Talk:Ammonoidea

Added text from article I originally wrote in 1998 and published it on the Web....

Dlloyd 20:05, 27 Jul 2004 (UTC)

Portions of this text are :

"Copyright © 1995-1997 The Fossil Company Ltd. © 1997-1999 The British Fossil Company Inc. and licensed by the owner under the terms of the Wikipedia copyright." Please contact me if you need further clarification on this.

Dlloyd 00:39, 30 Jul 2004 (UTC)

Aptychus

Could use some more clarification on the aptychus/anaptychus. I've also heard the term diaptycus used. There is now also an article at aptychus. --DanielCD 20:51, 4 May 2005 (UTC)

Classification

I am currently working on getting the classification straightened out in this article and standardized across all the ammonite articles. --DanielCD 15:20, 6 May 2005 (UTC)

Fantastic! - UtherSRG 16:09, May 6, 2005 (UTC)

Hey, I corrected "Ceratida" to "Ceratitida" on this page -- sorry if that screws up the other pages, Daniel! - PKaplan

I don't think the current classification on the page is OK. Here is what I came up after some research. I tried too look up references for each entry. I'll finish this tomorow and after everything is verified I will replace the current one or create a "List of families" page. Any additions are welcome. Lejean2000 16:31, 31 January 2006 (UTC)

---

Moved to my user page Lejean2000 20:54, 7 February 2006 (UTC)

---

I did a lot of searching for proper classification, and it's a royal pain. There are a multitude of different schemes. Also: several people have monkeyed with it since I last looked at it. If you think you've got one that works, please put it up for discussion. --DanielCD 19:59, 31 January 2006 (UTC)

I did some more work on this. You are right - it is insane. I decided to doublecheck all taxa for references in peer-reviewed journals and include them in the final list only after I am sure there is at least some consensus among researchers. For now I think we should stick with this scheme: order-superfamily-family. I am not sure I want to include subfamilies because there are lots of problems even at the superfamily level. So I guess this will take a while. I will keep my latest list here; it's been verified to some extent, but I had to make some hard decisions myself. After I decide its finished I will email this list to a few researchers in the field for comment. The links above are just for reference, they do not point to any definite sources. By the way, does anyone know how many families are there in total?

Lejean2000 16:15, 1 February 2006 (UTC)

Whoa. Anyone have any ideas as to exactly how many orders of ammonite there are? The classification here only gives a few, but the Sepkoski database seems to list some others which I may have missed while compiling the List of ammonites. Any help finding what orders are really ammonites in that database that didn't get added to the list would be appreciated. Abyssal leviathin 17:50, 13 October 2007 (UTC)

Irridescence

I noticed someone put the term ammolite in the sentence on irridescent ammonites. It should be noted, however, that ammolite and the irridescent ammonites are not quite the same thing. I'll have to look into it again and refresh my memory before I make any changes though. If anyone can clarify the difference, please do. --DanielCD 14:44, 29 November 2005 (UTC)

Ammon

Ammon, as well as being the name of an Egyptian god (also spelt "Amun", "Amon", "Amen" and "Imanand"), is the name of a people living along the Jordan river in biblical times. Unfortunately the link 'Ammon' takes us to the Jordanian peoples, not the Egyption god. I am not sufficiently trained in editing Wikipedia pages to fix this. I think the 'Ammon' Page needs a Disambiguation Page. —This unsigned comment was added by 139.168.9.181 (talk • contribs) .

I'll try to look at it today sometime. --DanielCD 13:06, 23 March 2006 (UTC)

The disambig already existed. All that was needed was a {{otheruses}} at the top of Ammon. - UtherSRG (talk) 18:40, 23 March 2006 (UTC)

Excellent article, one query

Only the last and largest chamber, the body chamber, was occupied by the living animal at any given moment. As it grew, it added newer and larger chambers to the open end of the coil. I've seen statements to this effect before, but I still don't understand how this proposition can be correct. It would mean that ammonites that died old would have more whirls than ammonites that died young. But, for example, Asteroceras Obtusum always has five whirls, regardless of size or age at death. Regards, Nick. Nick 08:50, 10 May 2006 (UTC)

Interesting question. If I come across an answer, I'll let you know. I do know that the modern Nautilus grows by adding new chambers, and I'm sure the ammonites did as well. As for the whirls... One of us might be missing something. I'll leave a message about it on Neale Monks' talk page as well. --DanielCD 22:42, 10 May 2006 (UTC)

I just consulted a book that tells me they contiued to grow more whorls as time passed. Is what you're referring to something peculiar to this certain species? Most ammonites didn't have just five whorls. They could grow many more than that. The book I have here refers to one with twelve. What is the source of the "five whorl" idea and I'll try to look it up. --DanielCD 22:55, 10 May 2006 (UTC)

Asteroceras obtusum does seem to have five whorls, if examples like this are any guide: <http://www.fossilwalks.com/ammonites/pages/aste.htm>

Most likely, all the specimens are found with five whorls because they're all adults, or almost fully grown. The modern nautilus (which is rather different from ammonites but whose shell provides the best living analogue) hatches with only a few chambers and grows by adding chambers toward the aperture and adding new whorls. All nautilus go through a stage with fewer whorls, yet most nautilus shells you'll see have the full adult number of whorls because juvenile shells are rarely recovered.

