Acrocoelites oxyconus

[Nipponites]

Hello,

I have recently bought this fossil as an Acrocoelites oxyconus, from the toarcien of Tournadous, France. 

But after seeing  the photos of Ludwigia, and others in the internet, it seems that it is not Acrocoelites oxyconus.

 

The fossil looks to be broken and glued:

 

Thanks!

[Ludwigia]

Yes, this rostrum is only partial and was in pieces before it was glued back together. What makes you think that this is not an A. oxyconus? @TqB ?

[TqB]

A. oxyconus is a possibility but it's incomplete as Roger says, and I'd hesitate to put a species to it without seeing the population of the bed it comes from. (This is true of many belemnites and other fossils, including ammonites.)

Edited October 12, 2021 by TqB

[Nipponites]

The difference that I see is on the shape;

Mine (my fragment), has a "conical" shape, making a straight line from the top to the bottom.

Those on the internet seems to end up more rounded.

Here a photo of mine and other from internet, to compare what I say.

 

 

Thank you so much for everything!

 

[TqB]

1 hour ago, Nipponites said:

The difference that I see is on the shape;

Mine (my fragment), has a "conical" shape, making a straight line from the top to the bottom.

Those on the internet seems to end up more rounded.

Here a photo of mine and other from internet, to compare what I say.

 

 

 

 

 

 

Belemnite species are often interpreted as rather variable, and the internet is often a poor source of ID material.  As I mentioned, you really need a population and identifying a single specimen to species level is very often unsafe. So I'd put a question mark on the label.

 

The description of A. oxyconus in Doyle's monograph "The British Toarcian (Lower Jurassic) Belemnites" allows for it to be conical or cylindroconical. 

 

More importantly, from the point of view of your specimen, the original type specimen from Zieten (1830-33) is decidedly conical. ("Die Versteinerungen Württembergs", pl. XXI, fig 5 - here it is:

 

Here is Doyle's plate of UK specimens. Nos. 1-4, and possibly no. 5, are given by him as A. oxyconus - so  you can see the permitted variability..

Edited October 12, 2021 by TqB

[Nipponites]

I found this article about belemnites from  Tournadous, where mine come from.

pinard-et-al_2014.pdf

A. oxyconus appears in E, Fig. 6, and it is the one that most resembles mine.

When you talk about a population, do you refer to a group of belemnites from the same species? Or to all the species that lived together?

In the first case, all the specimens from the seller (around 10), had the same shape, in the second case, the pdf gives an idea of what swam in those times.

Thanks!

[TqB]

54 minutes ago, Nipponites said:

When you talk about a population, do you refer to a group of belemnites from the same species? Or to all the species that lived together?

Either, but ideally all the species that lived together. Then you can do useful comparative biometrics which are a bit lacking in many publications, especially older ones.

 

I'm glad you've sorted yours out.

[Nipponites]

Thank you very much, discovering this forum has been a great joy.