Quantification of the position and depth of the flexor hallucis longus groove in euarchontans, with implications for the evolution of primate positional behavior.

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2017-06

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Abstract

On the talus, the position and depth of the groove for the flexor hallucis longus tendon have been used to infer phylogenetic affinities and positional behaviors of fossil primates. This study quantifies aspects of the flexor hallucis longus groove (FHLG) to test if: (1) a lateral FHLG is a derived strepsirrhine feature, (2) a lateral FHLG reflects inverted and abducted foot postures, and (3) a deeper FHLG indicates a larger muscle.We used linear measurements of microCT-generated models from a sample of euarchontans (n = 378 specimens, 125 species) to quantify FHLG position and depth. Data are analyzed with ANOVA, Ordinary and Phylogenetic Generalized Least Squares, and Bayesian Ancestral State Reconstruction (ASR).Extant strepsirrhines, adapiforms, plesiadapiforms, dermopterans, and Ptilocercus exhibit lateral FHLGs. Extant anthropoids, subfossil lemurs, and Tupaia have medial FHLGs. FHLGs of omomyiforms and basal fossil anthropoids are intermediate between those of strepsirrhines and extant anthropoids. FHLG position has few correlations with pedal inversion features. Relative FHLG depth is not significantly correlated with body mass. ASRs support a directional model for FHLG position and a random walk model for FHLG depth.The prevalence of lateral FHLGs in many non-euprimates suggests a lateral FHLG is not a derived strepsirrhine feature. The lack of correlations with pedal inversion features suggests a lateral FHLG is not a sufficient indicator of strepsirrhine-like foot postures. Instead, a lateral FHLG may reduce the risk of tendon displacement in abducted foot postures on large diameter supports. A deep FHLG does not indicate a larger muscle, but likely reduces bowstringing during plantarflexion.

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10.1002/ajpa.23213

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Yapuncich, Gabriel S, Erik R Seiffert and Doug M Boyer (2017). Quantification of the position and depth of the flexor hallucis longus groove in euarchontans, with implications for the evolution of primate positional behavior. American journal of physical anthropology, 163(2). pp. 367–406. 10.1002/ajpa.23213 Retrieved from https://hdl.handle.net/10161/18077.

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Scholars@Duke

Yapuncich

Gabriel Yapuncich

Assistant Professor of the Practice of Medical Education

I hail from the great mountain states of Montana (the state of my birth) and Wyoming (the state of my childhood). I have a bachelor's degree in English literature from the University of Wisconsin and a bachelor's degree in the evolutionary biology from Columbia University. I completed my PhD in evolutionary anthropology at Duke University in March 2017, working with Dr. Doug M. Boyer. I have taught gross and microanatomy to Duke University School of Medicine students since 2018. In 2021, I joined the DUSOM MD program as an Assistant Professor of the Practice of Medical Education and Director of Accreditation and Continuous Quality Improvement.

Boyer

Douglas Martin Boyer

Associate Professor of Evolutionary Anthropology

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