Bringing back extinct species is a real possibility. In fact, scientists have announced a plan to clone woolly mammoths using remains preserved in the Siberian permafrost.
They hope to create mammoth embryos by replacing the nuclei of elephant egg cells with preserved mammoth nuclei, then implanting those embryos in elephants.
A possible alternative is to assemble the genetic code of a dinosaur-like animal with a computer, using ancient, ‘switched off’ dinosaur genes that still exist in the DNA of possible dinosaur descendants, such as birds. We don’t have the necessary technology today, but scientists haven’t ruled out this possibility.