Niobrara Sponge???

[Castle Rock]

About a week ago, I was visiting relatives in Western Kansas and was taken to a very small exposure of Upper Niobrara chalk on the family farm.  I have been hunting in the area for many years and I had never paid any attention to this particular location.  I did not see much material that was worth picking up, BUT then..the unusual texture of this particular "stone" caught my eye.  Because the exposure consisted of a few feet of the Upper chalk covered by a thin veneer of sand and gravel (Ogallala?) and then the top soil, I am not at all certain of the geologic age of this specimen.  The relative absence of wear does not suggest that it was transported with the sand & gravel, BUT I have NEVER heard of any fossil sponges (or coral for that matter) from the Smoky Hill Chalk.  I would VERY much appreciate your suggestions as to the age & identity of this find.  Dave

[Xiphactinus]

That looks like the rudist clam Durania 

[Castle Rock]

@Xipahctinus Well, that would certainly make more sense to me. I might have made the same conclusion, however there is no defined aperture on the top.  I might say that I have only found one small fragment of Durania before and, once again, the upper surface has a clearly defined opening.   Certainly a unique find in my experience!   Dave 

[Xiphactinus]

That’s weird looking for sure. 

[Castle Rock]

I have some additional photos of the one Durania fragment that I collected a few years ago.  The surface texture has clear similarities to the more recent find. I would be inclined to agree that the newest specimen is, in fact, Durania.  I can only explain the different appearance of the top as the result of post burial deformation.  As I stated in an earlier note, it certainly remains a most unique specimen!   Any thoughts/feedback is welcomed!   Dave