These are not the Androgs you’re looking for – the Liparoceratidae

Liparoceras (Becheiceras) gallicum

While colloquially these will always remain the “Androgs” (and “Lipos”), these are the
genera that this blogpost will be about, and not many are actually Androgynoceras
by the most recent  naming convention.
I have been attempting to write this blog post on and off for the last years and always
found groups of ammonites easier to research and describe and the Liparoceratidae
always went into the backlog again. This may be due to their variability and also due
to the impression you get when you look into the standard monograph, the 1938
“A catalogue of The Ammonites of the Liassic Family Liparoceratidae” [1],
written by Leonard Frank Spath. The table of contents lists no less than 93
species and variants, and there is no easy approach for this monumental work.

The Liparoceratidae can be categorized by their obvious morphology :
(only the species I have so far found in or photographed from Yorkshire
shown here)

  • The “capricorns” are evolute ammonites where the consecutive whorls don’t
    overlap each other a lot – the result is the typical open spiral ammonite.Aegoceras (Beaniceras) luridum
    Aegoceras (A.) maculatum
    Aegoceras (A.) maculatum var. leckenbyi
    Aegoceras (A.) maculatum var. atavum
    Aegoceras (A.) lataecosta
    Aegoceras (A.) artigyrus
    Aegoceras (A.) capricornus
    Aegoceras (Oistoceras) figulinum
  • The “sphaerocones” where consecutive whorls widely overlap each other a
    lot which creates inflated ammonites with deep umbilical funnels :Liparoceras (Liparoceras) cheltiense
    Liparoceras (Liparoceras) divaricosta
    Liparoceras (Liparoceras) naptonense
    Liparoceras (Becheiceras) gallicum
  • Morphologically linking capricorns and sphaerocones are the so called “hybrids”
    which have capricorn inner whorls,  but develop large Liparoceras-style outer whorls:Androgynoceras sparsicosta
    Androgynoceras heterogenes

This classification also used by Spath this is a purely morphological approach, that does
not include any interpretation of relationships or evolution.
We´ll get to that later in this blog post…

Aegoceras (Beaniceras) luridum (SIMPSON, 1855)
luridum sz

Beaniceras luridum

This species has so far eluded me apart from a very small, almost undiagnostic ammonite,
and some doubtful fragments.The small ammonite sits on the whorl of a larger Lytoceras
in a nodule characteristic for the subzone.
Beaniceras luridum is quite similar to Aegoceras (A.) maculatum, ribs while strong on the
flank are not as prominent on the venter as on A. maculatum and swing forward on the
venter to create convex curves. Well preserved specimen show thin intermediate ribbing.

 

Beaniceras luridum, Ehenfeld/Germany

The german specimen pictured above shows the characteristics a bit better than the small
Robin Hoods Bay specimen. Hope to find a well preserved bigger Yorkshire specimen some
time…

Aegoceras (A.) maculatum (YOUNG & BIRD)
maculatum sz

Aegoceras maculatum

This is the standard “Androg”, a relatively common ammonite, depending if you´re in the
right place at the right time. In the 1990s we used to pick up 10 specimen in an hour on
Bay Ness, probably because debris from earlier cliff falls was “ripe”, i.e. nodules were
washed out of the bigger blocks. Today you need to search long and hard in the same
place to find a decent ammonite.
Robust ribbing, between 20 and 22 ribs / whorl at around 70 mm. Mature specimen
with suture crowding show a characteristic hood at the mouth border as pictured on
the specimen above. Strong calcite shell which unfortunately often stays in the negative
when nodules are hit with a hammer, but that also means that perfect splits revealing
all (inner mould) whorls of the ammonite are relatively common.
Shell preservation is rarely seen in collections as the Yorkshire matrix is
usually not abradable.  The species is quite variable, we´ll see some variants below.

Aegoceras maculatum, mostly preserved with shell

Aegoceras (A.) maculatum from lower in the maculatum subzone can be found in
septarian sideritic nodules (e.g. Bairstow bed 581, 585) with some interesting
preservation where the sideritic veins seem to have grown between inner mould
and shell :

Aegoceras maculatum in septarian nodule

There are large specimen of A. maculatum that maintain the “normal” ribbing pattern of
A. maculatum at sizes above 70 mm,  SPATH seems to have called them “var. arcigerens”
and considered them late developments.
Two 80 mm examples shown below, I have heard of specimen around 100 mm.

 

Aegoceras maculatum – large specimen

Aegoceras (A.) maculatum (YOUNG & BIRD) var. leckenbyi SPATH, 1938
maculatum sz

Aegoceras maculatum var leckenbyi

Aegoceras maculatum var leckenbyi

The var leckenbyi of A. maculatum retains a whorl section and ribbing pattern which at
approx. 60-70 mm is not distinguishable from a normal A. maculatum, after which size
the whorl starts to swell and develops bi-tuberculation and a liparoceratid ribbing pattern.
Andogynoceras heterogenes in contrast has more massive whorls at 60-70 mm already
which can be separated from var. leckenbyi and A. maculatum.
Both specimen shown here are fully septate, so fully complete specimen including the
body chamber would have been significantly larger, e.g. 20-30 cm.

Aegoceras (A.) maculatum (YOUNG & BIRD) cf. var. atavum SPATH, 1938
maculatum sz

Androgynoceras maculatum cf. var. atavum

I have one specimen that might fit into the atavum variant for A. maculatum.
It has ribbing much reduced in depth, which could also (and in my view probably
more likely) be the result of a pathology, also given the apparent rarity of this form.
The specimen does have a mostly complete body chamber.

 

Aegoceras (A.) artigyrus (BROWN, 1837)
capricornus sz

Aegoceras artigyrus casts from geoed.co.uk

The two lower specimen have been figured in [8], table 4 as syntypes for
“Defossiceras defossum” ; I have not been able to trace the origin of the first one.

I’ve been on the hunt for this ammonite quite a while, even bought some casts
from GeoEd some time ago to get an impression of the morphology.

Unfortunately these casts, while their details are absolutely stunning in detail,
did not help me then,because they were missing a crucial element, the original color.
Only at the beginning of this year, when John Fam re-posted a tweet from Zoe Hughes
on the Ammonite facebook group, I restarted my search for this morphology in my
collection again. The proverbial light bulb moment came when I finally realized that
A. artigyrus is found in the capricornus sz in the oyster bed or above – ammonites
from these beds in Yorkshire are readily recognizable due to their light rusty
brown color !

Aegoceras artigyrus in sideritic matrix

Aegoceras artigyrus multi

Ammonites from the capricornus sz are not often well preserved, inner whorls can be pure
calcite and when weathered this calcite often has a soft chalky consistency… Despite this I
have in my 30+ years of collecting found a couple of well preserved specimen which I had
previously all labeled as A. lataecosta…

At 2.5 cm diameter : 26 ribs/whorl
Outer whorls of bigger specimen : 20-22 ribs/whorl
Difference to A. capricornus, A. lataecosta : Swelling of whorls at smaller diameters

 

Aegoceras artigyrus

The above specimen was bought from Byron Blessed, originating from an old
collection.

A. artigyrus is also where the name “Defossiceras defossus” has found it´s home,
see Hugh Torrens wonderful compliation in the Geocurator 2/6 here :

” Detection at the Sedgwick: An illustration of the Importance of Data Retention”
https://www.geocurator.org/images/resources/geocurator/vol2/geocurator_2_6.pdf

and M.K. Howarth´s description in [2], pg. 143.

The “Defossiceras defossum” in Whitby museum is a mis-identified Euagassiceras.

