Crinoid question

[Older The Better]

I was looking at this rock I found, it’s almost entirely crinoid fossils. Then I noticed the sutures on this segment, it almost looks more like a ammonite or a squid. What do you think? do crinoids have that complex sutures or is it something else? .... Pennsylvanian age limestone in se Kansas for what it’s worth


Here’s one showing more normal sutures

 

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[old digger]

Yes, that is normal for the joining of the segments. You will also notice the center star shaped core. I have found a spot where the ant hills are sometimes loaded with the star shaped centers. I give my two granddaughters tweezers so that they can find and sort out the stars from the ant hills gravels. They have taken them to school and shared them with their fellow students.

 

[Older The Better]

Thanks. I guess I was over thinking a bit. The segments I find are generally pretty straight maybe with the real fine saw tooth like your pic but I haven’t noticed any with such an irregular division I think theres a term for it that escapes me... one used to describe suture patterns on ammonites

I’ve never noticed little stars in the dirt but rock around here tends to hang on to its fossils I rarely find any not locked in a rock I would guess they would be hard to come by but I’ll keep an eye out

 

[Red-Coat]

You’re correct that sutures like that are not something one would expect to see on a crinoid columnal. They’re associated with ammonoids in particular, and also known as “septal arms”.

Much of what can be seen in your rock specimen is representative of sections of crinoid columnals and the section seen end-on is very typical. Pentameral symmetry is not seen in nature outside of the Echinodermata I think, so when you see five-pointed stars and other five-sided structures then they will be from that phylum (which includes crinoids).

However, crinoidal limestone may also contain other marine fossils and the cylindrical item laying diagonally across your rock specimen may be something else. How sure are you that the rock is actually Pennsylvanian and not from younger overlaying strata? The reason I ask is because the most likely fossil with that sutured appearance would be something like Baculites… but not in the Pennsylvanian.

Baculites is a “heteromorph” ammonite… one of a group where the shell is not conventionally coiled and may have a long straight cylindrical section, but which is chambered with septa in the same way. There are some good pictures in the Wiki entry, but these fossils are most usually Cretaceous and you wouldn’t find them in Pennsylvanian rocks.

https://en.wikipedia.org/wiki/Baculites

 

[Kray Gelder]

You’re correct that sutures like that are not something one would expect to see on a crinoid columnal. They’re associated with ammonoids in particular, and also known as “septal arms”.

Much of what can be seen in your rock specimen is representative of sections of crinoid columnals and the section seen end-on is very typical. Pentameral symmetry is not seen in nature outside of the Echinodermata I think, so when you see five-pointed stars and other five-sided structures then they will be from that phylum (which includes crinoids).

However, crinoidal limestone may also contain other marine fossils and the cylindrical item laying diagonally across your rock specimen may be something else. How sure are you that the rock is actually Pennsylvanian and not from younger overlaying strata? The reason I ask is because the most likely fossil with that sutured appearance would be something like Baculites… but not in the Pennsylvanian.

Baculites is a “heteromorph” ammonite… one of a group where the shell is not conventionally coiled and may have a long straight cylindrical section, but which is chambered with septa in the same way. There are some good pictures in the Wiki entry, but these fossils are most usually Cretaceous and you wouldn’t find them in Pennsylvanian rocks.

https://en.wikipedia.org/wiki/Baculites

Yes, yes, yes, and yes. Well said.

 

[Older The Better]

Thanks for the detailed response, no Cretaceous rocks around here, I will double check on that but to the best of my knowledge all Mesozoic rocks are gone/never deposited in this corner of the state

 

[Older The Better]

Yeah never going to find a dino around here, or any marine contemporaries.

 

[Red-Coat]

You’re right. Several Cretaceous deposits in Kansas, but none in you corner of the state:

https://mrdata.usgs.gov/geology/state/fips-unit.php?state=KS
https://mrdata.usgs.gov/geology/state/fips-unit.php?code=f20133

There are numerous isolated exposures of the Cretaceous Niobrara formation randomly dotted around the state, but it’s distinctly chalky and not reported in Neosho County.

