Sutures of Phylloceras (Zetoceras) zetes, upper Pliensbachian, Reutlingen / Germany

The Phyllocerataceae are a superfamily of ammonites that is very much like the Lytocerataceae – they’re thought to have been deep water denizens, often only straggeling into Yorkshire from the Tethys  when a passage opened up, they’re quite conservative (there’s not a lot of change and not many species, at least not in Yorkshire), they’re not very common (though probably slightly less rare than Lytoceras) and they’re very beautiful and highly sought after ammonites.

Two families of the Phyllocerataceae are represented in Yorkshire, the Phylloceratidae with the genus Phylloceras in the Toarcian and the Juraphyllitidae with Tragophylloceras in the Pliensbachian and (rare to the extreme) Meneghiniceras in the lower toarcian with the following species :

• Phylloceras heterophyllum (SOWERBY, 1820)
• Tragophylloceras numismale (QUENSTEDT, 1845)
• Tragophyllocas loscombi  (SOWERBY, 1817)
• Meneghiniceras lariense (MENEGHINI, 1875)

The index fossil of the ibex zone, Tragophylloceras ibex, has not been found in Yorkshire, neither have been to my knowledge the species Tragophylloceras undulatum and Tragophylloceras carinatum.

For this post I’ve nevertheless decided (apart from the title picture) to include some reference specimen of T. ibex and a coarsely ribbed T. undulatum from my collection from the french Fresney-le Puceux quarry, which I had the opportunity to visit on a guided excursion more than 30 years ago,  and a beautiful complete finer ribbed specimen of T. undulatum from the Radstock/Somerset area which by wonderful coincidence came up in the eBay shop of Mark Varah while I was writing this post – of course it was a chance  too good to miss…

Tragophylloceras numismale (QUENSTEDT, 1845)

Tragophylloceras numismale, 1.6 cm, Robin Hoods Bay

Tragophylloceras numismale, 12 cm, Robin Hoods Bay

Tragophylloceras numismale can sometimes be found in the polymorphus subzone as small pyritized phragmocones, the body chamber usually either not preserved at all or flattened. The small ammonites show characteristic repeating constrictions on the inner mould which do not persist onto larger whorls.

The larger specimen above was a lucky find from a very fresh small cliff fall maybe 2-3 m above the beds where the pyritized specimen occur. It must literally have fallen only hours before I passed the area about 3 hours after high tide as it had not been touched by the sea.

Tragophylloceras loscombi (SOWERBY, 1817)

Tragophylloceras loscombi, 3 cm with Androgynoceras maculatum, Robin Hoods Bay

In contrast to similar beds in Dorset, where Tragophylloceras loscombi and Androgynoceras often occur together, the Yorkshire  T. loscombi specimen only rarely accompany Androgynoceras in the Yorkshire maculatum subzone and are generally very hard to find and most of the time relatively small.
It´s range seems to be rather long, from the luridum subzone up to the stokesi subzone. The ammonite exhibits fine ribbing, and only very fine undulations at the venter.

Tragophylloceras undulatum (SMITH, 1817)  (coarsely and finely ribbed variants)

Tragophylloceras undulatum, finely ribbed variant, complete shell with mouth border, 5 cm, Radstock / Somerset

Tragophylloceras undulatum, coarsely ribbed variant, 7 cm, Fresney-le-Puceux / France

More or less fine ribbing with regular undulations at the venter.

Tragophylloceras ibex (QUENSTEDT, 1843)

Tragophylloceras ibex – 6 cm, Fresney-le-Puceux/France

Tragophylloceras ibex has the most coarse undulations at the venter.

Phylloceras heterophyllum (SOWERBY, 1820)

Phylloceras heterophyllum, 12 cm, Kettleness

A large 3D preserved Phylloceras is most fossil collector’s dream – it still is for me, the largest Phylloceras I’ve found is about 4″ / 10 cm…

Phylloceras is a genus which can get quite large, probably one of the largest genera in the Yorkshire lias, up there together with some of the Schlotheimia and Coroniceras genera from the lower lias.

This flattened specimen pictured below is from the falciferum zone at Ravenscar and is about 80 cm in diameter, it must have been a marvellous sight when alive, leisurely and majestically drifting through the liassic seas…
It also shows the broader waves of seconday ribbing on the body chamber that develops on larger specimen.

