Abstract
The hypothesis that variation in craniofacial shape within and among species is influenced by spatial packing has a long history in comparative anatomy, particularly in terms of primates. This study develops and tests three alternative models of spatial packing to address how and to what extent the cranial base angle is influenced by variation in brain and facial size. The models are tested using mouse strains with different mutations affecting craniofacial growth. Although mice have distinctive crania with small brains, long faces, and retroflexed cranial bases, the results of the study indicate that the mouse cranial base flexes to accommodate larger brain size relative to cranial base length. In addition, the mouse cranial base also extends, but to a lesser degree, to accommodate larger face size relative to cranial base length. In addition, interactions between brain size, face size, and the widths and lengths of the components of the cranial base account for a large percentage of variation in cranial base angle. The results illustrate the degree to which the cranial base is centrally embedded within the covariation structure of the craniofacial complex as a whole.
Highlights
IntroductionAnatomists have traditionally divided the skull into three primary units: the face, neurocranium and basicranium (each comprising further sub-modules)
The skull is both a highly modular and a highly integrated structure
We focused on three strains with mutations that have known developmental effects on cranial growth and which lead to predictable changes in cranial base angle based on the spatial packing models described above
Summary
Anatomists have traditionally divided the skull into three primary units: the face, neurocranium and basicranium (each comprising further sub-modules). These units are known to be partially independent because of their distinct embryonic origins, different processes of development, and disparate functional roles (de Beer, 1937; Cheverud, 1982, 1996; Lieberman et al 2000a). Despite their independence, these three major regions interact considerably during development via many processes to generate a highly integrated whole. How developmental changes to these cranial modules and how their processes of integration lead to predictable variations in overall skull form, both within and among species, are questions of considerable and longstanding interest.
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