A little more than 55 million years ago there was a split in primate evolution.

These conflicting classifications lie at the heart of the debate over early primate evolution.

Consequently, the gray mouse lemur has once again been used as a model organism for studying lemur and primate evolution.

During primate evolution, a shift from nocturnal to diurnal activity in tarsiers, monkeys and apes (the haplorhines) brought with it an increased reliance on vision at the expense of olfaction.

Some neuroscientists suggested that this apparent difference distinguishes tarsiers from all other primates, reinforcing the view that they arose in an early, independent line of primate evolution.