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

Changes in paranasal sinus volumes, temporal bone pneumatization, internal acoustic canal and olfactory cleft dimensions over the centuries: a comparison of skulls from different epochs in Anatolia

OBJECTIVES

Investigating changes in temporal bone pneumatization (TBP) and paranasal sinus volumes (PSV) across different eras may help understanding not only changes in skull anatomy but also pathophysiology of chronic otitis media and sinusitis, respectively, which are common health problems.

METHODS

Eight skulls from the second century AD, 20 skulls were from the 10th-11th centuries AD, 20 skulls from the 16th-19th centuries AD, and 60 contemporary skulls were included in this cross-sectional observational study. Using computerized tomography (CT) scans, the PSV were calculated by multiplying the height, width, and antero-posterior distance of the sinuses. TBP was divided into three types. Internal acoustic canal (IAC) length and width, and olfactory cleft (OC) width were measured.

RESULTS

No statistically significant differences were found between the paranasal sinus (frontal, maxillary, and sphenoid) volumes between the groups. However, TBP decreased statistically significantly over time on both sides of the skulls (p = 0.001). The contemporary IAC and OC measures were found to be significantly lower on both sides compared to the skulls from the other three eras (p < 0.001 for both).

CONCLUSIONS

Although no significant change was observed in PSV, decreases were evident in TBP, OC width and IAC length and width over time. It appears a fair inference that changes in size of OC and IAC might be another indication of the fact that olfaction and hearing were more vital for survival in old eras. Since we do not know incidence of chronic ear problems in old eras, we cannot speculate outcome of increased TBP in terms of developing chronic ear diseases. On the contrary, increased TBP was likely to play a protective role in traumas in old ears. Additionally, the environmental influences may be crucial role in the development of paranasal sinuses.

Personal identification using frontal sinus coding methods: The effect of mixed image modality comparisons

Several code-based methods have been created for comparing the frontal sinus in skeletal identification scenarios. However, little is known regarding matched-pair accuracy rates of these methods or how varying image modalities may affect these rates. The goals of this study were to validate the exclusion rates and to establish matched-pair accuracy rates of two well-cited coding methods, Cameriere et al. [23] and Tatlisumak et al. [24]. Additionally, individual variables were assessed for consistency in scoring between image modalities. Using a sample of U.S. African American, Native American, and European American females and males (n = 225), we examined individual variable scoring and string codes between two different image modalities (radiographs and CT-based 3D models). Arcades showed poor scoring consistency between modalities (p < 0.001). Although exclusion rates were similar to those reported in the original studies (93%-96%), matched-pair accuracy rates were low (13%-18%). None of the demographics (collection, sex, age, ancestry, and orientation) had an effect on the odds of a match. Interobserver and intraobserver analyses showed moderate to near-perfect agreement for all variables except supraorbital cells, which had minimal to no agreement. Currently, we do not recommend the application of these frontal sinus coding methods independent of other supporting identification methods given low variable consistency and accuracy rates. Visual identification should still be used to include or exclude an identification when using the frontal sinus.

Variation, sexual dimorphism, and enlargement of the frontal sinus with age in adult South Africans

OBJECTIVES

To document frontal sinus volume (FSV) in a sample of sub-Saharan Africans with a view to evaluating claims that such populations exhibit comparatively small sinuses. This study also addresses questions related to sexual dimorphism, incidence of sinus aplasia, and the possibility that FSV continues to increase through adulthood.

MATERIALS AND METHODS

FSV was measured from CT scans of adult crania from the Dart Collection. Sex and age were known for each individual. Linear cranial dimensions were used to compute a geometric mean from which a scaled FSV was computed for each cranium.

RESULTS

FSV does not differ significantly between sexes, but females exhibit a higher incidence of aplasia. There is considerable variation in FSV in this sample, with the average ranking among the higher means reported for other population samples. The incidence of FS aplasia falls within the range of values recorded for other population samples. Although our study is cross-sectional rather than longitudinal, there is strong evidence that FSV continues to increase with age throughout adulthood.

DISCUSSION

The FSV mean of our sample contradicts the notion that sub-Saharan Africans possess small sinuses. In a global context, geography (climate and altitude) does not appear to be related to FSV. The absence of sexual dimorphism in our sample is unexpected, as significant dimorphism has been reported for most other population samples. Our results support other indications that the frontal sinus continues to expand throughout adulthood, especially in females, and that it is likely due to bone resorption.

