A prickly ammonite and it’s spine-less partner – Xipheroceras and Promicroceras

Glorious Xipheroceras ziphus, width 8 cm, venter view, with spines mostly intact. Purchased from Mike Marshall.

Glorious Xipheroceras ziphus, width 8 cm, venter view, with spines mostly intact.
Purchased from Mike Marshall.

Since approximately the 1800s there have been single observations (d’Orbigny, … ),
since the 1960s (Makowski 1962, Callomon 1963),it was scientifically recognized that
there are certain ammonite shells, found in the same beds, that may be showing
signs of sexual dimorphism – usually with these specimen, the most inner whorls are
the same for the dimorphs, after that growth of the partners diverge, with one partner,
today assumed to be the female (= macroconch) showing continued growth and/or
changes in the sculpture of the shell, while the other, assumed to be the
male (= microconch) , remains relatively small with little sculptural changes.

One of the most obvious potential (we shall never know for sure…) dimorphic pairs is
Promicroceras / Xipheroceras.

Xipheroceras ziphus, width 8 cm, with spines mostly intact.

Xipheroceras ziphus, width 8 cm, with spines mostly intact.
“Promicroceras” early growth stage clearly visible.

Promicroceras planicosta 23 mm. In this view the flattening of the ribs at the venter can be seen.

Promicroceras planicosta 23 mm. In this view the flattening of the ribs at the venter can be seen.

For about the first 15-20 mm, the whorls of Promicroceras and Xipheroceras are
indistinguishable, after that, Xipheroceras as the macroconch develops broader whorls,
strong spines and a change in ribbing, attaining sizes up to more than 30 cm
while Promicroceras as the microconch does not grow much beyond 30-40 mm,
never changing its sculpture.

The following species have been found at Robin Hoods Bay:

Xipheroceras ziphus (ZIETEN, 1830)
Cluster of 2 Xipheroceras ziphus, both 4 cm. This one has a spine nearly fully preserved.

Cluster of 2 Xipheroceras ziphus, both 4 cm.
This one has a spine nearly fully preserved.

Cluster of 2 Xipheroceras ziphus, both 4 cm

Cluster of 2 Xipheroceras ziphus, both 4 cm

Xipheroceras ziphus, 5 cm. Not all specimen come as beautiful preserved as the other ones shown - this was found on the bottom of a 20 cm deep seawater puddle...

Xipheroceras ziphus, 5 cm.
Not all specimen come as beautiful preserved as the other ones shown –
this was found on the bottom of a 20 cm deep seawater puddle…

Small 22 mm specimen of Xipheroceras ziphus. When prepping, I thought this was a Promicroceras - until I found the first spine !

Small 22 mm specimen of Xipheroceras ziphus.
When prepping, I thought this was a Promicroceras – until I found the first spine !

Small 22 mm specimen of Xipheroceras ziphus, venter view. Broadening of the ribs on the venter clearly visible, also the first spine & widening of the shell

Small 22 mm specimen of Xipheroceras ziphus, venter view.
Broadening of the ribs on the venter clearly visible, also
the first spine & widening of the shell

On the first 15-20 mm the ammonite develops just like a Promicroceras, after
which the shell shows strong spines at about every 30-40 degrees and an otherwise
weakening of the ribs inbetween.
Spines stop at about 50-70 mm, only the weak ribbing continues.

Xipheroceras dudressieri (D´ORBIGNY, 1844)

Xipheroceras dudressieri, 6 cm. Holderness coast specimen, D. Pearson collection

Xipheroceras dudressieri, 6 cm. Holderness coast specimen, D. Pearson collection

Xipheroceras dudressieri, 6 cm, keel view. Holderness coast specimen, D. Pearson collection

Xipheroceras dudressieri, 6 cm, keel view. Holderness coast specimen, D. Pearson collection

Xipheroceras dudressieri, 8 cm. Somewhat crushed and oyster encrusted specimen from RHB

Xipheroceras dudressieri, 8 cm. Somewhat crushed and oyster encrusted specimen from RHB

In contrast to X. ziphus, the ribbing of X. dudressieri continues well beyond the
“Promicroceras” stage, and the spines are nowhere near as strong, but on every rib .
EDMUNDS et al suggested a potential synonymy with X. planicosta as a
junior synonym, see literature.

Promicroceras planicosta (SOWERBY, 1814)

Promicroceras planicosta in typical nodule, ammonite diameter 22 mm

Promicroceras planicosta in typical nodule, ammonite diameter 22 mm

Promicroceras (2 small specimen), Xipheroceras (specimen in middle, 2 cm ) and Asteroceras blakei (6 cm)

Promicroceras (2 small specimen), Xipheroceras (specimen in middle, 2 cm ) and Asteroceras blakei (6 cm)

Promicroceras is relatively common and can be found associated with Asteroceras and
of course Xipheroceras.
Promicroceras planicosta has about 24 ribs/whorl at 3 cm, and a characteristic
broadening/flattening of the ribs on the venter.

Promicroceras capricornoides (QUENSTEDT, 1884)

From a lower level (birchi – lower obtusum), occurs at RHB but has not been found by me yet –
it is characterized by less ribs/whorl (19 @ 3 cm vs 23-24 for planicosta) and a less pronounced
broadening/flattening of the ribs on the venter – something to go looking for next year !

Marston Magna specimen

Promicroceras and Xipheroceras from Marston Magna area. Xipheroceras approx 4 cm in width.

Promicroceras and Xipheroceras from Marston Magna area. Xipheroceras approx 4 cm in width.

Xipheroceras and Promicroceras have been described in great detail from an excavation
in the Marston Magna area recently by
EDMUNDS,WHICHER, LANGHAM, CHANDLER (see literature).

This specimen was obtained through ebay as a comparison example for Promicroceras,
the later discovery of a well spined Xipheroceras was an added bonus !
Rarity (I´ve found less than 10 specimen in 27 years) and a potentially stunning
preservation make up the appeal of these ammonites, and there is certainly much still
to be learned about their evolution.
The beds in Robin Hoods Bay are not exposed often, and are protected as an
SSSI – only responsible collecting is allowed.

