Ammonite reconstructions with aptychus


Apr 10, 2006
As some of you probably know I made several small nautiloid-models some time ago. I wanted to sculpt another bigger (and more detailed) model, similar to the giant orthocone from the sea monster documentation of the BBC, because this reconstruction looks very impressive. The shell is already made, and the radula too. OK, at this this step problems began. I used mainly nautilus beaks as pattern, but then I discovered that their beaks were really completely different from those of nautilus and that there is furthermore the problem of the correct reconstruction and position of the aptychus. Most models and illustrations show no aptychus but more some kind of hood-like skin double similar to those of nautilus. I have now really the problem that I have no good pattern of orthocone beaks, radulas and aptychus.
During my search for immages of nautiloid oral anatomy, I found a very interesting site which deals with this topic. There are also some very good reconstructions of ammonites with several types of aptychus:
The site is in german, but the pictures alone are surely very interesting (and still a bit confusing).
Coincidentally some of those wonderfull fossils with complete aptychus were found only about 30km away from where I live.
By the way, has somebody a picture of the ammonite with the preserved soft body?
Thanks for the link Sordes -- I'm making this sticky to give it front page promotion! Good content here. As with others, I'll "unstick" this thread once it ages off the "...More recent announcements" section at the bottom of the homepage.
Wow Sordes - thank you for the link - I learned some new things even though I can't read German! I thought the hood (and I guess that was the way paleontologists originally depicted ammonites) was on the dorsal side of the tentacles, not ventral. I guess you can't really apply much of what is known about living Nautilus to ammonites. Living Nautilus cannot totally retract its tentacles inside the shell but it seems like paleontologists think that ammonites could (in panic mode :goofysca:).
I think your giant orthocone would be fine with the beak and hood of a Nautilus. Orthoconic nautiloids are probably more closely related to Nautilus than they are to Coleoids or ammonoids.

As far as I know no fossil has ever been found showing the soft parts of any externally shelled cephalopod, so whatever you come up with is just as right as anyone elses idea of what they actually looked like. In the latest issue of Palaeontology there is an paper on fossil jellyfish showing quite remarkable preservation (they look like molds in soft bottom sediment[lithographic limestone like the sediment in your link, where only the shell and aptychus are preserved]), meaning maybe their bodies (the jellyfish) were more robust than any externally shelled cephalopod(?).

As for the aptychus being used as an operculum, the link has some very convincing illustrations. Myself, I still think they were just very large lower jaws that got repositioned in the shell prior to fossilization. But then I still picture dinosaurs dragging their tails on the ground behind them. :wink2:
The fossil of the orthoconic Orthoceras shows also a very well-developed aptychus. Does anybody have a good reconstruction of a nautiloid beak? Nautilus beaks are comparably easy to sculpt, and I think nautiloid beaks wouldn´t be more work, but I have to know how they looked. It is often very frustrating that the reseach for a sculpture can need more than the the scultping itself. Perhaps I´ll find the time to translate some parts of the link.
Great find Sordes, thanks for posting it. :cool2:

I can't read German, so I ran the page through the Google translator to convert it to English here

--Carl - noting that Mr Google has lousy syntax :hmm:
So, that´s my translation. I did not translate everything word by word, but more to translate the sense of the article. Sorry for the many grammatical mistakes, but my english is not best. Hopes it helps you anyway:

Nautiloids and squids have since their very early beginnings small beak-like jaws.
Ammonites in contrast had much larger "shovel-jaws" (Anaptychus and Aptychus) and it seems that even the early ammonites from the early shale deposits had such shovel-jaws.
There are different views of the acception of the aptychus which are sometimes seen as cap (opercula) instead as an enlarged lowe jaw, but the known fossils indicate more a function as seen in the models. Ammonites are often shown with predator´s tentacles, but the fossil contents of their guts show only a diet which consisted of very small animals. Furthermore strong predator´s tentacles seems to fossilize comparably often as seen in finds of coeloids, so the tentacles of ammonites were probably not very strongly built. Since 1976 it seems to be a fact that the aptychus was an enlarged lower jaw, which seems to be part of the apparatus the ammonite used to catch prey, because it was useless for a predatory lifestyle and much to big with a hypothetical buccal-musculature for a retraction in the living-chamber of the shell. Ammonites possed a radula, but their shovel-jaws can´t be compared with the much smaller jaw-apparatus of all recent cephalopods. But to see the aptchus simply as some kind of lid, similar to those of nautilus, is in contrast to the ammonite-research of the last decades.

A less known fossil of Orthoceras sp. from the swedish silurian with aptychus in closure-position. The author don´t think that it is a real "cover-position", but it could be that there were already "drawbrige-function" in the early silurian, similar to those of the models.

A Gyroceratides with lower jaw shows that already the early ammonites had another trend in jaw-development than other cephalopods.

The first sensational find of a Radula of the giniatite Eoasiantites from the
carboniferous of Uruguay which were also discovered in some jurrasic ammonites in the following years.

Isolated parts of the oral apparatus of ceratites show that ceratites had more a shovel-jaw than a beak-jaw.

As the author found this 3,4cm long Lissocerate with aptychus in clossure-position, he recognized that the aptychus could not have had a similarity with a beak-jaw.

A nautilus from the limestone of Nusplingen shows how small the beak jaws of nautilus are and that it makes no sense to compare them with the huge shovel-jaws of ammonites.

An interesting find of a aspirocerate from the limestone of Nusplingen which shows a lower shovel-jaw and a rudimentary upper "jaw". This picture shows the enormours difference in size to the jaws of nautilus.

