Small is beautiful

This find is, like so many, a find I did not expect but one that likely has a link to a previous find.

As is my usual habit, I do a quick photograph of all the finds on a daily basis,
this one was found at Stoupe Beck Sands on June 12, 2023.

I had been out collecting with Neil the previous day on this stretch of the coast and wanted to check up on a crinoid slab that Neil had got a small crinoid off on that occasion. The crinoid slab proved to hard to find again after it had been mostly sanded over by the previous tide, but also ultimately free of other fossils.

I continued checking for any new fossiliferous rocks in the area and found this small 15 cm wide flat nodule ex situ with small unidentifiable ammonite sections showing on the top. I gave it a tap with the hammer on the side to see if there would be any more inside, but stopped there when the venter of one of the ammonites was exposed, and bagged the nodule.

If you look closely at the picture above, I had at the time of photographing the specimen already done a „scratch test“ with my fingernail to see if that specimen would be abrade-able, and it looked like it.

Back at home, I put that assumption to the test and quickly got hooked abrading the fossils in this small piece of rock.

This picture shows why :

About 10 hours prep time, mostly abrading with soft iron powder

Preservation is quite wonderful, luckily there were more ammonites than initially showed on the surface, but also a few well preserved double sided Cardinia and other bivalves, and also some beautiful gastropods that showed in the course of the preparation.

The question then of course was : What genus/species are these ammonites ?

With small ammonites (and the largest of these is just under 2 cm or 3/4 of an inch in diameter) that is always difficult, as characteristics may not be fully developed.

These are mostly smooth, with very fine growth lines on the shell, and a faint keel on the venter that shows developing side furrows on one of the ammonites.

The same ammonite is also the only one that shows the beginning of some wavy ribbing on the last whorl.

As all of the ammonites are mostly preserved with shell, no sutures are visible, so no help there. I’d be tempted to carefully polish away a bit of shell to get to them though…
There is one very small fragment of a larger ammonite as well :

Since it is so small, really just 2 ribs, less than 1 cm width, and shows no other characteristics, no real help there either. It is good to know though, that larger ammonites co-existed with these smaller ones.

From the locality, stratigraphy and lithology we can assume this is lower lias, most likely sinemurian. Bivalves are only rarely useful for indicating stratigraphy, we know that for example the Cardinia genus commonly occurs throughout the hettangian and sinemurian.

Lithologically, the nodule seems to be a bit closer to nodules I have found with Caenisites, being a bit harder and in parts slightly pyritized, you can guess that from the first picture by the slight yellowish-green tinge of parts of the nodule.

The ammonites look very much like an Arnioceras miserabile I have posted before :

Given the lithology of the rock I would think it would be higher than semicostatum zone that the above A. miserabile comes from, but I have posted about an Arnioceras cf. hartmanni from the brooki subzone before, and looking at the inner whorls of that ammonite it seems we could have a match :

So, still not proof that these occur together with Caenisites, but we’re getting closer…

As for the smaller bivalves apart from the Cardinia, here are my tentative Identifications :

Tutcheria sp.

Pteria sp.

For the two beautifully preserved gastropods I would suggest Promathilda sp.

as an Id, if anyone has a better idea, please let me know !

Promathilda sp.

Promathilda sp.

14 ammonites including partials, 4 gastropods, about 15 various bivalves and 1 tubeworm – not a bad result for this small piece of rock !

AndyS

by andysfossils on September 24, 2023  •  Permalink
Posted in Uncategorized

Posted by andysfossils on September 24, 2023

https://andysfossils.com/2023/09/24/small-is-beautiful/

Small Ears

After 2 years of not being able to come to our favourite place in the UK,
we finally made it back for 2 weeks in June and one week in November 2022.

Now, in the days between Christmas and the New Year, I also found some time to prepvsome of my finds. One, which is rather small, has made me unproportionally happy, so happy in fact that I just need to show you…

It was the first collecting day of our week in November, the early morning low tide point had already passsed so I only went out to Stoupe Beck Sands. I picked up a few likely looking nodules, and found little bits & pieces.

One ex situ nodule I opened with the hammer and it revealed a small ammonite, apparently split though the middle exposing a calcified inner whorl. It looked like the bigger outer whorl was also preserved, and I remember speculating if this might be something special… I bagged the two pieces of the nodule, but back in our holiday home when I did my find notes and a picture „as found“ I filed it under “small Euagassiceras”.

Split nodule with small ammonite

Back home, I looked again at the two nodule pieces, and found that the matrix seemed just soft enough for air abrading, so after marking where I would have to expect the ammonite I glued both halves of the nodule together again, and reduced the rock down to shortly where the ammonite would be with an air pen.

