Burlington Bone?

[minnbuckeye]

@CabinetOfCuriosities recently posted a Devonian bone for identification. Having just read the post, I headed downstairs and split open a piece of matrix from the fish layer of the upper Burlington, lower Keokuk Formation and a boney looking fossil presented itself. What a coincidence! It vaguely mimics turtle remains I have found in Florida. Thoughts of what this is are welcomed!!!!!! By the way, the size is 2.5 by 2.0 cm.

 

[Fossildude19]

@jdp

 

Looks pretty thick. Maybe a piece of skull?

 

[Rockwood]

I think this might actually be cartilage rather than bone. 

[jdp]

Definitely bone. Maybe a chondrichthyan fin spine? 

 

Keokuk is Mississippian, not Devonian, by the way.

[minnbuckeye]

My mind is elsewhere. Yes this is Mississippian. @jdp, thanks for the mental nudge.

[FossilDAWG]

Looks like bone to me also.  Don't know what critter though.

 

Don

[minnbuckeye]

Thanks for everyone's opinions!! I am a bit confused on the mixed responses. My understanding is that chondrichthyans were not boney fish including their spine.  How does one determine fossilized cartilage from that of bone? At least I can remove Turtle from the list of possible identities for this fossil. Now it appears to be  boney fish verses chondrichthyans.

[jpc]

I am not familiar with boney things form the Mississipian, but this looks extremely boney.

[Rockwood]

Were there many things around then that had very boney looking bones? 

[westcoast]

11 hours ago, Rockwood said:

Were there many things around then that had very boney looking bones? 

Boney fish or boney tetrapod, but not Boney M.

[Rockwood]

53 minutes ago, westcoast said:

Boney fish or boney tetrapod, but not Boney M.

I can see this looking like large placoderm armor, but I assumed that fish or amphibian bone would look, well, fishier. 

[westcoast]

Sarcopterygians were large bony fish that were very similar to the closely related tetrapods which evolved from them, their bone structure would be basically identical. So similar they are lumped together as Tetrapodomorphs. Not saying that tbe OP's specimen is sarcopterygian but a definite answer may not be possible.

[Paul1719]

My first thought was that ornament looks placoderm but the Dev/Mississippian extinction event ended the Placoderms also the Tristichopterids. It must be a sarcopterygian. Maybe Rhizodont but I am not familiar with their ornament. 

[jdp]

On 1/6/2024 at 5:17 PM, minnbuckeye said:

Thanks for everyone's opinions!! I am a bit confused on the mixed responses. My understanding is that chondrichthyans were not boney fish including their spine.  How does one determine fossilized cartilage from that of bone? At least I can remove Turtle from the list of possible identities for this fossil. Now it appears to be  boney fish verses chondrichthyans.

Compare with the acanthodian fin spines in figure 16 here:

 

https://www.researchgate.net/publication/299452946_The_diplacanthid_fishes_Acanthodii_Diplacanthiformes_Diplacanthidae_from_the_Middle_Devonian_of_Scotlan

 

[minnbuckeye]

@jdp, Thanks for the impressive article. Fig 16 does show the trabecular nature of the base of the fish spine!!        

"These early Diplacanthid fish were superficially shark-like in appearance. Though they had cartilaginous skeletons they also had bony bases in their fins." 

Does this apply to  Chondrichthyan fishes also?? 

[Paul1719]

The Ctenacanthid sharks had bony spines but with longitudinal ridge ornament. As far as the Acanthodians, I believe the Gyracanthids are the only taxa to survive into the Carboniferous??? They have diagonal ridges. Here is a recent example from latest Devonian Red Hill site in PA. The right unornamented side is where it would insert into the body of the fish. 

 

[jdp]

Yes. Spine bases in sharks are similar. Remember that sharks are just a specialized type of acanthodian.

 

In addition to gyracanthids, a few other acanthodian groups survived the end-Devonian, mostly acanthodidids. Within gyracanthids, there's also some variation on structure; your fragment doesn't look much like Gyracanthus but isn't too dissimilar from Oracanthus. But there are also a bunch of true chondrichthyans this could be as well.