Gene-splicing scientists are working to resurrect the extinct woolly mammoth. Also the thylacine, a sort of marsupial wolf that looked like a stripy skinny dog. Of course, it's not even kind of a dog. All marsupials are more closely related to each other than to any of the mammals to which they bear superficial morphological similarities. They're like us; what ends up shaping you is the niche you occupy. Which, getting back to the mammoth, is why I don't think it's a good idea. Can you imagine anything lonelier than being born 40 centuries after your last relative had died?