ummm kinda looks like a femer bone. from the proximal head near your hip down into the shank of the bone. that would be a little unnerving though.....
yeah at first i did think it was a bone but you can flake part of it off sort of like a tree and it has properties of wood... if it was bone i would of thought it would be a little harder but it does look like a bone.
and for the rest, the root just seems odd... not to sure it could be a mangrove who knows...
does anyone know anyone who does lab work that might want to do a fun test project on this? i saved it just as pictured and it is out of water just in case there was anyone wanting to do some research or something with it trying to find out what it is/ how old it is