Aegoceras (A.) lataecosta (J. de C. SOWERBY, 1827)
capricornus sz

 

Aegoceras lataecosta

Aegoceras lataecosta seems to be a relatively rare species in Yorkshire.
It’s inner whorls cannot be distinguished from A. artigyrus or A. capricornus,
but it retains a constant 26 ribs/whorl even at bigger diameters,
and whorl section remains relatively compressed.
A. lataecosta does have quite a thick shell, which in most cases with Yorkshire
material is either chalky white and/or very brittle and is relatively easy to remove
with an air abrader. The pictured specimen also is an inner mould, and therefore
looks slighty different than the normally shelled A. lataecosta from Dorset.

Aegoceras (A.) capricornus (SCHLOTHEIM, 1820)
capricornus sz

Howarth 2013  does not list a Yorkshire Aegoceras capricornus amongst the finds
of Leslie Bairstow [2], neither does Spath in the specimen list in his 1938
Liparoceratidae monograph.
The Rotunda Geology Group (web site link http://www.rotundageologygroup.org/)
figures a specimenfrom the Robinson collection, clearly from the  sideritic beds of the
capricornus sz, but unfortunately the keel is not shown.

So I’m rather happy that I have two specimen that show the classic feature of a
A. capricornus, the flattened ribs crossing the venter.

Aegoceras capricornus

 

Aegoceras capricornus, flattened ribs on venter

Some rib statistics : 25 ribs/whorl outer whorl, next whorl in 21 ribs/whorl
Looking at these ammonites it is likely that A. artigyrus, A. lataecosta, and
A. capricornus are only slightly different morphologies of the same species.

Aegoceras (Oistoceras) figulinum (SIMPSON, 1855)
figulium sz

 

Oistoceras figulinum

The beds Aegoceras (Oistoceras) figulinum occurs in are in general relatively soft
and erode easily, and in my observation there is no significant hard nodule development
protecting the ammonites from being destroyed in the waves. Therefore it took a
relatively long time until I found well preserved specimen in a relatively freshly fallen
block in 1997. The above ammonite came from this fall.
As I´m both a collector of ammonites and starfish/crinoids, I was especially pleased
when Mike Marshall offered me (and he knew I could not resist ! ) a specimen of both
on one small block !

Oistoceras figulinum and Palaeocoma milleri brittle stars

2 other species of Aegoceras (Oistoceras) also occur on the Yorkshire coast,
A. (O.) angulatum and A. (O.) sinuosiforme in slightly deeper beds than
A. (O.) figulinum. I have not found any well preserved specimen from these
beds so far.

Androgynoceras sparsicosta (TRUEMAN, 1919)
luridum/maculatum sz

 

Androgynoceras sparsicosta

Possibly bed 585 , on lighter brown, very slightly septarian nodule
15-16 ribs/whorl.

This one surprised me, I had not expected to have it in my collection.
I found it in the cellar in my prep backlog while looking for unprepped specimen that
would fit into this blog post, only the outer whorl was visible, so I was happy to see an
acceptable inner whorl after prep.

Aegoceras sparsicosta from maculatum sz

I always knew this bigger specimen on a maculatum sz type nodule was different,
it did not fit the pattern of A. heterogenes developing liparoceratid ribbing at larger
diameters. Only when I realized it also occurs in maculatum subzone and counted
the ribs, it struck me that this is also a A. sparsicosta.
Unfortunately it is an ex-situ nodule, it would have been interesting to know at which
exact level it occurs.

Phelps 1985 [7] postulated a division of the maculatum subzone into a sparsicosta zonule
and a maculatum zonule, which Howarth 2002 [2] rejected due to the ammonite figured
as A. sparsicosta in this paper being a complete non-match for the holotype, and a
typical A. maculatum instead.

Bairstow had not found any specimen matching Trueman’s A. sparsicosta holotype,
figured in Spath 1938, plate V, fig. 7, so Howarth had no indication they ocurred on
the Yorkshire coast. Spath does not mention any finds from the Yorkshire coast
either (he mentions most of his Yorkshire specimen came from Bairstow anyway),
so A. sparsicosta indeed seems to be quite a rare ammonite on the Yorkshire coast.

The bigger specimen shows the specific preservation characteristics mentioned
by Howarth [2] for Bairstow bed 590.61, high in maculatum sz – the white chalky
circular spots.
If this preservation is indeed specific for this bed, it would mean that A. maculatum
and A. sparsicosta share the same stratigraphical distribution, thus the
sparsicosta zonule would be identical to the maculatum zonule.

A. sparsicosta has elongated nodes on the outer whorl :

Nodes Andogynoceras sparsicosta

Left maculatum sz specimen, right luridum sz specimen

As with A. maculatum, Androgynoceras sparsicosta can also be found in sideritic
septarian nodules, but often torn apart or squashed :

Androgynoceras sparsicosta in septarian nodule

This specimen is probably transitional to A. heterogenes.

Androgynoceras heterogenes (YOUNG & BIRD, 1828)
maculatum sz

Androgynoceras heterogenes + maculatum

Again a wonderful specimen found & prepped by Mike Forster, kindly sold to me.
It contains an incomplete, fully septate A. heterogenes and a mostly complete A. maculatum.

Androgynoceras heterogenes

Specimen found & prepped by Mike Marshall, kindly sold to me.
Strong capricorn inner whorls and good development of liparoceratid ribbing, but still septate.

Androgynoceras heterogenes + 3 Aegoceras maculatum

A specimen I found quite a long time ago with 1 large A. heterogenes (fully septate) and
3 A. maculatum. There´s a slight pathology of the ribbing on the capricorn part of the whorl.

Androgynoceras heterogenes – possible microconch

A possible microconch with mostly complete body chamber.
The rate of whorl breadth increase is higher than on any other A. heterogenes
in my collection.

Comparison (left to right)
A. sparsicosta
A. heterogenes
A. maculatum

Comparison of similarly sized specimen of (from left to right) A. sparsicosta,
A. heterogenes,  and A. maculatum. Androgynoceras heterogenes is really only
comparable to Aegoceras  maculatum in the first 3-4 centimeters, where specimen
of this size cannot be separated.
After this diameter, the whorl of A. heterogenes begins to quite massively swell,
at a higher rate than A. sparsicosta. After about 7-8 cm the normal ribbing changes
over to bi-tuberculation and liparoceratid ribbing pattern.

Androgynoceras heterogenes – different sizes

The first two specimen in this series are possible microconchs (unfortunately the
relevant area still has shell) and show possibly complete body chamber, while the
right two are fully septate, imcomplete specimen. Both A. heterogenes and
A. sparsicosta have elongated nodes on the ribs after about 3-4 cm.

As already indicated, also the large liparoceratid forms of A. heterogenes are most
often  found as fully septate phragmocones, indicating that at least half a whorl of
body chamber is missing. A section of a liparoceratid body chamber fragment from
maculatum sz is shown below, indicating possible sizes of complete specimen to be
in the area of 20-25 cm.

A. heterogenes body chamber fragment

Liparoceras (Liparoceras) cheltiense (MURCHISON, 1834)
masseanum sz

Liparoceras in general is probably less common on the Yorkshire coast than in Dorset,
and well preserved specimen are a rarity, which also can be difficult to prep.
The relatively small specimen of L. (L.) cheltiense is an example, it was painstakingly
prepped with air pen and abrader from a block of solid ironstone :

Liparoceras cheltiense –
as found

Liparoceras cheltiense

Liparoceras (Liparoceras) divaricosta (TRUEMAN, 1919)
figulinum sz

 

Liparoceras divaricosta

This rather water worn specimen is from figulinum sz, its whorl is much thinner
than that of Liparoceras (Becheiceras).

