Fossil Bone - Femur?

[MeerCat]

I hate to be a newbie who joins a forum just to get help identifying a mysterious item, but since that's what I'm doing - I promise to attempt to be a valued member in the future!
 

I found this 8.4" item yesterday on a Pacific NW beach.  It is very heavy, gray rock - like slate.  I know next to nothing about fossil bones, but it just doesn't look like a 'natural' rock to me.

 

Any thoughts would be appreciated.  

 

 

[Shellseeker]

It is possible that it might equally be a humerus...  Here is one from a land turtle.

 

Here are others from Sea Turtles,

https://www.researchgate.net/figure/Line-drawings-of-various-chelonian-left-humeri-all-reduced-to-the-same-length-after_fig6_233175938

 

 

Welcome to the Fossil Forum,  I hope you like it here.

[Lorne Ledger]

looks more like a rib to me, from something rather large

[Harry Pristis]

Somehow, I can't imagine how this could ever have been a bone.  The interior of the find shows no hint of cancellous bone, and the putative ball doesn't look like it ever articulated with another bone.  I think this is a section of domichnia, a cast of a dwelling burrow.  The ovate prominence may be a resting place or a turnaround for the burrower.  That's my impression anyhow.

[MeerCat]

Thanks for your responses.

Interesting - I had never heard of a 'domichnia'.  

[MeerCat]

So is this something that is common, very old...?  Since it was found laying on the sand of a beach, is it likely to be from some sort of sea animal?  Googling 'trace burrow fossil' I was unable to find anything similar, but I get that it doesn't have any bone characteristics other than general shape.  Thanks.

[Andúril Flame of the West]

Hello and welcome to the forum!
 

I cannot comment on how old or common this particular fossil is since I am not familiar with the geology of your area. It was likely created by a marine animal since a large proportion of fossils have a marine origin, but knowledge of the formation it originated from would be needed to confirm this. 
 

@Harry Pristis identified this as a cast of the burrow of an organism. Essentially, during the time the formation was being deposited (when it was a sea floor, mudflat, etc.) some organism burrowed into the sediment. The burrow was filled with sediment which eventually hardened into stone in the shape of the burrow. Natural forces weathered the matrix around the burrow until it was removed from the matrix and ended up on the beach where you encountered it. Another more familiar with Domichnia could give a better explanation and may know the age of your specimen. 

[Harry Pristis]

One possibility is Thalassinoides (often associated with shrimp) burrows.

[MeerCat]

Thanks - I'm just trying to learn.  It kinda bugs me to have an item laying around the house that I need to research.  Perhaps I will display this with a large plastic shrimp