DOI: 10.5061/dryad.69p8cz913
title: Data from: A model of developmental canalization, applied to human cranial form

description: Developmental mechanisms that canalize or compensate perturbations of
 organismal development (targeted or compensatory growth) are widely
 considered a prerequisite of individual health and the evolution of
 complex life, but little is known about the nature of these mechanisms. It
 is even unclear if and how a "target trajectory" of
 individual development is encoded in the organism's
 genetic-developmental system or, instead, emerges as an epiphenomenon.
 Here we develop a statistical model of developmental canalization based on
 an extended autoregressive model. We show that under certain assumptions
 the strength of canalization and the amount of canalized variance in a
 population can be estimated, or at least approximated, from longitudinal
 phenotypic measurements, even if the target trajectories are unobserved.
 We extend this model to multivariate measures and discuss reifications of
 the ensuing parameter matrix. We apply these approaches to longitudinal
 geometric morphometric data on human postnatal craniofacial size and shape
 as well as to the size of the frontal sinuses. Craniofacial size showed
 strong developmental canalization during the first 5 years of life,
 leading to a 50% reduction of cross-sectional size variance, followed by a
 continual increase in variance during puberty. Frontal sinus size, by
 contrast, did not show any signs of canalization. Total variance of
 craniofacial shape decreased slightly until about 5 years of age and
 increased thereafter. However, different features of craniofacial shape
 showed very different developmental dynamics. Whereas the relative
 dimensions of the nasopharynx showed strong canalization and a reduction
 of variance throughout postnatal development, facial orientation
 continually increased in variance. Some of the signals of canalization may
 owe to independent variation in developmental timing of cranial
 components, but our results indicate evolved, partly mechanically induced
 mechanisms of canalization that ensure properly sized upper airways and
 facial dimensions.
description: We studied developmental canalization in human cranial size and
 shape using a longitudinal sample of 26 untreated individuals (13 girls,
 13 boys) from the Denver Growth Study, a longitudinal X-ray study carried
 out in the US between 1931 and 1966. On a total of 500 lateral
 radiographs, covering the age range from birth to early adulthood, 18
 landmarks were digitized by Ekaterina Stansfield (see Figure 2 of the
 paper). Six semilandmarks were located on the external outline of the
 frontal bone, which were allowed to slide along the bone outline so as to
 minimize the bending energy of the data set around its Procrustes average.
 Additionally, the area of the lateral projection of the frontal sinuses
 was measured on every radiograph. Further information on the Denver Growth
 Study and the original X-rays are available at
 https://www.aaoflegacycollection.org/aaof_collection.html?id=UOKDenver. 
description: individuals.txt: Contains the sex and the number of measured
 radiographs for each individual (a total of 500).
 age.txt: Contains the individual's age for all 500 measured
 radiographs. sinus.txt: Contains the area of the
 projection of the frontal sinuses for all 500 radiographs.
 landmarks.txt: A 500 x 36 array containing the x and y
 coordinates of all 18 landmarks for all 500 measured radiographs. The
 coordinates are in units of pixel size, which is 0.15625mm.