Investigating the relationship between infraorbital canal morphology and maxillary sinus size

The purpose of the current study was to investigate relationships between maxillary sinus (MS) dimensions and the bony structures associated with the infraorbital nerve (ION). Computed tomographic scans of 87 adult crania (174 sides) from four morphologically diverse groups (West Africans, East Africans, North Asians, Europeans) were utilized. Seven primary variables were collected: infraorbital canal (IOC) type; infraorbital foramen (IOF) shape; distance from the foramen rotundum to IOF (FR-IOF); distance from the posterior wall of the infraorbital groove to IOF (IOG-IOF); and MS length, breadth, and height. Chi-square analyses indicated a significant association between IOC-type and IOF-shape (Pearson chi-square = 12.710; p-value = .013), with the most common pattern being oval IOFs and Type-I IOCs (45.68% of the sample; 74/162 sides). Analysis of covariance indicated a significant effect of ancestry (F = 8.333; p < .001) and MS length (F = 15.406; p < .001) on IOG-IOF distance. Ordinal regression analyses indicated that MS length (Wald chi-square = 7.103; p = .008) also maintained a significant effect on IOC-type, while multinominal regression analyses indicated that none of the measured parameters had a significant effect on IOF-shape. These results have clinical implications: recognizing IOC-type and IOF-shape relative to the MS is important to avoid ION damage during medical procedures. Overall, this study found most individuals possess Type-I IOCs (housed in the maxillary sinus roof) and oval-shaped IOFs. Most aspects of the ION pathway, including IOC-type and IOF-shape, were not influenced by ancestry or sex. However, antero-posteriorly longer MSs tend to possess Type-III IOCs protruding into the sinus, which could lead to surgical complications.

New insights into the variability of upper airway morphology in modern humans

The biological adaptation of the human lineage to its environment is a recurring question in paleoanthropology. Particularly, how eco-geographic factors (e.g., environmental temperature and humidity) have shaped upper airway morphology in hominins have been subject to continuing debate. Nasal shape is the result of many intertwined factors that include, but are not limited to, genetic drift, sexual selection, or adaptation to climate. A quantification of nasal airway (NA) morphological variation in modern human populations is crucial to better understand these multiple factors. In the present research, we study 195 in vivo CT scans of adult individuals collected in five different geographic areas (Chile, France, Cambodia, Russia, and South Africa). After segmentation of the nasal airway, we reconstruct 3D meshes that are analyzed with a landmark-free geometric morphometrics method based on surface deformation. Our results highlight subtle but statistically significant morphological differences between our five samples. The two morphologically closest groups are France and Russia, whose NAs are longer and narrower, with an important protrusion of the supero-anterior part. The Cambodian sample is the most morphologically distinct and clustered sample, with a mean NA that is wider and shorter. On the contrary, the Chilean sample form the most scattered cluster with the greatest intra-population variation. The South African sample is morphologically close to the Cambodian sample, but also partially overlaps the French and Russian variation. Interestingly, we record no correlation between NA volume and geographic groups, which raises the question of climate-related metabolic demands for oxygen consumption. The other factors of variation (sex and age) have no influence on the NA shape in our samples. However, NA volume varies significantly according both to sex and age: it is higher in males than in females and tends to increase with age. In contrast, we observe no effect of temperature or humidity on NA volume. Finally, we highlight the important influence of asymmetries related to nasal septum deviations in NA shape variation.

Using Optimal Transport to Improve Spherical Harmonic Quantification of Complex Biological Shapes

The knowledge of the anatomical shape of both gross and microscopic structures is the key to understanding the effects of disease processes on cellular structure. Geometric morphometric methods, such as Procrustes superimposition, and Spherical Harmonics (SPHARM), have been used to capture the biological shape variation and group differences in morphology. Previous SPHARM-MAT techniques use the CALD algorithm to parameterize the mesh surface. It starts from initial mapping and performs local and global smoothing methods alternately to control the area and length distortions simultaneously. However, this parameterization may not be sufficient in complex morphological cases. To bridge this gap, we propose SPHARM-OT, an enhanced SPHARM surface modeling method using optimal transport (OT) for spherical parameterization. First, the genus 0 3D objects are conformally mapped onto a sphere. Then the optimal transport theory via spherical power diagram is introduced to minimize the area distortion. This new algorithm can effectively reduce the area distortion and lead to a better reconstruction result. We demonstrate the effectiveness of the method by applying it to the human sphenoidal paranasal sinuses.

Human maxillary sinus size, shape, and surface area: Implications for structural and functional hypotheses

OBJECTIVES

Although research into human maxillary sinus (MS) morphology has overwhelmingly focused on sinus volume, other aspects of morphology (e.g., overall shape, mucosal surface area) factor prominently in hypotheses regarding MS form and function. Here, we investigate MS volume in conjunction with measures of MS shape and surface area in a large, diverse sample of modern humans. We test whether variation in MS volume is associated with predictable changes in MS shape (i.e., allometry) and investigate the influence of MS size-shape scaling on mucosal surface area dynamics.

MATERIALS AND METHODS

Measures of MS volume and surface area were obtained from computed tomographic (CT) scans of 162 modern human crania from three ancestral backgrounds-Equatorial Africa, Europe, and East Asia. 3D coordinate landmarks and linear measurements were also collected. Multivariate analyses were employed to test for associations between MS volume and other morphological variables.

