Kind Of Shell On Ammonites With Ammonitic Sutures?

[bugsheep]

I have a few questions I’m unable to answer about ammonites.
I’ve been doing some casual research, but it seems to lead to more confusion on
this. I would really appreciate it if anyone could suggest more sites to look at as well.

What kind of shell “decoration” is present on ammonites with
ammonitic sutures? Was there any “normal” combination of shell and suture
mark, or could their shells have any pattern of ridges, knobs, etc.?

I’ve been hoping to find a sort of before and after polishing
photo/sketch set, showing what shell went with what suture pattern, but have
been unable to find anything.

While trying to find the photo/sketch, I realized all
photos of ammonitic sutures I’d found were of creatures that were involute, the
outer whorls almost completely covering the inner. Is this just a coincidence,
or were most/all ammonites with ammonitic sutures so involute?

Also, did any/some/many/all ammonites with ammonitic sutures have an aptychus?

I've been able to find all sorts of information on these features individually, but not on co-incidence, so to speak.

[Wrangellian]

All ammonites, whether involute or evolute, planispiral or heteromorph, will have sutures if you peel away the shell from the chambered part of the conch (behind the living chamber) (or if the shell is already peeled/dissolved by nature or by someone who didn't think to collect the shell that remained stuck to the matrix around the ammonite! I hate that). I don't have a website or scan handy but there should be lots of info out there, we'll see if anyone else has it.. I do have papers that show the suture patterns for Nanaimo Group ammonites in my area.

I don't think there is any particular correlation between sutures and outer shell ornamentation. All ammonite sutures are complex (nautiloids and goniatites etc are simpler), but ornamentation can vary quite a bit.

Edited April 4, 2013 by Wrangellian

[PFOOLEY]

I hope any of this is of help. You have many questions, so this will be a ramble of sorts.

Ammonites are such a diverse group of animals. Many fossils are casts (mineralized infill of the shell). I don't think enough specimens with the shell intact have been found to answer the questions you have about "combination of shell and suture".

In my experience, all ammonites have an "ammonitic" suture pattern (which is the "fingerprint" for species i.d.) and is a difference (along with siphuncle location) between ammonites and nautilus.

I have found ammonites with parts of the shell intact and they do have ornament (i.e. ridges and/or knobs) that differ species to species.

I would assume that they all had an aptychus for protection, but confirmation of that seem impossible.

Not all ammonites are involute (i.e. heteromorphic) but I would guess that most species were. Seemed to be a very successful shape.

[Wrangellian]

Involute does not mean heteromorph.. Involute means the whorls overlapped more than evolute ones, and heteromorph means the shell had an altogether different shape (=hetero-morph) than planispiral.

Also I think the aptychus was a jaw/beak, was it not? If so it would seem reasonable to assume all ammonites had them. For some reason they are rare to find, maybe because 1) they were not attached to the shell but to the soft body so when the body decayed they would get separated and 2) it was made of something like chitin which didn't always preserve as well as the fossil.

Edited April 5, 2013 by Wrangellian

[PFOOLEY]

Is evolute a term to describe heteromorph ammonoids?

[PFOOLEY]

I should do more research on the aptychus.

Learning is fun.

[Uncle Siphuncle]

evolute means whorls dont overlap much, so you see many whorls exposed toward the center. involute means fewer whorls exposed so you dont see many whorls inside the outermost, adult whorl.

in texas ammonite terms, eopachydiscus is involute and peroniceras is evolute. images should come up readily in a google search (sorry, i'm on my phone)

[Wrangellian]

Is evolute a term to describe heteromorph ammonoids?

I guess it could be used for heteromorphs, but it's more useful as an identifying characteristic to distinguish the different planispiral types - I would describe most of the heteromorphs as evolute!

[bugsheep]

Wrangellian: Great, that's exactly the info I'm looking for (: I was under the impression that ammonites can have three types of sutures (ceratitic, gonatitic, ammonitic), but ammonitic being the defining type. As I understand it, the aptychus is a flap that protects the creature when it is retracted in the body chamber. I think they are difficult to find because they were hinged, I'm sure that "hinge" was not as well preserved.

theCretaceous1: I'm mostly curious about how strongly involute it is. The left (with sutures showing) in this image is very tight, but the one on the right has more "relaxed" whorls. Not evolute, but not as closed in on itself as the left example. http://en.wikipedia.org/wiki/File:Haeckel_Ammonitida.jpg

I'm under the impression that evolute always refers to heteromorphs, but all heteromorphs are not necessarily evolute.

Those seem like a great find!

Thank you for the examples, danwoehr.

Most of the information I have is self-taught; I may be getting a bit ahead of myself, but I can't help it! I appreciate your responses, those questions were driving me a little crazy.

Edited April 5, 2013 by bugsheep

[Terry Dactyll]

We try and keep the shell intact as much as possible which will obviously cover the internal sutures underneath so you wont see them... Sutures are beautiful to see but very often the fossil is viewed less scientifically important maybe once the shell has gone (although this is often done to determine the sutures for Id in the first place)... That is why you will be struggling finding some examples... I dont have many with sutures showing but heres a couple...

