Variation in the Morphology of the Maxillary Sinus among Anthropoids and Its Potential for Phylogenetic Analyses

Abstract

The maxillary sinus communicates with the middle meatus of the nasal cavity through a narrow ostium. Here, I have surveyed variations in the maxillary sinus anatomy of extant and fossil anthropoids which have been examined using computed tomography (CT). The CT studies have identi.ed the sinus by its ostium that opens exclusively to the middle nasal meatus, because the ostium marks site from which the pneumatization to form the sinus begins. A sinus pneumatizing the entire maxilla is shared by all extant hominoids. In contrast, cancellous bone completely .lls the maxilla in extant cercopithecoids, with the exception of macaque monkeys which have a small sinus. Among platyrrhines, the entire maxilla is pneumatized by the sinus in the Atelidae, Cebus, and Callicebus, whereas only the medial part of the maxilla is pneumatized by the sinus in the Callitrichinae and Aotus. Pithecia exhibits a unique conformation in which the maxillary sinus and another cavity expands from the inferior meatus pneumatize the posteromedial and anterolateral parts of the entire maxilla, respectively. Saimiri has no sinus, as in the case of cercopithecoids excluding macaques. In Chiropotes and maybe Cacajao, the inferior meatus expands into the area between the middle meatus and medial surface of the maxilla thereby disturbing sinus formation. The sinus was lost independently in Saimiri and Cacajao-Chiropotes clades, and in the common ancestor of cercopithecoids. The sinus pneumatizing the entire maxilla is argued to be a primitive feature in anthropoids. This hypothesis is supported by the results from studies of fossil anthropoids. This information may be relevant to the phylogenetic analyses of unclassi.ed fossil anthropoids. I hope this paper will also stimulate future studies on the variations in sinus anatomy in prosimians and other mammals, and on other inner structures of the cranium in primates. Potentially, such information probably will further facilitate the phylogenetic analyses of fossil specimens.