A specimen of Eleganticeras elegantulum wit large lamellar aptychus which were the basis of the examinations of Prof. Lehmann, that the aptychus a in biological sense a large-grown lower jaw.

Prof- Lehman published this jaw-apparatus in 1976 , but it has still to much similarity to the beak of nautilus. Such a jaw with its buccal-musculature would be much to large for a retraction in the living-chamber, but many people still overlook this.

Orthaspideoceras uhlandi with Laecaptychus shows us that the aptychus had no function as some kind of jaw apparatus, but a completely other function.

The big aptychus must have had another function, and the way of live of some ammonites could indicate the it had more a protective function and was probably part of the skin between the tentacles and used to catch prey, as shown at this model.

This model shows the aptychus as part of the capture-apparatus. Reconstruction of Kosmoceras with granula-aptychus.

Model-test with Taramelliceras, whose origianal aptychus was not able to cover the living-chamber completely.

In this Distichoceras for example the Aptychus fits best in a drawbridge-function. That means that ammontites "draw their lower jaws over their heads" when they were in danger.

Model-test with colour, some ammonites show relics of colour.

The meaning of colour was probably more important for camouflage than for beauty

When ammonites did swim, the tentacles with the folded skin between them were situated on the aptychus. But it seems that the favorite swimming-orientation was forwards and not backwards.

The chalky aptychus was covered with an organic surface, which would only make sense if it was situated on the surface of the animal.

Oppened capture-funnel of a Distichocerate. Two of the (suposed) original 8 tentacles bolster the moves of the aptychus at the capture-funnel.

Ammonites had probably analogous to sepias spheric lense-eyes, because they had a similar lifestyle.

There are several isolated finds of ammonites with closed "lower-jaw protection-shield", and it seems probable that there was some kind of drawbrige-function, but the dream-fossil of an ammonite which shows all details is still not known.

Prof Lehmann:" There was a huge differenciation in ammonites, and only because some of them had proably such a function of their aptychus, not all of them must have had it. Probably a shovel-beak was used to chase swarms of ground-living epibiontes. The extraordinairy jaw-apparature had its origins in the head of the gullet."
Theo Engeser has a hypothesis here stating some orthocerids, the ammonoidea and the coleoidea may belong to a group, the Neocephalopoda, based on the number of radular teeth and size of eggs among other things, perhaps this group could be divided further into those with large lower beaks used as opercula. Of course this would mean dividing them up into those with external shells needing opercula and those with internal shells not needing opercula. First the existence of large lower jaws would have to be shown in all ammonoids, and small upper and lower jaws would have to be shown in the remaining nautiloids. Or maybe some of each used the lower jaw or something else(?) as an operculum... sure would be nice to find some fossils that could answer all these questions.
Well, the nautiloid-model is nearly finished and just in the oven. The only thing which is still absent is the cap on the top of the head, but I´m still not sure if I should scuplt it with or without such a cap, because it looks also very good without it. The whole model is now about 25cm in length and will also get a comparbly big base with corals, sponges and rocks.
I decided to sculpt it with a cap on the top of the head, similar to those of Nautilus and finished today the model. Now I need only a base for it.
I posted the photos of my model in the thread Phil opened "Sordes amazing nautiloid models".
But to come back to the main topic, the aptychus. Two days ago I was once again in the paleontological institute in Tübingen and discovered some nice nautiloid models with relics of the aptychus.
The largest one was neraly the size of a car tyre and showed a real large aptychus, from which each part was about 10cm or so in length. Sadly the photo isn´t very sharp.


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The "Orthoceras with aptychus" is an oddity to me... but it does indeed appear to be a nautiloid with an aptychus. Of course the ammonoids may have inherited the aptychus from their ancestors; the more modern nautiloids do not have one. I think, however, that this specimen may be a mislocalized baculitid ammonoid or else that rather than being an aptychus, this is a calcified hood. It does appear to have 3 components, which aptychi do not.

Earlier ammonoids (eg ceratites and phylloceratoids) had an anaptychus, which is a unitary lower jaw. These can be locally common, often with no signs of shells, as I have seen in the field not too far from my home. Anaptychi are deeply convex. They are about the right size to seal the aperture, with the tip of the beak laid against the previous whorl of the shell and somewhat resembling the hood of Nautilus. The aptychus was a solid object, and appears to have been a fully functional biting jaw. Phylloceratoidea, the only superfamily to survive the Triassic-Jurassic extinction event, had an anaptychus. At least the middle Triassic members of Ussuritidae did. However the lower jaw, aptychus, of their descendants was hinged in the middle, and the preserved parts are flat; when the animal was fully retracted the aptychus neatly closed the aperture. The aptychus would appear to have lost its biting function; perhaps, as well as functioning as an operculum, it also was used as a scoop, either to feed off the bottom or to remove captured (filtered??) food from the tentacles.

I don't know when the anaptychus evolved into the aptychus. Perhaps it happened within Phylloceratoidea. Psiloceratidae appear to belong in the Phylloceratoidea, but I don't know whether thay had an anaptychus or aptychus.

Nautiloid lower jaws are very solid and not so small. I have compared those of Nautilus with those of the Norian Proclydonautilus mandevillei, and both are almost identical in structure and shape. Fossil lower jaws are known as rhyncholites and would be easy to sculpt.

Complete Nautilus beaks are offered for sale on as "peck of Nautilus". This is where I got mine to study.

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