Smashed-up something in a stepping stone, any idea?

[Fishkeeper]

I got this at a place that sells bulk rocks. It was in a batch of rocks meant to be stepping stones, and I have no idea where in the world it's from. I know it's too messed up to ID well at all, I'm just wondering what general category of animal this is. My best guess is it's the outside of a large fish skull. There's nothing inside the slab, and the area in the right side of the pic looks like a shattered gill plate to me. It's about 8" across, and the rock it's in feels harder than most limestone I've come across. I didn't see any other fossils in the other slabs, and I doubt the stepping-stone-store is selling rocks from a rich fossil site.

Any idea? I'd be happy with just "yeah, that's definitely a fish" or something similar. It's staying outside as a stepping stone, as I'm of the opinion that all stepping stone paths should have a large and interesting stone to stop on, and it's definitely not in good enough shape to be worth displaying. It's neat, though. 

 

[ynot]

Pictures?

[Fishkeeper]

Whoops, my bad. Added one in.

[ynot]

Hard to say what that was.

[Peat Burns]

I was thinking fish or trilobite.  Reminds me of a blown up Isotelus 

[abyssunder]

Maybe an inoceramid valve. Inoceramus

 

[Peat Burns]

6 minutes ago, abyssunder said:

Maybe an inoceramid valve. Inoceramus

 

That's a real good possibility.  Here's a Cretaceous inoceramid I found this summer

[izak_]

I'm definitely seeing an inoceramid. The shell texture is very similar to what we find at Richmond QLD, and you can see the shape:

[Fishkeeper]

I think you're right about it being an inoceramid. The texture in some spots is a bit weird for bone, it's rough and almost like a serration across a plane, and it feels exactly like the texture on that big specimen in the photo. That also explains the lack of features that would suggest an eye socket or jaw hinge, and that oddly shaped bit to the left of the photo. It looked like the hinge tip of an oyster to me, but I've never seen a fossilized shellfish go that dark in such light rock until that photo. Must be something in the shell that makes it go that color.

 

I wonder if that means there's another half in the rock? I'd almost be tempted to go digging for it if the visible portion wasn't so badly smashed up. If I somehow managed to get all the fragments out, I'd just have a bad puzzle, it's probably not worth the effort. The rest of it probably went with the other half of this slab, too bad I didn't find that piece. 

 

This is a much more specific ID than I was expecting, thanks! And almost cooler than a fish skull, I didn't know bivalves got that big. It's like an oyster that serves as your table and stew pot at the same time.