Exploring morphological shape variation in modern human tali

Recent contributions have employed digital methods to investigate shape variation in hominoid tali. However, little of this work has assessed talar morphology within modern humans. Here we apply (semi)landmark based method to assess talar morphological differences between groups of modern human living in different terrain. A template of 251 (semi) landmarks was digitized on 3D digital models of 88 modern human tali: 26 hunter-gatherers, 15 mountain dwellers and 47 farmers occupying relative flat terrain. Models were Procrustes superimposed and Principal Component (PC) analysis was used to explore observed morphological variation. We also computed degree of morphological integration between trochlear, subtalar joint and talar head articular surfaces using two-block partial least squares (PLS). The first three PCs describe 33.3% of morphological variation in the sample. Even though most specimens overlap in the PCA plot, clustering of hunter-gatherers and the other groups tend to separate on PC1 (18.8%). Negative scores (hunter- gatherers) reflect mediolaterally wider and dorsoplantarly compressed corpora, as well as enlarged necks and talar heads Positive scores reflect more cuboidal corpora, less posteriorly extended flexor hallucis longus grooves, reduced anterior extension of trochleae, and smaller talar heads. No significant differences were foundthrough PLS analysis, suggesting that different talar regions are not tightly integrated. Overall, the talus seems promising for informing our understanding of terrain use among modern humans. These results could have importantmimplications for the interpretation of fossil specimens and the likely landscapes they occupied. Future studies could increase the sample size to test the effects of subsistence economy.