In a solo game you have 3 territories. Each one of these territories has a boss. Then you have a final boss. For single player only, each Apex Dinosaur is a final boss but only one is chosen randomly. So If you play as Rex, Spinosaurus could be your final boss. You also have the Universal Final bosses Titanoceratops and G.Rex that can be used as a final boss for either Single Player or Multiplayer.
So in total in a one player game you will take on 2-3 territory bosses and a final boss. You must dominate 2 out of 3 territories by the time the final boss shows up. If you don;t, you lose. If you beat the final boss you win. If you dominate 3 territories before the final boss shows up you win.
There is also different difficulty levels.
Hope this helps.
Thank you very much for clearing this up.