I am unaware of any examples of normally functionally hermaphroditic mammals, and unaware of but less confident in the same for tetrapods (four limbed vertebrares that came onto land and their descendants). I am aware of tetrapod species that became almost entirely female, reproducing primarily by cloning. I am also aware of tetrapods that switch sex during their lifetimes, though you could call that a form of hermaphroditism. Tetrapods also exhibit all of the above methods of sex determination.

The pattern of hermaphroditism in ray finned fish, a very diverse and old vertebrate lineage, however suggests multiple conversion events back and forth some of which are recent. See http://evolution.berkeley.edu/evolibrary/images/hermaphroditismtree.gif . Of note, cichlid fish are listed as hermaphroditic on there but recently went through a huge evolutionary radiation and several of their sublineages have been caught in the act of reevolving most of the above sex determination systems.