New Article on The Cephalopod PAge

Phil

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Very good article. Clearly written and informative.

Thanks!
 

tonmo

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Yes, thanks Dr. James... related to this, as has been stated on the TONMO.com ticker for some time now, we'll have our own Ammonite article to post soon... Phil provided a basic overview for the TONMO.com community, which I greatly appreciate! I just have to get around to posting it... :roll: This week Phil, I promise... :oops: :)
 

Fujisawas Sake

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Outstanding article! Must study more... :read:

Sushi and Sake,

John
 

Fujisawas Sake

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Dr. Wood,

Great article! I noticed though that it seems to hint that the cephalopod lineage is somewhat polyphyletic. I see three distinct lines, but is there any idea or theory on what the "proto-cephalopoda" may have been? Also my invert zoo instructor liked to nickname cephs "siphonopoda" because he believed that the siphon evolved from the foot. Any thoughts?

Years ago there was a concept known as the "Hypothetical Ancestral Mollusc" or H.A.M. theory. I posted a subject last year called "H.A.M. and Legs" which asked about the development of the cephalopod arms from the bauplan of the "general" mollusc. I know that H.A.M. theory has gone the way of the of the Ammonites, but is there any thought on what the "proto-cephs" may have actually looked like, and from what branch these creatures may have sprouted?

Thanks for the great article!

Sushi and Sake,

John
 

GeoffC

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Cool article Phil, looks like a lot of work into went into that. I havent got much time but I wanted to let you know, cheers!

Geoff
 

Phil

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Fujisawas Sake said:
Years ago there was a concept known as the "Hypothetical Ancestral Mollusc" or H.A.M. theory. I posted a subject last year called "H.A.M. and Legs" which asked about the development of the cephalopod arms from the bauplan of the "general" mollusc. I know that H.A.M. theory has gone the way of the of the Ammonites, but is there any thought on what the "proto-cephs" may have actually looked like, and from what branch these creatures may have sprouted?
Yo John,

Why has the HAM theory been disregarded these days? Is it because it implies the existence of an animal for which we have no evidence for, or has it gone the way of the dodo due to modern cladistic analyses? I suppose the HAM would imply that all the forms of mollusc originated at a single point in time from a single ancestor. I know that there has been much debate about the origin of molluscs recently with some researchers placing the molluscs in early lineages with ancestral annelids. Much of this work comes from recent advances in molecular biology examining RNA sequences in annelids and molluscs. (Just don’t ask me to explain it).

What on earth was going on in the late Precambrian to the Cambrian ‘explosion’ is totally obscure, relying on trace fossils and enigmatic faunas such as the famous Australian Ediacaran fauna. Even the animals that we know of from this mysterious dark age often defy easy description, weird quilted mattresses that may have been animal or vegetable or something in between and tiny impressions of worms and segmented enigmas that seem to have left no clear descendents.

I think it is generally accepted that the earliest molluscs may well have resembled aplacophora such as the ‘living fossil’ Neopilina that was dredged from the ocean floor in the 1950’s. That there were such creatures in evidence in the late Precambrian is highly likely. Scrape marks on rocks are recorded from the late Precambrian period that may well have caused by such primitive molluscs and tiny cap-like shells (a couple of millimetres across in most cases) have been recorded from the Tommotian faunas of Siberia, datable to about 550mya, at the beginning of the Cambrian. Some of these resemble monoplacophora and some bear a similarity to the earliest cephalopods in the late Cambrian such as Palaeoceras and Plectronoceras, though it is clear that they were not cephalopods as they do not have chambered shells containing a siphuncle.

I always imagined that the arms/tentacles on the head of these late Cambrian primitive cephalopods developed from sensitive patches on the head of the primitive proto-cephalopods somewhere in the late Precambrian or early Cambrian, these must have been devices used to feel the immediate local environment, possibly used as a survival aid. Indeed, I imagine they may well have predated the evolution of eyes in molluscs. Perhaps these feelers later developed the secondary function of ensnaring prey when the primitive arms were developed enough to grasp whatever they came across in the environment and push it towards the radula. Thus the path towards a predaceous life amongst cephalopods was set at the earliest days of their ancestry.

I know this is all speculation of mine, and I have never studied zoology, but it sort of makes sense to me!

Cheers,

Phil

(Almost glad he’s off sick for the day; it gave me time to write this!)


BTW, Cheers, GeoffC!
 

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