Liparoceras (Liparoceras) naptonense SPATH, 1938
luridum/maculatum sz

 

Liparoceras naptonense (Bolton collection)

This Liparoceras (Liparoceras) naptonese is in the T. Bolton collection, picture by kind
permission. What is immediately evident is that the ammonite has quite a long capricorn
stage which looks quite like Androgynoceras sparsicosta, I would in fact go as far to say
that this is the macroconch for the A. sparsicosta microconch.

Liparoceras (Becheiceras) gallicum
figulinum sz

Liparoceras (Becheiceras) gallicum

This truly stunning specimen was found and very nicely prepared by Mike Forster,
who kindly sold this specimen to me. It is an inner whorl of a large
Liparoceras (Becheiceras) cf. gallicum that sits inside its
partially removed (I assume because it was crushed) outer whorl.
I assume from the preservation that this came from the figulinum sz, which matches
literature and also my own observation, as the whorl section below showing the complex
suture of Liparoceras (Becheiceras) was found 1997 inside a fallen block that was also
full of Aegoceras (Oistoceras) figulinum – the A. figulinum pictured above also came
from that same block.

Liparoceras (Becheiceras) gallicum – suture

A very large liparoceratid outer whorl found in 2006 has been donated to the Robin Hoods Bay
Old Coastguard station, and gives an indication what sizes could be possible.

Liparoceras (Becheiceras) gallicum

A wider interpretation

The naming of the ammonites above is according to the latest published literature.

Looking closely at the ammonites, for me a pattern becomes apparent, that would
reduce the number of species quite drastically. As I´ve already indicated above,
Androgynoceras sparsicosta looks very much like a capricorn microconch /
immature version of a liparoceratid macroconch L. (L.) naptonense. Similarly, there
seems to be a micrococh/macroconch pair for Androgynoceras heterogenes.
If you regard A. maculatum var. leckenbyi as the liparoceratid macroconch for the
capricorn microconch A. maculatum, there is another pair.
If you allow for extreme variation in developing mature macroconch liparoceratid
characteristics, you could even go as far as including
A. maculatum/A. maculatum var leckenbyi in the same chronospecies as
A. heterogenes – they seem to at least share a few cm of an indistinguishable
capricorn nucleus.

Allthough not shown here, and as far as I know not found in Yorkshire so far,
but known from Dorset, are similar pairs for A. lataecosta, A. capricornus and A. figulinum.

The Liparoceras ammonites from the ibex zone do not seem to have a recognizable
capricorn nucleus, neither does L. (B.) gallicum or L. divaricosta from the figulinum sz.
Liparoceras and Aegoceras/Androgynoceras are clearly related, but a common ancestor seems
to be lower in the ibex zone.

Unlike Liparoceras (L.) divaricosta, Liparoceras (Becheiceras) continues on into the
margaritatus zone, this is one of the reasons it is seen as a separate branch in the tree
of Liparoceratid genera, even by Spath.

There are more Liparoceratidae species out there…

As always, a blog post represents the specimen I have in my collection or am able to
photograph, and as such is a snapshot of the interpretation and knowledge derived
from these. While I wrote this, I took a lot of notes to check for certain beds, hunt for
certain ammonites, view certain ammonites in museums, view certain collections and
photograph some more ammonites, all the things I would have loved to do before
posting this.

Due to the current situation all this has not been possible this year, and I´m missing the
Yorkshire Coast and the people living on it badly. We certainly hope this will change next
year , and then there will most likely be additions to this post.

Many thanks for online discussions go to Murray Edmunds.

Literature

[1] SPATH, L.F. (1938), The Ammonites of the Liassic Family Liparoceratidae in the
British Museum (Nat. History),  British Museum, London
[2] HOWARTH, M.K.(2002),  The Lower Lias of Robin Hood´s Bay, Yorkshire, and the
work of Leslie Bairstow, Bulletin  58/2 of The Natural History Museum, London
[3] PAGE,K.N.(2004), Normanby Stye Batts – Miller´s Nab (Robin Hood´s Bay),
North Yorkshire (NZ 972 025- NZ 952 075), in : British Lower Jurassic Stratigraphy,
Geological Conservation Review Series, JNCC Peterborough 2004, pp. 250-262
[4] SCHLEGELMLICH, R.(1992) ,Die Ammoniten des süddeutschen Lias, 2nd revised
and extended edition, Stuttgart & New York
[5] EDMUNDS, M. (2009), A revision of the Lower Jurassic Ammonite Genus
Eoderoceras SPATH and its Immediate Descendants and Other Relatives,
Palaeontographical Society
[6] HOWARTH, M.K. (2013), Treatise of Invertebrate Palaeontology, (Number 57), Part L,
Revised, Volume 3B, Chapter 4: Psiloceratoidea, Eoderoceratoidea, Hildoceratoidea,
University of Kansas
[7] PHELPS, M.C.(1985), A Refined Ammonite Biostratigraphy for the Middle and Upper
Carixian (Ibex and Davoei Zones, Lower Jurassic) in North-West Europe and
Stratigraphical Details of the Carixian-Domerian Boundary, John Murray, London
[8] DONOVAN, D.T. & FORSEY,G.F.(1973), Systematics of Lower Liassic Ammonitina,
The University of Kansas Plaeontological Contributions

Pieces of a puzzle – 2 new Eparietites species for the collection

Visiting a location, especially a coastal one, over a long period of time again and again has
it’s benefits. Exposures can change every day,but extreme conditions like a bed scoured
clear off it’s usual overlying layer of pebbles can be rare, so coming often gives you more
of achance to experience this and may be even find fossils you’ve not found before
(or did not recognize before as we shall see…).

On one such occasion during the summer of 2019 I found a bed in the lower part of the
denotatus subzone scoured and some ammonites I had not found before in this
completeness in it. On a solo trip I found a large specimen to which access was
unfortunately prevented by a large beach boulder hanging over it,
which I could not move on my own.

Big ammonite on the beach wedged under a big beach boulder – I could not move it on my own !

I was however successful in finding a small nodule on the surface of the bed, with
an ammonite embedded perpendicular to the bed surface, which apparently had
already either been partially eroded by the sea or touched by another collector,
because part of the outer whorl was already missing.

On a trip a few days later together with Adrian, we were able to shift the beach
boulder together and extract the large ammonite without breaking it.
Thanks again for your help, Adrian !

Large Eparieties successfully extracted.
An outer whorl of an Aegasteroceras can be seen on thebottom left of the picture


In the immediate vicinity of the ammonite within the same bed there were also
remnants of other fossils, including a crushed Eparietites, an outer whorl of an
Aegasteroceras (crassum or sagittarium) and a crushed nautilus, which were left in place.
The Aegasteroceras would indicate this bed to be Bairstow 455.x

Small Eparietites and Aegasteroceras in the same bed as the big Eparieties


The size of the ammonite and the bed it was found in initially led me to hope it could
be an  Eparietites bairstowi, but once the umbilical width couldbe clearly measured
during the early stages of preparation, it became clear that Eparietites bairstowi
has a significantly higher umbilical width than this specimen.

Back at home I prepped both the small and the big specimen and also went through
my unprepped specimen pile, because I remembered I hadfound an outer whorl
of a similar specimen some years earlier but had not prepped it yet.

So here are the 3 specimen :

Eparietites undaries, 6 cm / 2.5 “

 

Eparietites undaries – 30 cm / 12″
Surprisingly most of the inner whorls are preserved.
Outer whorls show only light undulations, no ribbing.