[painshill]

Wrangellian: Great, that's exactly the info I'm looking for (: I was under the impression that ammonites can have three types of sutures (ceratitic, gonatitic, ammonitic), but ammonitic being the defining type. As I understand it, the aptychus is a flap that protects the creature when it is retracted in the body chamber. I think they are difficult to find because they were hinged, I'm sure that "hinge" was not as well preserved.

theCretaceous1: I'm mostly curious about how strongly involute it is. The left (with sutures showing) in this image is very tight, but the one on the right has more "relaxed" whorls. Not evolute, but not as closed in on itself as the left example. http://en.wikipedia.org/wiki/File:Haeckel_Ammonitida.jpg

I'm under the impression that evolute always refers to heteromorphs, but all heteromorphs are not necessarily evolute.

Those seem like a great find!

Thank you for the examples, danwoehr.

Most of the information I have is self-taught; I may be getting a bit ahead of myself, but I can't help it! I appreciate your responses, those questions were driving me a little crazy.

Yes, those are the main types.

Goniatitic = numerous undivided lobes (typically 8 around the conch) and saddles. Characteristic of Paleozoic ammonoids.

Ceratitic = lobes with subdivided tips having a saw-tooth appearance and rounded undivided saddles. Characteristic of Triassic ammonoids and Cretaceous pseudoceratites.

Ammonitic = lobes and saddles with much subdivision that are fluted and have a rounded rather than saw-tooth appearance. Characteristic of Jurassic and Cretaceous ammonoids, but also extending back to the Permian.

The aptychus (more accurately aptychi since they were symmetrically paired) is now generally recognised as a lower jaw structure, not an operculum. They are calcite structures (rather than aragonite like the shell) and not uncommon as fossils… it’s just rare to find them in situ at the shell aperture. The “jaw” theory has overtaken the "operculum” theory only relatively recently.

In general, those are quite big questions you are asking. It’s difficult to do justice with a short answer.

Edited April 5, 2013 by painshill

[Wrangellian]

Wrangellian: Great, that's exactly the info I'm looking for (: I was under the impression that ammonites can have three types of sutures (ceratitic, gonatitic, ammonitic), but ammonitic being the defining type. As I understand it, the aptychus is a flap that protects the creature when it is retracted in the body chamber. I think they are difficult to find because they were hinged, I'm sure that "hinge" was not as well preserved.

theCretaceous1: I'm mostly curious about how strongly involute it is. The left (with sutures showing) in this image is very tight, but the one on the right has more "relaxed" whorls. Not evolute, but not as closed in on itself as the left example. http://en.wikipedia.org/wiki/File:Haeckel_Ammonitida.jpg

I'm under the impression that evolute always refers to heteromorphs, but all heteromorphs are not necessarily evolute.

Those seem like a great find!

Thank you for the examples, danwoehr.

Most of the information I have is self-taught; I may be getting a bit ahead of myself, but I can't help it! I appreciate your responses, those questions were driving me a little crazy.

In that picture, the middle left one is involute, the middle right one is more evolute. Evolute doesn't mean heteromorph, it just means there is less overlap between the whorls - ie more of each whorl showing. You could say heteromorphs are generally very evolute because the whorls are actually detached from each other but I never hear that term used to describe them because it is more useful to distinguish the different planispiral ammos, the ones with less whorl overlap from the involute ones with more overlap. Heteromorph shapes are classified by their resemblance to well-known examples such as 'turricone' to describe ones similar to Turrilites which looks like a high-spired snail (turret).

One point on usage: Only the ammonitina or -ida (Jurassic-Cretaceous) are true ammonites; everything else that looks like an ammonite but isn't is called an ammonoid, including goniatites and certatites (ie. everything from the Triassic on back. I think I read somewhere that the first true ammonites in North America appeared in the late Triassic and in Europe at the beginning of the Jurassic.)

Edited April 5, 2013 by Wrangellian

[Al Dente]

The aptychus (more accurately aptychi since they were symmetrically paired) is now generally recognised as a lower jaw structure, not an operculum. They are calcite structures (rather than aragonite like the shell) and not uncommon as fossils… it’s just rare to find them in situ at the shell aperture. The “jaw” theory has overtaken the "operculum” theory only relatively recently.