RESULTS

Significant associations between MS volume and 3D shape were identified both across and within the subsamples. Variation in MS volume was found to predominantly relate to differences in MS height and width dimensions relative to MS length. This pattern of allometric scaling was found to differentially influence total mucosal surface area and the SAV ratio.

CONCLUSION

This study suggests that variation in MS volume is disproportionately mediated by MS width and height dimensions. This finding has implications for hypotheses which structurally link MS morphology to craniofacial ontogeny and those which suggest that MS morphology may perform adaptive physiological functions.

Cone-beam computed tomography-based analysis of maxillary sinus pneumatization extended into the alveolar process in different age groups

Objective

This study aimed to measure the amount of maxillary sinus pneumatization (MSP) extended into alveolar processes in different age groups via cone-beam computed tomography (CBCT) and its association with age.

Methods

The data of 293 adult patients (533 maxillary sinuses) who underwent CBCT at our hospital from January 2020 to October 2020 were analyzed and divided into the following age groups: group I (18–34 years old, youth group), group II (35–59 years old, middle-aged group) and group III (≥ 60 years old, elderly group). The distance between the lowest point of the maxillary sinus floor and nasal cavity floor in the central area of the maxillary posterior teeth was measured and recorded as the amount of MSP. Further, according to the positional relation between the maxillary posterior teeth and maxillary sinus floor, MSP was divided into type I (normal pneumatization) and type II (extensive pneumatization). The distribution of pneumatization types and degree and change of pneumatization for the different age groups were also analyzed. P < 0.05 was used as the threshold for statistical significance.

Results

The amount of MSP of group I [(3.75 ± 3.77) mm] was significantly higher than that of group II [(2.30 ± 4.48) mm] and group III [(2.09 ± 4.70) mm], but there was no significant difference between group II and group III. We also found that the amount decreased gradually with increasing age (rs = − 0.2), with the youth group showing a higher prevalence of extensive pneumatization (youth vs. middle-age vs. elderly: 66.44% vs. 36.81% vs. 22.28%, respectively). There was no statistically significant difference in the amount of MSP between males and females and between left and right maxillary sinus in each group (P > 0.05).

Conclusion

The amount of MSP was significantly higher in the 18–34 years old group compared to older age groups, showed a decreasing trend with age and was not associated with sex and maxillary sinus sides.

Global patterns of the cranial form of modern human populations described by analysis of a 3D surface homologous model

This study assessed the regional diversity of the human cranial form by using geometric homologous models based on scanned data from 148 ethnic groups worldwide. This method adopted a template-fitting technique for a nonrigid transformation via the iterative closest point algorithm to generate the homologous meshes. Through the application of principal component analysis to 342 sampled homologous models, the largest variation was detected in overall size, and small South Asian crania were clearly verified. The next greatest diversity was found in the length/breadth proportion of the neurocranium, which showed the contrast between the elongated crania of Africans and the globular crania of Northeast Asians. Notably, this component was slightly correlated with the facial profile. Well-known facial features, such as the forward projection of the cheek among Northeast Asians and compaction of the European maxilla, were reconfirmed. These facial variations were highly correlated with the calvarial outline, particularly the degree of frontal and occipital inclines. An allometric pattern was detected in facial proportions in relation to overall cranial size; in larger crania, the facial profiles tend to be longer and narrower, as demonstrated among many American natives and Northeast Asians. Although our study did not include data on environmental variables that are likely to affect cranial morphology, such as climate or dietary conditions, the large datasets of homologous cranial models will be usefully available for seeking various attributions to phenotypic skeletal characteristics.

Ontogenetic patterns in human frontal sinus shape: A longitudinal study using elliptical Fourier analysis

