Cretaceous marine reptile limb bones?

[Creek - Don]

I keep finding these that resembles bones in the Dallas creeks last few months.    I have dozen of these possible limb bones.  They look like small swamp reptile limb bones that may once belonged to crocks or marine reptiles when Dallas was coastal swamp or marsh.   Compare to other rocks,  these bones are also very hard to break.    Could these be possible reptile limb bones of crocks or unknown reptile feet or leg bones?     

[JohnBrewer]

They look geological too me. What say you @ynot?

[Creek - Don]

That 3rd bone from the top awfully looks like early Cretaceous amphibian called Koolasuchus limb bone which are found in Australia.   

The 3rd bone from the right looks like fossilized turtle bone from Cretaceous period from Kansas. 

[ynot]

These pieces look like burrow cast to Me, not bone of any kind.

They do not have any features of bone other than a vague resemblance of shape (the last thing that should be considered when determining what a fossil is).

[Creek - Don]

Great! Thanks.  I didn't really care whether these were fossil or not.  Was trying to figure out what these things once belonged to.  

[erose]

Definitely burrows. There is a name for the larger ones like this. Recently I heard speculation that they were made by heart urchins.  But there are many other suspects including all sorts of soft bodied critters we can only guess at.