Gorillas occupy a variety of habitats from the west coast to eastern central Africa. These habitats differ considerably in altitude, which has a pronounced effect on forest ecology. Although all gorillas are obligate terrestrial knuckle-walking quadrupeds, those that live in lowland habitats eat fruits and climb more often than do those living in highland habitats. Here we test the hypothesis that gorilla talus morphology falls along a morphocline that tracks locomotor function related to a more inverted or everted foot set. This proposed morphocline predicts that gorillas living in lowland habitats may have a talocrural joint configured to facilitate a more medially oriented foot during climbing, suggesting that they may be more adaptively committed to arboreality than gorillas living in highland habitats. To quantify the relative set of the foot in gorillas, we chose two three-dimensional measurements of the talocrural joint: mediolateral curvature of the trochlea and relative surface area of the lateral malleolus. Our results show that, in comparison to their eastern counterparts, western gorillas have talar features that reflect a more medially directed sole of the foot. This morphology likely facilitates foot placement in a wider range of positions and minimization of shearing stresses across the joint when the foot is loaded on more curved or vertically oriented substrates as occurs during climbing and other arboreal behaviors. In contrast, eastern gorilla talar morphology is consistent with habitual placement of the foot with the sole directed more inferiorly, suggesting more effective loading during plantigrade push-off on terrestrial substrates.

Results support the hypothesis that differences in MTF form between anthropoids and "prosimians" reflect greater use of inverted foot postures and grasp-leaping in the latter group. Although fossil "prosimians" do not have the extreme MTF dimensions that characterize many extant acrobatic leapers, these variables by themselves provide little additional behavioral resolution at the level of individual fossils due to strong phylogenetic signal. ASR suggests that some specialization for use of inverted foot postures (as required in a fine-branch niche) and modifications for grasp-leaping evolved independently in basal strepsirrhine and haplorhine lineages.

More than 25 new specimens of Teilhardina brandti, one of the oldest known euprimates, are reported from earliest Eocene strata of the southern Bighorn Basin, Wyoming. The new fossils include the first upper dentitions, a dentary showing the lower dental formula for the first time, and the first postcrania ascribed to T. brandti (tarsals and terminal phalanges). The elongated navicular and long talar neck suggest that T. brandti was an active arboreal quadruped, and the terminal phalanges constitute the oldest evidence for nails in Euprimates. Phylogenetic analysis incorporating the new data indicates that T. brandti is more derived than T. belgica but less so than T. americana. The hypothesis that Teilhardina originated in Asia (T. asiatica) and dispersed westward to Europe (T. belgica) and then to North America (T. brandti and T. magnoliana) during the earliest Eocene Paleocene-Eocene Thermal Maximum is most consistent with available evidence, including the relative age of fossil samples and their stage of evolution.

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