Bloated crinoid stem

[TeslaHarmonix]

What would be the reason this stalk is so bloated?

 

 

[Thomas.Dodson]

Looks more like a brevicone nautiloid to me.

[westcoast]

Crinoid stems can be bloated due to parasitic borings, called Oichnus. See Donovan and Hoare 2018

[Fossildude19]

I agree with brevicone nautiloid. 

 

[FossilDAWG]

I see the similarity to a brevicone cephalopod, but I think the swollen crinoid stem ID is the correct one.  The shell wall is much thicker than one would expect for a cephalopod shell, and there are fracture patterns typical of crystaline calcite one would expect for an echinoderm.  Also the segments are not all evenly spaced, they fuse in the middle in a way that cephalopod suture lines/camerae never would but crinoid  stem segments sometimes will do.

 

Don

[hadrosauridae]

I cant tell you what this is, but I can tell you its not a crinoid stem.

[PaleoOrdo]

I agree with brevicone nautiloid. It seems to resemble an orthoconice brevicone one, but it is not perfectly orthoconic. The siphuncle, it seems, is shown on the top as relative big or broad. Maybe it belongs to the oncocerid order, since oncocerids often display more or less strongly contracted or constricted apertures.

Where was it found and in which formation? I know that oncocerids is not too common in the fossil record, but was plenty in Iowa.  

[Oxytropidoceras]

As westcoast noted, similarly deformed (swollen) crinoid stems (pluricolumnals) associated with Oichnus simplex from the the Mississippian of the British Isles can be found in:

 

Donovan, S.K. and Hoare, G., 2018. Site selection of small round holes in crinoid pluricolumnals, Trearne Quarry SSSI (Mississippian, Lower Carboniferous), north Ayrshire, UK. Scottish Journal of Geology 55(458), pp.1-5

 

Link to PDF file of this paper

 

Figure 2. Oichnus simplex Bromley infesting cf. Ureocrinus bockschi

 

Figure 3. Oichnus simplex Bromley infesting cf. Ureocrinus bockschii

 

Other PDF files by the same author

 

Yours,

 

Paul H.

Edited May 31, 2021 by Oxytropidoceras
added credit

[PaleoOrdo]

1 hour ago, FossilDAWG said:

I see the similarity to a brevicone cephalopod, but I think the swollen crinoid stem ID is the correct one.  The shell wall is much thicker than one would expect for a cephalopod shell, and there are fracture patterns typical of crystaline calcite one would expect for an echinoderm. 

You made nice observations and you may be right, Don. I do not know much of the fracture pattern of echinoderms, but calcite is common in camera deposits which could make the nautiloid shell look thicker than it was. Cameral deposits are developed commonly in the orders Discosorida and Oncoceratida.

1 hour ago, FossilDAWG said:

Also the segments are not all evenly spaced, they fuse in the middle in a way that cephalopod suture lines/camerae never would but crinoid  stem segments sometimes will do.

Among the speciemen of nautiloids I have displayed here on this website there are some which shows displaced suture lines, like this one, due to pressure and erosion:

[erose]

My money is on a parasitic gall. You can see the source in that indentation on the second photo.  They are fairly common in the Pennsylvanian of Texas.  The thing I have noticed is that they are almost always on smoother stems, never the ornate bumpy ones.

 

[TeslaHarmonix]

This is from the Edwardsville formation. Montgomery Co., Indiana. 

[minnbuckeye]

I can go either way but will side with a crinoid. What do we always ask people when they request an ID? LOCATION!!! Crawfordsville equals crinoid.

  

Mike

[PaleoOrdo]

I understand crionids were very abundant in that formation: the age is lower Carboniferous, the Mississippian. The Oncocerida nautiloids are found from the Middle Ordovician to the Mississippian. Two families of oncocerids are known at that age: Poterioceratidae which have exogastric shell, and that does not fit with the OP specimen. The other family I cannot find any information on online. I tend also to side for crinoid now.