>OK. Why does Thatcheria mirabilis have that unusual screwlike shape?
>I love that shell, but I haven't a clue as to why it's shaped that
>way.

Several "turrids" have evolved in this direction. Parasyrinx, Aforia
& Cochlespira leap to mind. Extinct fossil species of Thatcheria are
somewhat less spectacular, with a sharply-rounded periphery.
Parsyrinx subalta, a NZ Oligocene-Miocene-boiundary species, can be
quite spectacular too.

There are 2 ways to develop such sculpture... one is for t he
periphery to become accentuated by flats developing above & below;
the other is for a Conus-shaped shell to broaden its shoulder and
increase the rate of translation along the axis, resulting in a
steepened suture, exposing more of the previous whorl.

I doubt that there is any ecological reason for Thatcheria to develop
like this... much evolution occurs just because it CAN, as random
harmless mutations may become fixed in the genepool.

The keel strengthens that part of the shell, but the surface abapical
of the keel remain extremely weak.

>My question about Thatcheria mirabilis has always been, What makes
>it a Turrid?

Turrids are problematic. I refuse to go along with the splitup of the
family, but embrace wholeheartedly its synonymization with Conidae.

>(Have I heard recently that it was being moved out of the Turridae
>to a family of its own?)

Don't know. But I wouldn't support it.

>The first time my dad saw a kid selling a bucket of them in Taiwan,
>I think, he thought they had been manufactured--and didn't buy any.
>Sure glad he later reconsidered.  I love the shape--though I have
>seen several whose tips are crooked.  Evidently the shape is a
>fragile one.
>
>Final thought:  you just can't "out-imagine" our Creator!

Which creator?? Each of us has two... Mum & Dad.
--
Andrew Grebneff
Dunedin, New Zealand
64 (3) 473-8863
<[log in to unmask]>
Fossil preparator
Seashell, Macintosh & VW/Toyota van nut
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I want your sinistral gastropods!
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Opinions in this e-mail are my own, not those of my institution
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A: Because it reverses the logical flow of conversation.
Q: Why is top posting frowned upon?