Who was first

Pangaea was what the land mass was called before the continental drift seperated it into the seven continents. The aleutian islands shared by Russia and Alaska were once the tops of mountains until it flooded. In the United States, the native tribes claim to have been here first. Some tribes, like the Aztec tribe, came up from mexico. Other tribes came from Russia along the Bering strait before it flooded, crossed through Canada into the states. We know this.
Who was already here when the continental drift happened? Was it one of the tribes that exist today? Did they join with a larger tribe for survival?  Or was it a race of people who got ran off and killed by the tribes coming in?