Carrillo: Using the number of existing primate species, along with measures of the genetic diversity among these prim...

I had interpreted their disagreement was best described by B. I don't understand how D is correct. I did not get the implication that Carrillo disagreed with Olson's date on the fossils. Even if those were the oldest fossils found, that does not necessarily mean that they are the very first and that Carrillo's method of calculation is incorrect. Any assistance would be greatly appreciated!