No new species this time or Ammonite pathologies

Dactylioceras semipolitum, 6 cm, showing both sides

Hildoceras semipolitum, 6 cm, showing both sides

From time to time you might come across ammonites that look like a known species but then again they are different.
Just like the above ammonite. I had been looking at it when I was selecting the ammonites for one of the previous posts (it´s a Hildoceras semipolitum),
but something just wasn´t right :
It has a steep smooth (apart from growth lines) umbilical wall with a sharply angled edge. The ammonite is like that as far as one can see down the umbilicus.
I was looking through my books to see what it could be – H. semipolitum does not have such a sharply angled umbilical edge – until I realized it is “just” a pathology
when I turned the ammonite to the other side : There it´s just like a normal H. semipolitum should be.
Some pathologies are just like that, only a small change, a missing rib, a slight change in ribbing pattern on the body chamber, a healed fracture etc, but overall the species is still recogizable. For others the change is more drastic: a missing keel, a complete change in ribbing pattern starting very early in the shell, a completely asymmetric shell etc. leading authors in previous centuries to create new species for them, examples are Hildoceras walcotti, Monestieria errata .
"Monestieria errata", 4 cm, a Cleviceras sp. forma aegra circumdata

“Monestieria errata”, 4 cm, a Cleviceras sp. forma aegra circumdata HÖLDER 1956

Complete loss of keel or any other structural elements on the keel.

Today it is generally being recognized that these changes in the ammonite shell might have been caused by predators, parasites, diseases or interaction with other
hard-ground settling organisms like bivalves or tube worms and have set up so called “forma aegra” or “sick form” types, describing the pathologies as what they are.
“Sick” forms sometimes offer interesting glimpses into how ammonite shell growth worked and how amazingly adaptable these animals really were.
We may never fully know what caused them in all cases , only where an external cause like a settling oyster, is still preserved with the ammonite, the cause becomes obvious.
Androgynoceras lataecosta with "hook", overgrown bivalve or worm,  6 cm

Androgynoceras lataecosta with “hook”, overgrown bivalve or worm, 6 cm

A relatively common pathology : A bivalve or worm settled on the shell and was overgrown by the ammonite – a typical “bend” is created.

I´d like to show some that I have accumulated over the years, either found myself or bought from known fossil dealers.
They do represent only a portion of the described pathology types, I may add additional ones when I should find them…

forma aegra juxtacarinata HÖLDER 1956

Asteroceras sp. forma aegra juxtacarinata, cast, 5 cm

Asteroceras sp. forma aegra juxtacarinata, cast, 5 cm

Keel drawn out and relocated to the flank – it seems like the keel producing tissue was stretched to the flank and produced the keel there.
This specimen is a cast kindly given to me by my friend Klaus.

forma aegra cicatricocarinata HELLER 1964

Pleuroceras paucicostatum forma aegra cicatricocarinata HELLER 1964, 7 cm

Pleuroceras paucicostatum forma aegra cicatricocarinata HELLER 1964, 7 cm

Keel, visible on the right side, “inversed” on the left side – the exact part of the shell where it happened is eroded…

forma aegra substructa HÖLDER 1973

Catacoeloceras sp. forma aegra substructa HÖLDER 1973, 4 cm

Catacoeloceras sp. forma aegra substructa HÖLDER 1973, 4 cm

Broken out shell underlaid with new shell, bulbous shell growth at break point

forma aegra excentrica HÖLDER 1956

Zugodactylites braunianus forma aegra excentrica, 4.5 cm

Zugodactylites braunianus forma aegra excentrica, 4.5 cm, top side concave

Zugodactylites braunianus forma aegra excentrica, 4.5 cm, underside convex

Zugodactylites braunianus forma aegra excentrica, 4.5 cm, underside convex

Dactylioceras sp. forma aegra excentrica, 8 cm, showing the bowl shape from the side

Dactylioceras sp. forma aegra excentrica, 8 cm, showing the bowl shape from the side

Growth out of the normal shell symmetry into a bowl shaped form, presumably to correct a shell imbalance

forma aegra verticata HÖLDER 1956

Peronoceras fibulatum forma aegra verticata, 7 cm

Peronoceras fibulatum forma aegra verticata, 7 cm

A punctate permanent injury of the shell secreting part of the mantle probably caused by something like a lobster’s pinch with its claws creates a continuous groove across the ribs as the shell continues to be generated.

