Burrow, Bone, or mineralized iron

[FlirtsWithChert]

Below are 2 items found on the same day after a few days of heavy rain/high creek water.  Both of these are heavy and have a hard iron-like shell or covering.  The 2nd item was split into 2 pieces when I found it.  It is made of the same material as the first.
 

We have iron in our well water at the base of the ridge so I’m very familiar with the color and the smell of iron.  These items don’t usually wash up in the creek.  I picked them up because their unusual shape and texture contrasted with the creek’s normal sand and gravel.  

[FlirtsWithChert]

Here is item#2

[FlirtsWithChert]

Here’s a similar item found on a different day.

[abyssunder]

All of them remind me of iron oxide concretions. The last one looks like an "Indian paint pot", to me.

[Planko]

+1 Iron

[Rockwood]

It's conceivable that some ironstone concretions like this formed as the result of a biological being, or activity, but there really needs to be clear evidence to consider any to be fossils.