Married, filing separately, with a stepchild.

Confused. I am married to my stepchild's mother. We intend to file separately for the 2013 tax year. Do I claim my stepchild as a dependent? Is my wife able to claim the child as dependent too, when she files separately? When the return talks about allowing/declining the child's "other parent" to claim her as a dependent, is it referencing my wife - my stepchild's mother - or our child's natural father?