AndyS

Literature :

Callomon J.H. (1963), Sexual dimorphism in Jurassic ammonites // Trans. Leicester Liter., Philos. Soc. Vol. LVII. P. 21-56.
Makowski H. (1962), Problem of sexual dimorphism in ammonites // Paleont. Polonica. no.12. 92 p.
Makowski H. (1971), Some remarks on the ontogenetic development and sexual dimorphism in the Ammonoides // Acta geol. Pol. V.21. no.3. Р.321-340.
Palframan D.F.B. (1969), Taxonomy of sexual dimorphism in ammonites: morphogenetic evidence in Hecticoceras brightii (Pratt) // Int. Union of Geol. Sci. Ser.A. no.1. P.126-154.
Rollier L. (1913), Sur quelques Ammonoïdes Jurassiques et leur dimorphisme sexuel // Arch. Sci. Phys. et Natur. Geneve. Sér.4. T.XXXV. P.263-288.
Schlegelmilch R. (1992), Die Ammoniten des süddeutschen Lias, 2nd Ed, Gustav Fischer Verlag
Cope J. (1994), Preservation, sexual dimorphism and mode of life of some Sinemurian
ammonites // Palaeopelagos Special Publication I, Rome
Howarth M.K. (2002),  The Lower Lias of Robin Hood´s Bay, Yorkshire, and the work of Leslie Bairstow, Bulletin of The Natural History Museum Geology Series Vol. 58/2, London
Edmunds M., et al. (2016), A systematic account of the ammonite faunas of the Obtusum Zone (Sinemurian Stage, Lower Jurassic) from Marston Magna, Somerset, UK. Proc. Geol. Assoc.

Robert´s Hammatoceras – a Yorkshire first ?

After I had met Robert for the crinoid & starfish block (see here), he also showed
me an ammonite he had found at Blea Wyke in situ on facebook :
Hammatoceras ammonite in situ, picture courtesy of R. Taylor

Hammatoceras ammonite in situ,
picture courtesy of R. Taylor

It came from the Grey Sandstone beds of the Grey Sandstone member of the upper lias,
?dispansum Zone.

We had briefly discussed it over facebook and consensus was that it could be a
Hammatoceras. I offered to prep it as well, price as usual – a photo for the book.
Unfortunately we had at that time already left Yorkshire again, so Robert posted
the ammonite to me, and after arrival  I could confirm that it is actually a
Hammatoceras.

I took a good look and did some exploratory prep of the inner whorls on one side.
Unfortunately it did not look so good, no inner whorl became visible, there were
only slight brown discolorations so I put it on side for a while.

All literature available to me did not mention any Hammatoceras from Yorkshire
so I contacted the Zoé Hughes, curator for ammonites at the NHM,
and Crispin Little, senior lecturer at Leeds University who had a project
cataloguing some finds of a student of his from the Ravenscar area,
but both confirmed they had not seen a Yorkshire Hammatoceras.

So when the time came to do the final prep on the ammonite
(I had promised to give it back to Robert this summer 🙂 ),
I decided to check the other side, where a part of the inner whorl was visible.

Hammatoceras ammonite as found, picture courtesy of R. Taylor

Hammatoceras ammonite as found,
picture courtesy of R. Taylor

Since most of the outer whorl on this side was eroded away, it was an easy decision to
remove the remnants of the outer whorl, bowling it out so it could still be seen from
the other side.

After about 10 hours total this is how it looks now :

Hammatoceras cf. semilunatum, 10 cm inner whorl

Hammatoceras cf. semilunatum, 10 cm inner whorl

It was relatively difficult to prep, what is preserved of the shell is mostly sideritic, at the
surface probably converted to limonite,  but overall very soft and brittle. The innermost
whorls are mostly not there.

But at  it´s still a very nice and especially rare ammonite – looks like a Yorkshire first !
Hammatoceras cf. semilunatum, 15 cm, keel view

Hammatoceras cf. semilunatum, 15 cm, keel view

Diameter of the inner whorl is 10 cm, including the crushed outer whorl it is about 15 cm.
I would tentatively put this towards Hammatoceras cf. semilunatum (QUENSTEDT, 1885)
– it has about 46 ribs on the whorl, and an umbilical width of about 30 %, which fits nicely.

Congratulations to Robert on this rare find – just goes to show what still can be found by
persistent collecting and a bit of luck !

And of course thanks very much for the opportunity to prep & photograph this ammonite !

AndyS

Addendum :
It looks like it was not actually the first Hammatoceras found in Yorkshire 😦 – Tate & Blake mention finds by Wright and Leckenby (from the Holderness coast), Wright describes finds from both the Grey and the Yellow sandstone beds at Ravenscar, but does not figure them. Since none of the newer literature mentions this, these finds may have either not been entered into a collection, lost or insufficiently documented.

Pleuroceras – the other amaltheid ammonite

Pleuroceras paucicostatum, 90 mm, Hawsker Bottoms

Pleuroceras paucicostatum, 90 mm, Hawsker Bottoms

The Yorkshire ammonites of the genus Pleuroceras have for some reason given me more
of a headache than other genera (not as much as the Aegoceras/Androgynoceras though !),
over the years I’ve made multiple attempts to get my head around the differences between
the species, but only the most recent and most thorough attempt has resulted in an
understanding satisfactory to me. At first glance, the species seem to be very similar, and
only when you dig deeper into morphological measurements such as rib count, relative
whorl height/breadth and most importantly, their stratigraphical position and  appearance
of their surrounding matrix, their differences and development become clear.

As M.K. Howarth noted in his 1958 monograph about the Amaltheidae, some of the
species appear to have evolved in Yorkshire and therefore, transitional specimen are
common, which adds to the difficulty distinguishing some of them.

The following species occur in Yorkshire :

  • P. solare
  • P. solare var. solitarium
  • P. apyrenum
  • P. hawskerense transient elaboratum
  • P. hawskerense
  • P. paucicostatum
  • P. birdi

For completeness, I’ve added one more species, which does occur in Britain,
though due to a non-sequence in the relevant beds, not in Yorkshire :

  • P. salebrosum
There potentially is a small overlap between genera Amaltheus and Pleuroceras,
but again it is  relatively unlikely to find those genera together due to a non- sequence,
i.e. missing beds in Yorkshire – find a list of all Amaltheus and Pleuroceras species and
the bed numbers for Hawsker Bottoms (compiled from Howarth 1958, Page 2004)
below :
Occurrence of Amaltheidae in Yorkshire

Occurrence of Amaltheidae in Yorkshire

This post also took longer to create due to the fact that I re-prepped a large portion of
the specimen, which predominantly have been found more than 10 years ago – that´s
not to say that chances to find specimen like these are lower today for most species,
though probably in no way as good as they were when M.K. Howarth wrote his
Amaltheidae monograph in 1958.
I had tried to air abrade a specimen that had a lot of fractured and torn light brown
shell and the result was so convincing (and addictive) that I did most of the specimen
in my collection.  Here is an example of the transformation :
Pleuroceras paucicostatum, 60 mm, before and after air abrading with iron powder

Pleuroceras paucicostatum, 60 mm, before and after air abrading with iron powder

But let´s get to the description of the different species, ordered more or less in ascending stratigraphical order.

