Well I was in one of my sciencey moods and got thinking. What eles could evolve intelligence if we were gone. Well the Dolphin came to mind. In my opinion the only thing keeping it from breaking through to the level we're at is the fact it lives in water and can't harness fire and therefore the foundation of modern tech. So in my scenario humanity ends up taking itself out and lots of other land animals. So some sea ones move back to land to fill the void and the dolphin is amongst them. This one's kind live in coastal colonies and have domesticated several land and water species and have started to use fire as a tool. Check back with these guys in say a thousand years or so. You might just find a dolphin version of Rome.