Assessing primate skull shape variation in relation to habitat: a 3D geometric morphometric approach

The advancement of digital imaging and open-source geometric morphometric (GM) software is positively impacting the way we understand morphological adaptation as an evolutionary response. Shape-space data and multivariate statistics quantify shape variation patterning and, therefore, consolidate hominoid systematic procedures. This thesis identifies ecomorphological patterns of variation within extant primates. Through a comparative, multivariate and geometric morphometric approach, this research provides a better understanding of the effects of the environment on craniomandibular form in early hominins. In this study, 107 cranial and 108 mandible specimens of 9 modern primate species were 3D imaged, and geometric morphometrics statistics were used to quantify and assess the patterns of variation between intra- and interspecific datasets concerning habitat type. Results were visualised through Principal Component scatter plots and Thin-plate Spline deformation warps, which identified critical morphological high-to-low-energy bending areas. This application addressed the questions: • to what extent does ecology influence craniomandibular morphology? • what are the main environmental pressures that encourage morphological variance in hominins? The main methodological aims sought to a) create accurate 3D digital renderings of primate skull specimens and b) define a reproducible geometric morphometric technique, which could be used as a valid and precise statistical procedure for future studies regarding hominin ecomorphology. This was achieved by pilot testing laser scanning hardware, digitising cranial and mandibular specimen, testing 3D scanning accuracy, and the best practice for capturing accurate 3D imagery, e.g. environment, lighting and meshing multiple scans. The pilot phase of this thesis also tested statistical programming toolkits capable of carrying out the finalised geometric morphometric methodology. This was achieved through trials of landmarking and statistical procedures on various data processing software, e.g. Checkpoint, TINA, and MeshLabs. Ultimately, the R Project software and accompanying IDE, R Studio, was used to collect, process and analyse the specimen shape data. This thesis contributes to the study of hominin ecomorphological patterning through a comparative approach investigating primate skull adaptation. The main findings showed habitat type as having statistical significance on the cranium's morphology but quantifiably more so in the mandible, which reported 63.71% of the overall variance observed in the first two Principal Components. This was an increase of 10.44% compared to the interspecific cranial dataset and was supported by Two-block Partial Least Squares and Procrustes ANOVA analysis. The geometric morphometric results showed significant environmental influence on the morphology of the primate cranium, most notably concerned with locomotive functions and visualises a distinction between primates who are more arboreally inclined versus those whose primary form of locomotion is terrestrial. The study also found that dietary specialisations are particularly distinguished by patterns of variation between highly folivorous versus more frugivorous species in both inter-and intraspecific groups.

Grantor dc:publisher

Oxford Brookes University

Year dc:date

2022

Author dc:creator

• Edwards, Sophie

Contributors dc:contributor

• Underdown, Simon

Statement dc:rights

• All rights reserved

Language dc:language

en

DOI dc:identifier

https://doi.org/10.24384/3rcs-wq24

OAI identifier oai:identifier

tle:1b34b79d-cce6-4236-b758-e84a74336a57:d6bd9758-527a-46cd-bfe2-c433766e8fca:1