 

Inner whorls of the big Eparieties – it seems the worm tubes are holding the inner whorls together, only the last 5 cm/2″ of whorls are not preserved

 

Outer whorls of an Eparietites undaries, 23 cm/ 9″,
found again in my prep backlog and finished for this blog post


Looking through some pictures I had taken for the book of ammonites in
J. Herring’s collection in 2012, I also found another specimen that neatly fits
into the size range of the others, being slightly bigger than the small one at 11 cm.

Eparieties undaries, 11 cm, Col. J. Herring
Ribs are vanishing at this size

From the whorl section of the smaller specimen it was clear that it could not be
an Eparietites impedens,  and that E. undaries would be a good candidate.
The E. undaries illustration of the lectotype in [4] and [5] shows a specimen
of about 150 mm diameter with little details of the inner whorls.
The description in [4] however states that the ribbing would change to soft
undulations of the shell at over 10 cm and that the shells of large specimens
are almost smooth.
Unfortunately the shells of the large specimen are not preserved,  but judging
from the internal moulds, this seems to be the case.
In Quenstedt’s own illustrations in [6] table 20, fig 2-6, E. undaries whorl
section for small and large specimen is clearly shown, also the gorgeous
fine shell structure seen also on the small specimen.  
A perfect picture for E. undaries from a specimen of Quenstedt’s collection,
which was the original to his illustration in [6] table 20, fig 2 is given in [7],
Plate XIII- it fits in all aspects with both my smaller specimen and the 11 cm
specimen from J. Herring’s collection.

So this settles it for these specimen – they are
Eparietites undaries (QUENSTEDT, 1884)

As the ammonites were found in close proximity to if not in the same beds
that Howarth mentions in his description for E. bairstowi, this poses the question
if E. undaries and E. bairstowi might be the same species after all.
This question has also come up in papers by Page in [2] and Edmunds in [3].

From the very large specimen Howarth figures the large E. undaries specimen
seems to be similar in all aspects apart from umbilical width. The smaller paratype
illustrated in [1], plate 2, fig 8 does seem to be more strongly ribbed on the inner
whorls compared to my small specimen, indicating E. bairstowi as likely a
separate species. Unfortunately I do not remember this specimen from my visit to the
Bairstow collection in the NHM , but comparing the 2specimen in the future would
be interesting.

Since Bairstow measured these beds between 92 and 55 years have passed
(he started in 1928 and retired in 1965) , so the illustrations of the bednumbers
given in [1] can only be approximations of the situation today.
There is no mention of any E. undaries found in these beds by Bairstow,
which returns us to what I described at the beginning of this blog post –
as these exposures are small and prone to rapid change, new finds
can be possible even after decades or centuries.

Many thanks to Murray Edmunds for discussions and showing different
Oxynoticeras and Eparietites specimen from his collection, which made me realize
that there is another Eparietites species sitting unrecognized in my collection.

They are from the other end of the Eparietites evolution towards
Oxynoticeras, I have a few specimen in my collection
where I had always been undecided between Eparietites and Oxynoticeras. 

Eparieties collenoti, Scunthorpe, 12 cm / 4 3/4″.
Purchased on eBay

Oxynoticeras simpsoni, 11 cm / 4.5″
A find from summer 2019


They show ribbing reduced to growth striations similar to Oxynoticeras, but there is still
a small shoulder on the venter revealing their relation to Eparietites.
In literature you find references to both Oxynoticeras collenoti and Eparietites collenoti.

Comparison between E. collenoti (top) and O. simpsoni (bottom). On E. collenoti a shoulder is still visible on the keel, with O. simpsoni it is missing


AndyS

Literature :

[1] HOWARTH, M.K.(2002),  The Lower Lias of Robin Hood´s Bay, Yorkshire,
     and the work of Leslie Bairstow, Bulletin  58/2 of
     The Natural History Museum, London 

[2] PAGE,K.N.(2004), Normanby Stye Batts – Miller´s Nab (Robin Hood´s Bay),
     North Yorkshire (NZ 972 025- NZ 952 075), in : British Lower Jurassic
     Stratigraphy,  GCR Series, JNCC Peterborough 2004, pp. 250-262

[3] 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.

[4] SCHLEGELMLICH, R.(1992) ,Die Ammoniten des süddeutschen Lias,
      2nd revised and extended edition, Stuttgart & New York

[5] S. GUÉRIN-FRANIATTE (1966) , Ammonites du Lias inférieur de France,
     Psilocerataceae: Arietidae, Paris

[6] QUENSTEDT, F.A. (1883-1885), Die Ammoniten des Schwäbischen Jura,
     Band 1, Der Schwarze Jura (Lias), Schweizerbart, Stuttgart

[7] REYMENT, R.A. (1958), On Liassic Ammonites From Skåne,
     Southern Sweden, Stockholm Contributions in Geology Vol II:6

The youngest Harpoceras or With a lot of help from my friends

One of the ammonites I‘ve conciously hunted and unsuccessfully so for at least 10 years is Harpoceras subplanatum, a species of Harpoceras from the fibulatum subzone. I‘ve even been desperate enough to buy a reference Harpoceras subplanatum from Deux Sevres / France a few years ago on eBay:

Harpoceras subplanatum , Deux Sevres / France, 16 cm diameter
Harpoceras subplanatum , Deux Sevres / France, 16 cm diameter


As you‘ve seen from the previous post about Harpoceras most members of the genus are actually from exaratum, falciferum and commune zone of the upper Toarcien, so Harpoceras suplanatum is the youngest Yorkshire member of the genus.

Harpoceras subplanatum is relatively similar to Harpoceras falciferum, so with the previous potential fragments I‘ve found, which were ex situ, in areas where there are also exaratum, falciferum and commune subzone sediments around, I just  could not be sure …

This all changed about 18 months ago, when I was fossil hunting with John at Ravenscar. There was a small fall that produced the usual fibulatum ammonites like Peronoceras and Catacoeloceras, so age was definitely confirmed. At the end of collecting at this location, we compared finds, and John showed me a discus shaped ammonite in a nodule saying something like „I think it‘s some kind of Haugia, I think I‘m going to give it a whack…“ˋ- and I said something to the effect of  

„Noooooo – Please don‘t, it‘s a rare Harpoceras subplanatum !“

This is what it looked like :

Harpoceras suplanatum in cement shale nodule as found
Harpoceras suplanatum in cement shale nodule as found


Later in the year, John decided to move south and sell off his collection in the process, and the unprepped Harpoceras went to Dave. Dave generously handed this ammonite to me this summer, and of course I was over the moon….

Howarth in his 1992 Harpoceratidae mentions 4 known Yorkshire specimen, so even if there may be more mis- or unidentified or unknown specimen in private collctions, this is definitely one of the rarer ammonites of the Yorkshire lias.

Of course it was one of the first ammonites on the prep list when I returned home after a glorious 3 week holiday in Yorkshire this summer.
Not knowing if the ammonite had inner whorls preserved, I first tackled one side which seemed the most likely to me to be preserved. I usually start ammonites in cement stone matrix by abrading off the soft outer layer to get an impression about preservation and possible cracks running through the fossil.

John or Dave had already secured one obvious crack in the nodule with liquid super glue, but I also found some more potential cracks into which I also let some liquid super glue seep in and let the nodule rest a day before I continued further  with the air pen.

Prep work with the pen turned out to be relatively easy and the matrix was not at all sticky to remove. I used magnification during air pen work to make sure I inflicted as little as possible damage to the ammonite shell.
In the end this the result of the first side, showing mainly the phragmocone of the ammonite :

Harpoceras subplanatum, first side prepped
Harpoceras subplanatum, first side prepped


The other side showed some potential to have more of the whorl, possibly a bit of the body chamber preserved, but most likley crushed to some extent.When you prep an ammonite completely free of matrix, which was my goal with this one,you have to take extra care about any potential cracks, so again this side was surveyed under magnification and all potential cracks secured with super glue, especially in the thin inner whorls and the ammonite rested for another day to have the supper glue fully solidify in the cracks.