Phylloceras heterophyllum, approx. 80 cm, Ravenscar

It was left in place as it was too large and possibly too fragile to attempt to split off – but I have no doubt that it will not remain there for long,

AndyS

Literature :

M. K. HOWARTH, D.T. DONOVAN :

M.K. HOWARTH:

Both these papers are available online at the Palaeontological Association at http://www.palass.org/beta/publications/palaeontology-backissues/

Cleviceras exaratum, two 4.5 and 5 cm microconches

In his 1992 monograph “The Ammonite family Hildoceratidea in the Lower Jurassic of Britain”, HOWARTH intoduced the new genus Cleviceras, named after the northern England area Cleveland (which by the way literally means “cliff land” (Wikipedia)). It was not that this was an ammonite genus that was newly established because new specimen had been found, it was done to recognize that an understanding about the phylogeny, the history of the evolution of that genus, had been reached, that made it necessary to separate it from the previous genus Harpoceras.

Previously, Cleviceras had been under the genus Harpoceras mainly for morphological reasons : The sickle-shaped style of ribbing is very similar to Harpoceras falciferum, the type species of Harpoceras, allthough there are differences in detail.
But it was then recognized that these ammonite genera belong to parallel evolutionary lineages with different ancestors :

Cleviceras : Tiltoniceras – Eleganticeras – Cleviceras exaratum – Cleviceras elegans
Harpoceras : Protogrammoceras ? – Harpoceras serpentinum – Harpoceras falciferum

In short words : Cleviceras is no longer considered to be the ancestor of Harpoceras falciferum, so it needs to be a different genus.

Another solution for this problem would be to put the Cleviceras species under Eleganticeras, which was put forward by GABILLY in 1976 and BÉCAUD in 2006.
HOWARTH still favoured the new genus to be able to generically divide the ammonites due to the big change in ribbing between Eleganticeras and Cleviceras,
and continued the use of the genus Cleviceras in the 2013 part L, Vol 3B, chapter 4 of the Treatise on Invertebrate Palaeontology, so we´ll stick to that as well…

For Cleviceras there are two Yorkshire species :

Cleviceras exaratum (YOUNG & BIRD, 1828)
Cleviceras elegans (SOWERBY, 1815)

Both exhibit a strong dimorphism, the microconch is considerably smaller than the macroconch, with an adult macroconch reaching up to 4 to 5 times the size of an adult microconch at maximum observed sizes. Largest macroconches can get close to 200 mm in size, while largest microconches have been found between 50 and 60 mm.

An adult shell can be recognized by approximation of the last sutures before the body chamber : growth of the shell slowed down and the last few chambers
are smaller than the previous chambers, i.e. the sutures are closer to each other.

Approximation of sutures before the body chamber, indicating a mature shell, in this case a microconch of Cleviceras exaratum.
The effect is especially visible at the umbilical edge.

I “found” this macroconch of Cleviceras exaratum in my “vault”, a large metal cabinet in my cellar, that houses all the “to be prepped” specimen,
after reading about the fact that large macroconches are rare and remembered I had actually found a somewhat crushed one some time ago…

Cleviceras exaratum, body chamber of a macroconch, 18 cm.
There is a pathology on the last 1/4 of the whorl.

Both species have a strong hollow keel, which is floored on the phragmocone, but not floored on body chamber, which easily explains why the keel most easily breaks off on the chambered part of the shell : this additional bit of shell creates a predetermined breaking point between the phragmocone and the keel.

Keel of Cleviceras exaratum : The keel has an extra floor on the chambered part of the shell, and the calcite keel easily gets lost during preparation.
Also visible here : The last chamber before the body chamber is smaller, indicating an adult shell (in this case microconch).

The difference between Cleviceras exaratum and Cleviceras elegans is easily explained when you look at the umbilical walls :

Comparison between Cleviceras exaratum (left, mature microconch) and Cleviceras elegans (partial macroconch), both 5 cm.

The umbilical walls of Cleviceras exaratum are vertical or even undercut, while the umbilical walls of Cleviceras elegans are beveled.

Comparison of Cleviceras elegans (left) with beveled umbilical walls and Cleviceras exaratum (right) with undercut umbilical walls.

