Skeletal Phenotypic Variation in Gorilla: Ecological, Phylogenetic, and Ontogenetic Perspectives
Open AccessWhen paleontological data are limited, we can use extant species to model how different evolutionary processes may have contributed to the variation we observe in the fossil record. Gorillas exhibit close relationships among habitat elevation, diet, and locomotion that make them a unique taxon for examining how the skeleton adapts to the behavioral demands of an individual’s immediate environment. Chapter 2 examined the relationships between elevation, phylogeny, and the morphology of the gorilla pelvis. There were differences in the morphology of the ilium between gorilla species and, to a lesser degree, between eastern gorilla subspecies. When pelvic shape was regressed against elevation, statistically significant relationships only emerged in specific sex categories and under specific phylogenetic assumptions. It was concluded that there is not a unified relationship between elevation and pelvic morphology that can be generalized across all gorillas.In the same spirit, Chapter 3 examined relationships between elevation, phylogeny, and the morphology of the gorilla cranium. Surprisingly, subspecific differences in expressions of sexual dimorphism had the largest role in structuring the total variation observed across the genus. There were significant relationships between elevation and the morphology of the palate and cranial base, suggestive of dietary and locomotor adaptation, respectively. However, these relationships were no longer significant after applying a strict phylogenetic adjustment. Ultimately, these mixed results were not sufficient to determine with confidence whether or not this morphological variation reflects adaptation to local habitats.Chapter 4 turned to ontogeny as an additional line of evidence for ecological adaptation in the gorilla face. The subspecies differences described in Chapter 3 were already present in the youngest specimens in the sample. Ontogenetic allometric scaling relationships were statistically indistinguishable, and there were no deviations in the trajectory of shape change associated with dental emergence or inferred weaning status in any subspecies. It was hypothesized that subspecies differences in the morphology of the palate present well before weaning may reflect the spatial requirements of the developing adult dentition, though more evidence is needed.Together, these studies presented in this dissertation highlight the sensitivity of models relating morphology and ecology to decisions about the statistical treatments of sex and phylogenetic information. Other lines of evidence, like ontogenetic analyses, can provide valuable context with which to interpret adult variation. While fossil data will always be limited, comparative studies of living species that integrate multiple kinds of data--phenotypic, phylogenetic, developmental--can offer insight into the evolutionary processes that may have shaped the evolution of our own lineage.
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