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Abstract ObjectivesModular architecture of traits in complex organisms can be important for morphological evolution at micro‐ and sometimes macroevolutionary scales as it may influence the tempo and direction of changes to groups of traits that are essential for particular functions, including food acquisition and processing. We tested several distinct hypotheses about craniofacial modularity in the hominine skull in relation to feeding biomechanics. Materials and MethodsFirst, we formulated hypothesized functional modules for craniofacial traits reflecting specific demands of feeding biomechanics (e.g., masseter leverage/gape or tooth crown mechanics) inHomo sapiens,Pan troglodytes, andGorilla gorilla. Then, the pattern and strength of modular signal was quantified by the covariance ratio coefficient and compared across groups using covariance ratio effect size. Hierarchical clustering analysis was then conducted to examine whether a priori‐defined functional modules correspond to empirically recovered clusters. ResultsThere was statistical support for most a priori‐defined functional modules in the cranium and half of the functional modules in the mandible. Modularity signal was similar in the cranium and mandible, and across the three taxa. Despite a similar strength of modularity, the empirically recovered clusters do not map perfectly onto ourpriorifunctional modules, indicating that further work is needed to refine our hypothesized functional modules. ConclusionThe results suggest that modular structure of traits in association with feeding biomechanics were mostly shared with humans and the two African apes. Thus, conserved patterns of functional modularity may have facilitated evolutionary changes to the skull during human evolution.
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Ontogenetic changes in magnitudes of integration in the macaque skull
Abstract ObjectivesMagnitudes of morphological integration may constrain or facilitate craniofacial shape variation. The aim of this study was to analyze how the magnitude of integration in the skull ofMacaca fascicularischanges throughout ontogeny in relation to developmental and/or functional modules. Materials and methodsGeometric morphometric methods were used to analyze the magnitude of integration in the macaque cranium and mandible in 80 juvenile and 40 adultM. fascicularisspecimens. Integration scores in skull modules were calculated using integration coefficient of variation (ICV) of eigenvalues based on a resampling procedure. Resultant ICV scores between the skull as a whole, and developmental and/or functional modules were compared using Mann–WhitneyUtests. ResultsResults showed that most skull modules were more tightly integrated than the skull as a whole, with the exception of the chondrocranium in juveniles without canines, the chondrocranium/face complex and the mandibular corpus in adults, and the mandibular ramus in all juveniles. The chondrocranium/face and face/mandibular corpus complexes were more tightly integrated in juveniles than adults, possibly reflecting the influences of early brain growth/development, and the changing functional demands of infant suckling and later masticatory loading. This is also supported by the much higher integration of the mandibular ramus in adults compared with juveniles. DiscussionMagnitudes of integration in skull modules reflect developmental/functional mechanisms inM. fascicularis. However, the relationship between “evolutionary flexibility” and developmental/functional mechanisms was not direct or simple, likely because of the complex morphology, multifunctionality, and various ossification origins of the skull.
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- Award ID(s):
- 1830745
- PAR ID:
- 10449256
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- American Journal of Physical Anthropology
- Volume:
- 174
- Issue:
- 1
- ISSN:
- 0002-9483
- Page Range / eLocation ID:
- p. 76-88
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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