Hi Andrew
 
    Re Tasty meal. Shell bite marks
 
    Yes, ammonites were prey as well as predators. It must be noted,
however, that there were many species, sizes, etc. with different
strategies. Just as all fish do not use the same strategy for defense or
protection of eggs, not all ammonites (or octopoids) would use the same
strategy. The 'ammonite' imitation for an egg case could have evolved as
the preferred strategy for a particular species. It doesn't need to be
an absolute defense but only an incremental evolution advantage.
 
    Re Mosasaur predation, etc.  Recent studies (especially in Late
Cretaceous fauna)show that most previously thought 'Mosasaur' bite marks
are actually limpet scars. These scars are common on large
'Placenticeras' ammonite specimens from Alberta. I have attended a few
lecture recently on this. Placenticeras specimens are fairly common from
the Bearpaw Sea Formation in Alberta. It is not hard to find enough
specimens where one or two will appear as a perfect match for teeth
punctures.  We have the same issue in looking at dinosaur
(Tyrannosaurid) puncture marks in fossil bones (especially vertebrae);
any small scar or opening will erode quicker than the surrounding
material and often appear as a circular hole that fits a tooth tip quite
nicely.
 
    Argonauts to ammonites to mosasaurs to dinosaurs. Somehow seashells
to dinosaurs. Thats what happens when we live in Alberta, surrounded by
dino bones and a thousand kms from the ocean. It shows, again, that any
'ology'  subject (such as mallacology or conchology) can not be studied
in a vacuum and that all of Nature is the classroom. We sometimes find
Cretaceous freshwater mollusca (viviparidae, etc.) when searching for
dino material: the shell hobby has given more meaning to these once
anonymous little  fossil critters.
 
 
 
>> Why the
>> ammonite shape? To really speculate, I think it may have been to do
>> with
>> Ammonites being nasty predators. The eggcase may have been a visual
>> deterent to some smaller predators who did not want to mess with an
>> ammonite.
>
> Actually, a number of other creatures found the ammonite to be a tasty
> meal. Many fossils are found with the teeth marks of mosasaurs,
> ichtheosaurs, and other large marine reptilian predators of the past.
> A few fossils have been found of ammonites that survived such a bite,
> but most look like they didn't make it
>
>>
>>
>>             We have about 400 species of fossil cephalopods in our
>> collection. Most have 'names', wheras many, like some of our
>> Carboniferous  nautiloids, are unstudied fauna.If there are many
>> unanswered qestions about extant species, then trying to find
>> relationships between extinct species is a real stretch. But maybe
>> this
>> is what makes paleontology so much fun; lots of speculation without
>> ever
>> being proved right or wrong.
>>
>>             As for 'giant' ammonites. There are a few specimens in
>> the
>> Jurassic here in Alberta that approach the 6 foot size in diameter.
>> They
>> have not been collected as they are in matrix at remote sites.  Now
>> we
>> will have to find one over 8 feet.  I do believe, however, that some
>>
>> straight 'Cones' were much larger; I will try and find a reference.
>
> You and Ken are right. I forgot about the conical, uncoiled forms,
> some of which were much longer than my 8 footer. I guess I was
> thinking about the total mass of the shell itself without considering
> the bulk of the animal that it contained. The Smithsonian has, or at
> least it used to have, some of the giant coiled forms on display. I
> was just a lad of thirteen when I viewed them in 1973, but in my
> memory they seemed 10 feet tall. If shells were that big today, we
> would all need dump trucks to transport our catch, and warehouses to
> display the specimens. It would be a very dangerous undertaking also.
> Such an animal could easily turn the tables on you.
>
>>
>>
>>             Well, back to work on my corals and brachiopods. I can
>> at
>> least pretend to be more authorative on these.
>>
>>                                                     Best Regards,
>>                                                     Joseph, Calgary
>
> Thank you all for the interesting discussion. It's nice to engage in
> some speculation once in a while, not just cold hard facts.
>
> Andrew