Perhaps Asteroceras obtusum has a range of sizes as an adult. Thus one may get the impression that there are juveniles with five whorls, when actually they are simply small adults. Some cephalopod workers, for instance Dr. Walter Manger at the University of Arkansas, have argued that ammonoids may have a life cycle like modern squid, spawning only once and then dying. That would explain why we find large numbers of adults buried at once, but few juveniles.

Cephal-odd 01:54, 11 May 2006 (UTC)

Thanks for your comments on my comments. It would also be interesting to count the chambers in a number of sectioned ammonites of the same species to see if the number of chambers was always the same (unfortunately, I don't have the material to do this). But if the number of chambers was always the same, there might be some more explaining to be done. Regards, Nick. Nick 11:36, 11 May 2006 (UTC). Added later for DanielCD: sorry, yes, I meant within any one species, but taking A. obtusum as an example because of the sheer number of specimens that have been recovered. Regards, Nick. Nick 11:52, 11 May 2006 (UTC)

I'm not sure where the "five whorls" idea came from. The ammonites I worked with, heteromorphs, often had fewer and many times had more whorls than that. It seems an arbritary number. It's also very difficult to count the whorls from a photo; in most species, the early whorls, particularly those of the larval "ammonitella" stage are obscured by the later whorls.

Ammonites didn't have a fixed adult size, but growth rate dropped considerably once they reached a certain size. You get something bext described as a bunching of the chambers, where instead of having them evenly spaced out, the last few chamber walls (septae) are bunched together, almost on top of each other. It's pretty obvious that these are adult specimens, and you even see deformities creep in on the very old specimens, analagous to those you see in other very old molluscs. But otherwise, I'm not convinced anyone really knows how old ammonites got, except to say that some species lived for longer than others, but all seem to have lived longer than the 1-4 years typical of modern coleoid cephalopods [1].

In my opinion, nautilus is a non-starter as a model for understanding ammonite growth rates. It lives in deep, cold water. Deep water means high water pressure, and that slows down the rate at which new chambers can be filled with gas. Cold water slows down metabolism, which slows down growth. So I'd expect nautiluses to be far slower growers than most ammonites, which seem to have favoured shallow, tropical and warm temperate seas.

I have heard the "live fast, die young" model applied to ammonites, and it is attractive. But I don't think it is likely. What growth rates we have, based on measuring seasonal changes in the isotope compositions of ammonite shells, seem to indictate that they lived for many years.

Neale Monks 15:23, 12 May 2006 (UTC)

Thank you for your response Dr. Monks. It is appreciated. --DanielCD 16:40, 13 May 2006 (UTC)

It's heartening to see world-class experts writing for Wikipedia and I'd like to second DanielCD's thanks. I might not have explained myself very well, so at the risk of dragging things out I'd just like to restate my problem.

A friend of mine has over the last thirty years or so has had hundreds of specimens of A. obtusum pass through his hands, mainly from Black Venn and from the area at Charmouth where the flatstones come down to the beach. In conversation he once mentioned that every complete specimen he had ever seen had five whorls; never four and never six, but always five. For myself, I've come to regard five whorls as being one of the defining properties of A. Obtusum and I think that a specimen having four whorls or six whorls would look so odd as to attract immediate attention.

The proposition is that the creature occupied a living chamber and that when it outgrew the chamber it created a new one next door and moved into it. Over the life-term of the creature this sequence was repeated many times and created the characteristic spiral shape of the ammonite. So, on the face of it, one would expect to find at least a few specimens of A. Obtusum with fewer or greater than five whorls, but so far as I'm aware such specimens do not exist. I find this difficult to reconcile with the idea that the creature repeatedly built and occupied new chambers in the way suggested (but from what I've written you'll be aware that I have no expert knowledge in this field).

Regards, Nick. Nick 09:51, 15 May 2006 (UTC)

Just a clarification really. I suppose by complete specimen what you actually mean is a fully-grown adult specimen, i.e., one that shows bunching of the septae when sliced in half. That would be fair statement to make, I would imagine. I don't know Asteroceras at all well, despite having collected a few as a kid in North Somerset. I really can only admit to being familiar with Albian and Cenomanian heteromorphs. Anyway, I'd see not problems with saying that once A. obtusum got to a certain size, growth slowed down dramatically, and most specimens probably died from old age or predation before they were able to grow a sixth whorl.

