The Cleveland ammonite – a question of ancestry and an unwanted oil find !

Cleviceras exaratum, two 4.5 and 5 cm microconches

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.

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

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).

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.

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.

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

Oil from a hollow chamber of Cleviceras exaratum

Needless to say, continuation of preparation will be difficult…

AndyS

Elegance in a tough package – Eleganticeras

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.

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.

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

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.

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

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

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

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

Found in the drawer – Tiltoniceras

Tiltoniceras antiquum (WRIGHT, 1882), 4.5 cm diameter

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)

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

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

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

Did you miss me ?

Long time, no blog post. Did you miss me ?

I´m currently working very hard. Sadly, not on the book, not on the blog, but in my bread-winning job, which is making me work a lot of hours these days,
on a very tight timeline, which has nothing to do with fossils. So I´m not really having much spare time at the moment, and if I do I need it to recover, reload my batteries so to speak. That´s also why I had to skip our traditional spring time holiday on the Yorkshire coast, which is quite annoying, but unavoidable.
So no fresh fossils at the moment…

But there is light at the end of the tunnel (or is it the oncoming train ?), and I´m slowly beginning to reclaim some of the things I love doing outside of my daily job.

This is probably the first fossil I laid hands on to do a little bit of prep work in 3-4 months, and I still have a pile of stuff to do from last year´s summer holiday…

Cleviceras exaratum, 6 cm

Cleviceras exaratum, 6 cm

It is a 6 cm Cleviceras exaratum, found at Hawsker almost exactly 5 years ago to the date. It was already mostly prepped before, but I decided to do some finishing by grinding the aperture to prepare it for the next “real” blog post which will start to cover some of the Harpoceratinae, i.e. Tiltoniceras, Eleganticeras, Cleviceras.

More soon…

AndyS

 

Gleviceras – a small Riparioceras in a big cloak

 

Gleviceras at Robin Hoods Bay is very rare – at least for me – to the point that I do not have much more than a small bit of a whorl, found at the time of the rebuilding of the sewage pipe (link) on May 1, 1996, a small bit of Gleviceras subguibalianum, from the upper Sinemurian, aplanatum subzone, Robin Hoods Bay  which is not really representable, and as usual, if you have a better one from the area, let me know !

 

The following is a Radstock/ Somerset specimen to show you what a whole Gleviceras looks like :

 
Gleviceras sp. from Radstock / Somerset, 17 cm, inner whorl not preserved

Gleviceras sp. from Radstock / Somerset, 17 cm, inner whorl not preserved

 

So did you wonder what I meant with the title of this post ?

 

Well, the astounding thing about Gleviceras is, and allthough I´ve had some discussion about it with a regular reader of this blog (that´s you Joe !) in 2012,
I’ve only relatively recently become really aware of this through Mike Howarth’s Treatise #57 volume, even as it looks very much like a member of the
Oxynoticeratidae family that it is from the outside, it starts as a tiny “Riparioceras” on the inside.

 
A 3.5 cm Gleviceras sp. from Gloucestershire shows where the journey is going...

A 3.5 cm Gleviceras sp. from Gloucestershire shows where the journey is going…

 

If you had found a pyrite “Riparioceras” at the usual size of e.g. max. 1-2 cm you’d be well excused to think that this could never,
ever develop into a Gleviceras like shown from Radstock above, and I would certainly have thought the same.

 

That is, before I saw final living (actually quite long dead) proof in this Dorset specimen on eBay below :

 
 

It is not the finest preservation that can be found, but it is just eroded enough around the umbilicus to reveal its “Riparioceras” state beginning,
something you would not see in the un-eroded state – I just had to get it, see it with my own eyes and show you…

 

Gleviceras BUCKMAN 1918 has precedence over Riparioceras SCHINDEWOLF 1962, so that “degrades” Riparioceras to a synonym for Gleviceras.

 

Just shows again, a species should never be erected on the basis of non-adult specimen only…

 

AndyS

A new Amaltheus species for the collection

Amaltheus gloriosus HYATT, 38 mm diameter

Amaltheus gloriosus HYATT, 38 mm diameter

I found a species new to my collection today – in the drawer !
After almost 25 years collecting on the Yorkshire coast, finding a species that I do not have yet in my collection does not happen very often.
I was labeling some finds that I had prepped recently and was sorting them into the appropriate drawer, when I looked again at an ammonite that
I had found at Hawsker in the summer last year. I remember the circumstances of that find very well, there was a piece of dark shale that had fallen from somewhere higher in the cliff, and the piece looked like it came from the upper lias. There was a small greyish nodule embedded in that piece of shale and something that looked like a separate, non-nodularized whorl of a flat ammonite beside it. The nodule looked like it was rebedded, it had what looks like cracks on the outside that had been filled again with shale material. I got curious and split the nodule – and was surpized to find a small Amaltheus inside. The separate piece of ammonite whorl looked very worn and I could not really identify what it was.

