We've got at least 4 different turtle Pokemon families though (Blastoise, Tirtouga, Torterra, Torkoal), so it's not like we're lacking in them.
I wouldn't mind seeing more Pokemon based off of prehistoric Pokemon though, but I expect that we'll continue seeing them come in fossil form in the future. Though, it would be kind of neat to see a Jurassic Park-esque Safari Zone that only includes restored fossil Pokemon. We're up to nearly a dozen of them now, which would be more than enough to populate a small area.