To be or not to be – a Harpoceras…

To be or not to be ... a Harpoceras ?

To be or not to be … a Harpoceras ?

Wait a second, you may say, I’ve seen this one before, but last time you called it an
Eleganticeras…!  Yeah, I know – sometimes you have to look somewhere else to find an
error in an ammonite identification.  In this case, it was my error
(you can see prominently featured it in the Eleganticeras post here),  and I only fully
realized it when I saw (and bought) an ammonite offered on eBay that looked very similar.

Harpoceras aff. serpentinum, 10 cm from Hawsker Bottoms (left) and Harpoceras serpentinum, 8 cm, from Altdorf/Germany (right)

Harpoceras aff. serpentinum, 10 cm from Hawsker Bottoms (left) and Harpoceras serpentinum, 8 cm, from Altdorf/Germany (right) – Thanks to Arno Garbe !

In my defense, I have to say that I’ve never really been 100 % comfortable with calling
it an Eleganticeras… I’m not really fully sure about the species of this one even now,
but I’m much more comfortable calling it a
Harpoceras aff. serpentinum (SCHLOTHEIM, 1813).

Because of the circumstances I vividly remember finding this specimen at Hawsker
Bottoms some years ago…

I was at Hawsker Bottoms and on my way back to Robin Hoods Bay and had decided to
inspect the channels and gullies that furrow the low tide reef, sometimes a good place to
find the odd nodule that rolled down the cliff  (and roll, or better shoot they do, I once
witnessed one flying at head height across the shore…) and found this round pyrite
nodule of- if memory serves me right- about 12 cm diameter. I gave it a whack, and the
top of the slightly weathered, crumbly nodule split off showing the ammonite, but part
of the shell on the body chamber came off as well, because there was an oil filled hollow
there – just as on the Cleviceras I have shown you before.
I bagged all parts and re-affixed the shell bits after removing the oil, and filling the cavity
with glue, which I only succeeded half-decently in because I did not quite get the level of
glue correct – but try to reconstruct a broken egg-shell of a blown out egg, and you’ll
understand what this was like…

The rest of the nodules’ pyrite shell developed severe pyrite rot in the years following, so
at some point I decided to fully remove the remaining matrix and so it represents itself
today.

For me, this was a typical Cannonball nodule from bed 33, and therefore allthough it
looked slightly different, had to be an Eleganticeras…

But was it a Cannonball nodule ? Would I be able to distinguish it from a Curling Stone
(bed 37) nodule in the slightly worn and obscured with algal growth state it was in ?

In hindsight, I don’t think so. But even so, if it really was a Cannonball nodule, there is
no reason whatsoever why this cannot be an early Harpoceras. These animals knew
nothing of the arbitrary boundaries of ammonite zones and subzones we draw today,
these boundaries have to be “fuzzy”and only hold true for a statistically very significant
majority of ammonites, but not necessarily for all, given there is a continuity of the
record, i.e. no hiatus or non-sequence in sedimentation.

Harpoceras serpentinum (it has a large list of synonymies including Harpoceras
alternatum and Harpoceratoides alternatus) is relatively rare in Yorkshire, it can be
distinguished from its later, more common descendant Harpoceras falciferum by the
less (if at all) expressed spiral groove and the slightly angled (instead of vertical
to undercut) umbilical walls.

The below pictured group of Harpoceras falciferum (SOWERBY, 1820) from Sandsend
was purchased from Byron Blessed.
Harpoceras falciferum, 12 cm and 8 cm, Sandsend

Harpoceras falciferum, 12 cm and 8 cm, Sandsend

Fragmentary Harpoceras falciferum on back of two other specimen, would have been about 30 cm in diameter if complete

Fragmentary Harpoceras falciferum on back of two other specimen, would have been about 30 cm in diameter if complete

I like specimen like this one, since it represents all stages of growth of the ammonite
species from a moderate size of 8 cm to what (if it were complete) must have been close
to the size of the magnificent “Harpoceras mulgravium” at Whitby museum. What is
especially evident is the umbilical width ratio growth at large sizes -i.e. the ammonite
shells became more evolute at large sizes – the 8 and 12 cm specimen have an U/D of
about 0.27, the large fragment on the back of the two smaller ammonites has an
estimated U/D of 0.5 !