Frontal sinus morphology is highly variable across individuals, but little is known regarding how or at what age that variation is reached. Existing ontogenetic studies are conflicting and often cross-sectional in nature, limiting understanding of individualistic growth. Studies investigating sinus growth with longitudinal series often focus on lateral cephalograms and consequently do not capture the sinus morphological features that are most relevant to clinical and medicolegal settings (e.g., arcade/scalloping, width-to-height dimensions, asymmetry). Longitudinal analysis of sinus morphology from frontal radiographs is important to understand when sinus morphology stabilizes. The purpose of this study was to investigate at what age the frontal sinus attains its final shape, and whether sex-based differences in ontogeny are evident, using a longitudinal sample of posterior-anterior (PA) frontal radiographs from the AAOF Legacy Collection. Frontal sinus outlines were manually traced in 935 radiographs from 111 individuals (55F/56M) spanning 8-29 years of age. Outlines were subjected to elliptical Fourier analysis (EFA) and underwent principal components analysis (PCA). PC1 (51.02% of variation) appears to represent the relative height and breadth of the sinus, PC2 (11.73%) and PC3 (10.03%) captures the degree of relative complexity in the outlines. Individual PC scores were plotted against age-in-months with individual Loess growth curves. Overall, younger individuals typically display relatively shorter, flatter sinuses, increasing in vertical complexity with age. Mixed-effect models on PC1 indicate significant effects for the repeated measure of years (p < 0.001). Within individuals, Euclidean distances of PCs between each sinus outline and their oldest-age outline (i.e., final morphology) were calculated and plotted against age-in-months with Loess growth curves. The results indicate that final frontal sinus morphology is mostly attained by 20 yoa regardless of sex. There is sexual dimorphism in ontogenetic trajectories: females attain frontal sinus shape earlier than males. Specifically, Loess growth curves of the Euclidean distances to final sinus shape indicate that female shape shows decreased development at 14-16 yoa, with males approaching stabilization at 18-20 yoa. These trends were supported by paired t-tests on PC1 between each year and the oldest age, whereby significant differences end for females starting at 15 and 18 yoa for males. The timing of shape-stabilization in the current study closely aligns with previous studies on linear and size dimensions, indicating a close relationship between the ontogeny of frontal sinus shape and size. This research has several implications in diverse fields. Documenting ontogenetic patterns in modern humans could lead to more accurate interpretations of frontal sinus variation in hominin lineages. Understanding the age at which frontal sinus shape and size stabilizes in pediatric populations has important clinical implications, with future studies needed to investigate if/how sinus development directly relates to sinonasal disease susceptibility (e.g., sinusitis), surgical complications, and/or expected trauma patterns. For forensic practitioners utilizing frontal sinus comparisons for decedent identifications, it is important to know at what age these features stabilize to understand how much change may be expected between antemortem and postmortem radiographs.

Ontogenetic variation in human nasal morphology

Internal nasal cavity morphology has long been thought to reflect respiratory pressures related to heating and humidifying inspired air. Yet, despite the widely recognized importance of ontogeny in understanding climatic and thermoregulatory adaptations, most research on nasal variation in modern and fossil humans focuses on static adult morphology. This study utilizes cross-sectional CT data of three morphologically distinct samples (African, European, Arctic) spanning from infancy to adulthood (total n = 321). Eighteen landmarks capturing external and internal regions of the face and nose were subjected to generalized Procrustes and form-space principal component analyses (separately conducted on global and individual samples) to ascertain when adult-specific nasal morphology emerges during ontogeny. Across the global sample, PC1 (67.18% of the variation) tracks age-related size changes regardless of ancestry, while PC2 (6.86%) differentiates between the ancestral groups irrespective of age. Growth curves tracking morphological changes by age-in-years indicate comparable growth trajectories across all three samples, with the majority of nasal size and shape established early in ontogeny (<5 years of age). Sex-based trends are also evident, with females exhibiting a more truncated growth period than males, particularly for nasal height dimensions. Differences are also evident between the anterior and posterior nose, with the height and breadth dimensions of the anterior nasal aperture and nasal cavity showing differential ontogenetic patterns compared to the choanae. Cumulatively, these results suggest that multiple selective pressures influence human nasal morphology through ontogenetic processes, including metabolic demands for sufficient oxygen intake and climatic demands for adequate intranasal air conditioning.

The role of the nasal region in craniofacial growth: An investigation using path analysis

This study focuses on the role of the nasal region and its interactions with adjacent facial elements during early ontogeny. A series of linear measurements, areas and volumes were extracted from a collection of 227 medical CT-scans of children from 0 to 6 years of age. These measurements describe aspects of the form of the orbit, maxilla, peri-alveolar (subnasal) region, nasal area, eye, oral region, masseter, and temporal muscles. Hypothesized interactions were then examined using path analysis. Two paths were designed: the first to investigate potential interactions in, and relative contributions of the nasal derivatives and adjacent regions to overall facial growth and development; the second path sees the addition of facial soft tissue measurements and aims to assess their effects on skeletal components, and on overall facial growth and development. The results of the first path indicate a large contribution of the nasal and subnasal regions to facial development. This indicates that the nasal septum and the developing dentition provide an important but variable contribution to facial ontogeny during early years. This result is confirmed in the second path, where the soft tissue elements were added to the diagram. Results of the second path indicate that the soft tissues contribute only locally to the development of some skeletal elements of the face. This indicates that the contribution of skeletal components has a more direct effect on facial height than soft tissue matrices, however there are complex interactions between soft tissues and skeletal elements throughout ontogeny.

