For Yorkshire, it is rare that Amaltheus occurs together with Pleuroceras – if you check the first table in my Pleuroceras blog post https://andysfossils.com/2016/01/31/pleuroceras-the-other-amaltheid-ammonite/, you’ll notice it is really just a few beds where this could theoretically happen.

So when you find an Amaltheus together with a Pleuroceras, you already know it’s really special…

Recently in one of the facebook groups, Phil Rann posted a picture of what looked like an Amaltheus together with Pleuroceras in the same rock, found on the Holderness coast , in a rock that seemed very much like the Yorkshire ironstone.

Phil very kindly offered to send it to me.

After about 3 weeks (and one week where it unnervingly seemed to be stuck in the carrier’s unknown depot, and I already feared it lost) it arrived.

I completed the preparation on this specimen and here it is now :

I have interpreted this ammonit as an Amaltheus reticularis (SIMPSON, 1843)

It is apart from Pseudoamaltheus engelhardti the only Yorkshire Amaltheid ammonite I’ve not yet had in my collection.

The specimen is 31 mm in diameter, and shows relatively strong sigmoidal ribbing with 18 ribs at maximum diameter, with the remaining part of the body chamber constituting approx. 40 % of the last whorl. Umbilical width is about 22 % at 31 mm.

The ammonite fragment in the upper right hand corner is of a Pleuroceras paucicostatum. On the same small block there is also a small P. apyrenum, a small Amauroceras ferrugineum and fragments of a Pleuroceras elaboratum beside the Amaltheus reticularis, making it a perfect match of the equivalent of Hawsker bed 33 where also the holotype came from.

Like Amauroceras it does not have the typical braided Amaltheus keel :

The venter is first relatively rounded and then sharpens up on the body chamber, only a few small crenations can be seen from ribs crossing over.

The next picture shows the specimen in UV light, a calcite vein runs across the whole little block and has also replaced a small part of the ammonite, unfortunately also the last suture before the body chamber.

The suture of Amaltheus reticularis exhibits unusual frilling of the first lateral saddle
(Howarth 1957, p. xix), which with this specimen due to above mentioned calcite vein can only be seen in its “infancy”, taken at around 15 mm diameter:

I’ve always been fascinated by the holotype specimen that is exhibited in Whitby museum (WM 217) with it’s spiral ornamentation criss-crossing with the ribbing on the outer whorl and thus creating a net pattern (hence the name, reticulum = latin for net).

It is also the very first ammonite figured in Buckman’s classic 1909
“Yorkshire Type Ammonites”, and I’ve scanned it in from my Buckman original, since all other available published pictures simply don’t do it justice:

The figure of the holotype shows also a Pleuroceras preserved with the Amaltheus, it also looks like a Pleuroceras paucicostatum. The figured ammonite is 61 mm in diameter, so considerably larger than the specimen at hand.

All of the other specimen figured in literature I know of are from Howarth’s Amaltheidae (if you do have any other specimen or know of any other figured specimen, please let me know !)
On a visit to the Sedgwick Museum Cambridge in 2012 I did actually take some snapshots of a display that included the two specimen Howarth figured :

Unfortunately, these have not been 3d scanned in the GB3D project (http://www.3d-fossils.ac.uk), probably
because they’re not type specimen, so we‘ll have to make do with these bad photographs of mine…

The cast of the more complete specimen above (from GeoEd Ltd https://www.geoed.co.uk) is more finely ribbed with about 22 ribs at the same diameter, with a sharper keel, but generally a good match in morphology.

It is hard to see the beginning spiral ornamentation on the specimen – I had to tease it out using some grazing light over the body chamber :

It does seem to be a bit more robust both in terms of ribbing and whorl thickness and the suture is unfortunately not completely “readable”, but I think that this is likely within the variation of the species, as the stratigraphical age is such a good match. The more robust ribbing lends some more weight to the theory that A. reticularis may be derived from A. margaritatus.

There are really no other specimen I know of to compare to other than the ones figured by Buckman and Howarth, so I hope I have added a little to the knowledge about this very elusive ammonite.

Many thanks again to Phil Rann for sending me this specimen !

Literature

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

K.N. PAGE : Castlechamber to Maw Wyke, North Yorkshire in : British Lower Jurassic Stratigraphy, JNCC Peterborough, 2004

S.S. BUCKMAN : Yorkshire Type Ammonites, Part 1, William Wesley and Son, London, 1909

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

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