Date of Graduation
8-2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Anthropology (PhD)
Degree Level
Graduate
Department
Anthropology
Advisor/Mentor
Ungar, Peter S.
Committee Member
Delezene, Lucas K.
Second Committee Member
Terhune, Claire E.
Third Committee Member
Tallman, Melissa
Keywords
Functional morphology; Geometric morphometrics; Humerus; Platyrrhine evolution; Platyrrhine primates; Talus
Abstract
Platyrrhines are a diverse radiation of primates that exhibit a range of locomotor adaptations. The relationships between extant primate locomotor behavior and variation in postcranial morphology are often used to make functional interpretations of skeletal anatomy in extinct primates. However, a comparative baseline of form-function relationships in the extant platyrrhine postcranium is lacking compared to other primates, which limits understanding of platyrrhine locomotor evolution. The humerus and talus are two of the best represented skeletal elements in the platyrrhine fossil record and are informative of locomotor behavior. Therefore, quantification of morphological variation in extant platyrrhine tali and humeri can provide a comparative context for interpreting the locomotor adaptations of fossil taxa. Three-dimensional geometric morphometrics (3DGM) analyses were used to characterize shape variation in the talus and humerus of a diverse extant platyrrhine sample within a phylogenetic context. The results of 3DGM analyses clarified allometric, phylogenetic, and functional influences on morphological variation in the platyrrhine talus and humerus. Allometric regressions showed significant associations between shape and size for the platyrrhine talus and humerus. Evolutionary relationships among platyrrhines also had a significant effect on talar and humeral shape variation. Analyses indicated talus and humerus morphology distinguished platyrrhine families and subfamilies. However, talus and humerus morphology did not usually differentiate between genera within a subfamily except for atelids. This study found that the morphology of the talus and humerus distinguish living platyrrhines based on reported differences in primary locomotor mode. These results provide further support for established associations between morphology and locomotion reported in prior studies. In comparison, the proportion of time platyrrhines spend using different locomotor behaviors were not always associated with morphological differences in the talus and humerus, particularly when phylogeny was considered. These findings suggest that functional morphology is directed by phylogeny, particularly among higher-order clades within platyrrhines. Despite significant phylogenetic and allometric signals, morphological differences in the talus and humerus of platyrrhines can be explained by functional differences associated with locomotion, particularly variation in joint range of motion. This thesis investigated the locomotor adaptations of platyrrhine paleocommunities from Patagonian Argentina, the La Venta Formation in Columbia, and fossil localities from the Greater Antilles. While the phylogenetic position of the Patagonian primates were not assessed, their morphometric affinities and functional morphology suggest a wider range of locomotor adaptations than previously hypothesized, which might indicate they are part of the extant platyrrhine radiation in support of the ‘long lineage hypothesis’. Platyrrhines from the La Venta paleocommunity had morphological similarity to extant platyrrhines in all cases. However, their locomotor adaptations largely indicated more generalized quadrupedal behaviors, and were in many instances morphologically similar to the Patagonian taxa. The morphometric affinities and morphological features of the humerus and talus of Antillothrix berensis led to different locomotor reconstructions, which highlights that a forelimb and hindlimb skeletal element used together can lead to a more nuanced interpretation of locomotor repertoire. Overall, this study contributes to understanding platyrrhine morphological evolution and has broader implications for several research foci within biological anthropology.
Citation
Zachary, L. M. (2023). Functional Morphology of the Platyrrhine Humerus and Talus: Implications for Inferring Locomotor Behavior in Extinct Primates. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/4853
