Maxillary sinus atelectasis in a wild born gibbon (Hylobates moloch)

Zygomaticomaxillary Morphology and Maxillary Sinus Form and Function: How Spatial Constraints Influence Pneumatization Patterns among Modern Humans

Previous research has suggested that the maxillary sinuses may act as "zones of accommodation" for the nasal region, minimizing the impact of climatic-related changes in nasal cavity breadth on surrounding skeletal structures. However, a recent study among modern human crania has identified that, in addition to nasal cavity breadth, sinus morphology also tracks lateral facial form, especially anterior-posterior positioning of the zygomatics. Here, we expand upon this previous study to further investigate these covariation patterns by employing three samples with distinct combinations of nasal and zygomatic morphologies: Northern Asians (n = 28); sub-Saharan Africans (n = 30); and Europeans (n = 29). For each cranium, 30 landmarks were digitized from CT-rendered models and subsequently assigned to either a midfacial or maxillary sinus "block." Two block partial least squares (2B-PLS) analyses indicate that sinus morphology primarily reflects superior-inferior dimensions of the midface, rather than either nasal cavity breadth or zygomatic position. Specifically, individuals with relatively tall midfacial skeletons exhibit more inferiorly and laterally expanded sinuses compared to those with shorter midfaces. Further, separate across-group and within-group 2B-PLS analyses indicate that regional differences between samples primarily build upon a common pattern of midfacial and sinus covariation already present within each regional group. Allometry, while present, only explains a small portion of the midface-sinus covariation pattern. We conclude that previous findings of larger maxillary sinuses among cold-adapted individuals are not predominantly due to possession of relatively narrow nasal cavities, but to greater maxillary and zygomatic heights. Implications for sinus function and midfacial ontogeny are discussed. Anat Rec, 300:209-225, 2017. © 2016 Wiley Periodicals, Inc.

Minor contributions of the maxillary sinus to the air-conditioning performance in macaque monkeys

The nasal passages mainly adjust the temperature and humidity of inhaled air to reach the alveolar condition required in the lungs. By contrast to most other non-human primates, macaque monkeys are distributed widely among tropical, temperate and subarctic regions, and thus some species need to condition the inhaled air in cool and dry ambient atmospheric areas. The internal nasal anatomy is believed to have undergone adaptive modifications to improve the air-conditioning performance. Furthermore, the maxillary sinus (MS), an accessory hollow communicating with the nasal cavity, is found in macaques, whereas it is absent in most other extant Old World monkeys, including savanna monkeys. In this study, we used computational fluid dynamics simulations to simulate the airflow and heat and water exchange over the mucosal surface in the nasal passage. Using the topology models of the nasal cavity with and without the MS, we demonstrated that the MS makes little contribution to the airflow pattern and the air-conditioning performance within the nasal cavity in macaques. Instead, the inhaled air is conditioned well in the anterior portion of the nasal cavity before reaching the MS in both macaques and savanna monkeys. These findings suggest that the evolutionary modifications and coetaneous variations in the nasal anatomy are rather independent of transitions and variations in the climate and atmospheric environment found in the habitats of macaques.

Aplasia of the maxillary sinus in a Tibetan macaque (Macaca thibetana) with implications for its evolutionary loss and reacquisition

The skull of an adult female Tibetan macaque, Macaca thibetana, was found to completely lack the maxillary sinus (MS). This absence was accompanied by a slight lateral concavity where the ostium should have formed in the MS, a slight drop of the orbital floor, posterior and medial displacement of the zygomaxillary suture, an unusual position of the lacrimal canal, malocclusion with severely worn cheek teeth, and abnormalities in the temporomandibular joints. The facial component was disproportionally large compared with the neurocranium and mandible. This hypertrophic face probably caused the malocclusion and associated anatomical disorders and simultaneously displaced the lacrimal canal posterior to other nasal structures to preclude the possibility of maxillary pneumatization. These modifications in the spatial relationships to nasal structures might help explain the evolutionary loss and reacquisition of the MS in some primate lineages displaying great variations in facial anatomy.

Reassessment of Dolichopithecus (Kanagawapithecus) leptopostorbitalis, a colobine monkey from the Late Pliocene of Japan

In the original description of Dolichopithecus (Kanagawapithecus) leptopostorbitalis, Iwamoto, Hasegawa and Koizumi, 2005, a moderately large-sized colobine monkey from the Late Pliocene of central Japan, affinities to the European Dolichopithecus rather than to the Transbaikalian Parapresbytis were noted based on the similarities in cranial morphology. Computed tomography scans confirm the presence of the maxillary sinus in the holotype, whereas it is probably absent in specimens of the European Dolichopithecus ruscinensis, the type species of this genus. This feature is either present or absent homogeneously in any given genus of living anthropoids. Its presence or absence is unknown in Parapresbytis, but the distinct morphology of the maxillary incisors in this taxon suggests that this form had different feeding habits from the Japanese colobines. These findings suggest that the Japanese colobine should be referred to henceforth as Kanagawapithecus leptopostorbitalis. Kanagawapithecus shares many important facial and dental features with Dolichopithecus rather than with Parapresbytis, but this association depends largely on the limited availability of comparable materials for the latter. Among colobines, the presence of the maxillary sinus is recorded only in Libypithecus and Cercopithecoides. The maxillary sinus is absent in all modern Asian colobines, implying that Kanagawapithecus is an isolated form without any relationship to living forms. Nevertheless, such phylogenetic interpretations are largely dependent on the restricted fossil evidence from the Pliocene and Pleistocene of eastern Eurasia and will be reexamined when new findings are made.