Back at home I prepped the little ammonite, put a label of “Amaltheus subnodosus” on it and forgot all about it.

So when I saw it again this morning, I took it out of the drawer and decided to take a second look…it looked different.
Counting the ribs I found it had 12 ribs at around 20 mm, and 17 ribs at around 35 mm, compared to an A. subnodosus with 16 ribs at 20 mm and 21 ribs at 34 mm.

On the inner whorls the tubercles are very strong and almost elongated, the tubercles almost are the ribs, on an A. subnodosus they are a lot less strong.

Direct comparison between Amaltheus gloriosus (left) and similarliy sized Amaltheus subnodosus (right)

Direct comparison between Amaltheus gloriosus (left) and similarliy sized Amaltheus subnodosus (right)

My conclusion is that this ammonite is an Amaltheus gloriosus HYATT, 1867.

Rib density matches well with what HOWARTH documented for another Hawsker specimen, as does the given description and a figure mentioned from QUENSTEDT´s
“Der Jura” (table 20, fig. 9-12). A very good match was also found in A.E. Richter´s Book “Südfrankreich und seine Fossilien”, page 69 fig 49.

And that´s one more ammonite off the “wants list”- the Yorkshire coast never ceases to surprise me !

AndyS

Literature

M.K. HOWARTH 1957, The Ammonites of the Family Amaltheidae in Britain, Palaeontographical Society

F.A. QUENSTEDT 1858, Der Jura, Reprint Goldschneck Verlag 1987
A.E. RICHTER, Südfrankreich und seine Fossilien, Kosmos Frankh 1979

The lost Porpoceras…

The lost Porpoceras...

The lost Porpoceras…

I bought the ammonite in the picture above on eBay UK in the middle of December 2013 and had it sent to a friend in the Whitby area to save postage – and I did not want it to get lost in the Christmas post rush on the way to Germany.

The courier’s tracking log shows delivery on December 19, shortly before 6 pm – but our friend was not in at the time, no package was in the post box and no note to say where it was delivered instead. All searches around the house and inquiries at the neighbours brought up no result, the courier insists it was delivered – in effect it seems the ammonite is lost.

I was really looking forward to this ammonite – it looks like it could have been the center piece for the next post – Should it turn up anywhere, just let me know.

AndyS

Looped ribs and spiny tubercles – Peronoceras

The result of my between-the-years prep project : A complete Peronoceras turriculatum, 9cm, and Peronoceras subarmatum, 6.5 cm from an Alum Shale nodule, Hawsker Bottoms

The result of my between-the-years prep project :
A complete Peronoceras turriculatum, 9cm, and Peronoceras subarmatum, 6.5 cm from an Alum Shale nodule, Hawsker Bottoms

At the top of the commune subzone, the spiny members of the Dactylioceratidae family developed, probably from an intermediate form between Peronoceras turriculatum and Dactylioceras athleticum. Over the years there have been some differences of opinion under which genus (Peronoceras, Porpoceras, Catacoeloceras) the different species have to be placed,
I’m here following HOWARTH’s 1978 classification which he has re-iterated in the 2013 Treatise of Invertebrate Palaeontlogy #57, Part L, Revised, Volume 3B, Chapter 4:”Psiloceratoidea, Eodoceratoidea, Hildoceratoidea” and will describe the following species under the genus Peronoceras in this post :

Peronoceras fibulatum (SOWERBY, 1823)
Peronoceras turriculatum (SIMPSON, 1855)
Peronoceras subarmatum (YOUNG & BIRD, 1822)
Peronoceras perarmatum (YOUNG & BIRD, 1822)

So if you see the same species name under another genus, e.g. Catacoeloceras perarmatum – it’s the same ammonite. I have only added synonyms to the species below if the synonym has a different species name.

What unites these species is their stratigraphical range (lower part of fibulatum subzone, Whitby beds 60-63 of the lower toarcian)), and their principal style of ribbing (fibulation – ribs pairwise looped together, forming a tubercle at the end, see graphic below), so HOWARTH placed them into one genus instead of dividing them into different genera.

Fibulation ribbing pattern

Fibulation ribbing pattern

Genera outside this stratigraphical range (Porpoceras – upper part of the fibulatium subzone, part of bed 72) and genera without or only very occasional fibulation (Catacoeloceras, Nodicoeloceras) will be described in later posts…

Peronoceras turriculatum (SIMPSON,1855)

 
Peronoceras turriculatum, 7 cm, with constriction at mouth border

Peronoceras turriculatum, 7 cm, with constriction at mouth border

P. turriculatum has very fine ribbing until approx. 3-4 cm. Ribs are sometimes looped together, but tubercles are very small or occur only occasionally.
On the outer whorl, nearly every primary rib carries a stong tubercle. The ribs cross the venter bending foward towards the aperture, almost at an angle.

