Pathological ammonites


Jun 25, 2004
Hello all

This is my first attempt to post an image so apologies if it all goes pear shaped.

The pic is of a Dactylioceras commune from Port Mulgrave on the Yorkshire coast. Found it earlier this year and took it into work to demonstrate how to pop a nodule to my colleague (with the promise to let here have it if it came out nicely). Needless to say I had to reclaim it when I saw the deformation :bugout: (Gave her a more perfect and therefore less interesting one in exchange)

Anyone have any ideas what could have caused the groove running through the second whorl? Its pre mortem and seems to have healed.

Best regards

Hi Andy and :welcome: to TONMO. Always good to have another fossil collector around here. Thanks for posting your ammonite find, nice specimen.

To be honest, I really have not got a clue what could have caused the scar. I'm just guessing here but could this have been damage to corresponding section of the edge of the fleshy mantle that left a residual scar on the shell as it was slowly secreted? Perhaps the wound repaired itself over time allowing normal formation of the shell in the outer whorls. It would be nice to think it was predation damage but I don't think that could be determined easily.

Kevin might be able to help here.....

Please post any details of cephalopod fossils you have found. I'm sure we would like to see them, especially natural snakestones! :smile:


:welcome: to TONMO Andy,

DISCLAIMER: I am not a Doctor, I just play one on TONMO :!:

Looks like your ammonite had a common case of "Forma verticata" brought on either by injury or parasitism, causing local dysfunction of the mantle, which caused the scar. Ref: Rainer Hengsbach, Ammonoid Pathology, pp. 581-602: in Landman et. al., 1996, Ammonoid Paleobiology, Plenum Press.

I think damage made by a predator would be more severe, causing a larger break and a larger scar. Just having a small portion of the mantle disfunctional would be more likely caused by parasites, a small collision, or maybe a sand grain or something stuck between the mantle and the shell.
Great fossil, thanks for posting the pic.
Thanks for the info. Dac commune is very common on the Yorkshire coast so I must have seen a few hundred. I've found them with smooth bumps and distortions before but nothing so drastic as that one.

I've been collecting on the coast for a few years now and have managed to obtain a variety of ammonites so I'll dust off the camera and take a few more snaps.

Also, the green blotches on the picture are an artifact of the image - not my poor cleaning methods! My carpet seems to have gone a funny colour to.

Best wishes

Proud to be a Larval Mass!
Interesting topic this one, so I had to step out of my lurking in the background. Here come two of the most prominently pathological ammonites from my collection :

The first picture shows a "Twoface" Hildoceras from Ravenscar, Yorkshire coast. It has two completely different sides, one side has lost the typical groove completely, the other side shows a typical Hildoceras sculpture.
(Followers of the discussions on ukfossils will know the story on this one)

The other pictures show different views of a Pleuroceras paucicostatum from Hawsker Bottoms, Yorkshire, that has at one point "inverted" its keel, size is about 3 inches.
Mother nature shamefully hid the point where the deed was done by eroding off that exact part of the whorl, but you can nicely see that before that point it had a normal keel, afterwards the keel is "inverted". The ammonite must have happily lived with that structural deviation, since the inversion shows on the last half whorl of the ammonite, covering the whole living chamber.

Would be interested to see other examples of pathological ammonites as well.

Best regards,

:welcome: AndyS,

These both seem to be the same form of pathology as the other Andys'.

The scar on the Hildoceras looks like it lasted right up until the ammonoid was mature.

Too bad the starting point of the scar on the Pleuroceras is gone. it would be nice to see how the keel inverted.

It seems the only pathology on any of my ammonoids is "Post-Mortem" . However, every one of the Mitorthoceras (orthoconic nautiloid) fossils I have, shows damage and repair to the shell at several locations.

Orthocone Pathology
Good day to you Andy and AndyS and willkommen,
It seems the only pathology on any of my ammonoids is "Post-Mortem"
Mine too Kevin, along the lines of BFH & questionable aptitude :frown: & I'm surprised at Phil :roll: he'd normally produce a photo of the event.

I take it we're working on the lines of BFH meets thumb producing deformed thumbnail :cry: scenario ? Kevin has ruled out any pliosaurian intervention & stop me if I'm wrong but I can't see any teuthid gladius damage or fragments so "squid choking" can be ruled out.

Cometary impact anyone ?

Phil, all the snakestones are gone ! St. Hilda Ogden killed them all dammit :evil:
After further study, and a view of a healthy specimen. (Thanks Andy) I can revise the two-faced pathology of AndyS' fossil.

The Hildoceras probably has a form of "Forma Circumdata", when the shell producing part of the mantle where the groove was supposed to be wasnt functioning, the ventral, rib producing, part of the mantle was stretched over and took over the shell producing function, causing ribs to be formed all the way to the umbilical seam.

Good thing these ammonites are long dead, they don't need to seek a second opinion, or even pay me, or file suit. :lol:

Thanks for the IDs and the ammonoid palaeobiology reference, seems to be a good book but at a hefty price ! :?
I have another one here, this time it is an Asteroceras obtusum forma juxtacarinata, found some time ago by a friend at Robin Hoods Bay in Yorkshire, he gave me a cast as a birthday present.
The keel is not at it's usual place but has wandered from the venter towards the flank. The mechanism is probably the same as you described for the Hildoceras, just this time it is more obvious, since you can still see on the inner whorls that it used to be quite normal.

Thanks for another great pic AndyS. Yes the book is quite expensive, I ordered my copy before publication, so I got it about 1/2 of the present price.

Has anyone seen, or know of, pathologic ammonites other than Jurassic in age? Was there an epidemic in the jurassic, or are there just more ammonites from jurassic rocks to increase the odds of finding pathologies? Is it just that parasitic pathologies are more common in jurassic ammonites?

:?: :?: :?: :?:
Very interesting discussion. I have two and a half questions for you:

1) Is it possible to differentiate between parasitic and fungal infection in ammonoids?

2) Has parasitic distortion of the shell been observed in Nautilus?
If so, is the modern Nautilus an appropriate baseline for comparison? Or do the differences in conch morphology not allow for a direct correlation?

Phil said Fungal 8)

That is the first time I have ever seen the words fungal and ammonoid used in the same sentence. Of coarse the fist time I really saw parasite and ammonoid in the same sentence, was just after this thread started. I was just starting to get a grip on the difference between injury and parasitic/"fungal"/viral/biologic.
This is all a long way of saying I dont know! :smile:

Nautilus kept in captivity produce a discolored and distorted shell...Fungal/parasitic :?:

Injury and repair is usually obvious, a jagged edge with new shell and ornamentation picking up where it left off, only offset. A parasite would probably cause a longitudinal scar that would last until it was extirpated. What would a fungal infection look like?

More study is needed, unfortunately I really must get back to work now :frown:
Architeuthoceras said:
Phil said Fungal 8)

OK, I could swear I saw a reference to this a couple of days ago, hence I posted the question. :? Typically, I am damned if I can find the reference now, despite extensive searching. Best forget I mentioned it unless I can turn up something substantial!

:bonk: (I've confused myself now....) :ammonite:

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