I then started abrading with iron powder and soon found the venter of the ammonite, unfortunately it seemed that this small ammonite had been preyed upon by cutting a small hole in the shell just where the body was attached. Nevertheless, the rest of the ammonite shell seemed solid and in good order and air abrading proceeded well.

“Riparioceras” keel and a few nice bivalves

Once I had exposed more of the ammonite, it became clear that it was not an Euagassiceras, but a „Riparioceras“, i.e. the inner whorl of a Gleviceras, see also

here (Link). At the time I wrote that blog post, I only had a fragment from an outer

whorl of a Gleviceras, and the other specimen I showed were from Dorset and Gloucestershire deposits. And now here is the Yorkshire „Riparioceras“ in all

its miniature 2 cm glory :

“Riparioceras” on nodule

Quenstedt, in his 1885 „Ammoniten des Schwäbischen Jura“ had under a subtitle „Allerlei“ („Miscellaneous“) rather endearingly described the particular ribbing style of the rare „Ammonites riparius“ as an ear-shaped loop, even proposed a byname of „auritulus“ (latin „long ear“) for it.

And that‘s exactly what we see here :

“Riparioceras” ear shaped ribbing

There aparently are different types of „Riparioceras“ style inner whorls for different Gleviceras species, but far as I‘m aware, there is no publication that shows the inner whorls of different Gleviceras species in sufficient detail
(and I guess Gleviceras itself is rarely that well preserved and that abundant for someone mad enough to break open the outer whorls to find out what the inner whorls look like).

So for this Gleviceras sp. we can only speculate as to its stratigraphic position, as it was not found in situ, but likely is from upper oxynotum subzone.

Anyway, this unexpected find was an absolute pleasure to slowly discover during prep – now I know that well preserved bigger Gleviceras must exist as well !

Fossil related New year resolutions for 2023:

  • Collect more ammonites, even and especially the small ones !
  • Write more blog posts
  • Re-invigorate my book writing

With best wishes for the New Year 2023,

AndyS

by andysfossils on December 31, 2022  •  Permalink
Posted in Ammonites, Literature, Preparation, Uncategorized

Posted by andysfossils on December 31, 2022

https://andysfossils.com/2022/12/31/small-ears/

A rare Amaltheid ammonite: Amaltheus reticularis

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 :

Amaltheus reticularis, 31 mm

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 :

Amaltheus reticularis – keel view

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.

View of specimen in UV light

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:

Suture at 15 mm – 2.5 x magnification stacked from 9 shots

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:

Amaltheus reticularis figure from Buckman´s “Yorkshire Type Fossils” from 1909

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 :

Amaltheus reticularis – Sedgwick Museum Cambridge
Amaltheus reticularis – Sedgwick Museum Cambridge

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…

GeoEd cast of Amaltheus reticularis, 40 mm

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 :

Amaltheus reticularis – spiral ornament on 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

by andysfossils on December 29, 2021  •  Permalink
Posted in Ammonites, Uncategorized

Posted by andysfossils on December 29, 2021

https://andysfossils.com/2021/12/29/a-rare-amaltheid-ammonite-amaltheus-reticularis/

One plus one is more than two

In memory of Jeff Mulroy

Coroniceras lyra (left, 85 mm) and Arnioceras ceratitoides (right, 55 mm)

This is one of the pieces I bought from the collection of Jeff Mulroy, who sadly passed away in October 2018. You will see a few more specimen from Jeff’s collection in the next couple of posts…
This specific one came to me through Mike Marshall, who had bought it from Jeff, re-prepped it and kindly sold it on to me; I do not know what it looked like initially, but I assume from what I’ve seen from Jeff’s prep work that Mike only had to further enhance the already good prep that Jeff had done a little. I guess it is either an erratic specimen from the Holderness coast or from the Redcar/Marske area where Jeff often collected, its origin is the lyra subzone of the semicostatum zone of the lower Lias.

Arnioceras ceratitoides, 55 mm and a small Coroniceras, 10 mm at the top

Arnioceras ceratitoides, keel view

As he sold it, Mike had quite correctly identified the larger 55 mm ammonite on the right as Arnioceras ceratitoides (QUENSTEDT,1848), a very finely ribbed species of Arnioceras which to that point I not had in my collection (or so I thought…) I’ve counted 45 ribs at 55 mm diameter, which is significantly higher than in all the other Arnioceras species I’ve described in https://andysfossils.com/2012/09/02/arnioceras-or-a-frustratingly-sticky-matrix/. In this specimen, there is no ribbing for about 1 cm, then radial ribbing until about 4 cm, then the ribs become concave, leaning a little forward at the venter.