Ancestry-based variation in maxillary sinus anatomy: Implications for health disparities in sinonasal disease

Paranasal sinus drainage is mediated by mucociliary transport and gravity. However, human orthograde posture, along with the superior positioning of the maxillary sinus (MS) ostium, increases reliance on the mucociliary system. Previous research has thus suggested that differences in MS size and shape may impede mucociliary clearance, potentially contributing to disparities in sinusitis susceptibility. To further investigate this hypothesis, this study collected 29 three-dimensional (3D) coordinate landmarks and seven linear measurements of MS morphology from 167 computed tomography (CT) scans of crania of European, East Asian, or Equatorial African ancestry. MANOVA results reveal the Asian-derived individuals are characterized by both a significantly taller MS (F = 14.15, p <  0.0001) and a significantly greater distance from the MS floor to the ostium (F = 17.22, p <  0.0001) compared to those of European and African ancestry. A canonical variate (CV) analysis conducted on 3D landmark data provides corroborative results, distinguishing Asian-derived individuals predominantly on the basis of a relatively lower MS floor. As a greater distance between the MS floor and ostium may impede mucociliary clearance, our results suggest MS anatomy may be a more prominent factor in chronic sinusitis among individuals of Asian ancestry compared to those of European and African ancestries. This provides tentative evidence of an anatomical etiology for chronic sinusitis even in the absence of anatomical variants/abnormalities (e.g., nasal polyps, concha bullosa, Haller's cells, and Agger nasi cells). Further research into the relationship between MS anatomy and sinusitis, in addition to socioeconomic inequalities of healthcare, is warranted to continue evaluating possible contributions to health disparities.

Respiratory adaptation to climate in modern humans and Upper Palaeolithic individuals from Sungir and Mladeč

As our human ancestors migrated into Eurasia, they faced a considerably harsher climate, but the extent to which human cranial morphology has adapted to this climate is still debated. In particular, it remains unclear when such facial adaptations arose in human populations. Here, we explore climate-associated features of face shape in a worldwide modern human sample using 3D geometric morphometrics and a novel application of reduced rank regression. Based on these data, we assess climate adaptations in two crucial Upper Palaeolithic human fossils, Sungir and Mladeč, associated with a boreal-to-temperate climate. We found several aspects of facial shape, especially the relative dimensions of the external nose, internal nose and maxillary sinuses, that are strongly associated with temperature and humidity, even after accounting for autocorrelation due to geographical proximity of populations. For these features, both fossils revealed adaptations to a dry environment, with Sungir being strongly associated with cold temperatures and Mladeč with warm-to-hot temperatures. These results suggest relatively quick adaptative rates of facial morphology in Upper Palaeolithic Europe.

A 3D analysis of growth trajectory and integration during early human prenatal facial growth

Significant shape changes in the human facial skeleton occur in the early prenatal period, and understanding this process is critical for studying a myriad of congenital facial anomalies. However, quantifying and visualizing human fetal facial growth has been challenging. Here, we applied quantitative geometric morphometrics (GM) to high-resolution magnetic resonance images of human embryo and fetuses, to comprehensively analyze facial growth. We utilized non-linear growth estimation and GM methods to assess integrated epigenetic growth between masticatory muscles and associated bones. Our results show that the growth trajectory of the human face in the early prenatal period follows a curved line with three flexion points. Significant antero-posterior development occurs early, resulting in a shift from a mandibular prognathic to relatively orthognathic appearance, followed by expansion in the lateral direction. Furthermore, during this time, the development of the zygoma and the mandibular ramus is closely integrated with the masseter muscle.

Revisiting global patterns of frontal sinus aplasia utilizing computed tomography

While frontal sinus aplasia (agenesis, absence) has been proposed as a potential marker in forensic positive identifications, frequency rates are likely dependent upon how presence is defined. This study investigates how two methods of defining frontal sinus presence affects aplasia frequency rates. Using CT scans of 772 adult individuals from diverse geographic regions, frontal sinus presence was assessed two ways: 1) the XR-method- coded present if the sinus extended above the supra-orbital line, and 2) the CT-method- coded present with any indication of the frontal sinus. The XR-method consistently provided higher aplasia frequencies, averaging an 18.31% discrepancy with the CT-method. Method discrepancies were higher in females (averaged-sides: 24.6%) than males (averaged-sides: 13.82%). Oceanian individuals displayed the highest aplasia rates using either method, and the highest discrepancy between methods (averaged-sides: 31.30%); Europeans, displaying the lowest aplasia rates in either method, also displayed the lowest method discrepancy (average-sides: 7.37%). Fisher's Exact tests on the biologically-defined CT aplasia rates indicate females are significantly different from males for unilateral aplasia (p=0.0035); Arctic populations are significantly different from most groups (all p<0.005), exception being Oceanian. Results suggest the lower, biologically-defined CT aplasia rates are more useful in corroborating identifications than the inflated XR frequencies and illustrate the importance of citing aplasia rates from similarly-composed samples. However, due to practicality and resource availability, the XR-method may be more appropriate. Most importantly, reported aplasia rates from one method should be cited in casework utilizing the other method.