Pleuroceras solare (PHILLIPS)

Pleuroceras solare, 80 mm, Hawsker Bottoms

Pleuroceras solare, 80 mm, Hawsker Bottoms

Pleuroceras solare for me is a rare species – I´ve only got one in my collection,
and I´ve only realized I´ve had it during the research for this post.
It is significantly bigger than the neotype shown by Howarth, which added to
the difficulty in correctly assigning it. Preservation is markedly different from all
the other species, most significantly the matrix it is embedded in is oolitic,
typical for Hawsker bed 25, and the internal mould is preserved in
light brown / light grey calcite.
Pleuroceras solare, detail of ribs & keel

Pleuroceras solare, detail of ribs & keel

Ribs are sharp and swing forward at the edge of the venter, they do not meet the even
on the internal mould strongly crenulated keel, smooth areas at the side of the keel
remain. On the bigger outer whorls of this specimen the ends of ribs at the are slightly
heightened.
Rib density appears to be relatively constant, the cast of the neotype I´ve procured
from GeoEd (see also here) has the same 28 ribs as myspecimen at almost double
the size.
Pleuroceras solare, 40 mm, cast of neotype, Hawsker Bottoms

Pleuroceras solare, 40 mm, cast of neotype, Hawsker Bottoms

Perceived rarity of these ammonites may also have something to do that Hawsker
bed 25, the “Pecten Seam” is only about 40 cm thick – my find did not come from
in situ, note to myself : Goal for 2016 = find bed 25 in situ…

 

Pleuroceras solare (PHILLIPS) var solitarium (SIMPSON)

Pleuroceras solare var. solitarium, 41 mm, Kalchreuth/Germany

Pleuroceras solare var. solitarium, 41 mm, Kalchreuth/Germany

This ammonite, though it should occur in Yorkshire, has not (yet) been found by me,
so I´ve procured a specimen from the german Kalchreuth quarry.
The only difference between this one and P. solare is that the var. solitarium has
larger tubercles on the inner whorls, and therefore a lower rib density up to 25 mm.
A specimen in the Whitby museum is displayed here :
http://www.whitbymuseum.org.uk/type/grp11/wm500.htm

 

Pleuroceras paucicostatum HOWARTH

Pleuroceras paucicostatum, 80 mm, with slight pathology, Hawsker Bottoms

Pleuroceras paucicostatum, 80 mm, with slight pathology, Hawsker Bottoms

P. paucicostatum has less dense ribs than P. hawskerense, especially visible on
the inner whorls. Ribs are straight and strong, there is a sharp bend forward
at the edge of the venter, the keel is strong and almost smooth on the internal
mould. Especially on the inner whorls the ribs are a little thicker and slightly
raised on both ends.
I my collection this appears to be the most common species, but I´m sure this
is due to severe collecting bias – once you know what nodules from Hawsker
bed 33 look like, and that they often contain ammonites, you´re more likely
to look for them again…
Detail of Pleuroceras paucicostatum, showing sutures and ribbing

Detail of Pleuroceras paucicostatum, showing sutures and ribbing

 

Pleuroceras birdi (SIMPSON)

I have not yet found P. birdi, which is very similar to P. paucicostatum in everything
except whorl breadth – the whorls of P. birdi are significantly thicker.
Only 2 specimen were known at the time of writing of Howarth´s monograph,
one from Hawsker Bottoms, one from Raasay.
The holotype is in Whitby museum (WM278) and can be seen on their website at

I have to look at that specimen “live”, from the picture there appears to be a bit of a
bend at about 1 o´clock in the shell and a successive increase in whorl thickness –
a possible parasitic growth on the shell and  potential cause of a forma aegra augata ?
The specimen seems to be preserved on one side only, the other side appears
to be eroded – if indeed the specimen is pathological, a possible structural
compensation cannot be estimated.

 

Pleuroceras salebrosum (HYATT)

Pleuroceras salebrosum, 60 mm, Holderness Coast (coll. A. Tenny)

Pleuroceras salebrosum, 60 mm, Holderness Coast (coll. A. Tenny)

Pleuroceras salebrosum is unlikely to occur in Yorkshire – both the transiens and
salebrosum zonules appear to be missing in the beds (PAGE 2004).
Nevertheless, a magnificent specimen has been found by A. Tenny
(superb prepwork by M. Marshall) on the Holderness coast – it´s pre ice age origin
is unclear.
Many thanks to Andy Tenny for letting me photograph this great specimen.

 

Pleuroceras apyrenum (BUCKMAN)

Pleuroceras apyrenum, 81 mm, cast of holotype

Pleuroceras apyrenum, 81 mm, cast of holotype

I´ve shown the GeoEd cast of the holotype before,  the main reason to procure
this cast was of course to verify identification of my Hawsker specimen
of P. apyrenum. Over the 27 years of collecting on the Yorkshire coast,
not many specimen of P. apyrenum have found the way into my collection,
and it is the Pleuroceras species I´ve had the most trouble of getting it
identified to an acceptable degree of probability.

With P. apyrenum, there appear to be 2 variants; one where the ribs get reduced
to a fine striation from up to 30-40 mm, and another one where this does not
happen, like in the holotype. I have so far at Hawsker only found specimen up
to 60 mm and a large fragment, where no reduction of the ribs takes place,
and some smaller specimen with an early reduction of ribs.

Measurements of P. apyrenum specimen

Measurements of P. apyrenum specimen

All specimen have been measured and fall into the variation breadth of P. apyrenum.
One specimen is somewhat closer to Pleuroceras quadratum, especially to the
specimen on table VIII, 4a,b which unfortunately has no measurements listed in
Howarth´s monograph and was not available as a cast.

Some of the specimen are also available on GB3D at http://www.3d-fossils.ac.uk/,
a great initiative making museum specimen available as high-resolution 2D and 3D
pictures.

At the moment I´m not totally convinced that P. quadratum is only occurring outside
of Yorkshire, or for that matter that some of the specimen listed in Howarth´s
monograph  as P. quadratum should not really be P. apyrenum.

A note for my continental readers who wonder about what P. apyrenum looks like in the UK –
the continental “version” of the same age indeed looks slightly different,
and often develops tubercles which are unknown in the Yorkshire population.

 

Pleuroceras hawskerense (YOUNG & BIRD)

Pleuroceras hawskerense, 107 mm

Pleuroceras hawskerense, 107 mm

The Hawkser Pleuroceras – an iconic ammonite, evolved in Yorkshire – so truly
born and bred Yorkshire !
P. hawskerense has characteristic densely ribbed inner whorls, strong radial
ribs and a stong keel, rib density is always bigger than P. paucicostatum apart
in large body chambers of both species. P. hawskerense is best preserved in
bed 42 (shown here (link)) and 43 at the top of the hawskerense subzone,
the specimen pictured above is from bed 43.
These beds, especially bed 43, where exposed, have been more or less exploited
over the centuries, so that well-preserved new finds are rare.

