Cephalopod Question

[hrguy54]

There's been a lot of discussion lately about cephalopods. They seem to come in three basic different shapes:

Round...

Flat on one side...

Oblong...

Are the shapes due to different kinds of cephs or just the way they fossilized?

[BobWill]

Those are some nice looking specimens. I think you may have a misunderstanding about what a cephalopod is though because they come in quite a few more than 3 shapes. What you have are orthocones, which is just a description of the nautiloids that have straight shells. Nautiloids can also have coiled shells like some ammonoids which are also cephalopods of a different sub-class, and then there are cephs with just an internal shell or none at all like an octopus. Those are another sub-class called coleoids. So cephalopod is a class of mollusk (so are gastropod and bivalve). Your cephs are nautiloids, and your nautiloids have orthocone shaped shells.

The orthocone with a flat side is probably worn down to that shape and the oblong one is just crushed as you said during fossilation. They are mostly round but can taper at different rates. Many nautiloids and most ammonids coil like a flat snail but some ammonites curve around in very odd shapes. Those are called heteromorphs. Hope this helps.

Bob

Edited July 17, 2013 by BobWill

[Bev]

I'm going to jump in on this because I basically have the same question. Above ARE cephalopods? And they are orthocone cephalopods, right?

Now I am out there on the gastropod question again. Gastro pod = stomach in foot.

Cephalopod = brain in foot

A gastropod is not a cephalopod? A class of its own?

I run across these somewhat curled, but loosely, things upon occasion (sorry, don't have a pic). I've always just figured they were broken gastropods and threw them on the reject heap. Could they could be cephalopods? I ask because recently I was at a museum and they had some really big cephalopods (labeled) that were in a loose curled shape.

Bev

[BobWill]

A gastropod is not a cephalopod? A class of its own?

I run across these somewhat curled, but loosely, things upon occasion (sorry, don't have a pic). I've always just figured they were broken gastropods and threw them on the reject heap. Could they could be cephalopods? I ask because recently I was at a museum and they had some really big cephalopods (labeled) that were in a loose curled shape.

Bev

That's right Bev, all gastropods coil with whorls touching. Any mollusk with loose curves is a cephalopod, and probably an ammonoid. But the biggest difference between the shells of two is what they leave behind their body as they make the shell. In a gastropod there is just water filling otherwise empty shell. In a cephalopod there are chamber walls (septa) which serve to seal off air pockets. This gives them the buoyancy, like a fishes swim bladder, to swim. Some were likely poor swimmers and probably crawled along the bottom like a gastropod. Google a picture of Nipponites for an example. Another heteromorph I find here in Texas is Ideohamites, it may have been able to swim but Turrilites probably didn't given it's spired coiling like a gastropod.

Edited July 17, 2013 by BobWill

[Bev]

Ah, ah, my understanding is that there are no ammonites in the Ordovician of Minnesota... Just what I think I understand.

Worse yet, the ammonites I see everyone putting up have coils touching... I have one from Morocco that way.

AND worse yet, some of the "cephs" I have pictured above do not have "chambers" showing... Not cephs?

[mikeymig]

Bev, Ammonites first evolved from Devonian cephalopods like Bactrites that I find here in NY. Some of your specimens may not exhibit chambers because they look like they could be cast but they are still cephalopods.

Mikey

[BobWill]

Mikey is right Bev, chambers only show on an internal mold. An external cast only shows features on the outside of a shell. Since the shells of cephalopods were fairly thin you can see mostly the same ornamentation on an internal mold or cast that you see on the outside. Compare that to a bivalve where you can see growth lines outside but only the smooth surface of the last layer laid down on the inside.

The part I find confusing is the term "ammonite". Even though there is an order of ammonoid called "ammonitida", not all ammonites are in it. For example lytoceratids are ammonites of another order. Also "ceratitida" and "goniatitida" are orders of ammoniod but every ceratitid is a ceratite and every goniatitid is a goniatite. The terms ammonite, goniatite, and ceratite are meant to be a comparative description of the complexity of the suture folding, not taxonomic terms. As Mikey suggested the complexity increased over time and no ammonoids had developed enough complexity in the suture folding to qualify as ammonites until very late in the Permian.

Bob

Edited July 17, 2013 by BobWill

[Wrangellian]

My understanding is that true ammonites did not appear until the latest Triassic in North America and lowest Jurassic in Europe.

