For the sake of argument, say that rather than Pangea breaking up, it moved closer together, creating a ring of mountains surrounding some parts of the West Coast of America and the North West area of the African continent. If this is impossible, then try to ignore that one impossibility for the sake of literary licence. So we have a large portion of the world rendered inaccessible to the rest of the world until the advent of mountaineering.
Obviously the isolation would have an effect on the evolution of the species that are "trapped" in that area, as we can see with Australia, but that is not the part that I am curious about. What I am more curious about is the social evolution of hominoid species in that land-locked island. I am aware that hominoids did not show up until long after the breakup of Pangea, but again for the sake of argument let us say that the precursors to hominoids were also trapped in the ring of mountains.
What are some of the likely social structures an intelligent hominoid species would develop in the tens of thousands of years that they would have been isolated from the world at large?