Observation of the Three-Dimensional Morphology of the Frontal Sinus in Pan troglodytes

Abstract

Extant African apes and humans share the frontal sinus while extant Asian apes don't. The analysis of the frontal sinus is essential for understanding the evolution of the great apes as well as the role of the paranasal sinuses. However, there is no concrete agreement on the phylogenetic and functional interpretations of the frontal sinus. Partly, this is due to the paucity of morphological information of the frontal sinus in African apes including ontogenetic and individual variations. This study examined the three-dimensional morphology of the frontal sinus in twelve chimpanzees' crania by using the Computed Tomography.
The frontal sinus in the chimpanzee grows upward from the nasal cavity and reaches the level of the superior orbital margin at the same chronological age as in humans. This fact probably suggests that the growth of the sinus in the chimpanzee is different from that in humans in terms of the biological age determined by dental development.
The frontal sinus morphology in the chimpanzee is as variable as that in Homo sapiens. The sinus volume clearly correlates with the cranial maximum length and scales in a positive allometric fashion relative to the length. The protrusion of the frontal sinus in the interorbital region is also related with the length.
The interspecific difference in the morphology of the frontal sinus between adult chimpanzees and humans is possibly resulted from the morphological difference of the skull and body size.