Ammonite Aptychi

[N.Monks@xxxxxxxxx (Neale Monks)]

Dear All,

Thanks to those who have already come up with ideas and comments...and so
damn quickly!

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.

As Paul Jefferies has pointed out, aptychi don't have any signs of wear,
but may fit the aperture badly. As opercula, note that many gastropod
opercula fit rather poorly, such as some Tuns and Volutes (thanks to Noel
Morris for that observation). Why do ammonites need heavily calcified,
spinose or ornamented jaw accessory plates where modern cephalopods do not.
The modern squid Dosidicus is able to bite through steel cables with only a
horny beak. What could ammonites possibly have been eating that needed more
resilient or massive structures!

So, in short, I don't believe that the aptychi controversy is as as dead as
Lehmann and others would have us believe!

Let me know what you think,

Thanks,

Neale Monks

Neale Monks, Department of Palaeontology,
Natural History Museum, London, SW7 5BD
Internet: N.Monks@nhm.ac.uk
Telephone: 0171-938-9007

"The first ten million years were the worst. And the second ten million.
They were the worst too. The third ten million I didn't enjoy at all. After
that I went into a bit of  decline"
 (Marvin, the Paranoid Android)