forma aegra pseudocarinata FERNÁNDEZ-LÓPEZ

Dactylioceras sp. forma aegra pseudocarinata, 7 cm

Dactylioceras sp. forma aegra pseudocarinata, 7 cm

Special form of forma aegra verticata, the adjoining ribs forming a keel like sculpture by themselves

forma aegra concreta HENGSBACH 1996

Dactylioceras sp. forma aegra concreta, pearl 2 mm diameter

Dactylioceras sp. forma aegra concreta, pearl 2 mm diameter

Pearl growth on the inside of the shell, probably similar to what happens with pearls in bivalves.

forma aegra inflata KEUPP 1976

Dactylioceras sp. forma aegra inflata, 4 cm

Dactylioceras sp. forma aegra inflata, 4 cm

Bulbous shell growth to heal a larger hole in the shell – this specimen even has septae build into the “bulb” as the animal continued to grow !

forma aegra undaticarinata HELLER 1958

Pleuroceras sp. forma aegra undaticarinata, 3 cm

Pleuroceras sp. forma aegra undaticarinata, 3 cm

Swinging keel, most often seen with Pleuroceras.

Left/right “hybrid”

Hildoceras bifrons, 12 cm  showing a strong difference between the sides

Hildoceras bifrons, 12 cm
showing a strong difference between the sides

One of the most intriguing types of pathologies : One side shows a normal Hildoceras sculpture, while on the other the spriral grove is completely missing, it looks like a bit like a Grammoceras.
This is of course no real hybrid, but the pathological side came to be through loss/damage/sickness of the spiral grove producing part of the mantle.

forma aegra undatispirata KEUPP & ILG 1992

Dactylioceras sp. forma aegra undatispirata, 6 cm (Col. D. Groocock)

Dactylioceras sp. forma aegra undatispirata, 6 cm
(Col. D. Groocock)

Dactylioceras sp. forma aegra undatispirata, 6 cm
(Col. D. Groocock)
Dactylioceras sp. forma aegra undatispirata, 6 cm (Col. D. Groocock), keel view

Dactylioceras sp. forma aegra undatispirata, 6 cm
(Col. D. Groocock), keel view

Swinging whorl, apparently to equalize an imbalance in the shell caused by e.g. an oyster settling on the shell

The mystery…

Amaltheus stokesi without keel, 11 cm

Amaltheus stokesi without keel, 11 cm

Amaltheus stokesi without keel, 11 cm, keel view

Amaltheus stokesi without keel, 11 cm, keel view

This pathology is still a mystery. What is hidden on the other side, still in the rock ?
Is is a forma aegra juxtacarinata, i.e. the keel has been dislocated to the (invisible) flank ?
Or is it a forma aegra circumdata, i.e. the keel is just not there ?
One of these days I will prep a window into the back of the matrix and see for myself…

AndyS

Literature :

Helmut Keupp : Atlas zur Paläopathologie der Cephalopoden, Berliner Paläobiologische Abhandlungen Band 12 – Berlin 2012

Frechiella or A nautilus with an ammonite suture…

Frechiella subcarinata (YOUNG & BIRD, 1822), 8.5 cm diameter, Port Mulgrave, with a Dactylioceras fragment and a belemnite phragmocone in the aperture

Frechiella subcarinata (YOUNG & BIRD, 1822), 8.5 cm diameter, Port Mulgrave, with a Dactylioceras fragment and a belemnite phragmocone in the aperture

Frechiella is one of the rarest Yorkshire lias ammonites and in some respects also one of the oddest.

It comes from a so-called “aberrant” line of ammonites, previously thought to come from one subfamily Bouleiceratinae of the family Hildoceratidae,
but nowadays after some more analysis (Rouleau et al 2003) is being split up into the 3 subfamilies Bouleiceratinae (lower Toarcian),
Leukadiellinae (middle Toarcian) and Paroniceratinae (upper Toarcian, including Frechiella) but all still under Hildoceratidae.
All are much more common in the tethyan realm, and are rare “strays” into the north-west european faunal province.
All members show a characteristically reduced, sometimes “ceratitic” suture (named after the triassic ammonite genus Ceratites, which showed a similar suture).
Oxyparoniceras telemachi (RENZ), 2 cm This is a member of the same subfamily, but not found in Britain, but somewhat further south from Barjac in the south of France (and purchased by me).

Oxyparoniceras telemachi (RENZ), 2 cm
This is a member of the same subfamily, but not found in Britain, but somewhat further south from Barjac in the south of France (and purchased by me).