This side proved to be similarly easy to prep but with a bit of a challenge because the body chamber had been crushed in severall layers towards the inside of the nodule, producing a stair like effect, where the edges of the next stair down needed to be detected very carefully. I decided not to prep the inner whorls more deep than on the other side, fearing to push through the inner whorls which had a crack running right through the middle anyway.


Here‘s the final result for this side :

Harpoceras subplanatum, second side prepped, 14 cm diameter
Harpoceras subplanatum, second side prepped, 14 cm diameter


When comparing Harpoceras falciferum and Harpoceras subplanatum side by side, H. subplanatum does have a less deep furrow in the middle of the whorl, and the angle of the ribs is less acute – H. falciferum has falcate ribbing, H. subplanatum falcoid ribbing. The relative umbilical width of H. subplanatum is smaller than that of H. falciferum.

Falcate Ribbing of Harpoceras falciferum
Falcate Ribbing of Harpoceras falciferum
Falcoid ribbing of Harpoceras suplanatum
Falcoid ribbing of Harpoceras suplanatum


Huge thanks to John who found this ammonite (and did not whack it) and to Dave who handed it on to me – this really means a lot to me !

AndyS

Who bit my ammonite ?

I showed you this 12.5 cm specimen of an Angulaticeras in the previous post,
but cunningly only from one side, stating it has these peculiar holes in what is left of the shell.
This specimen is wholly septate, the body chamber is completely missing, as is a part of the outer whorl.

Here now both sides of the specimen, with the location of the holes marked in different
colours for the different sides.

Both sides of ammonite shown with bite marks shown in red and blue, also possible sratch marks and tear-outs

Both sides of ammonite shown with bite marks shown in red and blue, also possible sratch marks and tear-outs

Interestingly, there seem to be roughly corresponding holes on both sides of the shell,
although this is hard to see side by side.

After a bit of Photoshop magic, making the above pictures slightly transparent and carefully
aligning the layers over each other, a more interpretable picture emerges :

Picture overlay of both sides of the ammonite, showing the bite marks. Green dots showing a potential jaw alingnment

Picture overlay of both sides of the ammonite, showing the bite marks. Green dots showing a potential jaw alignment

Tentative alignment of the holes has been added in green dots in form of a triangular jaw
geometry (and this is of course not the only possible interpretation, as we shall see),
which would indicate the application of at least 3 bites of a marine predator
e.g. Ichthyosaur, plesiosaur, crocodile, large fish !
If one follows this interpretation, the first two possible bites probably were softer bites
to grab the ammonite, stop it from escaping while the third bite targeted the juicy
content of the body chamber, biting it off thus separating meat from shell.

Diameters of the single holes on each of the sides vary between 4 and 8 mm,
there appear to be several combined holes from the consecutive overlapping
bites. There are no visible rims around the edges of the holes, and no apparent
shell material in the holes, but the holes seem to be fully sediment filled and could
be explored more by further preparation.

Single, double and triple bite marks

Single, double and triple bite marks

Detail of shell with double bite mark, scratch mark and bitten off shell line

Detail of shell with double bite mark, scratch mark and bitten off shell line

Detail of bite mark with tear-out

Detail of bite mark with tear-out

Now there’s some very interesting literature about cretaceous ammonites showing
potential mosasaur bite marks, and some also very interesting literature showing
that these marks could also be crushed-in resting scars of patellid limpets
(literature references see below).

Kase, Seilacher et al had 1998 offered a convincing alternative explanation for the
holes to be limpet resting scars punched through by sedimentary pressure.
They had even found limpet scraping traces and limpet shells to underpin their theory,
so some significant doubt was cast over the mosasaur bite hypothesis,
as tests performed by them on nautilus shells also showed that shells were more
likely to disintegrate  than be punctured when bitten.

In 2001, the mosasaur bite hypothesis was defended again (Tsujita & Westermann),
by examining a larger number of bitten shells and coming to the conclusion that,
given the rarity of limpet shells in the cretaceous Bearpaw formation of Alberta,
the mosasaur bite explanation was more likely.

In 2009, as part of an MSC thesis (D.S.King), experiments again performed on nautilus
shells,  showed that punctures were very possible on the nautilus phragmocone,
that certain double holes could result from crooked teeth and that indentations
do no always necessarily have to be on both sides of a shell.

In this case however, the limpet hypothesis seems very unlikely, the holes are
relatively small, they are on the phragmocone, and there are also roughly
corresponding holes on the other side of the ammonite.

The dense lobes on this entirely septate part of the shell would probably
have provided enough structural integrity to stop this part of the ammonite
shell being broken apart in contrast to the tests having been conducted the
nautilus shells, which caused the nautilus shells to split entirely.
Other tests (King 2009) showed that holes punched into she shell are even
possible on a nautilus shell, and that it is possible that not all teeth need to
leave a mark on the shell, when the predator only administered a less powerful bite.

Interpretation as bite marks is always more interesting and headline-grabbing,
but I think in this case probability for this theory to be true is very high.

As for the question in the title of the post (who actually bit the ammonite),
I guess we can only speculate.
The bite is relatively small, the angle would probably favour a slender snout.
We know that ichthyosaurs were around, less fossil remains are known of
plesiosaurs or crocodiles in the Yorkshire lower lias.
Diameter of the holes would probably not rule out any of the predators,
so unless somebody more knowledgeable in the diagnosis of bite marks comes
up with a clever idea, the question has to remain unanswered.

The whole appearance of the Angulaticeras is extraordinarily similar to what
Kaufmann & Kesling 1960 described from cretaceous Placenticeras,
albeit this one is about 100 million years older and of course mosasaurs
did not exist then.
In my opinion this is a very likely example of reptilian bite marks on a
lower liassic ammonite and  generally the oxycone shell of these types
of ammonites offers a favourable chance of preservation of these bite marks.

I had initially intended to also provide a 3D image of the ammonite,
but due to my limited spare time at the moment and the requirements
of the method (100+ pictures…) this will have to wait until a later time –
I did not want to hold posting of this blog post for much longer.

If you do have similar ammonites or want to provide feedback on this
blog post, please use the e-mail address provided in the “About me”
section of this blog.

The ammonite shown is not for sale, and my intention is to donate it to a
suitable UK museum in the future.

AndyS

Literature : (links were checked at time of posting but are not guaranteed to be functional for any length of time)

  • Mosasaur bites and limpet scrapes – Wired April 11, 2012
  • The Abilty of Mosasaurs to produce unique puncture marks on ammonite shells, MSC thesis Daniel Steven King, Bowling Green State University 2009

Angulaticeras – or Schlotheimiinae part 2

No, you did not miss anything, I just decided to do part 2 before part 1,
because it fits so nicely with my previous post – a few of the ammonites for this
post was actually found on th e same day as the Bifericeras from the last post !

The whole set will be in 3 parts, part 1 will be about the Schlotheimia species
that can be found in Yorkshire only as erratics, but we will of course include
the Redcar & Cleveland Schlotheimiids (with some gaps).
Part 3 will take longest, because many of the ammonites from this part still
require careful (re)preparation and more research -part 3 will cover the genus
Phricodoceras, for which there is mounting convincement that it does not
belong, as previously thought, to the Eoderoceratidae, but to the S chlotheimiidae.

