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. 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.