Comparison of the venter of Peronoceras turriculatum (top) and Dactylioceras cf. praepositum (bottom)

Comparison of the venter of Peronoceras turriculatum (top) and Dactylioceras cf. praepositum (bottom)

When I compared one of the ammonites from the previous post about Dactylioceras (link) – I had then called it D. cf. athleticum – with the P. turriculatum in the first picture at the top of this post, it occurred to me that there is just a small step, the addition of fibulation, to go from this ammonite to a P. turriculatum.

HOWARTH frequently names Dactylioceras praepositum (BUCKMAN) as a possible ancestor to P. turriculatum, unfortunately the figure of the holotype in BUCKMAN´s Yorkshire Type Ammonites 6, table DCCI, is somewhat blurry and I have found no other good figure in any other publication – but I think this is it – I´ll have to change the name of this one to Dactylioceras cf. praepositum (BUCKMAN).

Peronoceras fibulatum (SOWERBY, 1823)

 
Peronoceras fibulatum, 6 cm

Peronoceras fibulatum, 6 cm

 

P. fibulatum has stronger ribbing on inner whorls and fibulation is rather the rule than the exception. Ribs are crossing the venter bending forwards, but in a less angled, more convex way than P. turriculatum.

Peronoceras subarmatum (YOUNG & BIRD, 1822)

(Syn. Peronoceras semiarmatum)
Peronoceras subarmatum, 6.5 cm

Peronoceras subarmatum, 6.5 cm

P. subarmatum is a more depressed (thicker) ammonite, with strong tubercles and fibulation also on the inner whorls.

Spines of Peronoceras subarmatum

Spines of Peronoceras subarmatum

Most of the time it is difficult to preserve the full beauty of the tubercles above the internal mould, but when possible like in this specimen,
where the nodule surrounding the fossil was sufficiently weathered (I found it at Bay Ness, probably from glacial drift) to soften the otherwise hard matrix, it shows what a spiny ammonite this really was when alive…

Peronoceras perarmatum (YOUNG & BIRD, 1822)

(Syn. Peronoceras andraei)
Peronoceras perarmatum, 8 cm, slight pathology on the body chamber

Peronoceras perarmatum, 8 cm, slight pathology on the body chamber

P. perarmatum differs from P. subarmatum in having mostly wider spaced, single ribs on the inner whorls. It tends to have even thicker whorls and very strong tubercles.

The direct comparison in detail pictures shows the diagnostic differences in the pair  of compressed forms (P. turriculatum and P. fibulatum)
and the in the pair of more depressed forms (P. subarmatum and P. perarmatum) :

 

Comparison of the inner whorls between Peronoceras turriculatum (left) and Peronoceras fibulatum (right), width of view both about 5 cm.

Comparison of the inner whorls between Peronoceras turriculatum (left) and Peronoceras fibulatum (right), width of view both about 5 cm.

 

Comparison of the inner whorls between Peronoceras perarmatum (left) and Peronoceras subarmatum (right), width of view both about 5 cm.

Comparison of the inner whorls between Peronoceras perarmatum (left) and Peronoceras subarmatum (right), width of view both about 5 cm.

P. fibulatum and P. turriculatum can often be found complete, with a strong constriction on the internal mould at the mouth border  – I have not seen this on P. subarmatum or P. perarmatum (and it does not show on that one complete specimen shown above – but this one has shell on the outer whorl and is also slightly pathological, so might not be representative) but this may just be a case of not having really found a fully complete, adult specimen without shell on the last whorl – if you have one with a constriction, I´d love to see it …

Looking through the lens to photograph these specimen has also (again) all too clearly shown me the limitations in my prepwork, the better specimen (especially on the inner whorls) are the results of lucky, clean splits. One of my New Year resolutions : Don’t hurry so much, take more time to do things (fossil prep work and removing dust from specimen before photographing them – amongst other things) properly…

Have a great 2014…

AndyS

Literature :
M.K. HOWARTH : Treatise of Invertebrate Palaeontlogy #57, Part L, Revised, Volume 3B, Chapter 4:”Psiloceratoidea, Eodoceratoidea, Hildoceratoidea”, 2013
M.K. HOWARTH : “The Stratigraphy and Ammonite Fauna of the Upper Lias of Northamptonshire”, 1978

 

Merry and Happy and A prep project for the days inbetween…

Merry and Happy !

Merry and Happy !

