ID Help: Southern California Fossils - Chivo Canyon

[ezeemonee]

Hi, appreciate any ID help on this one from Chivo Canyon in Southern California.  About 4-5" in diameter found inside of a roughly 1 foot diameter rock.  The area is known for Eocene and Oligocene period fossils.  Guessing this may be a sponge, coral, or possibly echinoderm like a Sea Urchin.  Stumped on the ID so far.  Most of the other fossils in the canyon are mollusks and gastropods.  Thanks!  -Chris.

[M3gal0don_M4n]

I may be mistaken, but there appear to be shell fragments scattered throughout your rock. As opposed to the bigger object, I am unsure.

[Fossildude19]

This may need to be prepped out more, to say anything further.

My first thought was crab, but, ... some sort of coral looks like a more likely candidate.

[Thomas.Dodson]

The irregularity, direction, and different planes of the holes make me think of something heavily bored/bioturbated (like by shipworms). I see some bivalves in position of holes that could be borers. As for what the original object is, it might not be in good enough condition to tell.

[FossilDAWG]

I don't think this is a coral, as the size and distribution of the "holes" is too random to be corallites, and there is no internal structure.  It also looks to be too random (no bilateral symmetry) to be a crab with the tubercles broken off.  I'd go with something heavily bored, as @Thomas.Dodson suggests, or a colonial tubeworm or something similar.

 

Don

[ezeemonee]

Thanks all!  I think Tubeworms could be the best bet!