What does "postorbital closure" indicate in primates?

Postorbital closure refers to a bone structure found in the skulls of some primates where the bony eye socket is completely enclosed at the back by a bony bar. This anatomical feature is significant because it provides additional protection for the eyes. By enclosing the eye socket, postorbital closure helps to safeguard the eyes from potential injuries and environmental hazards, such as debris or branches in the habitat where these primates may move.

In contrast, while a larger field of vision might be associated with the positioning of the eyes on the face (which can be independent of postorbital closure), and the ability to see in low light is more related to the presence of certain types of photoreceptor cells in the retina, these factors do not directly connect to postorbital closure. The enhanced sense of smell is generally not linked to the presence of this feature but involves other cranial adaptations. Thus, the main function of postorbital closure is clearly linked to the protection of the eyes, making this the correct interpretation of the term in the context of primate anatomy.