Hemispherical Maastrichtean fossil

[Hapchazzard]

I've been wondering for some time about this thing for some while now:

 

 

Most of the fossil is not exposed, but it seems to have a hemispherical shape. It does not seem like any kind of bivalve that I am aware of. What could it be?

 

Age: Maastrichtean

Locality: Čerevićki potok formation

Environment: shallow marine Sphaerulites radiolitid rudist thicket(likely somewhat protected waters)

[Miocene_Mason]

I don’t see any real features, perhaps just a concretion? If bivalves are common, it could also be a worn steinkern.

[GeschWhat]

You may want to post some additional photos from other angles. It looks like there might be a texture in this area that could be diagnostic to those who know more than me. 

[KimTexan]

Yes we need close up pictures of it. It has the shape and a quality about it that makes me suspect echinoid, sea urchin. I just finished cleaning some echinoids about an hour ago that had that exact appearance to them and now I don’t have a good example to show of the likeness! This one isn’t cleaned up, but the stuff doesn’t look quite like that in the pic, but I just removed the white stuff off of others that looked almost exactly like that.

[KimTexan]

Oh, we need something for scale too, to be able to tell the size or you can give measurements.

I’d like to see a pic from the top, bottom, each end as well as close up of anything that reveals original texture of the fossil or openings. If it is an echinoid, they have mouths where food goes in and a bottom where processed food comes out. On irregular echinoids the bottom is on the back end and the mouth is on the under side. Regular echinoids the mouth is on the top and bottom on the bottom. Echinoids can be very complex to ID even when in great condition.

[Hapchazzard]

10 hours ago, KimTexan said:

Oh, we need something for scale too, to be able to tell the size or you can give measurements.

I’d like to see a pic from the top, bottom, each end as well as close up of anything that reveals original texture of the fossil or openings. If it is an echinoid, they have mouths where food goes in and a bottom where processed food comes out. On irregular echinoids the bottom is on the back end and the mouth is on the under side. Regular echinoids the mouth is on the top and bottom on the bottom. Echinoids can be very complex to ID even when in great condition.

 

Sorry for the late response!

 

Here's the pictures from the top, same end as in the OP (with a better view of the bottom), and the bottom. I didn't take pictures of each end since they're completely covered by rock. If they're important for making an ID, I'll take pictures of them too.