 

Pleuroceras hawskerense (YOUNG & BIRD) transient elaboratum (SIMPSON)

 
Pleuroceras hawskerense transient elaboratum, 82 mm, Hawsker Bottoms

Pleuroceras hawskerense transient elaboratum, 82 mm, Hawsker Bottoms

 
P. hawskerense transient elaboratum, in newer literature just P. elaboratum,
is a Pleuroceras population ancestral to P. hawskerense, specimen have the
same densely ribbed inner whorls, but higher rib density
(30 – 38 ribs instead of 25-30 in P. hawskerense) on whorls of more than
40 mm. Both the specimen in Whitby museum (WM:SIM302) displayed here :
and the specimen in my collection display a slightly sunken in keel on the
outermost whorl.
Pleuroceras hawskerense transient elaboratum, 130 mm, Hawsker Bottoms

Pleuroceras hawskerense transient elaboratum, 130 mm, Hawsker Bottoms

 

Summary of measurements
All measurements for the Pleuroceras species mentioned here, both for the specimen in Howarth´s monograph and the specimen in my collection
can be found here :
Measurements of Pleuroceras species

Measurements of Pleuroceras species

Rib density curves showing the complete variation of the species´rib density based
on ammonite diameter can be found in Howarth´s monograph.

So far this has been the blog post I invested the most work in – both in terms of
re-prepping specimen in my collection, and the amount of research needed until
I myself was happy with the result.
I´ve got a feeling that Pleuroceras is somewhat under-represented in Yorkshire
collections, may be because the ironstone nodules containing the ammonites
can be excruciatingly hard and tough – the name “ironstone” already says it,
I´ve many times given up on large nodules myself.
Therefore they rarely “pop open” with a perfectly preserved fossil, and
subsequently require significant work to prep the fossil – if at all possible,
when the inner whorls are preserved in a single “crystal” of solid calcite.

I hope I´ve shown that the result can be well worth the effort –
Pleuroceras is a stunning ammonite and some species are more or less
unique for Yorkshire.

AndyS

 Addendum Feb. 26, 2017 :

 Well, the Holderness coast has again delivered a surprise…
A friend who has recently visited the coast, sent me a picture today for identifiction.
The ammonite shown is a large, 140 mm diameter specimen and judging by the keel, is a
Pleuroceras – but it has massive thorns on the inner whorls !

Pleuroceras cf. yeovilense, 140 mm, Holderness Coast

Pleuroceras cf. yeovilense, 140 mm, Holderness Coast

 The only Pleuroceras species that has thorns like this is Pleuroceras yeovilense, not usually known from this high up,
below the GeoEd cast of the holotype :

Cast of holotype of Pleuroceras yeovilense, 60 mm diameter

Cast of holotype of Pleuroceras yeovilense, 60 mm diameter

Congratulations to the finder and thanks for sending me the picture !

Literature

M.K. Howarth : The Ammonites of the Jurassic Family Amaltheidae in Britain, Palaeontographical Society London, 1958
K.N. Page : Castlechamber to Maw Wyke, North Yorkshire in : British Lower Jurassic Stratigraphy, JNCC Peterborough, 2004

Gemmellaro*´s ammonite – scratch one off the “Wanted” list !

Gemmellaroceras rutilans (SIMPSON, 1843), diameter 40 mm

Gemmellaroceras rutilans (SIMPSON, 1843), diameter 40 mm

 

In May this year, Byron messaged me a picture of an ammonite which had been found
by Ricky at Ravenscar (presumably the side towards Robin Hoods Bay, i.e. Wine Haven),
asking me for an identification.

The small ammonite has a diameter of exactly 40 mm and is preserved as a somewhat
pyritic internal mould on a small block of shelly matrix.

Significantly, this matrix also contains pieces of Pinna bivalves which is usually indicative
of the jamesoni zone, taylori subzone, of the lower lias – so no guessing necessary for
identifying the stratigraphy, which can be a big bonus when identifying ex-situ ammonites
from the Yorkshire coast.

At that point I was prepping another small specimen from this zone with an Apoderoceras
so I figured it had to be the same thing and identified it as such…

A few days later Byron put this ammonite up for sale and (you know me) I could not resist….
The ammonite was picked up from Byron´s shop in Whitby this summer and went home
with me. Usually, ready-for-drawer ammonites like this one queue up on my desk for final
identification and a label.

A few months later, until this weekend in fact, it was still sitting on my desk for
identification…It had turned out that identification was not as easy as I had hoped,
it was not an Apoderoceras, no nodes on the thin ribs, and from the small remaining
bits of shell it looks like the ribs would barely be visible under the shell…

The ammonite at 40 mm diameter is a mostly complete adult, as the crowding of the sutures
suggests, and has about half a whorl of body chamber preserved.

Trifid lateral lobe of the suture (marked L) and crowding of sutures towards the aperature, indicating an adult specimen

Trifid lateral lobe of the suture (marked L) and crowding of sutures towards the aperature, indicating an adult specimen

I had identified a possible match with Epideroceras sociale, especially with the style of
ribbing on the inner whorls, but since Epideroceras is getting much larger and develops
much thicker whorls when adult, this match fell through…

Having about half an hour to kill before lunch would be ready this Sunday,  I was
browsing Howarth´s 1962 “The Yorkshire Type Ammonites and Nautiloids of YOUNG
and BIRD, PHILLIPS, and Martin SIMPSON”, looking for something entirely different
and stumbled across the pictures of Polymorphites rutilans (SIMPSON, 1843)
(now Gemmellaroceras rutilans) on table 15 – a perfect match with the crenelated keel
of my ammonite.

The ribs crossing the venter created a crenelated keel

The ribs crossing the venter created a crenelated venter

I had not had Gemmellaroceras on my list assuming they would only be much smaller
(like Gemmellaroceras tubellum), but reading HOWARTH´s
“The Lower Lias of Robin Hood´s Bay, Yorkshire, and the work of Leslie Bairstow” again,
found that this is indeed the larger species and can be found,
(how blind can one sometimes be…)  explicitly mentioned, in Bairstow bed 530,
associated with Pinna folium…

There is another subgenus which is apparently similar, just stratigraphically slightly
older – Leptonotoceras – in which the lateral lobe of the suture is only split twice
(bifid) instead of three times (trifid) as in Gemmellaroceras – the lateral lobe is trifid
in this ammonite so we´re also clear about this.

So that´s about enough to round up this identification, and it´s also a species that can be
scratched off my “Wanted” list – done !

Scratched off the "Wanted..." list !

Scratched off the “Wanted…” list !