In the Jet rock, ammonites of both species are often hollow and filled with natural oil – just like the one I tried to re-prep for this blog post :
It is a 12 cm macroconch of Cleviceras exaratum, the body chamber cut open by a lobster, found in 1995. I knew there was oil in this one,
for it had already coloured the label it lay on brown, but I hoped after almost 20 years the oil would be gone…
When I tried to prep the other side, a crack opened up, a piece of the shell fell off and the hollow shell presented itself –
I could literally pour about 20 ml of liquid oil out of this ammonite – what you see on this picture on the kitchen towel is just what dribbled out afterwards !

Oil from a hollow chamber of Cleviceras exaratum

Needless to say, continuation of preparation will be difficult…

AndyS

Aperture, front and keel view for macroconch of Eleganticeras elegantulum (YOUNG & BIRD, 1822). At 10.5 cm this is close to the average size for macroconches.
The ribbing is relatively strong on this specimen, it came from a large Cannonball nodule at Hawsker Bottoms.

I’ve recently leafed through the 1981 english edition of Ulrich Lehmann’s book “Ammoniten – Ihr Leben und ihre Umwelt” (“The ammonites – Their life and their world”).
Lehmann describes in the foreword how the book came to be in the making of an ammonite exhibition in the Hamburg “Geological-Palaeontological Institute” at which he was a Professor for Palaeontology.

Reading the foreword brought back long forgotten memories of this exhibition – Hamburg is the town where I was born, and I remember a visit to the exhibition and how in awe I was seeing nodules not unlike the Cannonball nodules off the Yorkshire coast (which I did not know then) with dense accumulations of Eleganticeras, but differing in their shell being preserved in a pearly white instead of black. The original german version of the book is from 1976, so I must have been between 10 – 13 when visiting the exhibition, and it was the first time I got into contact with ammonites – and they´ve kept me fascinated ever since !

There are some pictures of white shelled Eleganticeras on the Steinkern internet web page here (scroll down to see the pictures) :
http://www.steinkern.de/steinkern-fossilien-zeitschrift.htmlfundorte/sonstige-bundeslaender/216-geschiebeammoniten-aus-mecklenburg-vorpommern-und-schleswig-holstein.html

Lehmann had been studying Eleganticeras from glacial drift exposures close to Hamburg at Ahrensburg that contained upper toarcian limestone nodules.
The origin of these nodules is assumed to be the somewhere west of the south swedish coast. Lehmann is widely credited as being the first to describe the sexual dimorphism of Eleganticeras, i.e. the recognition of female (macroconch) and male (microconch) shells within the context of the same species.

Howarth very nicely statistically reproduced this for the Yorkshire population of Eleganticeras in his 1992 Palaeontographical Society publication of “The Ammonite Family Hildoceratidae in the Lower Jurassic of Britain”, taking into account at total of 392 (227 macroconchs and 165 microconchs) specimen from 6 localities on the Yorkshire coast.

A size comparison between a 140 mm macroconch and a 30 mm microconch (positioned for this photograph on the body chamber of the macroconch) of Eleganticeras elegantulum.

It is an essentially unprovable but very likely extrapolation from some living cephalopods that the Microconch (male) is very often significantly smaller than the Macroconch(female) of the species. This argument is also underpinned by the discovery of a likely egg sac in the body chamber of a macroconch Eleganticeras.
The adult male microconch can be recognized by the constriction at the mouth border and is with max. about 30 mm very much smaller than the female macroconch with max. about 150 mm .

As mentioned above, the best preserved Yorkshire 3D Eleganticeras specimen occur in the so-called “Cannonball” nodules of the Jet Rock, falciferum zone, exaratum subzone, beds 33 and 34 of the upper toarcian. “Cannonball” is a very fitting name for these nodules, since they’re often very round nodules and they’re also very hard – their outer layer consists mostly of pure pyrite and they are tough package to crack – even sometimes sending off sparks when hit with the hammer’s steel.

