Southeast indiana, Ordovician Period. Thought it was a cephalopod at first, but I’m not sure

[Harrison Smith]

 

 

 

 

 

[TheInvertebrateGuy]

Welcome to the fossil forum! 

 

Seems like you have a Diplichnites trace fossil alongside Rugose corals and brachiopods.

[Harrison Smith]

19 minutes ago, TheInvertebrateGuy said:

Welcome to the fossil forum! 

 

Seems like you have a Diplichnites trace fossil alongside Rugose corals and brachiopods.

Interesting, this is the first one I’ve ever found. I never would of guessed it was arthropod tracks. Now I have something else to look out for, thanks!

[DPS Ammonite]

It really looks like a creature with traces of gray shelly material on the straight vertical sides. I see differential weathering where the gray material, probable a carbonate, has weathered quicker than the tan matrix.

[Harrison Smith]

On 7/6/2022 at 11:02 PM, DPS Ammonite said:

It really looks like a creature with traces of gray shelly material on the straight vertical sides. I see differential weathering where the gray material, probable a carbonate, has weathered quicker than the tan matrix.

Yeah the very straight sides and the way it narrows towards one end are what originally led me to believe it was a cephalopod. 

[JohnJ]

1 hour ago, TheInvertebrateGuy said:

Welcome to the fossil forum! 

 

Seems like you have a Diplichnites trace fossil alongside Rugose corals and brachiopods.

Wouldn't the shell hash present the most unlikely environment to create a trackway?

[TheInvertebrateGuy]

On 7/6/2022 at 11:02 PM, DPS Ammonite said:

It really looks like a creature with traces of gray shelly material on the straight vertical sides. I see differential weathering where the gray material, probable a carbonate, has weathered quicker than the tan matrix.

If I’m being honest, the carbonaceous material within the area of the trackway is probably just pieces of brachipod shell.

On 7/6/2022 at 11:25 PM, JohnJ said:

Wouldn't the shell hash present the most unlikely environment to create a trackway?

I suppose you’re mentioning how pieces of brachiopod shells could affect the way an arthropod could’ve moved along the seabed. In that case, I suppose an arthropod could potentially have easily walked over such material without burrowing.

 

On 7/6/2022 at 11:13 PM, Harrison Smith said:

Yeah the very straight sides and the way it narrows towards one end are what originally led me to believe it was a cephalopod. 

Diplichnites can sometimes start or end in a narrow path.

Feel free to correct me, I may be wrong on my identification.

[Harrison Smith]

6 minutes ago, TheInvertebrateGuy said:

If I’m being honest, the carbonaceous material within the area of the trackway is probably just pieces of brachipod shell.

I suppose you’re mentioning how pieces of brachiopod shells could affect the way an arthropod could’ve move along the seabed. In that case, I suppose an arthropod could potentially have easily walked over such material without burrowing.

 

Diplichnites can sometimes start or end in a narrow path.

Feel free to correct me, I may be wrong on my identification.

I believe you’re correct, and lord knows you are more experienced with this than me. I’ve found pictures from a quick google search of diplichnites that resemble this one.

[JohnJ]

19 minutes ago, TheInvertebrateGuy said:

I suppose you’re mentioning how pieces of brachiopod shells could affect the way an arthropod could’ve moved along the seabed. In that case, I suppose an arthropod could potentially have easily walked over such material without burrowing.

Actually, I was referring to the shell hash as not being a medium where trackways form, and it seems unlikely there would be a tiny patch of mud or sand amidst the shells to 'record' tracks.

[TheInvertebrateGuy]

36 minutes ago, JohnJ said:

Wouldn't the shell hash present the most unlikely environment to create a trackway?

I’m quoting this reply again because it leads to another point about paleobiology. 
 

Potentially, instead of a shell hash being an unlikely environment to create a trackway in, what if it was the most likely environment for creating a trackway? A shell hash environment would be full of organic material from previously alive shelled organisms, such as brachiopods, and potentially attract organisms, which would then make trackways.

[westcoast]

Interesting piece, i don't have an ID but it is not Diplichnites

[IsaacTheFossilMan]

My first thoughts are that it's a graptolite. Seems reminiscent of Diplograptus folium, I'll try to find papers on the formation and compare to known graptolids.

[IsaacTheFossilMan]

Reading from Fossils and Stratigraphy of the Upper Ordovician Standard in South Eastern Indiana (core.ac.uk), it could also be an actinoceroid (cephalopod). My bets are still on it being a graptolid, you can see the curving of the "teeth"-like hooks.

'

 

Do you know what formation you collected this from? 

[IsaacTheFossilMan]

6 hours ago, TheInvertebrateGuy said:

If I’m being honest, the carbonaceous material within the area of the trackway is probably just pieces of brachipod shell.

 

I find this unconvincing:

 

Near the top, you can see a line carved into the side of the fossil in relief - much like something has dissolved. The gray material seems to permeate underneath the fossil within the bounds of this line, which can also be seen at the bottom.

 

This is a diagram of Amplexograptus (varying species) from Three-dimensionally preserved specimens of Amplexograptus (Ordovician, Graptolithina) from the North American mid-continent: Taxonomic and biostratigraphic significance (researchgate.net).

 

Isaac

 

 

[Carl]

I agree that the likelihood of this being a trackway is exceptionally low. It's just not the kind of substrate that tracks are ever recorded in. I agree that this is probably some kind of invertebrate body fossil, but what kind eludes me. I can see elements of graptolites and cephalopods, but neither is a solid match.