Now let´s see if I have the smaller species of this genus, G. tubellum, hiding in my collection
somewhere…

AndyS

* Gaetano Giorgio Gemmellaro (1832-1904) was an italian paleaontologist and geologist,
founder of the Palermo Geological museum and researcher, among many other topics,
on sicilian pygme elephants. Alpheus Hyatt named the genus after him in 1900, presumably
to reciprocate for an honour which  Gemmellaro had bestowed upon him in 1887 by naming
a permian ammonite genus (Hyattoceras) after him…

What´s in a name – Catacoeloceras

Catacoeloceras cf. jordani GUEX, 5 cm diameter

Catacoeloceras cf. jordani GUEX, 5 cm diameter (or Catacoeloceras cf. engeli forma jordani if you prefer the forma type )

In summer 2012 I had the good fortune to find the above pictured ammonite at Hawsker.
I have pictured the unprepped specimen before here and finished the preparation early this
year. The preservation was somewhat special since the ammonite´s outer whorl was covered
by softer matrix and could be prepped with the air abrader straight away, allowing the spines
to be preserved.Only the inner whorl was covered by a small knob of harder matrix that had
to be carefully removed with an airpen.

I did initially have some trouble identifying the species – the outer whorl is close to what SCHLEGELMILCH lists as Peronoceras andraei, which according to HOWARTH is a synonym of Peronoceras perarmatum, but I could not find any visible fibulation on the inner whorls, which are also quite finely ribbed.

Catacoeloceras cf. jordani, inner whorls without visible fibulation

Catacoeloceras cf. jordani, inner whorls without visible fibulation

Generally, the features of this ammonite (more on this see below) point more to
Catacoeloceras,HOWARTH lists a Catacoeloceras dumortieri but the measurements
do not agree – Catacoeloceras dumortieri seems to have more depressed (wider) whorls
and a lower rib density (and we´ll get to it later).

Browsing french literature I then saw Catacoeloceras jordani, which is also noted by
GUEX (1972) as the oldest Catacoeloceras and whose measurements, taken from pictures
in literature, are pretty close to this specimen, but I still left the naming at
Catacoeloceras cf. jordani, also due to the factthat the specimen was not found in situ,
but in cliff fall debris.
I find it relatively easy to see how Peronoceras subarmatum (through loss of fibulation)
could have evolved into this species, and with the few specimen in my collection, I can see
intermediates between the two forms, but lacking the necessary amount of specimen to
prove it, this remains speculation.

Assignment of different species to Catacoeloceras or Nodicoeloceras varied wildly by author
until the late 1970s / early 1980s, HENGSBACH in 1985 defined the morphological
differences between Catacoeloceras and Nodicoeloceras as follows :

 

  • Catacoeloceras never ever shows (real) fibulation
  • Nodicoeloceras sometimes shows fibulation on the inner and/or outer whorls
  • Intermediate ribs crossing the complete whorl without bifurcation are relatively common
    with Nodicoeloceras, relatively rare with Catacoeloceras
    (e.g. 2-4 per whorl, the above pictured Catacoeloceras has 6)
  • Nodicoeloceras usually has more dense ribbing

 

Catacoeloceras seems to be a very variable genus in whorl section, in 1985 as Hengsbach
worked on Catacoeloceras, instead of creating different species names for every different
whorl section, he created forma types of C. raquinianum and C. engeli and applied some
other existing species.
The only issue with his work in relevance to Yorkshire is that most of his specimen were
quite small, mostly in the range below 30 mm, so with most Yorkshire specimen exceeding
this size, his work his difficult to apply (if you do not want to break apart you rare & prized
specimen…). Additionally most of his ammonites were not collected from specific known
horizons, which can also be difficult in the steep-hilled badlands of the french Causses,
where most of the ammonites he examined came from.
I’ve decided to not use the forma type names and stick to simple species names here –
I lack the amount of material to do any meaningful statistics to distinguish forma types
anyway…
HOWARTH defined the Ranges for Catacoeloceras and Nodicoeloceras in Yorkshire in
1978 as follows, so once you know which bed the ammonite is from, the distinction is clear :

 

Ranges of Catacoeloceras and Nodicoeloceras, compiled from HOWARTH, RIEGRAF

Ranges of Catacoeloceras and Nodicoeloceras, compiled from HOWARTH, RIEGRAF

In April this year, when visiting Mike Marshall, he showed me this beautifully prepped,
7 cm, Catacoeloceras raquinianum (which I naturally could not leave without & bought
it off him…) :

Catacoeloceras raquinianum (D´ORBIGNY, 1844), 7 cm, complete specimen

Catacoeloceras raquinianum (D´ORBIGNY, 1844), 7 cm, complete specimen

Another Catacoeloceras raquinianum procured some years earlier also from Mike shows
how difficult it is to estimate the appearance of a complete adult ammonite form an inner
whorl (which this seems to be, and a bit pathological as well) :
Small inner whorl of Catacoeloceras raquinianum, 3 cm, purchased from Mike Marshall

Small inner whorl of Catacoeloceras raquinianum, 3 cm, purchased from Mike Marshall

When you compare the coronate inner whorl of the two ammonites, it becomes clear that
they’re the same species. The fully grown adult specimen shows characteristics of
Catacoeloceras crassum on the outer whorl, though the whorl is probably not as wide.

 

Coronate inner whorl of Catacoeloceras raquinianum

Coronate inner whorl of Catacoeloceras raquinianum

When looking again at Catacoeloceras dumortieri in the latest Ammonite volume of the
TREATISE, the resemblance of at least a few specimen with what I used to lump into
Catacoeloceras puteolum struck me, especially when looking at a specimen found in April
at Ravenscar (unfortunately I cannot show a comparison picture from the Treatise due to
copyright) :
Catacoeloecras dumortieri (DE BRUN), 6 cm, complete specimen with hood at mouth border, unfortunately inner whorl not preserved

Catacoeloecras dumortieri (DE BRUN), 6 cm, complete specimen with hood at mouth border, unfortunately inner whorl not preserved

I could not find any mention anywhere that Catacoeloceras puteolum had been renamed
Catacoeloceras dumortieri, in fact they were both mentioned as early as in HOWARTH´s
1962 paper “The Jet Rock Series and the Alum Shale Series of the Yorkshire Coast”,
with C. dumortieri from the Peak Shales at Ravenscar, and C. puteolum as “not found”.

