Jurassic World Evolution has your prehistoric animals covered.
I feel like a lot of people are making the mistake of comparing Planet Zoo too closely to Zoo Tycoon. The latter didn't really bother with being 'realistic' or driving a certain point (in PZ's case, education, conservation, what zoos actually do, etc.), it was just meant to be a game for being a game's sake. PZ has a lot more riding on its message, so I don't think Frontier will deliberately detract from that to add fantastical or prehistoric elements (especially since, as I said, the latter is already covered as far as they're concerned with JWE, which is also a Frontier game).
I think the only extinct animals I would be okay with including would be a small selection of animals we drove to extinction deliberately, as a way of making virtual ammends. Things like the thylacine, for example. Even then, I wouldn't want to see it until much further down the line, when all the more traditional zoo animals are covered (we're still seriously lacking in plenty of real and extant animals as it is, despite a fairly large roster).