Everything that came before is either an ammonoid (Goniatites, Ceratites..) or a Nautiloid (Bactritids, orthocones, etc). Nautiloid may be even more of a catchall term than ammonoid, speaking of the Paleozoic at least.

[BobWill]

My understanding is that true ammonites did not appear until the latest Triassic in North America and lowest Jurassic in Europe.

Everything that came before is either an ammonoid (Goniatites, Ceratites..) or a Nautiloid (Bactritids, orthocones, etc). Nautiloid may be even more of a catchall term than ammonoid, speaking of the Paleozoic at least.

That's what I told someone a while back and someone on here brought up an ammonite from the Permian. I can't find the post but I see in the "Treatise on" where Perrinites hilli is described as an ammonite even though it is in the Goniatite order. This means I am wrong in comment #7 here when I said that all goniatids are goniatitic.

The quote in the treatise is "...well-developed ammonites (e.g., Perrinites) are known from the middle Permian."

[Wrangellian]

That's what I told someone a while back and someone on here brought up an ammonite from the Permian. I can't find the post but I see in the "Treatise on" where Perrinites hilli is described as an ammonite even though it is in the Goniatite order. This means I am wrong in comment #7 here when I said that all goniatids are goniatitic.

The quote in the treatise is "...well-developed ammonites (e.g., Perrinites) are known from the middle Permian."

Well then I wonder, having not read that work, if the term 'ammonite' in this case is used to describe complexity of sutures, rather than relationship to the Jur/Cret group.. (assuming the Jur/Cret group is not directly descended from Perrinites/etc)

[Wrangellian]

These could be better but are the best I could find via Google Image search in a short time. Apparently these are from the Neb State Museum and I already lost track of the photog's name(s) so hope I dont get reprimanded for copyright issues. (I altered them slightly for size/clarity). I'd like to see a better version of these, in drawing form rather than photo, with clearer age ranges - if anyone has them please contribute!

Anyway, I have always understood that the Ammonitina as labelled here are the true Ammonites whereas everything else, on separate branches, are called ammonoids due to their relation or resemblance to the Ammonites.

EDIT: Just remembered that Lytoceratina and Phylloceratina, although survived into Cretaceous, are on separate branches but are commonly referred to as ammonites as well, so in that sense the term is polyphyletic. (Also the Ancyloceratina? Does that include the heteromorphs? I'm not sure on these details)

Point is I guess you could define an ammonite (etc) on the basis of its suture type or on its presumed genetic relationship, and the results won't necessarily be the same. Apparently 'Goniatitid' is also a grab-bag term, speaking genetically.

Edited July 24, 2013 by Wrangellian

[BobWill]

I know we've come a long way from my 1957 edition of "The Treatise on Invertebrate Paleontokogy -Part L- Mollusca - Cephalopoda Ammonoidea" but even back then it describes the terms ending in "ites" as being "useful in a broad way, as well as in a very restricted sense for genera with relatively narrow limits". It says the terms originated as generic names when classification was primitive and that now (1957 lol) intermediate forms allow less latitude.

To make sense of it all it may help to focus on the ending of the words and maybe a professional can round off my corners here but looking at definitions I could find I have concluded:

"ites" is used for a description of sutures, e.g. ammonite, goniatite

"tic" is the adjective for those descriptions. e.g. goniatitic

"tina" is the ending for the order, e.g. Goniiatina, Ammonitina, Lytoceratina

"oidea" for a sub-class, Ammonoidea, Nautiloidea

"tid" may be one of those corners but from the context just seems to refer to an individual specimen.

Edited July 25, 2013 by BobWill

[PA Fossil Finder]

That's right Bev, all gastropods coil with whorls touching. Any mollusk with loose curves is a cephalopod, and probably an ammonoid.

Not completely true. Sorry to confuse you more Bev but take a look at the recent shell of the worm snail, Vermicularia knorrii.

Pictures can be found of it here. I wouldn't be surprised if there were fossil examples as well.

Edited July 25, 2013 by PA Fossil Finder

[Wrangellian]

I know we've come a long way from my 1957 edition of "The Treatise on Invertebrate Paleontokogy -Part L- Mollusca - Cephalopoda Ammonoidea" but even back then it describes the terms ending in "ites" as being "useful in a broad way, as well as in a very restricted sense for genera with relatively narrow limits". It says the terms originated as generic names when classification was primitive and that now (1957 lol) intermediate forms allow less latitude.

