Locomotion Study of Bekantan (Nasalis larvatus)

The locomotion system in the primate is developed and diverged following the pressure of the environment. To survive, each species of primate will push their locomotor’s evolution to accommodate their foraging activities. Generally, the primate locomotion system is classified into vertical clinging and leaping (such as Tarsius), quadrupedalism (such as guenon), brachiation (such as gibbon), and bipedalism (human). Classification is usually based on the intermembral index, the ratio between the arm and leg length in percentage. The intermembral index of bekantan is about 90 on average; means the arm length is 90% of leg length. Based on the intermembral index, bekantan's locomotion system is hindlimb dominated gait and supposed to be quadrupedal terrestrial. However, in their natural habitat, bekantan spend their daily activities mostly on the trees. Terrestrial and arboreal movements were observed during foraging. Arboreal movements of bekantan are dominant where the forest canopy is remaining good. On the other hand, in open areas and where they have adapted to human existence, quadrupedal terrestrial behaviors will be dominant during foraging. Further observation in various areas is still needed to strengthen the type of locomotion system of bekantan.