells all look pretty old. I think the hydrobiids
>are washing down to the outer shelf and thence, with the trochids
>(which may be Pleistocene relicts), slumping down into the upper
>canyons.
>
>I have also seen the outer-shelf species Calliostoma blacki,
>Cominella nassoides and Provocator mirabilis wash up on beaches...
>probably brought up by hermitcrabs, but also possibly by marine lab
>bopat dredging activities (due to the latter, i would be surprised if
>these species and others are not actually living in the harbor!).
>--
>Andrew Grebneff

Harry G. Lee
Suite 500
1801 Barrs St.
Jacksonville, FL 32204
USA
Voice: 904-384-6419
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Visit the Jacksonville Shell Club Home Page at:
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