Question

Which old world monkey is of special interest to paleoanthropologists because it lives in savannahs like those in which we expect ancestral humans may have lived?

Answer 1

The old world monkey that became special interest to paleoanthropologists because it lives in savannahs like those in which we expect ancestral humans may have lived is: baboons
the paleoanthropologists paid a lot of interest to this animal because their behavior and decision-making process is very close to human.
For example, in their baboons' group, there will be some type of leaders that lead through tyranny and some leaders that lead through cooperation and understanding. (just like humans) 
On top of that, many of the baboon leaders that led with tyranny often betrayed by its subordinate and killed while sleeping (again, just like human)