Assessing zygomatic shape and size for estimating sex and ancestry in a South African sample

Unidentified, decomposed and skeletonised human remains are frequently found in South Africa, therefore, standardised, reliable and relevant sex and ancestry estimation methods are required for forensic identification. This study assessed sex and ancestral variation in zygomatic size and shape in a South African population using geometric morphometric analyses. The zygoma of 158 South African individuals were sampled. Eight zygomatic landmarks were captured in 3-dimensions using a Microscribe G2 digitiser and assessed using procrustean geometric morphometrics. Shape and size differences were analysed using multivariate linear regression, discriminant function and canonical variate analyses. Males had significantly larger zygomas than females. Significant shape variation was found between ancestral groups. Bantu-speaking and Mixed ancestry individuals had narrower, shorter and more anteriorly projecting orbital margins, whilst Europeans had vertically elongated and receded orbital margins. European ancestral groups were most discernible from Bantu-speakers and Mixed ancestral groups. Ancestry estimation accuracies improved when ancestry was aggregated with sex. Pairwise ancestry-linked comparisons in females were as follows; Bantu-speakers (76%) from Europeans (72%), Bantu-speakers (71%) from Mixed ancestry (59%) and European (72%) from Mixed ancestry (63%). Similarly, ancestry-linked comparisons in males were as follows; Bantu-speakers (77%) from Europeans (81%), Bantu-speakers (53%) from Mixed ancestry (59%) and European (72%) from Mixed ancestry (82%). Size differences are putatively linked to variations in hormone-regulated growth and muscular robusticity between males and females. Shape variations between ancestral groups are likely attributable to the heterogenous genetic and ancestral origins of the South African population. It is challenging to distinguish between South Africa Bantu speakers and Mixed ancestry people due to Mixed ancestry individuals having variable genetic contributions from Khoesan, Bantu-speakers, Europeans and Asians. Bantu-speaking and Mixed ancestry people had zygomatic morphologies consistent with historical thermoregulatory adaptations to sub-Saharan climates, reported in African-descendants. Zygomatic morphology in European descendants suggests ancestral origins from colder climatic regions. This study demonstrated the utility of the zygoma in distinguishing between ancestral groups in South Africa, but further research is required to develop population-specific standards to distinguish between South African populations with shared African ancestry. The zygoma shows a promising ability to estimate sex and ancestry in South Africans, suggesting population specific standards for this bone may be of forensic interest.

Climatic adaptation in human inferior nasal turbinate morphology: Evidence from Arctic and equatorial populations

OBJECTIVES

The nasal turbinates directly influence the overall size, shape, and surface area of the nasal passages, and thus contribute to intranasal heat and moisture exchange. However, unlike the encapsulating walls of the nasal cavity, ecogeographic variation in nasal turbinate morphology among humans has not yet been established. Here we investigate variation in inferior nasal turbinate morphology in two populations from climatically extreme environments.

MATERIALS AND METHODS

Twenty-three linear measurements of the inferior turbinate, nasal cavity walls, and airway passages were collected from CT scans of indigenous modern human crania from Equatorial Africa (n = 35) and the Arctic Circle (n = 35). MANOVA and ANCOVA were employed to test for predicted regional and sex differences in morphology between the samples.

RESULTS

Significant morphological differences were identified between the two regional samples, with no evidence of significant sexual dimorphism or region-sex interaction effect. Individuals from the Arctic Circle possessed superoinferiorly and mediolaterally larger inferior turbinates compared to Equatorial Africans. In conjunction with the surrounding nasal cavity walls, these differences in turbinate morphology produced airway dimensions that were both consistent with functional expectations and more regionally distinct than either skeletal component independently.

CONCLUSION

This study documents the existence of ecogeographic variation in human nasal turbinate morphology reflecting climate-mediated evolutionary demands on intranasal heat and moisture exchange. Humans adapted to cold-dry environments exhibit turbinate morphologies that enhance contact between respired air and nasal mucosa to facilitate respiratory air conditioning. Conversely, humans adapted to hot-humid environments exhibit turbinate morphologies that minimize air-to-mucosa contact, likely to minimize airflow resistance and/or facilitate expiratory heat-shedding.

Nasal cavity and maxillary sinuses form variation among modern humans of Asian descent

OBJECTIVES

This study explores variation, covariation, and ecogeographic pattern of the nasal cavity, maxillary sinuses, and external midfacial skeleton across 15 populations of east Asian origin inhabiting the Far East, Siberia, Alaska and Greenland.

MATERIALS AND METHODS

We have collected linear measurements of the internal nasal cavity, maxillary sinus and external midfacial skeleton as well as volumes and surface areas of three-dimensional models of the cavity. A set of seven climatic variables, mtDNA and Y-chromosome genetic matrices and a matrix of geographic distances were also utilized.

RESULTS

A strong association between form of the nasal cavity and climate was found, whereby all north Asian groups display increased volumes, areas and lengths of the cavity, and surface area to volume ratios (SA/V). Most of Siberian groups exhibit not only large and long, but also wide and tall nasal cavity. The Eskimo-Aleutian speaking groups possess cavities that are vertically short and narrow but of a high SA/V ratio. The sinuses exhibit an exceptionally high level of within- and between-group variation which supports the views on the sinus as an architectural byproduct. Both volume and area of the nasal cavity can be reliably estimated based on a set of simple and repeatable linear measurements.