[BobWill]

10 hours ago, Harrison Smith said:

I believe you’re correct, and lord knows you are more experienced with this than me. I’ve found pictures from a quick google search of diplichnites that resemble this one.

 

11 hours ago, TheInvertebrateGuy said:

Welcome to the fossil forum! 

 

Seems like you have a Diplichnites trace fossil alongside Rugose corals and brachiopods.

@Harrison Smith my quick Google search was not so convincing. It may help convince others if you or @TheInvertebrateGuy could post an image of a dipichnites that is the closest thing to this specimen you can find. I'm looking for features to match; the consistency of the bumpy texture down the center, the hook-like appendages that seem to be part of the material in the center and the abruptness of the terminal edges.

 

edit: I am also struck by the difference between the surface of the fossil and the the surface of the hash. It would almost require a moving creature to act like a road grader, burying the hash and smoothing out the rough texture below.

 

another edit: I may have missed seeing mention of the size. That and the size of a diplichnites for comparison could help.

Edited July 7, 2022 by BobWill

[Fossildude19]

Partial graptolite was my first thought. 

[Harrison Smith]

3 hours ago, IsaacTheFossilMan said:

Reading from Fossils and Stratigraphy of the Upper Ordovician Standard in South Eastern Indiana (core.ac.uk), it could also be an actinoceroid (cephalopod). My bets are still on it being a graptolid, you can see the curving of the "teeth"-like hooks.

'

 

Do you know what formation you collected this from? 

I don’t know the formation, how would I go about determining that? It’s fairly remote private land, so I doubt many people have collected nearby. It is a tributary of Indian creek though.

 

8 minutes ago, BobWill said:

 

@Harrison Smith my quick Google search was not so convincing. It may help convince others if you or @TheInvertebrateGuy could post an image of a dipichnites that is the closest thing to this specimen you can find. I'm looking for features to match; the consistency of the bumpy texture down the center, the hook-like appendages that seem to be part of the material in the center and the abruptness of the terminal edges.

This is the kind of image I was referencing, but I see what you mean now. The indentations along the center of the fossil as well as the lines along each side aren't consistent with diplichnites.

[minnbuckeye]

3 hours ago, Carl said:

I can see elements of graptolites and cephalopods, but neither is a solid match.

 

I have been watching the discussion here and agree with Carl. With that said, I looked at images of graptolites on line and can not find a single image that shows the "shell like " substance surrounding this specimen. So I lean towards cephalopod.  

 

If one was to prep this a bit, an ID may become more likely! Thanks for posting this. 

 

Mike

[Top Trilo]

My vote is for cephalopod for the reasons already mentioned and this image, looks very similar.

 

It was a post on TFF, this thread, where it was quickly identified as an "orthoconic nautiloid" While there are a few differences such as the size of the 'knobs' on the side being wider than the OP's specimen, that could be explained by the variety of orthocene cephalopods and the OP's is from the Ordovician where as the image I attached is from the Permian. I still think its a close match.

 

Would the ridge down the middle not be evidence of a siphuncle, pointing to cephalopod?

 

Edited July 7, 2022 by Top Trilo

[FossilDAWG]

I'm confident it is a cephalopod.  Some of the actinocerids have a very large siphuncle, leaving only a small open space for the camerae (chambers of the phragmocone).

 

Don

 

Note: Top Trilo posted a nice image of an actinocerid nautiloid.  Closer to the tip of the shell the siphuncle is proportionally larger, leaving smaller spaces for the camerae as in the OP's specimen.  Also the siphuncle was close to or right at the ventral side of the shell, where it acted as a weight to keep these animals close to the sea floor; they were not active swimmers in the open water but rather prowled the sea floor for prey.  Often the phragmocone broke (after death) to remove the more fragile dorsal side where the camerae were more open, leaving the siphuncle and the adjacent part of the shell with the heavier, stronger, more "filled in" camerae.

[JohnJ]

1 hour ago, Harrison Smith said:

This is the kind of image I was referencing, but I see what you mean now. The indentations along the center of the fossil as well as the lines along each side aren't consistent with diplichnites.

Note that the substrate is not a shell hash.  Nor is a shell hash likely to record an army of arthropods marching across it.

 

It looks like finer sediments on one end of the pattern boundary and larger shell fragments on the other.  To me, this suggests the infilling of a shell.

[FossilNerd]

I think Occam’s razor needs to be applied here. Seems we are over thinking it. 
 

I agree with @FossilDAWG. Looks to me to be a highly worn cephalopod.

[TheInvertebrateGuy]

I hadn’t noticed the lining along the sides and middle of the fossil earlier, and now it looks like a very eroded cephalopod to me. The raised lining along the center looks like a siphuncle, and my guess is that this is a well eroded orthoconic nautiloid, since such fossils have been found near southwest Indiana.

[IsaacTheFossilMan]

8 hours ago, IsaacTheFossilMan said:

it could also be an actinoceroid (cephalopod)

 

Referring to my previous post; I have studied the morphology of the fossil, and I almost 100% certain we are looking at a cephalopod here. You can see remnants of a 'shell' casing around the fossil, and the presence of a tract likely to hold a siphuncle makes me think this is a lateral cross section of an orthocone cephalopod. 

 

As others have consolidated my view that this is an actinocerid, I'm convinced this is what we are looking at.

 

As you do not know the formation @Harrison Smith, I will check the libraries for generalised papers on cephalopods for the area, and flick through them - you can expect me to be done with this in about an hour to an hour and a half!