What is also evident of course from this story is that it  most of the time really matters
for ammonite identification to better know exactly which bed the ammonite came
from – which of course can be difficult when collecting on the Yorkshire coast…

There´s only a few members of the Hildoceratidae left we still need to take a look at
including Harpoceras subplanatum and Hildaites sp. and they are also some of the
rarest Hildoceratidae in Yorkshire – we´ll cover them in one of the next posts…

 

AndyS

 

Phyllocerataceae – the leaf horns – a conservative group with very few (Yorkshire) members

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

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.

The sculpture of the Phyllocerataceae consists mostly of finer or coarser ribs but the beauty of these ammonites also lies in the sutures they show when preserved as an internal mould :  Complex leaf-like structures of an almost fractal nature, which also have been immortalized in the genus name Phyllo-ceras = Leaf horn, as shown above.

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)
Meneghiniceras has most probably been found only once (see literature section at the bottom) – if you think you have another one, let me know…

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, 1.6 cm, Robin Hoods Bay

Tragophylloceras numismale, 12 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

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

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

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 – 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

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…

The specimen pictured above has been purchased from Mike Marshall.

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

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,

as natural erosion will soon take its toll.

AndyS

Literature :

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

Ammonites of the Liassic Family Juraphyllitidae in Britain,
Palaeontology Vol 7, part 2, 1964, pp 286-305, pls 48-49

M.K. HOWARTH:

An Occurrence of the Tethyan Ammonite Meneghiniceras in the
Upper Lias of the Yorkshire Coast
Palaeontology, Vol 19, part 4, 1976, pp 773-777

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

Caught in the act – Xenomorphism

Xenomorphic oyster on a crushed Arietites - diameter of the Arietites 6.5 cm

Xenomorphic oyster on a crushed Arietites – diameter of the Arietites 6.5 cm

Every once in a while isolated fossil oyster shells turn up that look like ammonites, sometimes the imitation is so perfect that you take them for the real thing.
This is called xenomorphism – a shell that looks like a positive image of an other animal, e.g. ammonite, brachiopod etc.
The above pictured oyster on a flattened Arietites from Redcar (bought via eBay – Many thanks,  Dave !) is a perfect example, and this time it is not isolated from its previous settlement ground but still attached to the ammonite – caught in the act - and is complete with both shells :
Xenomorphic oyster on a crushed Arietites - side view

Xenomorphic oyster on a crushed Arietites – side view

Xenomorphic oyster on a crushed Arietites - detail of the oyster

Xenomorphic oyster on a crushed Arietites – detail of the oyster

The lower shell is attached to the ammonite shell and copies the ribbing of the ammonite. The upper, unattached shell then creates a positive image of the lower, attached shell in an attempt to create a proper closing between both bivalve shells.

 

Detail of xenomorphic oyster on brachiopod - with ribbing of the brachiopod replicated on oyster

Detail of xenomorphic oyster on brachiopod – with ribbing of the brachiopod replicated on oyster

The same thing happened with this Oyster that settled on a brachiopod : there is a faint copy of the ribbing of the brachiopod on the unattached shell of the oyster.
Oysters on brachiopods on Androgynoceras - width of specimen 6 cm

Oysters on brachiopods on Androgynoceras – width of specimen 6 cm

It seems with this specimen that hardgrounds to settle on at the time were extremely difficult to come by, this could actually be a settlement of brachiopods on an Androgynoceras ammonite, and on almost every brachiopod, there´s an oyster…

While this post quite literally was only indirectly about ammonites, the following posts will be about “the real thing” again:
The next one will be about the Phyllocerataceae (text is ready, photos still to be done), and I still need to continue with the Harpoceratinae, which will
begin with an erratum on one of the previous posts – did you spot it ?

 

AndyS

It’s all in the umbilicus (and in the provenance) – Pseudolioceras

Pseudolioceras lythense, 7.5 cm, phragmocone only

Pseudolioceras lythense, 7.5 cm, phragmocone only

Pseudolioceras boulbiense, 7 cm

Pseudolioceras boulbiense, 7 cm

Pseudolioceras is a relatively common ammonite with 2 to 3 Yorkshire species, with P. lythense from the bifrons zone (commune & fibulatum subzones) being considered the ancestor of the later, thouarsense zone (striatulum and above subzones) P. boulbiense.

