Hi Andrew,
 
 
Joe here (on Nora's E-mail).
        We both enjoyed your comments on cephalopods. This class
emphasizes the necessity for an understanding of fossil evidence to
understand extant species and their physical adaptions.
 
        I found your explanation for the evolution of the argonaut egg
case very interesting. Your use of other fauna groups to emphasize
parallel behaviors was revealing.
 
    So much cephalopod speculation is based on a very questionable
evolutionary relationships. I am still not comfortable with most
evolutionary lines of cephalopods as they have been defined by
paleontologists. Too much speculation and too many ages being covered. I
haven't 'studied' cephalopods but I have studied paleozoic corals
(Carboniferous & Permian) and even in this 'shorter' period there is
rapid evolution along various tangents, etc. No consensus as to
relationships, etc.  When a whole Class is taken from Cambrian to modern
with numerous offshoots, incomplete fossil records, etc. , then it is
all like a House of Cards. Most Paleozoic coral  researchers do not even
put Paleozoic and recent corals in the same phylum. Too many 'stretches'
of imagination to relate them together other than the name 'coral'.....
Yes, cephalopods are probably all related but the evolutionary lines are
'iffy' and 'iffier'.
 
        Returning to the Argonaut. I have no better explanation of the
ammonite-like egg case than the excellent one you propose.. It is hard
to understand, however, how it evolved. What were the intermediate
stages to produce an ammonite-looking case? And if the argonaut
propagated quite well before this 'shape' evolved (it would have taken
time), why did the egg case  keep evolving to this shape? Why not some
other equally functional shape? Some paleontologists see Octopoids as an
early offshoot of ammonoids, perhaps there was some vestigal protoconch
that had the ability to undergo relatively quick evolution. 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.
 
            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.
 
            Well, back to work on my corals and brachiopods. I can at
least pretend to be more authorative on these.
 
                                                    Best Regards,
                                                    Joseph, Calgary
 
Kay Lavalier wrote:
 
>  Andrew Vik
> Tampa, FL., USA.
> [log in to unmask]
>
> Nora:
>
> Yes, I do study cephalopods, both living and extinct forms. I am
> interested in all aspects of  molluscan taxonomy. The molluscs are the
> most amazingly diverse phylum of multi-celled life on this planet.
> Zoologists have trouble just in defining what a mollusc is.
> All arthropods possess certain features (i.e., chitonous exoskeleton,
> jointed limbs) that are easy to see. Our phylum, the chordata, is
> readily diffident by the presence of a backbone in all of it's
> species. But there is no one feature that is common to all molluscs.
> The shell? No, very many molluscs have abandoned their shells. The
> radula? No again, the bivalves and many gastropods have no radula. It
> is no wonder that there is so much confusion with taxonomic
> nomenclature at all levels in the mollusca.
>
> Back to the subject of cephalopods. I think it is amazing that the
> argonaut's egg case resembles certain species of ancient ammonites.
> Argonauts are dibranchiate (possessing two gills) cephalopods, while
> it is inferred that ammonites were tetrabranchiate (four gilled) like
> the living Nautilus. These two groups of cephalopods both have very
> long fossil histories. Octopoids, including Argonauta, are not thought
> to have evolved directly from the tetrabranchia. That is why I believe
> that the ancient ancestors of Argonauta used to brood their young in
> empty ammonite shells. Back when there were thousands of species of
> ammonites alive, their old shells would have been plentiful and were
> probably utilized by other creatures in various ways. As the ammonites
> gradually declined, the argonauts had to improvise new shelter for
> their eggs. They learned to create their own ammonite shells over
> time. This is just my own speculation, I have not seen this proposed
> in the literature, nor have I seen any fossil evidence for this (I
> don't know if there is any fossil evidence of the argonauts at all).
>
> There are modern animals which tend to make me believe that my theory
> is correct. There is an indo-pacific sea anemone which has a
> mutualistic partnership with the local hermit crabs. Most hermit crabs
> have to find larger gastropod shells as they grow larger in size. If
> they have sea anemone partners, they must coax the anemones to attach
> to the new shell. But the anemone that I speak of has learned to
> secrete an artificial gastropod shell. The fake shell grows at the
> leading edge, just like a real snail does, and the crab never has to
> waste time finding new homes or relocating it's anemone partner. This
> fake shell looks like a Natica that has been plated with gold, but is
> of a similar texture to the argonaut shell. At one time, it was
> actually thought to be a gastropod shell.
>
> Another animal that creates an artificial snail shell is the aquatic
> insect larva of the damselfly Helicopsyche. It glues sand grains
> together and the result is about the same shape and size of  the
> Valvata sincera which live in the same waters. There is a small
> article about this insect in a recent issue of American Conchologist.
>
> Well, you can tell that I enjoy speculating about nature. Just one
> more musing about the ammonites before I go. Certain species of
> cretaceous ammonite in the genus Parapuzosia were the largest shelled
> molluscs of all time. The shells were about the same shape and size
> (2.5 meters, or about 8 feet in diameter) as tractor tires. And you
> would have needed a tractor to bring them home for your collection.
> For the sake of sea navigation, it's a good thing that they went
> extinct. Dead ammonite shells floated on the surface for long periods
> of time, just like modern Nautilus and Spirula do. Can you imagine
> hitting an 8 foot shell in a small boat at high speed?
>
> Andrew
>
>
> Nora Bryan wrote:
>
> Hi Andrew,
> Do you study ammonites or cephalopods? My husband attended a talk last
> week at our Paleo Society and the presentation was on ammonites and
> modern cephalopods.  (I wish I'd gone). The presenter expressed the
> same thing about the argonaut egg case looking like an ammonite. He
> also said that the argonaut egg case is rather "spongy".  I've never
> seen one, other than in pictures.
> James Wood, in the cephalopod link I've pointed out shows argonauta as
> an octopus, and not closely related to modern nautilus. I think that
> is old news to those who study cephalopods, but I was surprised to
> learn this. Paleontologists also believe that ammonites and nautilus
> are not closely related.
>