DISCUSSION

While the nasal cavity and maxillary sinus are both larger in a larger facial skeleton, there is a strong inverse relationship between them at a given facial size. Our results do not support the notion that the shape of the internal nasal cavity is more strongly associated with climate compared to the external midfacial morphology.

Big Choanae, Larger Face: Scaling Patterns Between Cranial Airways in Modern Humans and African Apes and Their Significance in Middle and Late Pleistocene Hominin Facial Evolution

This study aimed to understand the ontogenetic and allometric relationships in scaling between the anterior and posterior openings of the cranial airways and facial size, in order to shed light on the mechanisms that might underlie the evolution of a large face and large airways in Middle Pleistocene hominins and Neandertals. Sizes were calculated from 3D landmarks measured on the facial skeleton and airway structures of 403 skulls from two ontogenetic series of H. sapiens and P. troglodytes, an adult sample of gorillas and 11 Middle Pleistocene hominins and Neandertals. RMA regression models were used to compare the patterns in scaling between the anterior and posterior airways in relation to overall facial size. Our results show that the size of the anterior airways correlates more positively with facial size than the size of the posterior airways. This ontogenetic mechanism could explain the large faces and noses in the Neandertal lineage despite the adverse effects of such a phenotype for respiratory air-conditioning in cold climates. A large facial size could be a developmentally constrained consequence of generating airways large enough to provide the necessary oxygen for high energy demand in this large-brained and heavy-bodied hominin lineage.

Anatomical Variation in Maxillary Sinus Ostium Positioning: Implications for Nasal-Sinus Disease

Among humans, superiorly located maxillary sinus ostia (MSO) result in drainage complications and maxillary sinus (MS) disease. While previous studies investigate maxillary sinusitis frequency or MSO-position relative to specific nasal landmarks, few explore MSO-position to overall MS dimensions. This study investigates whether MSO-position relates to MS size/shape and if sex-based differences exist. Twenty-nine landmarks, placed on magnetic resonance images (MRIs) of 109 individuals (males = 57; females = 52), captured maximum dimensions of the cranium, MS, nasal cavity, and MSO-position relative to the MS floor (MSO_MSF) and nasal floor (MSO_NCF). Landmark coordinates were used to calculate centroid sizes and 13 linear distances; distances were size standardized by cranial centroid-size. Principal components analysis (PCA) on 3D-coordinates indicates that variation in MSO-position relates to superior-inferior MS positioning within the face (PC1 22% variance) and MS height (PC2 12% variance). Regression analyses indicate that MS size (r² = 0.502; P < 0.001) and height (r² = 0.589; P < 0.0001) strongly contribute to MSO_MSF: larger, taller MSs exhibit greater MSO_MSFs. Sex-based differences were not evident in PC shape-analyses nor among size-standardized dimensions. However, Mann-Whitney U-tests indicate females have absolutely smaller MSs (P = 0.001) and MSO_MSF distances (P = 0.001). Further, regressions indicate females exhibit lower MSO_MSFs for a similar MS height. Overall, MSOs superiorly placed relative to the MS floor correlate with larger, taller MSs and/or sinuses positioned inferiorly within the face. While craniofacial surgeons/clinicians should be aware of potential sex-based differences in MS size and MSO position, this study does not suggest that higher incidences of female-reported sinusitis relate to sex-based differences in MS anatomy. Anat Rec, 302:917-930, 2019. © 2018 Wiley Periodicals, Inc.

Frontal sinus ontogeny and covariation with bone structures in a modern human population

In humans, the frontal sinus (FS) is located in the medial part of the supraorbital region, sometimes expanded throughout the frontal squama. It exhibits high morphological variability, but its general form appears to be constrained by surrounding structures. The goal of this study is to analyze FS growth and test for covariation between FS volume and the glabellar region, upper nasal region, bone thickness and endocranial size in a human sample from Argentina. The sample comprises 149 reconstructions derived from computed tomography images of individuals aged 0-31 years. Volume of the FS and measurements of the surrounding structures were recorded. The FS growth trajectory was assessed by parametric and nonparametric methods, and covariation was determined using correlations and partial correlations. The FS volume could be measured at an age of about 6 years and older; adults had no aplasia but hyperplasia was found in some cases. Since the most conspicuous characteristic found was variation among individuals, the nonparametric smoothing spline produced very poor fitting. The modified logistic function was the only parametric method providing significant parameters. Sexes differed in the age at which FS growth began and ended, with FS developing earlier but at a slower rate in females than in males. The FS volume did not correlate with either upper nasal width or endocranial volume, but it correlated with bone thickness measurements (mainly from the glabellar region), even when age was held constant. Expansion of the FS at the frontal poles also correlated with frontal bone thickness. Despite the difficulty in modeling and predicting the trajectory and morphology of FS, our results suggest that it is affected by its surrounding bony environment.