I wish you a Merry Christmas and a Happy New Year…

For the days inbetween, I´ve picked myself a prep project that is also leading to the topic of my next post,
it is an Alums Shale nodule with a large 9 cm Peronoceras turriculatum and another smaller Peronoceras, possibly P. subarmatum.

Alum shale nodule with 2 Peronoceras, found summer 2013

Alum shale nodule with 2 Peronoceras, found summer 2013

Unsharp picture (just teasing !) of a 9 cm Peronoceras, half prepped (I just could not wait...)

Unsharp picture (just teasing !) of a 9 cm Peronoceras, half prepped (I just could not wait…)

Looking through my collection, I´ve also found some more Peronoceras specimen that need a re-prep to make them presentable,
so you´ll see the next post some time shortly before or after the new year…

Until then, have a great time and be safe.

AndyS

The Whitby Ammonite or a Whole lot of variation…

2 large D. commune adult specimen - both 10 cm - as large as they come !

2 large D. commune adult specimen – both 10 cm – as large as they come !

If there is one ammonite genus that is typical for the Yorkshire coast, more specifically for the coast around Whitby,
it has to be Dactylioceras. Do a search on UK ebay for “Whitby ammonite” and what you get is at least 50 % Dactylioceras, in natural form or sliced and polished…

The Whitby Town coat of arms (fuimus et sumus – we have been and we are – quite fitting)  bears 3 Ammonites, most likely Dactylioceras, with snake heads attached to commemorate the legend of abbess Hilda (see also link).

This all of course is due to its abundance on this stretch of coast, when walking on a beach where the cliff exposes the upper toarcian beds of the lias,
there is almost no way you cannot find a Dactylioceras (fragment), if you keep your eyes open…

A very worn pebble with a Dactylioceras sp. on Robin Hoods Bay beach

A very worn pebble with a Dactylioceras sp. on Robin Hoods Bay beach

In this blog post I´d like to introduce you to the 2 most common species of Dactylioceras : Dactylioceras commune (SOWERBY, 1815) and Dactylioceras athleticum (SIMPSON, 1855).

For the main comparison I´ve chosen two similarily sized, mid size ammonites (each about 7 cm) :

Direct comparison between D. athleticum (left) and D. commune (right), both about 7 cm.

Direct comparison between D. athleticum (left) and D. commune (right), both about 7 cm.

So what differences are there ?

Whorl section : First of all, D.commune has a whorl section that`s as round as a circle, while D. athleticum´s is more oval. I’ve re-prepped these two specimen especially to show this characteristic.

Ribbing : With D. commune the ribs run straight or just slightly convex across the venter, while with D. athleticum the ribs cross in a much more convex way, sometimes almost angled. With D. athleticum, ribbing is much finer on the inner whorls, and the rate of ribs/whorl does not change much on the outer whorls. D. commune has more coarse ribbing on the outer whorls, and finer ribbing on the inner whorls.

Both D. commune and D. athleticum occur in the commune subzone of the upper toarcian, in the Main Alum shale beds, D. commune in the lower part of the subzone (commune biohorizon) down into the Hard Shales (beds 49-54, approx. 15.9 m),  D. athleticum in the upper part (athleticum biohorizon), beds 55-59, approx. 2.8 m.(at Whitby according to K.N.Page in “British Lower Jurassic Stratigraphy”).

The maximum size for these 2 species seems to be around the 9-11 cm mark, with D. athleticum usually a bit smaller, but finding one of this size is quite rare these days. Adult specimen develop a constriction at the mouth border, which is mostly invisible on the surface of the shell, only showing clearly on the internal mold when the shell is removed. As seen on the D. athleticum above, there are some very fine ribs that mark the very end of the adult shell, when preserved.

So far, so good…

Now consider these ammonites :

More ribs, less ribs, round whorl section, oval whorl section, they all do look different from the two above ammonites that I’ve shown you as characteristical for the species, but are they different species or is it just whole lot of variation ?

These were not taken from in-situ off well-defined beds, but collected from the more or less wave rolled cliff debris on the beach, as most of us collectors do, as most of previous centuries’ collectors have done.

The answer probably is : Most of it is just natural variation within a species, with some you can take established species as a reference point and call them e.g. Dactylioceras cf. athleticum (cf : latin confer, compare to) . With some of them, if you don´t really know which bed they come from, it´s sometimes best to just call them Dactylioceras sp. – until you find another one in a defined bed.
Too little work has been done to really identify bed-by-bed variation of the Dactylioceras genus – imagine what could have been done in this regard when the big Yorkshire coast alum quarries were dug in the 18th and 19th century…

Saltwick Bay at low tide - Black Nab at the water line, the disused Alum works in the left background

Saltwick Bay at low tide – Black Nab at the water line, the disused Alum works in the left background

We’ll continue looking at the Dactylioceratidae on the next posts…

AndyS

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