 

A survey of measurements of “Catacoeloceras puteolum” held among the members of the
“Yorkshire fossil hunters” Facebook group revealed the potential existence of two groups
which differ in their maximum whorl width, one group with a maximum whorl width of up
to 20-25 mm, the other one with a maximum whorl width of up to 30 mm :
Catacoeloceras dumortieri (DE BRUN), 6 cm, complete specimen with mouth border, associated with severall Pseudolioceras boulbiense, purchased from Mike Marshall

Catacoeloceras dumortieri (DE BRUN), 6 cm, complete specimen with mouth border, associated with severall Pseudolioceras boulbiense, purchased from Mike Marshall

Catacoeloceras dumortieri (DE BRUN), 6 cm, complete specimen with mouth border

Catacoeloceras dumortieri (DE BRUN), 6 cm, complete specimen with mouth border

Venter view of Catacoeloceras dumortieri (DE BRUN), 6 cm, complete specimen with wonderfully carved out mouth border, a work of prep art by Mike Marshall

Venter view of Catacoeloceras dumortieri (DE BRUN), 6 cm, complete specimen with wonderfully carved out mouth border, a work of prep art by Mike Marshall

Catacoeloceras puteolum (SIMPSON, 1855), 7 cm, only a few mm missing of the mouth border, purached from Byron Blessed

Catacoeloceras puteolum (SIMPSON, 1855), 7 cm, only a few mm missing of the mouth border, purchased from Byron Blessed

Venter view of Catacoeloceras puteolum (SIMPSON, 1855), 7 cm

Venter view of Catacoeloceras puteolum (SIMPSON, 1855), 7 cm

Until about 2-3 cm, the inner whorls look the same for both groups with a rib density of
about 32/whorl, then the specimen of the group reaching a larger whorl width continue
the growth in whorl width beyond about 20-25 mm up to 30 mm and reach a higher rib
density on the outermost whorl of > 36 ribs/whorl (i.e. retaining an almost constant
distance between ribs), while he group with a smaller max. whorl width do not increase
their whorl width and have a constant rib density of about 32 ribs/whorl on the outermost
adult whorl (i.e. increasing absolute distance between ribs on the outer whorl).

I´m almost sure the group with the bigger maximum whorl width can be associated with
Cataceloceras puteolum, while the group with the smaller max. whorl width is
Catacoeloceras dumortieri – if proven to be found within the same bed (which seems
possible, given the same association with Pseudolioceras boulbiense), they could –
given their similarity in the inner whorls – as well be variants of the same species or
sexual dimorphs.

When writing this blog post, I had the most difficulty finding a representative example
for Catacoeloceras crassum. I have a few candidates, some are inner whorls, one is slightly
pathological, none are complete adults, with the associated uncertainties this poses
(as seen above…). Catacoeloceras crassum is characterized by not having significant
tubercles at the bifurcation points of the ribs, being much like an inflated
Dactylioceras commune.

2 inner whorls Catacoeloceras crassum, 4 & 5 cm

2 inner whorls Catacoeloceras crassum, 4 & 5 cm

Catacoeloceras crassum (YOUNG & BIRD, 1828), 6 cm, slightly pathological

Catacoeloceras crassum (YOUNG & BIRD, 1828), 6 cm, slightly pathological

Catacoeloceras crassum, 5 cm diameter

Catacoeloceras crassum, 5 cm diameter

 

What I mentioned earlier about finds not being collected from known horizons applies to
many of the finds from Yorkshire as well – what we amateurs find most often comes from
cliff falls, most of the time touched by the sea – more work is needed to clarify exact horizons
in which these ammonites occur. Catacoeloceras is a very interesting but also intensely
variable genus – only collections from specific horizons can quantify that variability.

Literature

R.HENGSBACH, 1985 : Die Ammoniten-Gattung Catacoeloceras im S-französichen und
S-deutschen Ober-Toarcien, Senckenbergiana-lethaea 65

W.RIEGRAF, 1986 : Stratigraphische Verbreitung der Ammonitengattung Catacoeloceras
im Toarcium Europas, Senckenbergiana-thethaea 67

M.K. HOWARTH, 2013 : TREATISE ONLINE 57, Part L revised, Volume 3B,
Chapter 4 : Psiloceratoidea, Eoderoceratoidea, Hildoceratoidea, The University of Kansas

R. SCHLEGELMILCH, 1976 : Die Ammoniten des süddeutschen Lias, Gustav Fischer Verlag

M.K.HOWARTH, 1962 : The Jet Rock Series and the Alum Shale Series of the Yorkshire Coast,
Proc. Yorkshire Geological Society 33

L. RULLEAU, P. LACROIX, M. BÉCAUD, J.P. LE PICHON, 2013 : Les Dactylioceratidae du
Toarcien Inférieur et Moyen, und famille cosmoplite, Dédale Editions

J.GUEX , 1972 : Réparation biostratigraphique des ammonites du Toarcien moyen de la bordure
sud des Causses (France) et révision des ammonites décrites et figurées par Monestier (1931),
Eclogae geol. Helv 65/3

 

From wreck to study ammonite or An Inbetweener

On days when I do not find very much, I tend to also take fossils with me that normally
would not be taking,  this wreck of an Amaltheus is such a case,  found in early April this year :

A wreck of an Amaltheus as found - hope for a salvagable inner whorl ?

A wreck of an Amaltheus as found – hope for a salvagable inner whorl ?

I was hoping for a good inner whorl to salvage and may be something subconsciously
registered as  interesting with this ammonite.I prepped the ammonite this weekend
and noticed (apart from it being a rather nice inner whorl) that it does have
rather strong ribbing :

A 7.4 cm Amaltheus stokesi/bifurcus "inbetweener"

A 7.4 cm Amaltheus stokesi/bifurcus “inbetweener”

So a candidate for Amaltheus bifurcus ?

The “Schlegelmilch” lists the variation for ribs/whorl for Amaltheus bifurcus as from
17 to 26,  and this ammonite fits right in there with 25 ribs at 7.5 cm
(Amaltheus stokesi, the other option, has a lot finer ribbing with 31-44 ribs/whorl)

So case closed – or is it ?

The “Schlegelmilch” also list the umbilical width of the ammonites, with
Amaltheus bifurcus at 34-45 %  and Amaltheus stokesi with 25 – 28 % –
and this ammonite has exactly 28 % !

So it looks like this ammonite is something of an in-betweener, a late A. bifurcus or an
early A. stokesi or even a hybrid, since these ammonite species did occur together.

Whatever it is, I´ve had so much fun prepping and wondering about it, that it´s been
really worth taking the chance with the wreck that it was. It´s so much better not
expecting a lot from a fossil and finding a little jewel hiding in there than expecting
a lot and finding it´s a wreck…

AndyS

 

Mostly wishful thinking – Hildaites murleyi

Small 2.5 cm Hildaites murleyi next to a small Cleviceras and a few ammonite aptychi and possibly belemnite hooklets (!)

Small 2.5 cm Hildaites murleyi next to a small Cleviceras and a few ammonite aptychi and possibly belemnite hooklets (!)

