Dear Andrew et al;-
   Here in Cincinnati, all our Brachiopods and Trilobites, Horn Corals, etc. are fossils. They range about 400 million years. Ordivician. The only sub-fossils we have serve on city council and the various judicial benches.
   But, seriously, is the term "sub-fossil" really relevant? Don't we have enough trouble with sub-species, form of, cf., "interesting variety", etc.?
   When does a shell jump from just plain dead to sub-fossilization? Is there a percentage of replacement that must be met? It's all very confusing. I think I'll collect match-book covers.
    Q-Man

>
> From: Andrew Grebneff <[log in to unmask]>
> Date: 2003/09/02 Tue PM 02:05:01 EDT
> To: [log in to unmask]
> Subject: Re: Subfossil versus fossil
>
> >One technical definition is to call everything Pleistocene and older
> >(over 10,000 years) a fossil and younger but long-dead material
> >subfossils.  However, telling the difference between a
> >well-preserved specimen just over 10,000 years and a highly altered
> >younger specimen may be difficult.  If the age is unknown, using the
> >condition of the shell as a practical division makes sense.
>
> Shells of 70 million years age can be in perfect preservation, so
> condition is not necessarily an indicator; bones are even more
> resistant. Generally speaking, subfossils will not be encased in hard
> rock (though exceptions certainly can occur, and true fossils
> commonly occur in utterly unconsolidated rocks).
>
> >     Doesn't "fossil" indicate that the material makeup is replaced
> >by some other mineral? If so, wouldn't a sub-fossil be a long-dead
> >critter to which that process had not begun---or proceeded very far?
>
> >Not necessarily; there are shells about 300 million years old that
> >still have original aragonite, and original calcite is known back to
> >about 450 million; some of these may also have traces of the organic
> >components as well.  However, these do show some alteration from the
> >original.  On the other hand, some fossils have no mineral at all
> >and are just impressions where the original shell dissolved away.
> >Only a few years in a poorly-buffered stream can be enough for a
> >unionid shell to dissolve away.  Some modification in the mineralogy
> >can also take place quickly, depending on the chemistry of the
> >environment.
>
> For sure. And fossil bone is normally still the original calcium
> phosphate, often with organics (the cell-spaces and cancellation may
> well be infilled with other minerals, but that's something else
> entirely). The bone is often in good enough condition that it can be
> examined for traces of strontuim and other isotpoes, which can yield
> data on paleotemperatures and even icecap volume at the time the
> animal died.
>
> Chemistry in the animal's environment can affect mode of
> preservation; so can subsequent conditions within the rock, which is
> when shells are often dissolved by groundwater. If this happens
> before the rock lithifies (hardens), if it ever does lithify, the
> fossil is reduced to a matrix "ghost", often slightly phosphatized,
> which may have internal and external details superimposed eg Latiarca
> with muscle scars and hingeteeth impressed upon the radial ribbing
> and the finer commarginal sculpture. If the rock has lithified before
> solution the shell may be preserved as an ampty mold, or it may be
> infilled by a mineral (calcite, silica, worst-case being marcasite,
> which breaks down nastily and messily).
>
> >  >    NOTE: I hope you tell the proper authorities at Alabama that
> >you can still kick extra points.<
> >
> >Naming a species for Bear Bryant might help funding around here.  In
> >fact, the collections building is named for Mrs. Bryant.  However,
> >fans of fossil mollusks may be more familiar with the namesakes of
> >Tuomey Hall and Smith Hall.
>
> What about Quantassaurus and Atlascopcosaurus? Dermochelys
> terrypratchetti? There's a trend to paid-for or bribing names...
> --
> Andrew Grebneff
> Dunedin, New Zealand
> 64 (3) 473-8863
> <[log in to unmask]>
> Fossil preparator
> Seashell, Macintosh & VW/Toyota van nut
> I want your sinistral gastropods!
> -----------------------
> Q: Because it reverses the logical flow of conversation.
> A: Why is top posting frowned upon?
>

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