It’s a shame we can’t see the end of that ‘cylinder’, which would likely tell us for sure whether it’s crinoid or not… but I haven’t seen sutures like that on the divisions of a crinoid columnal. Maybe it’s possible, but not something I have ever seen in real life or in literature.

There are no Pennsylvanian heteromorph ammonite possibilities. The only other potentially Pennsylvanian fossils which could have a cylindrical structure with sutures that I can think of would be Orthocone nautiloids. Clutching at straws though, I think. These normally have a distinctly tapered profile such that, even on a short section, one end is noticeably fatter than the other; and the septal divisions are characteristically more widely spaced and usually exhibit curvature (although straight parallel rings are possible).

Please keep us posted if you learn more.

 

[Older The Better]

I thought about looking at the end last night then forgot about it
Maybe it is just a crinoid but still interesting I wouldn’t image it’s something new but seems to be at least uncommon form.



It does appear tapered for what it’s worth

 

[Red-Coat]

Thanks for the better pictures. Based on what I see, in combination with Pennsylvanian deposits, I think it is a broken section of an internal cast from an orthocone cephalopod and not a crinoid columnal.

Suture patterns in cephalopods can be generalised as related to the complexity of the overall shell shape as shown below, and I would suggest that those patterns are distinctly “ceratid” in nature.



My best guess is that it’s an orthoceratid (subclass Nautiloidea) for which the dating could be between 490-203.7 mya and certainly within the Pennsylvanian (323.2-298.9 mya).

 

[old digger]

If it is okay, here is a sample of the patterns on an ammonite and belemnite.




Ammonite




Cross-section of a belemnite.

 

[Red-Coat]

If it were an ammonite (subclass Ammonoidea within Cephalopoda) then it would have to be a heteromorph with at least some straight portion as part of its shell… and as I said earlier, those wouldn’t be found in Pennsylvanian deposits.

The belemnite rostrum you’re showing is a lateral cross section, so you wouldn’t see any sutures, even if it had them. However, it’s not a chambered structure like ammonoid shells. It’s an internal ‘skeletal’ structure which grows concentrically and so doesn’t have sutures as such. Belemnitida are also Late Triassic to Late Cretaceous (234–66 Mya) so, again, you wouldn’t find them in Pennsylvanian rocks.

 

[Older The Better]

Cool great info, I find a ton brachiopods, crinoids and bryozoans. One spot in a draw produces lots of carbonized leaves. as far as other creatures go I’ve found two trilobites, two ammonites now I can throw in a nautolid... would love to find a bone of anything, it’s high on the wish list

 

[Charlie P. (NY)]

I believe the creature was an "Orthoceras". A relative of ammonites that has a straight shell. Bah! I see Red-Coat already named them.

Too many damned "protected" images to get you a good example, but here's a try.

 

[Red-Coat]

I believe the creature was an "Orthoceras". A relative of ammonites that has a straight shell. Bah! I see Red-Coat already named them.

Too many damned "protected" images to get you a good example, but here's a try.

Orthocone nautiloid yes (as I suggested), but not Orthoceras. That genus has been re-defined in recent times as applying only to Orthoceras regularis/regulare and perhaps a few related species from the Mid-Ordovician (470-458 Mya) of the Baltic States and Sweden. Neither the time frame nor the location are consistent with this find.

In earlier years “Orthoceras” was indiscriminately used as a palaeontological dumping ground (what’s known as a “wastebasket taxon”) for all manner of indeterminate conical nautiloids with straight cylindrical shells. We now know from detailed examination of their internal structures that they represent a wide array of genera that are only loosely related to one another and in some cases not even from the same taxonomic order.

There are more than 30 species formerly dumped in the Orthoceras genus which either have been reassigned or are awaiting decisions on reassignment. The picture you were able to show is of Moroccan specimens which, although the vendor (?) is describing as Orthoceras, he’s out of date. Most Moroccan specimens have now been re-assigned to Michelinoceras, Orthocycloceras or other genera.

Orthoceras was therefore redefined in the Treatise on Invertebrate Paleontology (Part K: Mollusca) as applying only to the time period and locations referenced above, but continues to be mistakenly used as the name for other fossils by those who haven’t caught up with today’s taxonomy.