Morphological consequences of artificial cranial deformation: Modularity and integration

Abstract

The cranium is an anatomically complex structure. One source of its complexity is due to its modular organization. Cranial modules are distinct and partially independent units that interact substantially during ontogeny thus generating morphological integration. Artificial Cranial Deformation (ACD) occurs when the human skull is intentionally deformed, through the use of different deforming devices applied to the head while it is developing. Hence, ACD provides an interesting example to assess the degree to which biomechanical perturbations of the developing neurocranium impact on the degree of morphological integration in the skull as a whole. The main objective of this study was to assess how ACD affects the morphological integration of the skull. This was accomplished by comparing a sample of non-deformed crania and two sets of deformed crania (i.e. antero-posterior and oblique). Both developmental and static modularity and integration were assessed through Generalized Procrustes Analysis by considering the symmetric and asymmetric components of variation in adults, using 3D landmark coordinates as raw data. The presence of two developmental modules (i.e. viscero and neurocranium) in the skull was tested. Then, in order to understand how ACD affects morphological integration, the covariation pattern between the neuro and viscerocranium was examined in antero-posterior, oblique and non-deformed cranial categories using Partial Least-Squares. The main objective of this study was to assess how ACD affects the morphological integration of the skull. This was accomplished by comparing a sample of deformed (i.e. antero-posterior and oblique) and non-deformed crania. Hence, differences in integration patterns were compared between groups. The obtained results support the modular organization of the human skull in the two analyzed modules. The integration analyses show that the oblique ACD style differentially affects the static morphological integration of the skull by increasing the covariance between neuro and viscerocranium in a more constrained way than in antero-posterior and non-deformed skulls. In addition, the antero-posterior ACD style seems to affect the developmental integration of the skull by directing the covariation pattern in a more defined manner as compared to the other cranial categories.

Early mandibular morphological differences in patients with FGFR2 and FGFR3-related syndromic craniosynostoses: A 3D comparative study

“…Of note, the mandibular shape and particularly intercondylar width, depend on the distance between the condylar fossa on the skull base, as shown in Crouzon and Apert syndromes [27]. Similar results have been found in artificially deformed skulls, where external mechanical constraints had been intentionally exerted on the skull vault with different deforming devices as observed worldwide [66][67][68][69]: secondary skull base modifications induced a shift in the position of the glenoid fossa, thus influencing mandibular shape [67,69]. In syndromic craniosynostoses, intrinsic skull base deformations could thus act as potential secondary influencing factors on mandibular shape.…”

Assessing thoraco‐pelvic covariation in Homo sapiens and Pan troglodytes: A 3D geometric morphometric approach

“…The vast majority of the research on patterns of integration and covariation in hominoids are focused on the skull (e.g., Ackermann, 2002; Bastir, 2008; Bastir et al, 2005; Bookstein et al, 2003; Bruner, Pereira‐Pedro, & Bastir, 2017; Mitteroecker & Bookstein, 2008; Neaux et al, 2018; Profico et al, 2017; Püschel, Friess, & Manríquez, 2020; Scott et al, 2018; Singh, Harvati, Hublin, & Klingenberg, 2012; Stelzer, Gunz, Neubauer, & Spoor, 2018), but studies investigating integration and covariation within and between elements of the torso are scarce (Arlegi et al, 2020; Grabowski et al, 2011; Huseynov et al, 2017; Lewton, 2012; Middleton, 2015; Torres‐Tamayo et al, 2018; C. V. Ward et al, 2015). Among those, Middleton (2015) quantified and compared for the first time trunk relationships between H. sapiens and Pan collecting linear metrics and 3D coordinates on disarticulated trunk skeletal elements.…”

The Skull’s Girder: A Brief Review of the Cranial Base

“…Ultimately, this procedure would improve masticatory function and possibly improve airway dimensions. Thirdly, studies that have investigated crania that are artificially deformed by applying compressive forces—a cultural practice common among certain ethnic groups across the globe—provided insights into the modularity and integration between anatomical units, particularly the neurocranium and viscerocranium [ 32 ]. In the artificially deformed skull, the cranial base showed a discernable abnormality, and this produced a restricted antero-posterior growth of the naso-maxillary complex [ 33 ].…”