Texas Cretaceous Mystery

[historianmichael]

On Sunday I was in North Texas collecting from several Cretaceous sites when I came across this object at an exposure of what I believe to be the Denton Clay (Washita Group). I do not discount that it is perhaps just a strange geological anomaly but it was interesting enough and reminiscent enough of orthocone cephalopods I have collected in the Texas Pennsylvanian (particularly Pseudorthoceras) to pick it up. What is strange is that the cross section of the object appears to be simply a mud filled tube, which is usually not characteristic of a cephalopod, which would have septae capping it off. The fact that there is hard matrix inside the "tube" and matrix glued to the outside makes me believe that it is natural rather than man-made. Any guesses on what this could be? I am truly stumped. 

 

 

 

 

 

[sharkdoctor]

Interesting. There are a lot of bite marks on that piece.

[JohnJ]

Is the darker area segmented?  

 

Was the stratigraphy definitely in the Washita Group or was it locally more complicated?

[Jeffrey P]

That looks like a baculite. Specimens I found in Colorado were often missing siphuncles and septa as the shell cavity was filled with sediment like yours is.  

[Plax]

crushed living chamber of baculite? this is a guess. 

[Wrangellian]

That was my thought too. I've got very similar specimens (from other places). My 2nd thought was a very large scaphopod but let's rule out baculite first.

[historianmichael]

2 hours ago, JohnJ said:

Is the darker area segmented? 

 

I do not see any noticeable segments. It is possible that they wore away but I don't see any.

 

 

2 hours ago, JohnJ said:

 

Was the stratigraphy definitely in the Washita Group or was it locally more complicated?

 

It was found as float so it is impossible to know where it came from. The exposure itself is small and isolated, and in the heart of an area mapped as Kpd. Unless someone deposited it there from somewhere else (always a possibility), I doubt it could have been washed there naturally from another formation because (1) it was not found in a creek and (2) I just did not see any other formations outcropping at the site.

[JohnJ]

Thanks, Mike.  The vertical 'lines' on the lower part of your photo gave me pause.  

 

7 minutes ago, historianmichael said:

 

I do not see any noticeable segments. It is possible that they wore away but I don't see any.

 

 

 

 

 

Does the adhering matrix match the insitu bedrock?

[historianmichael]

12 minutes ago, JohnJ said:

Does the adhering matrix match the insitu bedrock?

 

Yes.

 

[RJB]

Living chamber of baculite

 

RB

[Uncle Siphuncle]

Too old for Baculites.

[Plax]

Living chamber of straight ammonite then, whatever the genus. Or if there is a straight ammonite genus of this age. This looks like the living chamber sans segmented portion of a baculitid ammonite shell. I googled that orthocerid nautiloids went extinct in the early cretaceous. Not sure of the age of the rocks in this discussion.

[historianmichael]

4 hours ago, Uncle Siphuncle said:

Too old for Baculites.

 

2 hours ago, Plax said:

Living chamber of straight ammonite then, whatever the genus. Or if there is a straight ammonite genus of this age. This looks like the living chamber sans segmented portion of a baculitid ammonite shell. I googled that orthocerid nautiloids went extinct in the early cretaceous. Not sure of the age of the rocks in this discussion.

 

Denton Clay is Early Cretaceous (Albian) in age, so I agree that it cannot be Baculites. I have seen reference to Sciponoceras in the Lower Cenomanian but I have not found anything that says that it extended back into the Albian. 

[JohnJ]

Can you see any additional details when it is damp?

[Pixpaleosky]

For me it looks like a pterosaur bone. Very thin bone and center made of rock.

[DPS Ammonite]

1 hour ago, Pixpaleosky said:

For me it looks like a pterosaur bone. Very thin bone and center made of rock.

Good suggestion since little exterior ornamentation or septae are visible.

 

@historianmichael
Put some HCl on the exterior shell/bone to see if it fizzes. Shell should fizz, bone should not. Don’t try to totally remove the matrix if it is a bone. HCl will slowly damage it.

[historianmichael]

7 hours ago, JohnJ said:

Can you see any additional details when it is damp?

Unfortunately not.

 

 

 

5 hours ago, Pixpaleosky said:

For me it looks like a pterosaur bone. Very thin bone and center made of rock.

 

3 hours ago, DPS Ammonite said:

Put some HCl on the exterior shell/bone to see if it fizzes. Shell should fizz, bone should not. Don’t try to totally remove the matrix if it is a bone. HCl will slowly damage it.

It is an interesting thought. It is shaped like a body chamber and is crushed in a v-shape like a body chamber. The outer surface is also almost crystalline, which is why it appears to have fractured in points, rather than porous like bone. I will see if I can get my hands on some HCl and report back.

Edited March 10, 2022 by historianmichael

[jpc]

I do not know about baculitids in this age group, but my first impression was also baculitid.  It is very 'pointy' compared to most late Cret Baculites. 

[abyssunder]

The HCL test may be important.