But back to Angulaticeras…

There are 2 species of Angulaticeras that I can show you, one is an early bucklandi
subzone species, that I plucked out of Byron‘s unprepped Redcar box a few years ago
for a good price, and the other a relatively rare  denotatus subzone species from
Robin Hoods Bay.

Angulaticeras often has a thin ventral groove created by rib ends projecting over
the venter line. This ventral groove is most often lost on larger specimen.
In contrast to Schlotheimia, Angulaticeras shows secondary ribbing,
i.e. bifurcating ribs, from very early on in the development.

But let‘s start with the bucklandi subzone one from Redcar :

Angulaticeras cf. charmassei (D´ORBIGNY, 1844)

Angulaticeras cf. charmassei, 9cm / 3.5 " diameter, bucklandi sz, Redcar

Angulaticeras cf. charmassei, 9cm / 3.5 ” diameter, bucklandi sz, Redcar

A big, robustly ribbed species. Angulaticeras can get quite big, I‘ve seen Somerset
specimen well above half a meter.

The next one is the denotatus subzone species from Robin Hoods Bay :

Angulaticeras sulcatum (SIMPSON, 1843)

I found the first fragmentary specimen of this species in 1996 as a small pyritic inner
mould, only a mere sliver of an ammonite:

First Angulaticeras fragment found in Robin Hoods Bay in 1996, diamater 1.6 cm

First Angulaticeras fragment found in Robin Hoods Bay in 1996, diamater 1.6 cm

I discovered my second specimen when formatting a little bit of matrix with an Eparietites
and found that there was a very small 7 mm Angulaticeras at the back :

Specimen of Eparietites denotatus, 4 cm, see next picture for what´s on the other side...

Specimen of Eparietites denotatus, 4 cm, see next picture for what´s on the other side…

Reverse of the previous specimen with small Angulaticeras sulcatum, 7 mm diameter

Reverse of the previous specimen with small Angulaticeras sulcatum, 7 mm diameter

Detail of small Angulaticeras sulcatum, 7 mm diameter

Detail of small Angulaticeras sulcatum, 7 mm diameter

Since then I‘ve been checking every likely nodule very carefully when splitting it and at
the day as mentioned above, found more signs of  ammonites :

Split nodule as found with 4 small Angulaticeras, one spilt in the middle...

Split nodule as found with 4 small Angulaticeras, one spilt in the middle…

The nodule showed signs of 3 ammonites, unfortunately one had been split in half.

I prepped the ammonite on the small bit of rock first, and discovered a tiny
Pleurotomaria gastropod sitting on it as a bonus !

Prepping the first Angulaticeras, if you look carefully you see that there´s also a gastropod...

Prepping the first Angulaticeras, if you look carefully you see that there´s also a gastropod…

Prepped Angulaticeras sulcatum, 2 cm diameter, with small Pleurotomaria, 4 mm diameter

Prepped Angulaticeras sulcatum, 2 cm diameter, with small Pleurotomaria, 4 mm diameter

The 2 remaining pieces of the nodule with the split ammonite were glued together again
after marking the position of the ammonites carefully.

Parts of nodule that contains 2 Angulaticeras glued together again and with ammonite locations marked.

Parts of nodule that contains 2 Angulaticeras glued together again and with ammonite locations marked.

The matrix was prepped down very carefully with the air pen and finished with the air
abrader once the smallest signs of ammonites showed themselves, revealing 2 small
further gastropods in the process :

The prepared specimen with two Angulaticeras sulcatum, 2 cm and 5 mm, an two small gastropods

The prepared specimen with two Angulaticeras sulcatum, 2 cm and 5 mm, an two small gastropods

The crowning specimen came along when in discussions on the Yorkshire fossil
hunters group on facebook, Mark Hawkes posted a much larger fragment of a
Robin Hoods Bay ammonite that was also identified  as Angulaticeras and which
Mark thankfully sold to me (also for a good price, thanks again Mark !).

Fragment of big Angulaticeras sulcatum, 10 cm wide

Fragment of big Angulaticeras sulcatum, 10 cm wide

This specimen is about 10 cm in width and includes inner whorls and part of a
still fully chambered next whorl, I would estimate it would have been more than
20 cm in diameter including the missing body chamber. It is very finely ribbed,
the ventral groove, being present in the juvenile, is now fully closed.
The matrix looks very much the same as the one for the smaller specimen, so it is
assumed it comes from a similar range of beds.

The Schlotheimiinae are known for large size differences of microconch [m] and
macroconch [M], and this is what we may see here as well, allthough the small
specimen show no signs of being mature, so could be juveniles as well.

What makes this specimen even more remarkable, besides its large size and
rarity, is the sharply localized, round holes in the shell, which are also
complemented by similar holes on the other side of the ammonite…

Since there´s a lot more to this specimen, it´s well worth another blog post
so we´ll explore this a bit(e) more in the near future, taking this to a
whole new dimension 😃

AndyS

Literature :

Schlegelmilch, R.,Die Ammoniten des süddeutschen Lias,
2nd revised and extended edition, Stuttgart & New York 1992

 

Howarth, M.K., The Lower Lias of Robin Hood´s Bay, Yorkshire,
and the work of Leslie Bairstow, Bulletin  58/2
of The Natural History Museum, London 2002

 

Edmunds,M., Varah, M., Bentley, A., The Ammonite Biostratigraphy
of the Lower Lias ‘Armatum Bed’ (Upper Sinemurian – Lower Plieansbachian)
at St. Peter´s Field, Radstock, Somerset, Proceedings of the
Geologists´ Assocation 114, 2003

 

Sheltered

For me the best fossils are the ones that surprise you when you prep them, because they turn
out so much better than you expected…
This specimen is one of those, this is how it was found in Robin Hoods Bay in July 2017:

Specimen as found

Specimen as found

It looked to me like a quarter section of a large Oxynoticeras, where some (I could see two)
Gagaticeras had been washed into the body chamber.
There was a little bit left of the inner whorl of that ammonite, and I decided that this might
potentially look nice when done.One additional specimen had crumbled off the relatively
brittle stone, it had lain a while in the water already.

At home, this was put on the back list of fossils that I would occasionally take another look
at, certainly not top priority. When I was air abrading another specimen, I tested the broken
off specimen, it abraded relatively easily, allthough the matrix was very sandy
(that should have told me something in the first place…).

I instantly saw that this was no Gagaticeras when the first spine appeared :

Bifericeras bifer (QUENSTEDT, 1845)

Broken off Bifericeras, diameter of ammonite = 3 cm

Broken off Bifericeras, diameter of ammonite = 3 cm

Bifericeras bifer is a very rare ammonite in the beds around Robin Hoods Bay, or,
to be more precise it is rarely found.
In all the years since 1989 I had only found Bifericeras bifer in 2016, after a cliff fall cut
through the specific beds of the bifer biohorizon.

The beds where Bifericeras bifer occurs are difficult to find in the reef, so one is
dependent on cliff falls, and of course on luck. to be there at the right time and place…

The ammonites in that fall were contained in highly pyritic lenses, unfortunately
neither very well preserved nor easy to prep.

Pyritic lens with multiple, badly preserved Bifericeras, diameter of biggest ammonite = 3 cm

Pyritic lens with multiple, badly preserved Bifericeras, diameter of biggest ammonite = 3 cm

So seeing this specimen from 2017, I was deligthed to have another Bifericeras bifer,
which had not been in my collection from Robin Hoods Bay yet, and more easily to
prep as well !

The specimen instantly went to the top of my prep list.
Preparation was not as easy as I had thought at first, the sandy matrix was made up
of harder and softer layers on the milimeter scale so I had to  alternate between air pen
to remove the harder layers and the air abrader to remove the softer layers which
were luckily mostly around the fossils.

