Belemnite soft tissue - muscle?

[TqB]

I've been looking at my specimens of Acrocoelites trisulculosus from the Toarcian Jet Rock (Mulgrave Shale Member = Falciferum Zone) of the north Yorkshire coast.

 

This is an anoxic mudstone deposited during a prominent worldwide Ocean Anoxic Event (OAE) and, as might be expected, the preservation is very good.

 

A number of them (7 so far) have a thin pyrite layer around the apex. This shows obvious lineation in all of them, mostly oblique to the axis of the rostrum.

As pyrite is often associated with soft tissue decay, I strongly suspect that this is preserving muscle texture. The texture is similar to that preserved in some other coleoids (e.g. from Solnhofen).

 

Has anyone else seen this? Comments welcome!

 

EDIT: I may be wrong about the soft preservation - a few well preserved specimens from other localities (though not from here) show similar texture on the calcite. Most belemnites look smooth though. (Comments and photos further down this thread)

 

Just two of the specimens here:

 

No. 1:

 

 

No. 2:

left lateral (with divided dorso-lateral furrow - a little unusual)

 

 

right lateral

 

 

[Tidgy's Dad]

Very interesting, I've not seen this before, but I would think it's more likely mineralogical in origin, something to do with the replacement of the calcite guard with the pyrite. 

[TqB]

3 minutes ago, Tidgy's Dad said:

Very interesting, I've not seen this before, but I would think it's more likely mineralogical in origin, something to do with the replacement of the calcite guard with the pyrite. 

Thanks, Adam. You may be right of course and I've considered that. The lineation doesn't follow any rostral calcite structure and is an extra layer rather than replacement. I've seen other belemnite rostra (Oxford and Kimmeridge Clays) with some pyrite (internal and external) but without the structure, so I'm inclined to believe it's a special feature of this bed. 

[Ludwigia]

I would go along with your train of thought, although I've little or no experience on the subject of pyritized soft tissues and have never seen anything like this before. Your points do speak well for the possibility at any rate. Maybe a study of the Solnhofen and Holzmaden ones might bring more light into the matter?

[TqB]

32 minutes ago, Ludwigia said:

I would go along with your train of thought, although I've little or no experience on the subject of pyritized soft tissues and have never seen anything like this before. Your points do speak well for the possibility at any rate. Maybe a study of the Solnhofen and Holzmaden ones might bring more light into the matter?

Thanks, Roger. Yes, more research needed - I haven't really gone far into the literature yet.

[westcoast]

Beautiful photos.

Great question, I know i've seen similar features in pyritised fossils before but never considered their origin. I will pay more attention in future...

[TqB]

11 hours ago, westcoast said:

Beautiful photos.

Great question, I know i've seen similar features in pyritised fossils before but never considered their origin. I will pay more attention in future...

Thank you. It's interesting here that the striations only seem to occur around the apex. I'm wondering if that relates to muscle for terminal fins supported by the three apical furrows.

[DE&i]

@TqB very interesting observation I'll have to look at the pyrite on some off my cylindroteuthis, see if I can detect some similar striations 

[TqB]

1 hour ago, DE&i said:

@TqB very interesting observation I'll have to look at the pyrite on some off my cylindroteuthis, see if I can detect some similar striations 

That would be interesting, thanks, you have many more of them than I! I've been looking at well preserved belemnites of various ages and have found more striations on three of them so far - a Cylindroteuthis from the Scottish Kimmeridgian and a couple of Pliensbachian Green Ammonite Beds Passaloteuthis. The striations are actually surface calcite on these so I'm not sure what's going on yet. The vast majority of belemnites show nothing.

[DE&i]

@TqB 

I managed to look at a few Cylindroteuthis that I thought could have had similarities focusing on this one in particular, I do have many more that I just can't get to at the moment. 

[TqB]

1 hour ago, DE&i said:

@TqB 

I managed to look at a few Cylindroteuthis that I thought could have had similarities focusing on this one in particular, I do have many more that I just can't get to at the moment. 

Very interesting, Darren! That seems to have the same sort of appearance as transverse muscle fibre patterns seen in things like Trachyteuthis and Plesioteuthis (speaking from memory - I'll have to check some references). 

[TqB]

Here's a very well preserved Cylindroteuthis cf. puzosiana (with some speckled pyritisation) from the Kimmeridgian Kimmeridge Clay of Scotland.

I've found a small number of specimens now from different Jurassic clays that show them on the calcite surface, so maybe the pyrite in my original post is reflecting this.

Most otherwise well preserved material doesn't though, so I'm not sure what's going on.

 

@DE&i

 

Ventral, apex with furrow:

 

Right lateral:

 

Right lateral, away from apex:

[DE&i]

I wonder if they are minute calcite crystals with the pyrite flecks just covering them . This could suggest why we see a thin trail of pyrite following one of the hairline fractures. 

[TqB]

18 hours ago, DE&i said:

I wonder if they are minute calcite crystals with the pyrite flecks just covering them . This could suggest why we see a thin trail of pyrite following one of the hairline fractures. 

That's a good suggestion. I also have this specimen (and others from the same bed), a Passaloteuthis from the Green Ammonite Beds (Lower Lias, Davoei Zone) of Charmouth. There's no pyrite to speak of but the striations are still there with no crystals evident. So I think this is an original rostral texture. Oh, for an SEM!

 

(It looks as if I've cleaned it with a wire brush but I haven't of course, in case anyone suggests it!  )

 

Right lateral:

 

 

Right dorso-lateral apical groove.

[Peat Burns]

I have found a similar texture on orthoconic nautiloids from the middle Devonian Silica Shale Formation.  The texture is on internal molds of the camerae at the interface with the septa.  When I found the first one, I thought perhaps some quarry equipment had scraped it against some gravel.  Then I found others with the same pattern in the same orientation.

[TqB]

15 hours ago, Peat Burns said:

I have found a similar texture on orthoconic nautiloids from the middle Devonian Silica Shale Formation.  The texture is on internal molds of the camerae at the interface with the septa.  When I found the first one, I thought perhaps some quarry equipment had scraped it against some gravel.  Then I found others with the same pattern in the same orientation.

 

So that's an impression of the inner surface of the septum? Strange, I wonder if it's preservational (preferred orientation crystal growth?) or original?

[westcoast]

Time to get some SEM images of these features..might not answer the question but they are always cool.

[Peat Burns]

8 hours ago, TqB said:

So that's an impression of the inner surface of the septum? Strange, I wonder if it's preservational (preferred orientation crystal growth?) or original?

Yes, exactly, an impression of the inner surface of the septum.  I've never seen this texture before in other orthocones that I've found elsewhere.  The texture on my orthocones seems similar to your belemnites, but coarser.  One potential common thread is that the Silica Formation is rich in iron pyrite (although not necessarily present in the orthocone fossils and not in the ones I photographed above - but perhaps involved at some point during preservation?).  I've always wondered what caused the texture or whether it was a taxonomic character.

[Peat Burns]

7 hours ago, westcoast said:

Time to get some SEM images of these features..might not answer the question but they are always cool.

I'd be willing to try it.  I'd have to nip off a piece of one of the orthocones (too big as they are for the SEM), but I have enough to make the sacrifice.