Regarding the development of 'fingers'. The first development seemed to be to 'strengthen' fins, and became 'fingers' as environmental and physical conditions provoked the optimum chance of their development.
There is a statement in the clip that should remembered whenever considering 'Scientific Discoveries' :
" Previous research, it turns out, had simply overlooked what was there. "
Every minute other discoveries show us that we can miss so many factors..until our minds are ready to see them.