I had finished the ammonite that is visible on the first photo and another one to the right
and was already smoothing the matrix between them, when I noticed another ammonite,
and while air abrading that one, even another one, better and bigger than all the previous
ones…

After about 6 hours of total prep time, this is the end result :

The finished specimen with 4 Bifericeras bifer within the body chamber of a large Oxynoticeras sp.

The finished specimen with 4 Bifericeras bifer within the body chamber of a large Oxynoticeras sp.

Detail of the better preserved ammonites - biggest Bifericeras bifer diameter = 3.5 cm

Detail of the better preserved ammonites – biggest Bifericeras bifer diameter = 3.5 cm

The ammonites were washed into the body chamber of the larger ammonites and were
sheltered there from compaction or getting  otherwise damaged before or during
fossilization, the shells all seem to be complete to the mouth border, though they are
most likely not adult.

They must have lain in a jumble right on the inside of the shell of the large ammonite‘s
body chamber, because there is very little matrix left at the other side, which necessitated
it being stabilized with liquid super glue to avoid accidently breaking through…
Note that the Bifericeras ammonites are all preserved with shells, so look slightly
different to those usually found elsewhere, e.g. in Gloucestershire, as pyritic inner
moulds from clay exposures, due to the preserved shell the spines are more pronounced
and seen on earlier whorls.

The most diagnostic characteristic for Bifericeras bifer is the double row of spines,
the spines being connected through a rib and the inner ones
often pointing inwards towards the center of the ammonite.  The innermost whorls up to
between 7—10 mm are smooth.

The 5 ammonites washed into the body chamber already show that there seems to be
quite some variation in spines and whorl width.

Detail of Bifericeras bifer showing double spines connected through a rib

Detail of Bifericeras bifer showing double spines connected through a rib

There are two more species of Bifericeras that occur in Robin Hoods Bay :

Bifericeras vitreum (SIMPSON, 1855) and

Bifericeras donovani DOMMERGUES & MEISTER, 1992

I do actually have a single Bifericeras vitreum, a small sharp shell preserved specimen
contained in a very similar sandy matrix as the Bifericeras bifer shown above.

Bifericeras vitreum, diameter = 2 cm

Bifericeras vitreum, diameter = 2 cm

View of the venter of Bifericeras vitreum with sharp ribbing, convex across the venter

View of the venter of Bifericeras vitreum with sharp ribbing, convex across the venter

Bifericeras vitreum has rather sharp ribs that run across the venter in a slightly convex manner.
This specimen has also been carefully prepped with air abrasion.

Bifericeras donovani from the base of the taylori subzone has so far eluded me,
allthough from the Wine Haven paper (see literature below) it appears they are
relatively abundant.

The only question now remains is : Is the ammonite that „provided shelter“
to the Bifericeras in it‘s body chamber really an Oxynoticeras or more likely
to be a Gleviceras ?

Section of Oxynoticeras sp with sutures showing, width = 9 cm

Section of Oxynoticeras sp with sutures showing, width = 9 cm

There really is not much to go from, but the venter seems to be very sharp and the
whorl lacks the fine ribbing characteristic for Gleviceras, so I‘d go for a late
Oxynoticeras grp. oxynotum, which with the sandy matrix lithology nicely fits
with (Hesselbo & Jenkyns numbering) beds 44-49 of the bifer biohorizon and their description
in PAGE 2004.

Detail of biggest Bifericeras bifer

Detail of biggest Bifericeras bifer

So in the end, that „ugly duckling“ of an incomplete ammonite has (been) transformed into
a stunning „swan“ of a multi ammonite, multi species specimen with a story to tell.

On the same day I found this specimen, two other, no less interesting ammonite
specimen were found, more about these soon…

AndyS

 

Literature:
  • Schlegelmilch, R.,Die Ammoniten des süddeutschen Lias, 2nd revised and extended edition,
    Stuttgart & New York 1992
  • Howarth, M.K., The Lower Lias of Robin Hood´s Bay, Yorkshire, and the work of
    Leslie Bairstow, Bulletin  58/2 of The Natural History Museum, London 2002
  • Meister/Eberhan/Blau/Dommergues/Feist-Burkhardt/Hailwood/Hart/Hesselo/Hounslow/
    Hylton/Morton/Page/Price,
    The Global Boundary Stratotype Section and Point (GSSP) for the base of the Pliensbachian
    Stage (Lower Jurassic), Wine Haven, Yorkshire, UK, 2006
  •  Page,K.N., Normanby Stye Batts – Miller´s Nab (Robin Hood´s Bay),
    North Yorkshire (NZ 972 025- NZ 952 075), in : British Lower Jurassic Stratigraphy,
    Geological Conservation Review Series, JNCC Peterborough 2004, pp. 250-262

The lost Arnioceras or The hunt for a name

There are specimen that are appear unremarkable when you collect them, and you don´t
have high hopes for them,  but you take them home anyway.

 

Nodule with ammonite in3 pieces as found

Nodule with ammonite in3 pieces as found

This was very much the case for this specimen shown as found ex-situ in
Robin Hoods Bay this March. It just showed the section of an ammonite
on the side of the nodule, when formatting the rock, the part containing the
ammonite also fell into 3 pieces due to natural cracks.
I think there might have been a moment when I thought of chucking the
bits into the sea,  but the breaks were clean and promised to be simple to
glue so it went into the bag…

For one of the final stages of prepwork, which the air abrading usually is for me,
I often accumulate a few specimen that have been previously roughly prepared
with a big pen, then fine prepped with a small pen and just need that little bit of
extra cleaning with the air abrader – preparations before and cleaning up after
air abrading take some time and I usually don’t do that for single specimen.

I had glued the parts of the small nodule back together again, and after finishing
my other specimen to be abraded,  I had a bit of powder still in the tank and
decided just to test the ammonite to see what it was.
With nodules that have been weathering or a while that usually works, even if
the nodule itself is not completely abradeable due to increasing hardness of the
matrix when the weathered layer is off.

To my surprise, I could just keep on abrading…
The matrix was soft enough to be abraded at a relatively low pressure (3.5 bar),
the ammonite´s shell was beautifully preserved in dark grey calcite, and the
ammonite had a very strong undamaged keel.

I had initially wondered if it could be an Arnioceras, and that seemed to be the
correct genus identification.

 

Arnioceras sp., 5 cm diameter

Arnioceras sp., 5 cm diameter

BUT: I had never found a Yorkshire Arnioceras that could be air abraded from the matrix.
I don´t think even a very weathered semicostatum  matrix e.g. from the Holderness Coast
ever becomes abradable.
AND it looked different from all the species I had described in an earlier blogpost (link).

The innermost whorls up to about 1 cm are relatively smooth just like in Arnioceras semicostatum,
but the ribbing is more straight and finishes almost abruptly at the edge of the venter.

 

Arnioceras sp., 5 cm diameter, view of keel

Arnioceras sp., 5 cm diameter, view of keel

 

The keel on the venter is very strong, similar to Arnioceras falcaries, but
it´s whorl section is more rectangular.
It also has less ribs per whorl than the species mentioned : about 25 ribs / whorl at 5 cm diameter.

 

Arnioceras sp., 5 cm diameter, view of keel & whorl section

Arnioceras sp., 5 cm diameter, view of keel & whorl section

So I started getting out the books…(which in these days most of the time is
starting the full text database on the computer)
First candidate I found was Arnioceras oppeli GUÉRIN-FRANIATTE, but while whorl
section,  style of ribbing and keel was a good match,  the count of ribs/whorl of my
specimen was lower, and A. oppeli seems to not have smooth innermost whorls.

