Organic Formations At The Head Of An Ammonite (And More)

[dragonzrmetal]

Hi, I have a few things to ask for ID here. I mean, I know it is an ammonite, but of course, soft body parts shouldn't fossilise, and even if these formations were tentacles, I would expect to see a "head" of the ammonite.

I'm afraid I can't give a specific era or locale for these ammonites because when I obtained these as a child I wasn't too meticulous about categorising, but it is possible I collected them myself from Charmouth.

I know there are different types of fossilisation depending on whether different minerals in the shell are replaced by others, all I can say regarding that is the shell feels smooth, like enamel, other than the rock that hasn't been removed from the material of the shell.

There are two fossils, one of which has more detail than the other. I hope someone could tell me what this smooth formation at the end of the shell is. It seems wishful thinking that it could be the tentacles. The second fossil has a similar formation with the same smooth texture, but it appears to have been worsely damaged.

It is possible if these are shop bought ammonites the "tentacles" are some sort of glue perhaps, but I'd be more inclined to say I found these at Charmouth; most my shop bought fossils have labels with them.

Here they are: (Apologies for the poor quality; these are the best pictures I could get with my phone.)

I also have some more pictures of other fossils I am unsure about, which I intend to post later after dinner.

Thanks for your time.

[dragonzrmetal]

Also, I noticed Nautilus has a second piece over it's head, in this picture.

http://upload.wikimedia.org/wikipedia/commons/f/f8/Nautilus_side.jpg

Did ammonites have these? Perhaps the organic structure I am seeing is muscle used to move that piece of shell?

[Auspex]

The form you see is the septa, the internal wall between the shell's chambers. Originally, the shell continued out and constituted the animal's living chamber, but this part of the shell is missing.

[dragonzrmetal]

The form you see is the septa, the internal wall between the shell's chambers. Originally, the shell continued out and constituted the animal's living chamber, but this part of the shell is missing.

That makes sense, thank you. It's interesting to be able to observe that since it is usually hidden.

After googling "Septa" I found a similar form here:

http://img2.wikia.nocookie.net/__cb20090226231755/fossil/images/d/d8/1212amma.jpg

I haven't seen a septa look so 3D before, I have another ammonite like this which has broken in places so the septa can be seen, and it is much thinner and flatter, rather than looking so alive. Here it is:

There is no sign of the tentacly/tubular projections on that septa, presumably that is just a case of poor fossilisation.

Would those tubular projections that looked so much like the stems of tentacles be the tubes which carried the gas between flotation chambers and the head of the ammonite?

I have another fossil which I would like help with. It is a partial tail/spine; this one was found loose on Charmouth beach, on the material surrounding a devil's toenail. (Forgive me for not knowing the correct name; I would be willing to learn it.) Unfortunately the rest of the animal is not present because the strata surrounding the devil's toenail runs out. The devil's toenail is much larger than the actual tail, so when the rock broke the rest of the fossil must have been lost, and the animal was not strong enough to hold the rock together.

Anyway, here it is. I have included a more contrasted version of the same image to show the vertebrae more clearly. I don't think it is a fish because I would expect to see a fishtail. Of course I don't know because that is why I am asking, but my guess is it would be a juvenile marine reptile such as a Mosasaur; that matches the locale and time period, but the vertebrae don't seem to match.

The fossil is untreated; I don't know if it should be, or how to do it. I did soak it originally to remove salt; I had atleast that much presence of mind as a child. Any help identifying that tail would be appreciated. I know it's difficult working from such a small fossil, but any ideas would give me more information than I knew beforehand.

Thanks

(Edit- perhaps this isn't a loose from Charmouth. I have several which are, and I don't believe this one is, I must have procured it from a fossil shop at some point; it's been prepared, unlike my others which are still covered in a lot of rock. It's a shame my collection has been so discordant; young children like myself at that time should not be allowed to collect fossils. Apologies.)

Edited July 6, 2014 by dragonzrmetal

[BobWill]

Hello and welcome to the forum. I'm not sure what the last are but they could be a section worn through the ribs of a bivalve.

That's a very nice septum (plural: septa) on your ammonite. What look like tubular projections around the septum are just the folds in the wall. The portion of the body that secretes the material that hardens into the septum (and outer) shell is called the mantel. The mantel that forms the septa is bigger around than the space it fits in so it is folded to fit and that's what forms those shapes. Sometimes the folds are folded again forming the elaborate sutures that can be found on some where the septa meet the inside of the shell.

The siphuncle, the tube that draws liquid from the chambers, goes around the very outer edge of the shell on ammonites but it is not always preserved.

[Auspex]

...I haven't seen a septa look so 3D before...

The edges of these chamber septa are what you see as 'sutures' on ammonites where the shell surface is missing. Different species have different convolutions (they tended to get more complex through time as new species evolved): LINK; the pattern is useful in determining species.

Your other specimen may be a section through the edge of a shell...in any case, it is not any tail spine that I have ever seen.

[dragonzrmetal]

That's greatly increased my knowledge of septa, thankyou. I wonder if that septa is the last the ammonite produced, or if the outer rim/s of the shell is actually missing.

I'm perplexed over this second specimen however. It doesn't seem to follow a natural curve like the edge of a shell would do. What I have just noticed however, is it continues round; it curves. It shows a very clear pattern of getting thinner. I think it might be a spine still, although I'm not pretending to be an expert. I don't know if anyone noticed this.

Were it some sort of marine plant, I would expect those triange protrusions on both sides; if it was some sort of leaf there would be no reason for them to all fall on one side. It doesn't match with vertebrae though because vertebrae tend to have triangle thingies on the top and bottom. Technical vocabulary here.

Edited July 6, 2014 by dragonzrmetal

[BobWill]

As an ammonite grew and built an ever-bigger shell around the body, it would occasionally move forward toward the new aperture, pull loose from the septum it just built and begin building a new one. You can't tell if a septum is last unless the body chamber is present. The body often takes up half a complete whorl. A whorl is one revolution around the shell. Sometimes when the sutures are visible on the surface you can see where they end and assume the rest of the shell housed the body.

For the other fossil, imagine a denture clam cut or worn long-ways in half. Yours may be something like that.

edit: I used to think the body chamber was usually missing because of predation but a forum member explained that that part of the shell was more vulnerable to breaking because it was not supported by septa which make a lot of sense.

Edited July 6, 2014 by BobWill

[dragonzrmetal]

They are two different patterns actually; they don't connect to each other. BobWill/Auspex were right in saying it's a section of a bivalve. There is also a shell on the bottom of the rock, so it would make sense that there were more shells in the strata. I'm very tempted to try and remove some of the rock above the edge to see how far the shell continues, but I'm not sure how I'd go about doing that.

I don't think I would try and extract any of the shell pieces because it looks difficult for little gain; all the pieces are broken, and they are probably better as part of the devil's toenail. I can see maybe six slivers of shell protruding from the strata, so this is some sort of necropolis. Presumably these are the result of the current carrying dead material to one place?

Thanks for all the help.

I just read the last post; I didn't know the body chamber was larger than the rest. I can tell therefore from my polished ammonites that the outer whorl has been broken off. Is this common practice, to make it look better? It seems unnecessarily destructive.

[Auspex]

...I just read the last post; I didn't know the body chamber was larger than the rest. I can tell therefore from my polished ammonites that the outer whorl has been broken off. Is this common practice, to make it look better? It seems unnecessarily destructive.

The final living chamber, not being buttressed by a septum (it is necessarily open at the end, to accommodate the animal), is thereby more fragile and doesn't always preserve.

[BobWill]

The body chamber isn't removed by collectors, it's just not present when found.