Help me ID -- middle tertiary

[Limestone]

Hello, I am new to the forum and new to fossil collecting. Last week I was exploring Limestone deposits in northern Puerto Rico. I found some fossils imbedded into the limestone but then I found this piece. From what I understand, this is a fossil bone because of its porous nature.  Could anyone tell me what I collected?

Thank you for any help! 

I plan on doing much more research and exploring in the next weeks. 

Thank you,

Miguel

Edited May 14, 2017 by Limestone
Add age

[Rockwood]

It would be an unusual preservation of bone. 

[abyssunder]

I agree.
It could be a bioeroded limestone piece, with those irregularly distributed little holes on the surface.

 

bioerosion

bioeroders

[Limestone]

Thank you for your replies, I picked this piece up because of the shape and because it was much more solid than other limestone pieces with visible fossils on them, which will crumble under little (relative) pressure. 
I will surely read up on bioerosion.