Final answer:
The primate species Darwinius sp. does indeed have a postorbital bar, a bony structure around the eye socket found in many primates, which informs us about primate evolution.
Step-by-step explanation:
The student asks if Darwinius sp., a primate species from the Middle Eocene epoch, possesses a postorbital bar. The correct answer is yes, Darwinius sp. does have a postorbital bar. This is a bony structure that forms a loop around the eye socket and is characteristic of many primate skeletons. It is significant in the study of primate evolution as it offers support to the eyes and face, particularly in those species who have larger eye orbits due to diurnal activities that require accurate vision. The presence of the postorbital bar in Darwinius contributes to understanding the anatomical features that distinguish primates from other mammals and aids in determining their place in the primate evolutionary tree.