However, while an obvious point, we should state it up front: juveniles must have had fewer than 5 whorls. Newly born ammonites (ammonitellas) have a single open whorl. Once out of the egg, they seem to quickly add the second, third, and subsequent whorls, until reaching some pre-programmed adult size, when growth slows down almost (but not quite) to a halt. In other words, if you had a life assemblage of A. obtusum, a mix of adults and youngsters, you'd find a variety of shells, many with 5 whorls perhaps, but some with fewer.

The difference between slow growth and no growth is subtle but important. In humans, for example, we reach adult size and stop growing (in height, anyway!). For any given sample of adults, the biggest specimens are not necessarily the oldest. Size depends on genes. Now, if you looked at reptiles, say crocodiles, you'd be looking at animals that grow continuously. The biggest specimens are almost always the oldest ones. Genes are a factor of course, but age is the prime one.

So far as I know, all living molluscs fit this pattern, and I don't see any reason to assume otherwise for ammonites.

Thus, even if all the adult Asteroceras have 5 whorls, if you actually counted the chambers, you'd probably find the largest specimens have more chambers, and many of the walls separating the later chambers would be bunched. Conversely, slightly smaller specimens would also have 5 whorls, but they hadn't reached the point where growth had slowed down, and hence would have few if any bunched septal walls.

Cheers, Neale

Neale Monks 17:38, 17 May 2006 (UTC)

Hello all! I am a Canadian paleontology grad student (graptolites) who previously worked on Jurassic ammonites. I thought I would offer an analogy that might clarify things.

Imagine studying a human ‘death assemblage’, i.e., a graveyard, and doing a study on size variations of the human remains. You would immediately notice that the vast majority fell within a size range of 5-6 feet. Perhaps if your sample were small enough you might not find any juvenile specimens. There are two reasons for this. First, after the initial risks of infant mortality, likelihood of death in a given year does not really start to substantially increase until old age (e.g., your '5 whorl' size). Second, humans, like ammonites, maintain their adult size for a longer period of time than then any given stage of their juvenile size. As Dr. Monks notes, although adult ammonites continue to grow, it is at a substantially decreased rate, and although new chambers are added, new whorls will likely not be. So, not only is a larger percentage of any given living population at the 'adult stage' than any intermediate stage, but the risk of dying in that stage is substantially increased, both because risk of death rises again at the end stages of life, and because the period of time occupied by the adult stage is so much longer than juveniles, so the cumulative risk of death is in this stage is higher. Now, humans are ‘adults’ for about 80% of their lives, and this is likely a much, much longer ratio than ammonites, but it should give an idea on how a palaeontological sample (which is a census of death, not life, remember) can be biased towards adult forms.

Add to this a few other points: 1) There is likely a preservation bias towards adult specimens, since the quiet death that results in a preserved shell (rather than a smashed one) disproportionately results from age related effects, e.g., disease, senility, etc, rather than, for example, getting eaten by a marine reptile; 2) There is likely also a collection bias, as the most prized specimens for any collector (the ones most likely to be taken out) are always large, complete ammonites; and 3) there may well be an additional geographic effect, i.e., it is possible that for this species different life stages were completed in different habitats and that the collecting areas represent only adult stage habitat (this is pure speculation for this species, I don't know anything about it). For example, mass accumulations of belemnites have been argued to result from post-mating die offs (like salmon) in shallow waters, while regular habitat was in much deeper waters, a pattern seen in some modern squids. If this were the case you would expect to see only sexually mature specimen, i.e., adult specimens, in some outcrops.

Hope this helps!

Cheers!

Jason Loxton —The preceding unsigned comment was added by 141.109.52.63 (talk • contribs).

Thank you for that. --DanielCD 04:47, 20 May 2006 (UTC)

GA Sweeps (on hold)

This article has been reviewed as part of Wikipedia:WikiProject Good articles/Project quality task force in an effort to ensure all listed Good articles continue to meet the Good article criteria. In reviewing the article, I have found there are some issues that may need to be addressed.

• There is a complete lack of inline cites that needs to be addressed.
• The cites that do exist need to be converted to {{citeweb}} format.

I will check back in no less than seven days. If progress is being made and issues are addressed, the article will remain listed as a Good article. Otherwise, it may be delisted (such a decision may be challenged through WP:GAR). If improved after it has been delisted, it may be nominated at WP:GAN. Feel free to drop a message on my talk page if you have any questions, and many thanks for all the hard work that has gone into this article thus far. Regards, Corvus coronoides _talk 00:28, 18 October 2007 (UTC)

GA Delist

In order to uphold the quality of Wikipedia:Good articles, all articles listed as Good articles are being reviewed against the GA criteria as part of the GA project quality task force. While all the hard work that has gone into this article is appreciated, unfortunately, as of October 25, 2007, this article fails to satisfy the criteria, as detailed below. For that reason, the article has been delisted from WP:GA. However, if improvements are made bringing the article up to standards, the article may be nominated at WP:GAN. If you feel this decision has been made in error, you may seek remediation at WP:GAR.

• Currently, in-line cites do not meet GA standards. Cheers, Corvus coronoides _talk 13:35, 25 October 2007 (UTC)