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