 

Arnioceras bodleyi (J. BUCKMAN), 7 and 5 cm diameter, Kilve/Somerset

Arnioceras bodleyi (J. BUCKMAN), 7 and 5 cm diameter, Kilve/Somerset

I then remembered the purchased Kilve/Somerset Arnioceras specimen I have in my
collection, which is Arnioceras bodleyi (J. BUCKMAN, 1844).
(incidentally it was James BUCKMAN, not SS BUCKMAN, who “founded” this species
(in the words of his son Sidney Savoury BUCKMAN, of “Yorkshire type ammonites”
fame)).
Very good match with the strong keel, style of ribbing, but again slightly less ribs/whorl
in my specimen, and maybe less compressed than the Kilve specimen, and no keel
furrows.
I was ready to call it a close enough match at this point in time. But I still had that
nagging thought that you have when something does not completely fit…

As a final check I consulted with some friends from the facebook Yorkshire fossils
collectors group if they had seen a similar Arnioceras from a soft matrix –
and Dave showed me a perfectly matched specimen from Redcar, in a very soft matrix !

Now two occurrences of Arnioceras in soft matrix make a pattern, so I scanned
HOWARTH´s summary of Bairstow´s collection again for Arnioceras from
Robin Hoods Bay – and found mentions of Arnioceras above the semicostatum
subzone, in the turneri zone, birchi/brooki subzone !

Ammonites from these subzones in Robin Hoods Bay show exactly the same style of
preservation and “abradebility”, unfortunately HOWARTH does not figure them,
the brooki subzone Arnioceras from the Bairstow collection are mentioned as
“?Arnioceras sp. indet. 1,lost”, and I unfortunately don´t remember from my last visit
what the two specimen from the birchi subzone housed in the collection looked like.

So back to the database…what species of Arnioceras occurs above the semicostatum
subzone ?

Kevin Page´s paper “The lower Jurassic of Europe: its subdivision and correlation”
delivers a hint on Arnioceras hartmanni from the brooki subzone, but no figure…

No luck in the Palaeontological Association´s “Fossils from the Lower Lias of the
Dorset Coast”  either – “not figured“.

But finally Alpheus Hyatt´s “Genesis of the Arietidae” has a figure (Plate II, fig. 17)  –
and it´s a perfect match and he also mentions that it can be found in the Whitby area !!!
Similarly fitting is D’ORBIGNY´s specimen of “Ammonites kridion” which was revised to
“Ammonites hartmanni” by OPPEL which I found after a bit of internet research in the
Paris Muséum National D’Histoire Naturelle’s online collection (very nice !)

It is still somewhat “circumstancial evidence”, since the ammonite was found ex-situ,
and of course therefore I cannot with absolute certainty know that this ammonite
really is from the brooki subzone but I think it´s close enough to give it a name,
at least with a “cf.” :

Arnioceras cf. hartmanni (OPPEL)

So if anyone has a Caenisites brooki together with an Arnioceras from Robin Hoods Bay,
please let me know, for final proof 🙂

Anyway, who would have thought that you can spend this much fun time on a rainy
weekend prepping and digging through palaeontological history on this (only seemingly)
unremarkable little ammonite ?
The excitement of the fossil hunt becomes the hunt for a name, which to me can be
almost as exciting.

AndyS

Literature and Links :

Paris Muséum National D’Histoire Naturelle’s online collection, “Ammonites kridion” :
Schlegelmilch R. (1992), Die Ammoniten des süddeutschen Lias, 2nd Ed,
Gustav Fischer Verlag
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
Oppel  A. (1856), Die Juraformation  Englands,  Frankreichs  und des südwestlichen Deutschlands.
Jahreshefte  des  Vereins  für  vaterländische  Naturkunde  in Württemberg
Hyatt, A. (1889), Genesis of the Arietidae, Smithonian Contr. Knowl., Washington
Page, K. (2003), The Lower Jurassic of Europe: its subdivision and correlation,
Geological Survey of Denmark and Greenland Bulletin 1

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.

“Show me the keel, please” – or : A nodular mystery

When I´m asked to identify an ammonite from a picture, I often have to say
“show me the keel, please”,  because especially with liassic ammonites, a safe
identification of an ammonite cannot be done without  having a view of the keel.
The following example illustrates this best…

 

The mystery nodule with a partially prepared ammonite

The mystery nodule with a partially prepared ammonite

This nodule with a partially prepped ammonite was shown by David in the Yorkshire
Fossil Hunters group on facebook a while ago.

The fossil was found on the Holderness Coast as a glacial erratic, so age wise this can
basically be anything – from lower jurassic to cretaceous.
The keel of the ammonite was not prepped at this state, so identification was pure
speculation –  Schlotheimia and Caenisites were proposed candidates.

Intrigued by the nodule and the mystery, I offered David to try and prep this ammonite.
We met this summer in Robin Hoods Bay, exchanged the ammonite, and David also
allowed me to photograph another beautiful and rare ammonite,
a Xipheroceras dudressieri, which you will see in another blog post soon…

The matrix the ammonite is embedded in – a greyish-brown, relatively hard clay ironstone
like concretion – did not aid a lot in the identification – it could still be
hettangian (Schlotheimia), sinemurian (Caenisites), or even pliensbachian (Pleuroceras)
or some non-liassic formation unknown to me.

When I returned home after my vacation, I started prep work on the ammonite.
The matrix was still just soft enough to be air abraded using iron powder,
so my first check was wether this ammonite actually had a keel
(Caenisites, Pleuroceras,…) or just a furrow (Schlotheimia..).

After about an hour of carefully working towards the keel, first with an air pen, and then
with an air abrader, it was clear that the ammonite does actually have a keel, so it had to
be Caenisites – but wait, the keel is relatively strongly crenelated – could it be a Pleuroceras ?

Counting the ribs it would have to be a Pleuroceras apyrenum, and there is a bed that actually
produces nodules like these, so I went on based on this assumption…

Is this a Pleuroceras keel which I see before me ?

Is this a Pleuroceras keel which I see before me ?

Seing the beautiful preservation of the ammonite
(a milk cholcolate brown shell on a solid calcite core –
doesn´t that make your mouth water 🙂 ), I decided to completely prep the side
of the ammonite still completely hidden in the  concretion as well.

It is never without risk to prepare an ammonite from both sides, the ammonite might
break, or the innermost whorl might just blow through.

Since the concretion had some calcite-filled shrinkage cracks as well which might be
breaking points, I had to prep it most carefully and as vibration free as possible, so I
did most of the work with the air abrader, after securing the innermost whorl with a
drop of super glue, from the other side, just to be safe 😉

Keel of ammonite with deep furrows

Keel of ammonite with deep furrows

A few hours on, the furrows on the side of the keel I exposed got deeper and deeper…
Back to the books – no, there is no Pleuroceras where the furrows are that deep, even
taking into account that this specimen has shell preserved.

That means, it has to be a Caenisites after all, more specifically a Canisites turneri .
I had previously only seen smaller specimen without shell, so the crenelated keel
on larger whorl sizes is new to me.

After about 10 prep hours, here in it´s full beauty :

Caenisites turneri BUCKMAN 1925, 65 mm, found Holderness coast, D. Pearson collection

Caenisites turneri BUCKMAN 1925, 65 mm, found Holderness coast, D. Pearson collection

In summary, I think this shows how difficult it is to identify an ammonite without
having full view of all the diagnostic characteristics.

It´s been an absolute pleasure to prepare this ammonite
(but remember : Don´t ask me, I will ask you…), and of course it yielded a few more
good pictures of this species for the book and this blog.
The ammonite will be returned in the next couple of weeks to David, with special thanks .

AndyS

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.