When it comes to filling a gap in our collection, we collectors become a bunch of wishful thinkers, easily taking the slightest hint that a specimen might be the sought after species as fact.  Please note that this explicitly includes myself, and I´ve got a feeling it is directly proportional to the time that gap is perceived to be open.

One of my examples in this area is the below ammonite, found in October 2010 at Hawsker Bottoms.
I was so ready to call it Hildaites murleyi, believe me, mainly for the fact that it exhibits a finer ribbing than the usual Hildoceras lusitanicum (see here). But a final niggle remained, the preservation just did not fit – it was a typical commune zone Hildoceras lusitanicum preservation, with a sugary pyrite/calcite shell, that was almost gone, and a pyritic internal mould with some replacement shell.

Finely ribbed 8.5 cm Hildoceras lusitanicum MEISTER from the commune subzone at Hawsker Bottoms

Finely ribbed 8.5 cm Hildoceras lusitanicum MEISTER from the commune subzone at Hawsker Bottoms

Hildaites murleyi is an exaratum/falciferum subzone ammonite on the Yorkshire coast and in my experience relatively rare.
I´ve only really got one Yorkshire specimen I´m 100 % sure of that it is Hildaites murleyi, and it is the one shown in the title picture.
You can´t beat a good ammonite association, even better one that is so diagnostic as the above one : The small ammonites next to the Hildaites murleyi are Cleviceras, this small 10 x 5 cm matrix sliver also has many small shiny black ammonite aptychi and possibly belemnite hooks, which are so typical for certain exaratum subzone beds.

When the opportunity came up to purchase a better sized, verified Hildaites murleyi from well known collector Arno Garbe via eBay,
I just had to take it, even though it is not a Yorkshire specimen, one has to do something to close that burning gap…

It was found at Hildesheim in Germany in the so called “borealis” nodules of the exaratum subzone, Hildoceras murleyi was previously named “Ammonites borealis”
by SEEBACH in 1864. Arno is well known for his craftsmanship in preparing shelled liassic ammonites and this one comes in a beautiful chocolate and
caramel coloured calcite shell:
Beautiful 8.5 cm Hildaites murleyi (MOXON) in a borealis nodule from Hildesheim/Germany

Beautiful 8.5 cm Hildaites murleyi (MOXON) in a borealis nodule from Hildesheim/Germany

Now when you closely compare the two ammonites you can see the difference immediately:

Direct comparison of inner whorls of Hildaites murleyi (left) and Hildoceras lusitanicum (right)

Direct comparison of inner whorls of Hildaites murleyi (left) and Hildoceras lusitanicum (right)

Hildoceras lusitanicum has a much more visible groove , and the smooth area next to the umbilical wall is much wider than in Hildaites murleyi, where the groove is almost non-existent and the ribs don’t fade out towards the umbilical wall – you see the same on the small specimen in the title picture.
Arno´s Hildaites murleyi certainly is a very beautiful (maybe even more beautiful than a Yorkshire specimen can be), well prepared ammonite, and very educational in showing the typical Hildaites murleyi features as well.
But, you know, it´s not from Yorkshire, and it´s not the same as found by myself … I´ll continue looking… 🙂
(and no, if you were going to ask, I did not get the Hildaites murleyi that Mike -by pure coincidence – posted earlier in his web shop – someone was faster !)

AndyS

 

Taking stock – Merry Christmas, but never mind the R, the Y and the I…

Santa is having a small Coroniceras sp. (left) and a Grammoceras thouarsense (right) leaned against his knees. Ravenscar in the background.

Santa is having a small Coroniceras sp. (left) and a Grammoceras thouarsense (right) leaned against his knees.
Ravenscar in the background.

Well, it’s that time of the year again, time for looking back, taking stock…
I often get asked, when the book will be ready…
2014 has been an extremely busy year for me professionally, with the effect that I
did not have much spare time to work on the book, and I’ve been to the UK only once
this year for collecting (strong withdrawal symptoms…).
Nevertheless I tried keeping up the work, doing at least 1 blog post in a month,
photographing and writing, though I’m not entirely happy with the progress,
but what can you do, the money has to keep coming in…and there are also limits,
how much time you can spend on the computer.
Short answer : It will probably take another year to finish all material,
so I need to look at 2016 as a rough estimate for publishing.

On a lighter note, on that one visit we met old and new friends,
photographed some stunning new specimen and became a fan of the lowest of the lias.
It was the 25th year we´ve been coming to Yorkshire and it continues to feel like
home from home, we can´t wait to be back in 2015 (hopefully at least twice !).

I have a few days off now, so I sat down before my drawers and looked for what genera
we have not covered so far (and the names mysteriously arranged themselves in a certain order) :

 

Mucrodactylites
Euagassiceras
Renziceras
Radstockiceras
Yet more :

 

Cymbites
Haugia
Riparioceras (synonym)
Incidentally also :
Schlotheimia (redcarensis)
Tropidoceras
Microderoceras
Angulaticeras
Schlotheimia (angulata)

 

Apoderoceras
Nodicoeloceras (incrassatum/crassoides)
Dactylioceras (the ones we have not covered yet)

 

Agassiceras

 

Harpoceras (subplanatum)
Arietites
Promicroceras
Pleuroceras
Yet more :

 

Nodicoeloceras (puteolum)
Eteoderoceras
Waehneroceras

 

Yet more :
Epophioceras
Androgynoceras
Rakusites (synonym)

 

By now of course you´ve got the message 🙂 and you probably also noticed that
I had to include some that we did in fact cover or might not even occur in Yorkshire
(look in the R´s)and that I did particularly struggle with the I and the Y´s
(there´s just no species names starting with those letters in the lias…)
but there are also some that did not fit in :

 

Liparoceras, Oistoceras :
We´ll have a lot of fun with these, including Androgynoceras, heavy stuff, and a
fellow countryman to thank for that…
Psiloceras, Caloceras, Coroniceras, Vermiceras, Alsatites  :
Some of the earliest lias ammonites, very interesting stuff, but so difficult to ID
when they´re small…
Crucilobiceras, Xipheroceras, Platypleuroceras, Bifericeras, Phricodoceras :
Finally – Spiny, spikey cephalopods !

 

Grammoceras, Phlyseogrammoceras  :
Together with Haugia and Harpoceras subplanatum the last of the Hildoceratidae
we´ll have to cover

 

Epophioceras :
Looks like an Echioceras, but seems to be related more to Asteroceras…

 

Leptechioceras :
A rare, almost smooth  member of the Echioceratinae

 

Catacoeloceras (crassum, raquinianum) :
Real “Fat Dacs” – we´ll have to work out their differences to Nodicoeloceras

 

So you see there´s still a lot to be done, chiefly in the Psiloceratidae, Arietitidae,
Cybitidae, Polymorphitidae ,Liparoceratidae, and we´ll have to finish off the
Dactylioceratidae and the Hildoceratidae – and that of course guarantees
that you´ll see some more blog posts next year !

