I'm not convinced why you'd want to. Same with the Mammoth really- what's the purpose apart from to prove we can? In my mind it's not about playing god but about reversing what nature intended, evolution etc. I think if you can prolong the timeline of an already existing endangered species (polar bears, tigers, whatever) then that's all good but bringing back the dodo, a mammoth or raptor just seems to be pointless. I'd rather see the funding going towards stem cell research or curing debilitating illnesses rather than reintroducing long lost species to the world that has no place for them anymore.