Ordovician Cephalopod/Siphuncle ID Help, please

[fossilized6s 760]

I can't seem to find an ID for this find. I believe this may be a siphuncle. What do you guys think? 

 

The "V" shaped sutures are really throwing me off. Has anyone seen a straight shelled cephalopod with this "V" pattern? 

 

 

Kinda neat how you can see how this was buried, preserving one side as it weathered the other. Then along came a dozen crinoids or so a used it as a nice base. 

 

 

 

[Rockwood 3,329]

I don't claim to know about the V shape, but siphuncle is also the best I can come up with.

[Johannes 284]

Its definitly a siphuncle. If we should try to give you something more specific, we need the stratigraphical background of your find. The V-shapes are the ridges, where the chamber walls were attached to the siphuncle. Meaning: it is definitly not from an Orthoceras... Maybe/most likely (?) an Endoceratid or Anthoceras species.

 

Concerning the adhesive discs, it is ususally hard to say, if they are from crinoids, better to asign them more general to Pelmatozoans... Interesting they have settled on an isolated siphuncle: a hint for erosional/redeposited setting...

[minnbuckeye 3,001]

1 hour ago, Johannes said:

The V-shapes are the ridges, where the chamber walls were attached to the siphuncle. Meaning: it is definitly not from an Orthoceras...

@Johannes, could you elaborate on this. I have a siphuncle "collection" from the Ordovician Period and did not realize one could possibly ID a cephalopod by a siphuncle. 

 

Much appreciated,

Mike

[Johannes 284]

Hi Mike,

 

there is a lot to say. Far too much for a fast and "all-inclusive" answer...

 

ID them by siphuncle is difficult, and nearly impossible on species-level. But you can rule some out, and sometimes ID the family or genera. Orthoceras has a completely central and generally thin siph and never such a steep cone-formed ending. Central position excludes such V-Structures as seen above, which are a result of the (here very) near position of the siph to the outer shell. Also the density of space beween the chamberwalls speakt agains Orthoceras.

 

In general:

Siphuncles of the early cephs differ a lot (in the fine details). A lot of them can only be IDed, when you make a cross section and have a closer look on the attachment beween chamber walls and sipuncle. Also the way of calcification can give you a hint. If you know, what pal-cephs are living in "your quarry" or the time-slice you are hunting in, you can determine some of their according siphs, too. (best way to learn here is to start a reference collection...)

 

There is some literature "on the market", some old basic papers from the beginning of the last century (and older), some of Dzik from 60s to 80s, and newer ones from Björn Kröger, now at the Nat.Hist.Mus. of Helsinki/Finland. Esp. the last ones you might find as pdfs... You may start with Kroeger 2003 "The size of the siphuncle in cephalopod evolution", Fig. 5 is very instructive to see some differences in the mode of attachment.

 

 

All the best

 

Johannes

 

[fossilized6s 760]

2 hours ago, Johannes said:

Its definitly a siphuncle. If we should try to give you something more specific, we need the stratigraphical background of your find. The V-shapes are the ridges, where the chamber walls were attached to the siphuncle. Meaning: it is definitly not from an Orthoceras... Maybe/most likely (?) an Endoceratid or Anthoceras species.

 

Concerning the adhesive discs, it is ususally hard to say, if they are from crinoids, better to asign them more general to Pelmatozoans... Interesting they have settled on an isolated siphuncle: a hint for erosional/redeposited setting...

Thanks for the info. This is from the Maquoketa Formation Elgin member of Iowa. 

[Johannes 284]

Hi Charlie,

 

I'm not so familliar with your regional geology, where is the Maquoketa-Fmn. in international stratigraphy?

[Tidgy's Dad 15,239]

Roughly 444 to 446 million years old, so Edenian to Maysvillian in the USA or Ashgill in the UK. Upper Ordovician.