P. subconcavum is at the moment considered to be a synonym of P. lythense but may also be an early form from lower in the commune subzone -
more zonally aligned material is needed for a statistically safe distinction.
The holotype of “P. subconcavum”, which can be seen at Whitby museum, differs from P. lythense in having thicker whorls and deeper furrows along the keel.
This form seems to be relatively rare – I may have a very small one in my collection, but as with most small non-adult ammonites,
this identification is really more wishful thinking than fact – I will not post it here, for a good picture see the excellent Whitby museum type & figured fossils catalog web page for this ammonite at

http://www.whitbymuseum.org.uk/type/grp04/sim214.htm

Large, complete, uncrushed specimen of Pseudolioceras are rather rare due to the apparent fragility of the body chamber -
most of the time you find only specimen with an uncrushed phragmocone and a crushed body chamber

Pseudolioceras lythense, 10.5 cm, with mostly intact body chamber

Pseudolioceras lythense, 10.5 cm, with mostly intact body chamber

 

Telling the difference between P. lythense and P. boulbiense is really rather simple and apart from the umbilicus also involves the bed and location you found it.

The following probabilities give some kind of a guideline :

  • If it´s above 7 cm, it is more likely to be a P. lythense – P. boulbiense above this size is rare.
  • If you found it in a striatulum subzone nodule at Ravenscar, it is most likely P. boulbiense
  • If you found it anywhere else other than Ravenscar it is most likely to be P. lythense
    since the striatulum subzone is only really well exposed at Ravenscar – of course there may be exceptions.
  • If you find it together with other ammonites of the same species, or even ammonite of other species, it is most likelyP. boulbiense.
    This is really somewhat obvious considering the previous critera – P. lythense is most often a “one ammonite per nodule” find,
    as they typically are in the alum shales (I can’t really remember if I have ever seen a Pseudolioceras lythense with another ammonite, I’m sure there must be some…)
    whereas P. boulbiense occurs most often associated with other specimen of the same species, sometimes even dozens or Grammoceras or even the odd Nodicoeloceras.
Pseudolioceras boulbiense loves company : Small Nodicoeloceras (2 cm) sitting on top of 5.5 cm P. boulbiense + severall small Pseudolioceras

Pseudolioceras boulbiense loves company : Small Nodicoeloceras (2 cm) sitting on top of 5.5 cm P. boulbiense + severall small Pseudolioceras

The U/D ration (width of umbilicus / diameter of shell) is usually smaller with P. boulbiense, with P. lythense´s wider umbilicus (with quite some variation) you can usually see more of the inner whorls when you look into the umbilicus as with P. boulbiense, where the inner whorls are just to be seen as a thin ledge inside the umbilicus, with the 7 cm specimen shown above, the width of this ledge is just 1 mm.

Pseudolioceras lythense, 7.5 cm, extra wide umbilicus, probably fibulatum subzone

Pseudolioceras lythense, 7.5 cm, extra wide umbilicus, probably fibulatum subzone

Pseudolioceras boulbiense, 4 cm, showing beveled umbilical wall and suture

Pseudolioceras boulbiense, 4 cm, showing beveled umbilical wall and suture

The umbilical walls of P. boulbiense are just slightly beveled, visible best with smaller specimen, whereas the umbilicals walls of P. lythense are vertical or even undercut.

Comparison of umbilici for P. lythense (left) and P. boulbiense (right)
Comparison of umbilici for P. lythense (left) and P. boulbiense (right)

Ribbing is also different, with P. lythense the ribs visibly swing forward towards the venter, whereas with P. boulbiense, you have to look very hard to see that -
the ribs “stop” more abruptly before the venter, there is only a hint of a rib swinging forward.
You can see this best in a direct comparison :

Pseudolioceras lythense, showing ribs swinging forward at the venter

Pseudolioceras lythense, showing ribs swinging forward at the venter

Pseudolioceras boulbiense, ribs do not visibly swing forward at venter

Pseudolioceras boulbiense, ribs do not visibly swing forward at venter

I’ve been prepping lots of Pseudolioceras these past few weeks – as so often, looking at ammonites again for research of a blog post,
I found the preparation of my specimen of this genus, some of which have already spent more than 20 years in the drawer,
somewhat lacking and not up to what I today regard as my standards for preparation.

And I can tell you, there’s nothing better than prepping for getting “close” to the fossils and understanding their morphology and species differences -
slowly peeling it out of the encapsulating rock makes it easier to capture and understand the essence of the ammonite.

AndyS

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
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