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Eocene belemnites

Hajar

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#1
Greetings cephalopodologists,

I join this forum with a question about Eocene coleoids.

I found the attached calcitic belemnite in rocks which have always been considered as Eocene. They occur above the basal conglomerates which rest on the Oman ophiolite in Muscat. The belemnite is 40 mm long, 10 mm high and 7 mm wide. There is a symmetrically arranged pair of grooves, one deep, one shallow. The shell around the alveolus (which is empty of phragmocone) is crushed. The preservation of this anterior end of the fossil indicates that it has not been reworked. Accompanying fauna is dominated by a diverse and abundant suite of gastropods and fewer bivalves. Sparse isolated colonial corals (upside down the ones I saw) occur in the interval this one came out of.

So,
1) Does anyone recognize this individual to genus or better? (I can make drawings to clarify the pattern of grooves if this helps)
2) What's current status on the survival of belemnites into the Paleogene?

Thanks for your help!
 

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Architeuthoceras

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#2
:welcome: to TONMO Hajar

Belemnites senso stricto became extinct at the K/T boundary. Here is an old thread about this subject. Your fossil could possibly be Bayanoteuthis, Here (pdf) it is mentioned from the Eocene (under Belemnitida but taxonomic position uncertain). Another pdf (here) by Neale Monks on Belemnites from Deposits Magazine, says Bayanoteuthis may be a Sea Pen (Coelenterate).

Do you have any photos showing the anterior end any better, a view showing where the phragmocone would have been would be useful.

Hope this helps
 

Hajar

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#3
Thanks very much Kevin,

Do you have a photo or drawing of Bayanoteuthis? I was browsing yesterday, but couldn't find one.

This individual is solid calcite apart from the anterior where the empty alveolus has collapsed during compaction.

Sea pen seems a wild and bizarre idea - on what evidence? Perhaps I'm about to learn something very new about sea pens!

Attached is a view of the anterior end. You can see the uncrushed guard behind the collapsed section.

Cheers,

Ru
 

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Architeuthoceras

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#6
It certainly looks like a Belemnite. Are there any Cretaceous or Jurassic formations in the area you found it? Are there any fossils like yours in these formations? Belemnoid guards are very resistant and it is possible that even with the anterior end still intact, or at least as intact as it is, it was reworked from older rocks.
 

Hajar

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#7
The nearest documented marine Cretaceous lies beneath a thick slab of obducted ocean crust! There is some terrestrial Late Cretaceous above the ophiolite (with dinosaur bones) and then onlapping Paleogene deltaic to shelfal marine deposits.

The fossil is unworn (with delicate grooves preserved), unbored and retains the very thin shell of the anterior part of the guard. Very difficult to envisage this as reworked from older deposits.

Intriguing hey?

Do you have an image of Bayanoteuthis? Neale Monks' posted photo from the NHM didn't seem to be there any more.
 

Hajar

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#11
Thanks! I also like the La Voulte specimen (and should try to find a name for it).

Provoked by the Paleogene specimen, I went looking for Cretaceous belemnites in the section beneath the ophiolite and found some (after a lot of igneous and metamorphic rocks on the way):
http://www.discussfossils.com/display_topic_threads.asp?ForumID=9&TopicID=3693&PagePosition=1

If anyone has images of Bayanoteuthis or Vasseuria (or any other Paleogene coleoids) very grateful if you could post them.
 

Neale Monks

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#13
Hajar;134171 said:
Greetings cephalopodologists,
1) Does anyone recognize this individual to genus or better? (I can make drawings to clarify the pattern of grooves if this helps)
Could certainly be a guard-like structure from any one of several cephalopods of the Tertiary that have such structures; indeed, some modern cephs have similar structures as well, e.g., the chitin guard on Moroteuthis, or the calcareous spur at the end of some Sepia shells. There isn't, unfortunately, an online source of comparative material that would help me (or you) identify this thing, and since I don't work on cephs anymore, my books and papers are all boxed up in the loft. But do take a peek at things like Spirulirostra, Beloptera, etc.
Hajar;134171 said:
Greetings cephalopodologists,
2) What's current status on the survival of belemnites into the Paleogene?
No-one knows. The problem is that the material is pretty scarce, and even when you see such material, it's really nothing more informative than a calcareous rod. Possibly electron microscope work or crystallography will help, but such work hasn't been done yet (that I'm aware of, at least).

