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MicroFossilMan
Just found this when rumaging and breaking up old specimens. A belemnite and phragmocone obviously. Not sure about the ID, maybe Cylindroteuthis. It's from the Callovian Kellaways Rock of East Yorkshire. What I'm interested to know about is the structure at the bottom of the rock in the second image - could that possibly be a proostracum? It's thin and doesn't seem to go deep into the rock so I'm pretty sure it's not an ammonite.

Cylindroteuthis small.jpg 
Proostracum small.jpg 


MFM
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yowdfossil
I don't no too much about fossils 😉 but im pretty sure your correct .. One thing i cant work out is how to post pictures :/
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MicroFossilMan
yowdfossil wrote:
One thing i cant work out is how to post pictures :/

If you're doing it from a mobile then I believe you have to add an attachment (I've never done it myself from a mobile). If you're using a PC then there's a toolbar with an "insert photo" button (the one that looks like a tree).
MFM
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TqB
You can see the septa so it'll be more phragmocone, from beyond the rostrum. Quite rare in that rock I think. [smile]

Pro-ostraca are very, very rarely found (although growth lines of the leading edge can be seen on the surface of well-preserved phragmocones.) The pro-ostracum is an extension of the phragmocone shell (conotheca) beyond the chambered part so won't show any septa.

As you say, it's almost certainly Cylindroteuthis.
Tarquin
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MicroFossilMan
TqB wrote:
You can see the septa so it'll be more phragmocone, from beyond the rostrum.

Rats! I was hoping I'd found a rare thing [frown] I can see where you're coming from now, having found this image, which looks quite like mine -

https://zh.wikipedia.org/wiki/File:Megateuthis_1.JPG

I hadn't realised that the phragmocone extended so far beyond the guard.

After thinking about it for a bit I realise I'm not at all clear on how belemnites developed (as individuals). Is it something like this -

  1. An initial “blob” developed a tiny shell (protoconch) and surrounded it, externally, with soft tissues.
  2. The critter then began to grow, developing a septa-ed phragmocone as it went. This part of the phragmocone was surrounded by the guard which grew in both length and diameter, secreted presumably by the soft tissues. The guard also grew backwards from the protoconch. Should one be able to see growth rings in cross-section, like those of a tree?
  3. At some point the creature decided to stop growing the guard forwards (but did it still grow backwards?), but the phragmocone continued to grow, so that it now extended beyond the guard. Did the pro-ostracum start to develop at this point or did it only appear once the phragmocone stopped growing? Is it internal to the creature? How thick is it? Any ideas as to what it was for? Do modern squids (whatever) have them? Are there any growth lines on them or are they featureless to the unaided eye? Some of the diagrams I've found out on the web seem to show transverse growth lines, which was what confused me with my specimen.
  4. The phragmocone stopped growing at some point but the pro-ostracum continued to grow (or started to grow) until it was well beyond the phragmocone.

Apologies for all these questions but there's more to belemnites than I remembered and I'm not finding clear answers on the web.
MFM
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MicroFossilMan
Answering one of my own questions ... after a bit of hunting around (things have been chaotic since we moved!) I found some more belemnites and, with a tail-wind, I can just make out concentric growth lines using a X5 hand lens. It would be fascinating to know if these are yearly, monthly or whatever. It might allow one to work out how old the belemnite was before it died. To the naked eye though (mine at least) the guard's growth just appears to be fibres (calcite crystals presumably) radiating away from the centre line of the guard.
MFM
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TqB
Hi again - a few papers worth in those questions but here's a quick reply. [smile]

1) Yes, probably hatched from an egg with a protoconch and probably with a primordial rostrum (guard) attached. 


2) Yes, but with organic pro-ostracum from a very early stage, which is a separate horny layer (actually three layers) between the calcite rostrum and aragonitic phragmocone. It projects forward beyond them as a dorsal hood all through the animal's ontogeny.
Rostrum growth rings are indeed clear - determining age is difficult but they probably didn't live more than three or four years, maybe only one or two like many modern coleoids.


3) The guard extends forwards as a thin layer a long way over the flaring out phragmocone, eventually wedging out presumably short of the pro-ostracum termination at any given stage.
The pro-ostracum is thin but I don't have a figure. It is internal and is the same structure as the gladius in many modern squid.
For growth lines, see the paper below.


4) The pro-ostracum grows in proportion to the rostrum and phragmocone, as above.


This is a really good paper - the first figure shows some magnificent juvenile pro-ostracal growth lines. I have a few specimens but nothing this clear:

https://www.researchgate.net/profile/Larisa_Doguzhaeva/publication/284168871_The_pro-ostracum_and_primordial_rostrum_at_early_ontogeny_of_Lower_Jurassic_belemnites_from_NW_Germany/links/58fb7ddaaca2723d79d84377/The-pro-ostracum-and-primordial-rostrum-at-early-ontogeny-of-Lower-Jurassic-belemnites-from-NW-Germany.pdf


Acrocoelites trisulculosus - the squashed bit at the front is all thin rostrum material, covering the concealed phragmocone. This rostral layer often (usually) flakes off when exposing specimens, showing the phragmocone if it's preserved. You can sometimes see pro-ostracum between the layers, as in the second photo.
IMG_3124.jpg 

A scrap of lineated pro-ostracum material visible under it (circled red above):
IMG_3125.jpg 

  





Tarquin
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MicroFossilMan
Thanks very much. I'll go and read the paper!
MFM
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Brittle Star
Hi,
Here is a couple of photos from a Gloucestershire specimen, I agree very flaky.
Click image for larger version - Name: BLQU-001B Belemnite with phragmacone.jpg, Views: 20, Size: 225.04 KB Click image for larger version - Name: BLQU-001A Belemnite with phragmacone.jpg, Views: 19, Size: 121.62 KB
JW

 Never ask a star fish for directions
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MicroFossilMan
Nice specimen! Have you identified it?
MFM
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Brittle Star
Hi

I found it at Blockley many years ago. I think it may be Cylindroteuthis. When I found it the end was perfect but as the clay dried being cross bedded it cracked and broke, I was gutted, then I was not as experienced as I am now and did not have the preservatives such as paraloid.
JW

 Never ask a star fish for directions
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TqB
[QUOTE=Brittle Star]Hi

"I found it at Blockley many years ago. I think it may be Cylindroteuthis." 

It's Lower Pliensbachian so is probably a Passaloteuthis. Too early for Cylindroteuthis!
Tarquin
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Brittle Star
Thanks
Not at home at the moment so I was guessing, will make a note to check my records.
JW

 Never ask a star fish for directions
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