Protocol for positioning metatarsal renderings and extraction of cross sections.

<p><b>A</b> Human (dorsal view) and <b>A’</b> Chimpanzee (lateral view): Landmarks positioned in centers of proximal (visible) and distal (not visible) articular surfaces were used to define the longitudinal axis of a diaphysis, which subsequently was aligned to the Z-axis in 3D space. Length refers to the distance between proximal and distal landmarks. Only the diaphyseal region between 25% and 65% length was investigated in the present analysis. Renderings (<b>A</b> and <b>A’</b>) illustrate broadly functionally equivalent positions of human and chimpanzee metatarsals during terrestrial locomotion, and thus the difference between functional and anatomical correspondence of cortices of the diaphysis. Specifically, and as explained in the method section (“Data Collection Protocol” subsection), the anatomical ML axis of chimpanzee (and gorilla) hallucal metatarsals is rotated internally 90 degrees, such that it becomes a ‘functional’ equivalent to the dorsoplantar axis of the human hallucal metatarsal. <b>B</b> Human and <b>B’</b> Chimpanzee (proximal views): After aligning the longitudinal axis of a rendering to the Z-axis in 3D space, and while viewing the proximal articular surface, each rendering was rotated about its longitudinal axis until the sides of the grooved proximal articular surface paralleled the Y-axis in 3D space. <b>C</b> Human and <b>C’</b> Chimpanzee: Cross section from 50% length of the rendering illustrated in <b>A</b> and 50% length of the rendering illustrated in <b>A’</b>. Note that in humans (<b>C</b>) 0 degrees corresponds to medial position on the diaphysis, 90 degrees to dorsal position, 180 degrees to lateral position, and 270 degrees to plantar position. In chimpanzees (and gorillas) (<b>C’</b>) 0 degrees corresponds to dorsal position on the diaphysis, 90 degrees to lateral position, 180 degrees to plantar position, and 270 degrees to medial position. Thus, functional comparisons between human and chimpanzee/gorilla hallucal metatarsal diaphyses compare the medial cortex in the former with the dorsal cortex in the latter, etc. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117905#sec002" target="_blank">method</a> section (“Data Collection Protocol” subsection) for additional explanation.