The naming of this species is due to its supposedly reduced, ceratitic sutures, which I could not see on this ammonite due to its preservation (this will shortly be added – I’ve just bought another A. ceratitoides on eBay which has a nice suture).

Coroniceras lyra, 85 mm
Coroniceras keel view
Coroniceras keel view

The larger 85 mm specimen on the left was a little more difficult to identify, but I could see that is was not the Euagassiceras resupinatum that Mike had identified it as when selling it through his website. This ammonite has furrows on the side of a prominent keel, which Euagassiceras resupinatum lacks. Also this ammonite has more dense ribbing with 32 ribs at 7 cm, a Euagassiceras has about 23 ribs at 7 cm.

Euagassiceras resupinatum, 70 mm for comparison

Over the years I have entered all the ammonite literature that I could get hold of in pdf format into a full text database, in total more than 600 books and articles, which makes life researching ammonites so much easier…
So what I did is I entered “Arnioceras ceratitoides” in the search to see if there are any hints with which other ammonites this species co-occurs. I got about 40 matches, but the most interesting came from M.J. Simms chapter about Hock cliff in the Severn Basin section of the “British Lower Jurassic Stratigraphy” (see literature section below), where he mentions it co-occurring in Hock Cliff bed 28 with Coroniceras lyra HYATT, 1889. Another search in the database for pictures of Coroniceras lyra found a good match in Hyatt´s “Genesis of the Arietidae” (table 5) and various other articles/books, also under synonyms Paracoroniceras lyra (which probably is the most current name) and Coroniceras reynesi.

Coroniceras lyra, 26 mm

As for the smaller ammonites on this specimen, as the 26 mm one above,
I think they’re “just” juveniles of Coroniceras lyra (which is nice in its own way – it’s always good to know what different growth stages of a species look like).

As a bonus, the Coroniceras shows a few smaller ammonites (which I assume are Arnioceras as well) washed into the body chamber, and just visible inside the internal mould.

Small Coroniceras lyra (21 mm) and 2 Arnioceras ceratitoides (25 and 35 mm)

Now when I put back this little multi block into the drawer, I noticed another multi specimen that I had also acquired from Mike Marshall, but already in 2014.

The Arnioceras ammonites (35 and 25 mm) on this multi are also Arnioceras ceratitoides, and the small ammonite on the left (21 mm) is most also a Coroniceras lyra – compare the odd splitting of some of the ribs from a small node at the umbilicus into two ribs.

This specimen also has a fragment of a larger Arnioceras on the left, and a convenient keel view of an an Arnioceras (or fragment thereof) embedded perpendicular relative to the other ammonites, showing clearly the furrows beside the keel, which in addition to the high number of ribs/whorl is another characteristic of A. ceratitoides.

The two different species are interesting and rare in their own right, but their combination on these fascinating little multi blocks creates a context where the sum is greater than the parts.

Literature


Schlegelmilch, R.,Die Ammoniten des süddeutschen Lias,

2nd revised and extended edition, Stuttgart & New York 1992


SIMMS, M.J.,(2004), Hock Cliff, in : British Lower Jurassic
Stratigraphy, Geological Conservation Review Series, JNCC
Peterborough 2004, pp. 164-170


Hyatt, A. (1889) Genesis of the Arietidae, Smithsonian Contributions to Knowledge, No. 673, Smithsonian Institution, Washington DC

by andysfossils on April 5, 2021  •  Permalink
Posted in Ammonites

Posted by andysfossils on April 5, 2021

https://andysfossils.com/2021/04/05/one-plus-one-is-more-than-two/

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

by andysfossils on September 13, 2020  •  Permalink
Posted in Ammonites, Uncategorized

Posted by andysfossils on September 13, 2020

https://andysfossils.com/2020/09/13/these-are-not-the-androgs-youre-looking-for-the-liparoceratidae/

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

by andysfossils on March 1, 2020  •  Permalink
Posted in Ammonites, Uncategorized

Posted by andysfossils on March 1, 2020

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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

by andysfossils on December 21, 2018  •  Permalink
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Posted by andysfossils on December 21, 2018

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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
by andysfossils on September 30, 2018  •  Permalink
Posted in Ammonites, Literature, Other fossils
Tagged

Posted by andysfossils on September 30, 2018

https://andysfossils.com/2018/09/30/who-bit-my-ammonite/

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

 

by andysfossils on March 18, 2018  •  Permalink
Posted in Ammonites, Preparation

Posted by andysfossils on March 18, 2018

https://andysfossils.com/2018/03/18/angulaticeras-or-schlotheimiinae-part-2/

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
by andysfossils on March 4, 2018  •  Permalink
Posted in Ammonites, Preparation

Posted by andysfossils on March 4, 2018

https://andysfossils.com/2018/03/04/sheltered/

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