To make sense of it all it may help to focus on the ending of the words and maybe a professional can round off my corners here but looking at definitions I could find I have concluded:

"ites" is used for a description of sutures, e.g. ammonite, goniatite

"tic" is the adjective for those descriptions. e.g. goniatitic

"tina" is the ending for the order, e.g. Goniiatina, Ammonitina, Lytoceratina

"oidea" for a sub-class, Ammonoidea, Nautiloidea

"tid" may be one of those corners but from the context just seems to refer to an individual specimen.

I think -id is anything that belong in a particular group. Eg. ceratitid = ceratite + -id = member of the ceratitids (a ceratite) Maybe I should wait for the pros to smooth this out too..

[Herb]

There's been a lot of discussion lately about cephalopods. They seem to come in three basic different shapes:

Round...IMG_0762 (1280x960).jpg

Flat on one side...IMG_0763 (1280x960).jpg

Oblong...IMG_0764 (1280x960).jpg

Are the shapes due to different kinds of cephs or just the way they fossilized?

Those are all the same type just preserved differently, or partial sections of orthocone cephalopods.

[Herb]

Molluscs include mostly cephalopods (squid-like critters), gastropods (snails), pelecypods (clams) and scaphopods and a couple rare side orders (monoplacophora and cricoconarida).

All lower Paleozoic cephalopodas are Nautiloidea with very simple suture lines, there are only 2 living Nautilus' today the paper and the chambered. Fossil nautiloids can be straight, curved, bulbous or coiled in form.

The hey day of the ammonites was the Mesozoic era where they flourished in many forms, mostly coiled but there were some loosely coiled forms also (see pix). There are no modern forms. They had complex, convoluted sutures. Ammonites died out at the end of the Cretaceous. Scaphopods are straight shelled molluscs (tusk shells). The two ammonites pictured at the bottom are loosely coiled types.attachment=199467:Audoliceras-t.jpg]ttachment=199468:Notoceras-indopacificum-t.jpg]

Gastropods (snails) come in many forms including tight and loosely coiled forms (Vermetus sp).

Hope this helped someone out .

Edited July 27, 2013 by Herb

[Wrangellian]

Herb, those pics you posted are heteromorph ammonites but their juxtaposition with your wording about loosely coiled gastros could be confusing to those who don't know!

[BobWill]

, there are only 2 living Nautilus' today the paper and the chambered. They can be straight, curved, bulbous or coiled in form.

This could be taken wrong too. I'm sure Herb means to say that "fossil" nautiloids may be coiled or not, not extant ones

Also I'm anxious to hear about any loose coiling gastropods from the fossil record. Thanks to PAFF for telling us about the worm/snail.

[Bev]

Wow, you guys lost me a long time ago...

Sorry, this is so much over my poor little pea brain that, well, all I can do is read words not understanding them. But at least you all seem to be having fun discussing it.

Bev

[PA Fossil Finder]

Also I'm anxious to hear about any loose coiling gastropods from the fossil record. Thanks to PAFF for telling us about the worm/snail.

Here is a few examples I found rather quickly searching the internet: here, here (those two shell pics on the bottom of the page), and a TFF post here.

[Herb]

Herb, those pics you posted are heteromorph ammonites but their juxtaposition with your wording about loosely coiled gastros could be confusing to those who don't know!

Thanks, I see your point. the editing might be less confusing now.

[Herb]

Herb, those pics you posted are heteromorph ammonites but their juxtaposition with your wording about loosely coiled gastros could be confusing to those who don't know!

Brutal! OK I reworded it.

[Bev]

This could be taken wrong too. I'm sure Herb means to say that "fossil" nautiloids may be coiled or not, not extant ones

Also I'm anxious to hear about any loose coiling gastropods from the fossil record. Thanks to PAFF for telling us about the worm/snail.

I'm doing some "re-reading" and slowly understanding more... :-)

Here is the gastropod Maclurites crassus. My understanding is that only 1 in 50 Maclurites in this area are the loosely coiled crassus - from Caleb. I actually prepped this one out so that you can see the loose coiling. And you can't tell from the front whether it is a Mac crassus or not - only from the back.