There is a lot of information on the internet that makes the claim that the aptychi functioned as a lower jaw but I think they also claimed it acted as an operculum at the same time. I haven't read every article so I might be mistaken but that is the general idea that I see. There are a couple of papers that describe ammonoid upper and lower jaws similar to the rhyncholite and conchorhynch of a nautiloid. I think some of the Solnhofen ammonites with aptychi indicate they probably acted as operculum since they were large enough to cover the entire opening of the shell. Here are a couple of photos:

One fo the images is from this web site -http://www.mineral-hub.net/musee-jura-museum-eichstatt.html

[painshill]

There is a lot of information on the internet that makes the claim that the aptychi functioned as a lower jaw but I think they also claimed it acted as an operculum at the same time. I haven't read every article so I might be mistaken but that is the general idea that I see. There are a couple of papers that describe ammonoid upper and lower jaws similar to the rhyncholite and conchorhynch of a nautiloid. I think some of the Solnhofen ammonites with aptychi indicate they probably acted as operculum since they were large enough to cover the entire opening of the shell. Here are a couple of photos:

solnhofen aptychi.jpg solnhofen aptychus2.jpg

One fo the images is from this web site -http://www.mineral-hub.net/musee-jura-museum-eichstatt.html

Abstract from “Aptychi: the myth of the ammonite operculum” by Nicole Morton in Lethaia (International Palaeontological Association) Vol 14, Issue 1 (Jan 1981):

“Re-examination of ammonite specimens with the aptychus apparently in place closing the aperture has shown that these are accidents of preservation and have been misinterpreted as indicating that aptychi functioned as opercula. There remain no convincing grounds for doubting that aptychi functioned only as lower jaws of ammonites, not as opercula. Chance preservation of exceptional specimens can sometimes be misleading.”

[Wrangellian]

Interesting. So these accidents are larger aptychi from larger individuals getting stuck in the apertures of smaller ones, or what?

Whatever they are I can't say I've ever found one in my area, and I've got enough ammonites. My guess is whatever dissolved half the ammonite shells (at my Mtn most of the ammos are half-ammos) also dissolved the aptychus if it was calcitic, or it got eaten by whatever animal preyed upon or scavenged ammonite bodies and likewise didn't survive.

[Uncle Siphuncle]

i've never found an aptychus in texas although i've looked at quite a few in 10 years, perhaps thousands. there must have been a preservational bias at play in the jurassic sediments of germany because i found several aptychi, some associated, on a 2 week trip in 2011. one was a physodoceras w/assoc aptychus from gräfenberg and the rest came from a solnhofen quarry. go figure!

[painshill]

Interesting. So these accidents are larger aptychi from larger individuals getting stuck in the apertures of smaller ones, or what?

No… it seems that the in situ examples largely belong to the ammonite shell they are found with, but the fact that they are large enough to close the aperture is coincidental, rather than an indication that they are too large for a jaw structure.

Another abstract from Nicole Morton (with Marion Nixon) in Lethaia in 2007 ("Size and function of ammonite aptychi in comparison with buccal masses of modern cephalopods"):

“Previous impressions that the size of ammonite aptychi is unusually large, thereby posing a problem to their interpretation as part of the jaw apparatus, are shown to be incorrect. The relative length of the aptychus for at least the Jurassic ammonite groups studied, at approximately 15% of the length of the body chamber, is remarkably constant in different taxonomic groups and sizes. This is well within the range for buccal mass length as percentage of mantle length of living cephalopods, being most similar to Octopus and Sepia and much smaller than Nautilus. The height and width of aptychi relative to whorl height and width are larger but again ammonites are probably not significantly different from modern cephalopods. The size and design, with no obvious structures for biting or crushing, suggest that ammonites were adapted to a particular type of relatively unspecialised feeding in which mostly small animals were ingested, possibly with some external digestion. The large shovel-like lower jaw may have functioned like a scoop for collecting large quantities of water and small prey, and movement of the buccal complex with the upper jaw almost closed against the lower jaw could have expelled water while retaining captured prey. Calcification of aptychi may have been protective, but more likely acted to weight the buccal mass for nektobenthic feeding and to make it more rigid.”

Edited April 5, 2013 by painshill

[BobWill]

I was under the impression that ammonites can have three types of sutures (ceratitic, gonatitic, ammonitic), but ammonitic being the defining type.

This may help: The three suture types are of ammonoids not ammointes. Ammonite just means having more elaborate sutures and mostly applies to the suborder Ammonitina of the order Ammonoidea. Edit: Ceratites and Goniatites are in other suborders.

The most convincing argument I've seen for aptichi to be jaw parts is the paper posted a while back about nautiloids.

I can't seem to find it, Maybe somebody else can.

Edited April 7, 2013 by BobWill

[FossilDAWG]

Just to clarify, the terms "involute" and "evolute" are only applied to planispiral ammonites. They are never applied to heteromorphs, where other descriptive terms, such as trochoid, scaphitoid, baculitid, etc. apply.

Regarding your original question, there is no relation between the complexity of the suture and the type of ornament on the shell. Ornament had more to do with the mode of living. Species with smooth hydrodynamic shells are thought to have been fast swimmers, living in the open water much as squid do today. Highly ornamented or spiny species probably crawled on the sea floor, much as octopi do today.

Don

Edited April 7, 2013 by FossilDAWG

[bugsheep]

I can't thank y'all enough!

Wrangellian, painshill, BobWill and FossilDAWG: I'm very glad to know the proper terms, I hadn't realized I was using them wrong. This will make future searches much easier.

danwoehr: that's really interesting!

Terry Dactyll: thanks for the photos.