My theory is that all the different ‘races’ developed simultaneously.
The Earth was once on big continent. There were animals that would eventually become human spread all over that single continent, Gondwanaland, Pangaea or whatever you wish to call it.
The different races became independent of each other and developed according to its own environment.
Africans, Asians and Caucasians with a few intermingling of races along the edges of their territories.........................
The Earth is Expanding and we don’t know why:
http://www.science-frontiers.com/sf037/sf037p11.htm
https://www.youtube.com/watch?v=oJfBSc6e7QQ
If I remember correctly, Pangaea existed before or early in the rise of the dinosaurs. Since the dinosaurs all died 65 million ya, there is no possibility that your theory could be correct.