| dc.description.abstract | Establishing form-function relationships between anatomy and locomotor behaviours in
extant taxa provides critical context for interpretations of extinct species. This study used 3D
geometric morphometric methods to explore talus and medial cuneiform shape variation among
taxa in Pan and to determine whether and to what extent any shape variation may be related to
differences in climbing behaviour. Current locomotor behaviour data suggest that bonobos,
western, and eastern chimpanzees do not differ from one another in total frequencies of
arboreality as much as once thought. However, these data do suggest that bonobos and eastern
chimpanzees more often use smaller diameter substrates (<10 cm) when climbing, while western
chimpanzees tend to climb larger diameter (>15 cm) tree trunks and boughs. The morphology of
the talus and medial cuneiform in Pan was predicted to reflect differences in locomotor
behaviour, showing a greater emphasis on hallucial grasping in bonobos and eastern
chimpanzees, and on an inverted foot set in western chimpanzees. This difference in emphasis
was expected to be more pronounced between bonobos and western chimpanzees, both of which
appear to climb more frequently than do eastern chimpanzees. The results of this study suggest
that the shapes of the bonobo talus and medial cuneiform covary as a functional unit that
emphasizes hallucial grasping in the medial cuneiform but not inversion at the talocrural joint.
The exact opposite pattern was observed in western chimpanzees, with features that emphasize
inversion at the ankle joint but not hallucial grasping. Eastern and central chimpanzee (and
possibly Nigeria-Cameroon chimpanzee) talus and medial cuneiform shapes fall in between
these two extremes. Overall, these results are reasonably consistent with the different styles of
arboreality observed in bonobos and western chimpanzees. Interestingly, the pattern of covariance observed in this study among chimpanzees and bonobos does not exist in modern
humans. If the pattern of covariance observed in Pan also characterized the Pan-Homo ancestor,
then it must have become dissociated at some point during early hominin evolution in order to
produce the combination seen in modern humans (i.e., an everted foot set combined with an
adducted hallux). | en_US |