My gut feeling is the belemnites died out towards the end of the Cretaceous, much as the ammonites did, and were comprehensively replaced by more advanced squid and squid-like animals by the start of the Tertiary. There may well have been some convergent evolution among squids and squid-like animals towards the belemnite shape through the early Tertiary, just as there was with nautiluses that evolved ammonite-like shapes (particularly suture lines).

Apologies for not replying sooner; my TONMO account was registered to a defunct e-mail, so I haven't been getting the messages sent to be via the site.

Cheers, Neale
 

Hajar

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#14
Thanks very much Neale and Kevin. Yes, it’s a shame there is not more reference material online (I also have boxes of literature in storage back in Europe).

This particular specimen has far more character than a simple calcareous rod, as do Spirulirostra, Beloptera and Belopterina (see below). It has a distinctive bilaterally symmetrical pattern of grooves and an alveolus. Thanks Kevin for the Vasseuria link. I already knew that one and thought it looked promising, although it’s clearly not the same as my specimen. It has many more grooves and, as you say, looks a little like one of those old Hematites!

Here’s a Miocene Spirulirostra from Germany (not comparable):
http://images.google.co.uk/imgres?imgurl=http://upload.wikimedia.org/wikipedia/de/thumb/1/1c/Spirulirostra.jpg/180px-Spirulirostra.jpg&imgrefurl=http://de.wikipedia.org/wiki/Posth%25C3%25B6rnchen&usg=__csZN6c-A1BP8xGWpig79bS8LWqo=&h=105&w=180&sz=6&hl=en&start=2&um=1&tbnid=D6VYt2SANGoG-M:&tbnh=59&tbnw=101&prev=/images%3Fq%3DSpirulirostra%26hl%3Den%26rlz%3D1T4GGLJ_en%26sa%3DN%26um%3D1

Here’s a French Eocene Beloptera (not comparable): http://images.google.co.uk/imgres?imgurl=http://eocene-corbieres.ifrance.com/fossiles/beloptera.jpg&imgrefurl=http://eocene-corbieres.ifrance.com/fossiles/fossiles.html&usg=__Xkf570tUux21VwZCYaKwv-rBAoc=&h=77&w=150&sz=11&hl=en&start=1&um=1&tbnid=Kc_bJXT4RkzBXM:&tbnh=49&tbnw=96&prev=/images%3Fq%3DBeloptera%26hl%3Den%26rlz%3D1T4GGLJ_en%26sa%3DN%26um%3D1

Here’s a French Eocene Belopterina (not comparable):
http://images.google.co.uk/imgres?imgurl=http://eocene-corbieres.ifrance.com/fossiles/beloptera.jpg&imgrefurl=http://eocene-corbieres.ifrance.com/fossiles/fossiles.html&usg=__Xkf570tUux21VwZCYaKwv-rBAoc=&h=77&w=150&sz=11&hl=en&start=1&um=1&tbnid=Kc_bJXT4RkzBXM:&tbnh=49&tbnw=96&prev=/images%3Fq%3DBeloptera%26hl%3Den%26rlz%3D1T4GGLJ_en%26sa%3DN%26um%3D1

Still no image of Bayanoteuthis! Has anybody actually done anything with this form since Doyle et al’s cautious “Bayanoteuthis has not been studied in sufficient detail to allow a definite decision."?

Thanks again,

Ru
 

Hajar

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#18
This is what Crick (1905) has to say on affinities:

"Whilst being most nearly related to such Eocene forms as Bayanoteuthis, and especially to Vasseuria, [it] forms a connecting link between these genera and the Cretaceous genus Belemnitella. Although only a single example is known, the form is so important that the writer proposes for it the name Styracoteuthis and, for its trivial designation, suggests the term orientalis."
 

Hajar

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#19
Just to show that there's microstructure preserved here is a couple of photos of a roughly polished longitudinal section. Field of view in the first photo is 6 mm.

I see what Crick means about the similarities between Belemnitella and Styracoteuthis and here's a picture of an 8 cm Belemnitella (below) together with a Styracoteuthis.
 

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