Many openly accessible exposures of the cannonbal beds have now been exhausted, leaving only circular craters in the jet rock shale, nowadays goods finds of cannonball nodules mostly come from cliff falls, just as the (uncharacteristically oblong) nodule shown here :

A 30 x 15 cm Cannonball nodule as found

This nodule was found below a pile of shale from a small fresh fall in July 2012 at Hawsker Bottoms. It looks like another collector had already tried to open the nodule, since the top part was missing and showed some sections of larger and smaller Ammonites.
Due to the size of the nodule (15 cm x 30 cm) and its inherent potential I decided to take it with me anway and, since I don’t really seem to have a talent to prepare these, gave it to Mike Marshall to try his luck on it (he initially looked a bit sceptical at it…)
Fast forward 9 months later, I visited Mike again, to pick up some fossils which I had bought from him.
As the very last item he gave to me, he revealed the magic he had worked on the above nodule :

The same nodule masterfully prepared by Mike Marshall containing 16 ammonites between 2 and 10 cm.

No less than 16 microconch and macroconch shells of Eleganticeras are contained in this nodule, ranging from 2 to 10 cm – you can imagine how pleased I was both with my find and the superb work Mike had done on it !

As tough as these nodules are when they are fresh, nothing lasts forever, and especially when the nodules are exposed for a longer time to the forces of breaking saltwater waves and being rubbed against other rocks in the surf, the pyrite skins are prone to decay through pyrite rot – the following picture shows the skin of a nodule almost violently erupting dense bushels of hairy gypsum crystalls and reducing the pyrite to a yellow-white powder in the process.

Nothing lasts forever – the pyrite skin of a Cannonball nodule with heavy pyrite rot

The ammonites (carcasses ?) themselves, before fossilization, where sometimes also under attack – it is assumed that lobsters, trying to get to the soft flesh, cut open the shells in a V-shapped pattern displayed below :

A 6 cm Eleganticeras elegantulum with a characteristically v-shaped cut in the shell of the body chamber

Traces of potential suspects for this deed are rare in the Cannonball nodules, but here is one especially impressive 4 cm long claw of a lobster called Uncina posidoniae,
for which a lifestyle preying on ammonite (carcasses) has been suggested, found in an unusually productive fall with Cannonball nodules in 1990 :

The 40 mm long claw of the lobster Uncina posidoniae QUENSTEDT from a Cannonball nodule

Eleganticeras certainly is one of the most interesting ammonites of the Yorkshire coast, hard to get at due to preservation in tough Cannonball nodules,
but with lots of appeal to the collector.

AndyS

Tiltoniceras antiquum (WRIGHT, 1882), 4.5 cm diameter

It´s more than 20 years ago that I found the above ammonite, and it has remained the only 3D preserved Yorkshire specimen of this species so far in my collection.
It was found, probably in a semicelatum subzone nodule, at Runswick Bay. “Probably”, because nothing much remained of the original nodule…

At that time, we used to sit down on the terrace of our then accommodation in nice weather and reduce weight on the fossils as much as we could, we were coming by plane to London and took trains and buses to Yorkshire, so luggage weight was restricted, both by the airline and the amount of rock we could carry…

The ammonite must have been damaged by splitting the nodule already and I obviously tried to extract the better preserved side by separating it from it´s heavy nodule matrix using only small chisels and hammer – this is why this ammonite ended being like it is today – a rather damaged specimen.

I must have also taken it for an Eleganticeras, because some years later when I was re-organizing my drawers I looked at my Eleganticeras specimen again
and found there was one that somehow did look different from a same sized Eleganticeras.

The umbilicus is the shell element that clearly distinguishes Eleganticeras and Tiltoniceras :
While Eleganticeras has an angled umbilical edge, Tiltoniceras has a smoothly rounded umbilical edge.

Comparison of umbilicus of approximately same sized Tiltoniceras (left) and Eleganticeras (right)

There are some beds on the Yorkshire coast where crushed, flattened Tiltoniceras are quite abundant, but I find it quite difficult to distinguish flattened Tiltoniceras from flattened Eleganticeras :

Bed with crushed Tiltoniceras antiquum, diameter of largest ammonite 4.5 cm

It is only quite clear when you find them with Dactylioceras semicelatum in the same bed, like in a photograph I´ve shown in an earlier post :

Flattened D. semicelatum and Tiltoniceras

Of course with hindsight, the ammonite would have deserved a much better preparation.
Today I´d probably recognize it for what it is and with much better tools and a lot more experience attempt a transfer preparation of the broken off pieces,
and display it on the half nodule, keeping it in it´s natural matrix. But – it is what it is, a product of what I knew and could do then.

AndyS