Re: Ammonite Aptychi

[Hilbrecht@xxxxxxxxxxxx (Heinz Hilbrecht)]

Neale Monks wrote: 
>My problem with ammonite aptychi is that I don't really believe that many
>species, like Scaphites, could have been bentho-nektonic predators. The
>head points the wrong way; the rostrum doesn't exactly aid forwards
>swimming; the aperture of the shell is narrow compared to the body chamber
>(suggesting long but weak arms rather than strong, thick ones); and
>ammonites are often common where the benthos is often rather scarce.

Isn't Scaphites a normal ammonite until it comes to the reproductive stage
and builds this hook-shaped appearance? My attention arose from ideas by my
colleague Danny Dahmer who looked at change in the functional morphology of
ammonites before and after they arrived at their reproductive stages. He
considered the attitude of some modern cepaholopods to migrate to mating
areas and thought the reproductive stage of some heteromorphous ammonites
may have allowed the animal to travel easier and faster than with the
pre-reproductive shell (a short mention of these ideas was published by
Dahmer & Ernst (1986): Lect. Notes in Earth Sc., Vol. 8 ("Global
Bio-Events"), 353-362). Did somebody look at such possible changes in the
functional morphology and published about this?

Heinz Hilbrecht




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