82 - Patterns of Cranial Integration Across Postnatal Ontogeny

Poster Board Number: 82
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Abstract Body : Primary growth progresses as a product of integrated cellular and mechanical processes – including genetic, developmental, and functional – that arise through nonlinear pathways. Suites of traits influence the growth of one another by constraining the rate and direction of morphological change or facilitating change within morphospace. How cranial traits covary across ontogeny is essential to model underlying developmental processes and identify sources of abnormal morphology. Our research explores whether integration patterns within and between the viscerocranium and basicranium change across periods of primary growth. In prior studies, overall integration patterns within the face are consistent; however, magnitudes of integration vary throughout ontogeny. Based on previous research, we hypothesize that both patterns and magnitudes of integration within the human skull change throughout primary growth, with increasing integration among cranial regions among older age groups.

We placed landmarks on segmented CT scans of 36 deceased juveniles from the Subadult Virtual Anthropology Database curated by the University of Nevada, Reno, and calculated thirty-two inter-landmark distances (ILDs) on the cranium and mandible. Data were scaled for size by dividing each ILD by the individual's height. The data were divided into three age groups for comparison – 'young child' (1-2 years), 'child' (6-7 years), and 'adolescent' (11-12 years) and variance-covariance matrices were calculated for each age group. We used the covariance matrix and heatmap to group ILDs for integration analysis. Integration statistics were calculated using two-block partial least squares between five nonoverlapping regions of the skull: the face, basicranium, sphenoid/mid-face, lateral cranial vault, and mandible.

Patterns of integration are not consistent across age groups. Within the young child age group, all craniofacial regions, with the exception of the face and basicranium, are significantly integrated. Among children, the face and basicranium, the mandible and lateral cranial vault, and the mandible and sphenoid/mid-face are statistically independent. Most cranial regions are significantly integrated within the adolescent age group, with the exception of the mandible and lateral cranial vault.

Although we used a small sample size, the results demonstrate that patterns of craniofacial integration change across ontogeny. Regions of the skull become more independent between early childhood and the age of 6, with higher integration returning as individuals age into adolescence. Adolescents exhibit a pattern of integration more like those reported for adult humans, which indicates that the adult pattern is established during later ontogeny. We hypothesize that the greater independence among regions of the cranium during childhood (6-7 years) reflects variation in relative growth among cranial regions during this ontogenetic period and that perhaps individuals are more constrained in early development, indicating an hourglass model for postnatal development. Further research to expand the sample size to include individuals ranging in age from 0 to 20 years is currently underway and aims to precisely explore the timing of changes in integration patterns and magnitude.