Robert´s Hammatoceras – a Yorkshire first ?

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

Hammatoceras ammonite in situ,
picture courtesy of R. Taylor

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

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

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

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

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

Hammatoceras ammonite as found, picture courtesy of R. Taylor

Hammatoceras ammonite as found,
picture courtesy of R. Taylor

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

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

Hammatoceras cf. semilunatum, 10 cm inner whorl

Hammatoceras cf. semilunatum, 10 cm inner whorl

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

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

Hammatoceras cf. semilunatum, 15 cm, keel view

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

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

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

AndyS

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

2 Comments

  1. Mark Varah

     /  June 11, 2016

    What a great find and congratulations on the prep job
    I think hammatoceras must have prefered warmer water than Yorkshire! Not uncommon in the Cotswolds cephalopod bed but never seen a Yorkshire one
    It’s good to know collectors are still adding to the record

    Reply
  2. Steve Livesley

     /  June 11, 2016

    Congratulations to Robert on the find and nice work Andy….
    Hope your keeping well…

    Reply

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