Ancient Mystery : Fossil Whale Bone?

I found this fist-sized rock along the shoreline yesterday, and immediately noticed some unusual things about it.  It is very heavy, and filled with linear vesicles - and reminded me of bone, especially whale bone. I don't know if that's what it is - fossil whale bone - but it certainly seems possible. I am going to do some tests, and maybe have someone look at it who might know more than me (which is almost everyone).  Stay tuned.

Follow-up  4/10/12 :  I took the sample to the Paleo team at the Burke Museum today to see if they had any reaction to it. They did, and it pretty much coincided with mine, e.g. "it might be bone....or it might not."  Hardly the conclusive verdict I was hoping for. But yes, it is pretty weathered, pretty small, and does not have any obvious structures that would help identify it.

MAY 2013 UPDATE: I finally got around to cutting  this puppy open and you know what?  It was nothing - some sort of mudstone devoid of any interesting pattern or structure...