Is This A Fossil?

[zdufran]

This is yet another rock I collected on the shorelines of Lake Texoma, Oklahoma in an area with lots of limestone from the Cretaceous. It reminds me of a sponge, but it may just be a rock. Does anyone know? (Pardon the tiny hand. My daughter was helping out with the staging of the item.)

[RyanNREMTP]

Need more pictures to be honest, from different angles. It could be anything from a block of limestone to a rudist reef piece.

[zdufran]

Here are some more pictures. Thanks for the help.

[zdufran]

One more:

[John K]

the side view looks a lot like a stromatolite, though those that I'm familiar with from around here are solid. But after looking at some images of other Cretaceous stromatolites, I'm thinking that's what it is.

[rwise]

Looks like stromatolites ( from colonies of algae) or rudists.

[Herb]

looks

like rudists to me

[zdufran]

Thank you all!

[BobWill]

Looks like natural erosion to me.