Mississippian shark

[Peat Burns]

This is a fragment of shark tooth (?) I collected yesterday.  Hoping someone will recognize the unique texture and be able to associate it with a known taxon.  This is from the Big Clifty Formation in Indiana  (Mississippian: Chesterian).  Ruler increments in photo are 0.5 mm.

 

[Al Dente]

I would be surprised if this is a shark tooth. It might be a fragment of a conularid.

[Peat Burns]

19 minutes ago, Al Dente said:

I would be surprised if this is a shark tooth. It might be a fragment of a conularid.

Yeah, I was just about to post that.  I thought about conulariid but had myself convinced against it due to the black, almost glossy nature of the fragment.  It does sure look like Conularia in structure though...

EDIT:  I am now convinced it's a Conulariid.  I'm pretty sure I can see the nodes now.  Thanks @Al Dente

[Ridgehiker]

Conularia and shark teeth are both calcium phosphate...usually preserves as bluish black (or some variation). In contrast non phosphatic carbonate based fossils like inarticlate brachiopods and corals are usually a lighter, duller colour...although they can be  darker because of the presence of trace amounts of magnesium, etc.

(articulate brachs are also calcium phosphate and thus also  preserve shiny bluish black )

 

The shiniest in part is due to acids in the matrix over time disolving surrounding carbonates but not impacting the calcium phosphatic so shiny smooth ( like having your teeth cleaned). 

[Peat Burns]

25 minutes ago, Canadawest said:

Conularia and shark teeth are both calcium phosphate...usually preserves as bluish black (or some variation). In contrast non phosphatic carbonate based fossils like inarticlate brachiopods and corals are usually a lighter, duller colour...although they can be  darker because of the presence of trace amounts of magnesium, etc.

(articulate brachs are also calcium phosphate and thus also  preserve shiny bluish black )

 

The shiniest in part is due to acids in the matrix over time disolving surrounding carbonates but not impacting the calcium phosphatic so shiny smooth ( like having your teeth cleaned). 

Thanks, I didn't realize they had calcium phosphate exoskeletons.  In that regard, are they still considered Cnidarians?  I can't think of any other examples of Cnidaria with calcium phosphate secretions.

[BobWill]

Considering they are thought to be in the class Scyphozoa the bigger mystery is probably that they secrete anything at all.

[Peat Burns]

18 minutes ago, BobWill said:

Considering they are thought to be in the class Scyphozoa the bigger mystery is probably that they secrete anything at all.

Yes, they would be unique in that regard. Although having scyphozoans that produced an exoskeleton would seem to be less of a surprise (analogy:  hydrozoans which have representatives that produce exoskeletons and others that don't) than a class that broke ranks from the rest of the phylum and changed exoskeleton chemistry.