This is also the main diagnostic feature, otherwise one could easily confuse these very involute ammonites with a nautilus , especially when they are wave-rolled –
In fact, Frechiella subcarinata was originally called Nautilus subcarinatus YOUNG & BIRD, 1822 –
you can just believe that, if it weren’t for the very characteristic suture, and I guess some of you might now go checking the nautilus in their collections …
(and of course : Frechiella is an ammonite, not a nautilus !)
Well preserved specimen show a faint keel on a rounded, sometimes slightly rectangular venter, faint radial ribs, sometimes flat waves can be seen close to the umbilicus.
With almost all specimen I’ve seen (and that’s not many…) the body chamber is more or less crushed or imploded.
Frechiella subcarinata (YOUNG & BIRD, 1822), 10 cm, Hawsker Bottoms

Frechiella subcarinata (YOUNG & BIRD, 1822), 10 cm, Hawsker Bottoms

Frechiella subcarinata (YOUNG & BIRD, 1822) , the only Yorkshire species in the genus Frechiella found so far,
occurs only in the main alum shales, commune subzone, bed 54 (HOWARTH 1992).
It is one of the rarest Yorkshire coast lias ammonites, and many regard it as the “holy grail” of upper lias ammonites.
I had for a time almost given up on trying to find one myself, and bought an unprepared specimen, found at Port Mulgrave (the one pictured below the title),
from Mike Marshall in September 2003.
But as it happened – and doesn´t it always happen like this ?!  – a year later in September 2004 one twinkled up at me from the cliff debris on one of my favourite
spots around Hawsker Bottoms – this is the one pictured above – I have not found one since, not even a fragment.
AndyS

You can´t find everything or Buying fossils

Every collector endeavours to make his collection as complete as possible. Whatever your collection object, that goal becomes easier to achieve when you specialize on a certain sub-group. For me, this is ammonites, liassic ammonites, Yorkshire liassic ammonites. I do stray from that path once in a while and get tempted , e.g. when a species cannot be found in Yorkshire at all, for example Prodactylioceras davoei , or can be found in another preservation from another location, like the beautiful white Marston Magna Asteroceras, Xipheroceras and Promicroceras,  but that is really only the exception.

“Yorkshire liassic ammonites” is still large enough a topic to collect a lifetime and not find every species there is to find. Cycles in erosion patterns can mean that certain beds high up in the cliff will only fall every x years, and even then you have to be on the right spot at the right time. Some beds may not be accessible at all anymore, because they have been exploited a long time ago or it is forbidden to collect there anymore.  Some species may be that rare that only very few can be found at all. From the entries in my little red book  I have estimated that from October 1989 until April 2012 I spent 450 days collecting, spending our holidays in Yorkshire. Conservatively estimating 4 hours per day, I get around 1800 hours. Put this together with my other estimate that I´ve achieved to collect about 50 % of the known species so far, then you know what is possible when you do not live close to location…
Does the above all sound very apologetic to you ? OK, I admit it : I do buy fossils, especially ammonites from time to time. Nothing to be ashamed of, really. I´m just human.
When I buy, it´s usually from well-known UK dealers like
(Disclaimer : I do not get or expect any preferrential treatment from these guys to mention them here, so they enjoy a rare spot of free advertisement now !)
Here are a few of the ammonites I bought from them in the past :
Paltechioceras planum, 8 cm, from fossilsdirect

Paltechioceras planum, 8 cm, from fossilsdirect

This beautiful Paltechioceras planum from the Holderness Coast came from fossilsdirect. It is a species that should occur at Robin Hoods Bay as well, but I´ve never found it there yet.
The ribbing on this species is not as dense as on Paltechioceras tardecrescens.
Dactylioceras (Orthodactylites) cf. crosbeyi, 7 cm, from Yorkshire Coast Fossils

Dactylioceras (Orthodactylites) semicelatum, 7 cm, from Yorkshire Coast Fossils

This irresistible (I´m only human !) Dactylioceras (Orthodactylites) cf. crosbeyi came from Yorkshire Coast fossils. Those thick variants of the Dactylioceras (Ortodactylites) genus are ever so rare, this is a particularly nice specimen and also very nicely prepped.
Dactylioceras sp, 8 cm, from Natural Wonders / Fossils UK

Dactylioceras sp, 8 cm, from Natural Wonders / Fossils UK

 This Dactylioceras sp. (we´ll leave it there for the moment, that´s another story !) came from Natural Wonders / Fossils UK. It is a very interesting Dactylioceras variant with strong ribbing,
we think it comes from the ovatum beds and the type of nodule it´s in seem to confirm that- this is one I´d like to check against some museum holotypes.
I do sometimes buy from ebay as well, very occasionally you can get a bargain there, but you have to know what to look for, and bidding for really good stuff can sometimes be fierce, exceeding the price that you would pay in a shop, simply because the group of bidders is global.
AndyS