Nasal variation in relation to high-altitude adaptations among Tibetans and Andeans

OBJECTIVES

High-altitude (>2500 m) populations face several pressures, including hypoxia and cold-dry air, resulting in greater respiratory demand to obtain more oxygen and condition inspired air. While cardiovascular and pulmonary adaptations to high-altitude hypoxia have been extensively studied, adaptations of upper-respiratory structures, e.g., nasal cavity, remain untested. This study investigates whether nasal morphology presents adaptations to hypoxic (larger noses) and/or cold-dry (tall/narrow noses) conditions among high-altitude samples.

METHODS

CT scans of two high- and four low-altitude samples from diverse climates were collected (n = 130): high-altitude Tibetans and Peruvians; low-altitude Peruvians, Southern Chinese (temperate), Mongolian-Buriats (cold-dry), and Southeast Asians (hot-wet). Facial and nasal distances were calculated from 3D landmarks placed on digitally-modeled crania. Temperature, precipitation, and barometric pressure data were also obtained.

RESULTS

Principal components analysis and analyses of variance primarily indicate size-related differences among the cold-dry (Mongolian-Buriats) and hot-wet (Southeast Asians) adapted groups. Two-block partial least squares (PLS) analysis show weak relationships between size-standardized nasal dimensions and environmental variables. However, among PLS1 (85.90% of covariance), Tibetans display relatively larger nasal cavities related to lower temperatures and barometric pressure; regression analyses also indicate high-altitude Tibetans possess relatively larger internal nasal breadths and heights for their facial size.

CONCLUSIONS

Overall, nasal differences relate to climate among the cold-dry and hot-wet groups. Specific nasal adaptations were not identified among either Peruvian group, perhaps due to their relatively recent migration history and population structure. However, high-altitude Tibetans seem to exhibit a compromise in nasal morphology, serving in increased oxygen uptake, and air-conditioning processes.

Moderate climate signature in cranial anatomy of late holocene human populations from Southern South America

OBJECTIVE

The aim of this study is to analyze the association between cranial variation and climate in order to discuss their role during the diversification of southern South American populations. Therefore, the specific objectives are: (1) to explore the spatial pattern of cranial variation with regard to the climatic diversity of the region, and (2) to evaluate the differential impact that the climatic factors may have had on the shape and size of the diverse cranial structures studied.

MATERIALS AND METHODS

The variation in shape and size of 361 crania was studied, registering 62 3D landmarks that capture shape and size variation in the face, cranial vault, and base. Mean, minimum, and maximum annual temperature, as well as mean annual precipitation, but also diet and altitude, were matched for each population sample. A PCA, as well as spatial statistical techniques, including kriging, regression, and multimodel inference were employed.

RESULTS

The facial skeleton size presents a latitudinal pattern which is partially associated with temperature diversity. Both diet and altitude are the variables that mainly explain the skull shape variation, although mean annual temperature also plays a role. The association between climate factors and cranial variation is low to moderate, mean annual temperature explains almost 40% of the entire skull, facial skeleton and cranial vault shape variation, while annual precipitation and minimum annual temperature only contribute to the morphological variation when considered together with maximum annual temperature. The cranial base is the structure less associated with climate diversity.

CONCLUSION

These results suggest that climate factors may have had a partial impact on the facial and vault shape, and therefore contributed moderately to the diversification of southern South American populations, while diet and altitude might have had a stronger impact. Therefore, cranial variation at the southern cone has been shaped both by random and nonrandom factors. Particularly, the influence of climate on skull shape has probably been the result of directional selection. This study supports that, although cranial vault is the cranial structure more associated to mean annual temperature, the impact of climate signature on morphology decreases when populations from extreme cold environments are excluded from the analysis. Additionally, it shows that the extent of the geographical scales analyzed, as well as differential sampling may lead to different results regarding the role of ecological factors and evolutionary processes on cranial morphology.

Evolution of the Jugal/Zygomatic Bones

This issue of the Anatomical Record is the second of a two-volume set on the zygoma (also called the cheek bone, the zygomatic bone, the malar, or the jugal, the latter term being used in vertebrates other than mammals). The zygoma is an important component of the craniofacial skeleton, in which the zygoma is a connection between the midfacial and the cranial skeletons; has a functional role as the origin of one of the masticatory muscles, the masseter muscle, and several facial muscles; has been considered as an essential buttress of the facial skeleton for resisting masticatory forces; and has importance for determining phylogenetic relationships. In humans, the zygoma is also of aesthetic significance for facial appearance, and its restoration following trauma has resulted in a large clinical literature. In this second half of the special issue on the zygoma, a series of papers discuss studies related to evolution of the zygoma and related parts of the craniofacial skeleton throughout the vertebrates, and in particular in human evolution. There are also a series of articles discussing variation of the zygoma in modern humans. This article is an overview in which we discuss the primary findings of these studies and some of their implications. Anat Rec, 300:12-15, 2017. © 2016 Wiley Periodicals, Inc.