 

In terms of visitors of the blog, it was another great year, getting close to 40.000
views in total,  about 15.000 this year. In terms of geography I guess by now we´ve
had visitors from most countries with Jurassic deposits, all though readers from
Greenland stubbornly refuse to visit 🙂 :

 

All time visitors by geography - not many white spaces left !

All time visitors by geography – not many white spaces left !

 

Not on the top 22, but all the same : Seasons greetings to a friend reading these pages
doing a gap year in Cambodia.

 

With best wishes for a peaceful, happy time for you and yours, wherever you are.

AndyS

Recognize it, peel it, glue it, bag it or The secret to complete ammonites is knowing when to stop…

Androgynoceras maculatum, 8 cm, split nodule as found. The end part of the body chamber is on the negative part of the nodule and had to be transfered to the positive side.

Androgynoceras maculatum, 8 cm, split nodule as found. The end part of the body chamber is on the negative part of the nodule and had to be transfered to the positive side.

Androgynoceras maculatum, 8 cm, with complete mouth border after preparation

Androgynoceras maculatum, 8 cm, with complete mouth border after preparation

The secret to achieving completely preserved ammonites is – do as little as possible in the field. The highest risk of loosing bits of the ammonite is when you work it with the crudest tool you have : Your hammer !

The ratio of ammonites on the Yorkshire coast preserved completely is relatively high, so here are some clues to increase your success rate of getting them into your collection that way :
  • Recognize it as early as possible : When you find a likely looking nodule, don’t just whack it, instead take your time looking at it from all sides to see if any part of an ammonite is showing. If it does, and the nodule is not too heavy to carry, just bag it and take it home.
  • If there is no outward sign of an ammonite in a likely looking nodule, don’t just whack it to split it through the middle : A perfect split is a very rare thing, and beach prepping is the worst sin an ammonite collector can commit IMHO (and I´m guilty of trying it myself sometimes, but less so in the last years). Instead try to “peel” the ammonite : Whack it very slightly around the edges, splitting off only small amounts of matrix, preferably in shards, turning it while you do so and observe if an ammonite becomes visible after every blow of your hammer. If it does, bag it and take it home
  • And one of the most important advice of all : Stop hammering before the last blow 🙂
  • Should during this process any part of the ammonite be split off : Do not throw the split off pieces away, even if they seem insignificant, try to glue them back on right away , if it’s a simple break. I carry both liquid and gel type super glue with me for this purpose in my collecting rucksack. I have found that many times the split off piece contained the mouth border, because I misjudged its position in the matrix. Don’t try to glue complex breaks in the field though, instead carefully wrap the broken off pieces and take them with you.
  • Complete the job, when you find a likely looking nodule – don´t stop after the first blow of the hammer does not reveal anything interesting.
    I´ve found many nice ammonites in half nodules that still had plenty of room, but had been left “for dead” by other collectors. It can sometimes also be interesting to split large solitary body chambers of nautiloids or large ammonites looking for smaller, potentially well-preserved, washed in ammonites or even inhabiting crustaceans…
Haugia in discarded nodule after another exploratory blow with the hammer...

Haugia in discarded nodule after another exploratory blow with the hammer…

Prepped Haugia variabilis, 7.5 cm, in 16 cm nodule

Prepped Haugia variabilis, 7.5 cm, in 16 cm nodule

  • Use enough wrapping material so that the pieces don’t rattle against each other in your bag/rucksack/etc. I’m using bubble wrap recycled from used jiffy bags – they make a nice pouch to put your fossil into.
  • Once you are at home, you have all the time in the world to glue any complex breaks, wash the nodule, think about your prep strategy and execute it leisurely. It can sometimes help to mark the position of the ammonite on the outside of the nodule before you glue any pieces back on, especially when the nodule completely hides the ammonite when the pieces are glued back on. Who knows when you will find the time to prep it – until then you might have forgotten what the position of the ammonite is in the nodule.
Nodule with Zugodactylites - approximate position of the ammonite marked before glueing the nodule.

Nodule with Zugodactylites – approximate position of the ammonite marked before glueing the nodule.

Nodule with Zugodactylites braunianus, 8cm, complete with mouth border after preparation

Nodule with Zugodactylites braunianus, 8cm, complete with mouth border after preparation

  • While prepping, try to find  the position of the aperture first. Always prep the outermost whorl following the direction of the aperture, not against the open aperture – you would not be the first one to find you’ve just prepped away the aperture while following the next whorl in the wrong direction…
  • Take your time prepping the specimen. Sometimes, especially when you’re relatively new to prepping, it is better to practise on not so well-preserved specimen, and leave the better preserved ones til later, when you have gained more experience.
Double Ovaticeras ovatum (8 & 7.5 cm) from the core of a septarian nodule. The smaller specimen split off with the wrong side and had to be re-affixed to the matrix after prepping from the other side as well - it was found in 2000 and finally prepped complete in 2014...

Double Ovaticeras ovatum (8 & 7.5 cm) from the core of a septarian nodule. The smaller specimen split off with the wrong side and had to be re-affixed to the matrix after prepping from the other side as well – it was found in 2000 and finally prepped complete in 2014…

  •  It takes time getting used to an air pen, and I’ve ruined many good ammonites because I was too eager to try the new tool…
  • Don’t prep in a rush – it’s no good trying to finish that ammonite in the short timeframe before you need to pick up your kids/lunch starts/your favourite TV series starts etc… I’ve found that my prepping is best when I’m relaxed and my mind is at peace.
  • If there are other faunal elements like bivalves, gastropods, crinoid pieces etc on the piece – leave them there, don´t try to get your ammonite on as little matrix as possible, sometimes these combinations of different types of fossils are much more beautiful (and scientifically interesting) than a single ammonite.
Nodule with 1 Eparietites ammonite and 1 Cardinia bivalve showing after first blow with hammer. The soft nodule would have been obliterated after another blow...

Nodule with 1 Eparietites ammonite and 1 Cardinia bivalve showing after first blow with hammer.
The soft nodule would have been obliterated after another blow…

Nodule with multiple Eparietites ammonites, Cardinia bivalves and a Hispidocrinus crinoid stem, width of nodule 11 cm

Nodule with multiple Eparietites ammonites, Cardinia bivalves and a crinoid stem, width of nodule 11 cm

It only takes a little more care and a little more patience, but it can mean the difference between a mediocre and a great ammonite specimen…
AndyS

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