Pedal grasping evolution in euarchontan mammals is of great importance as it bears on the adaptive significance of specialized hallucal grasping and arboreal niche use related to the group differentiation. Basally divergent arboreal tupaiid treeshrews are very suitable for testing pedal grasping modes and associated substrate correlates and provide insights on euarchontan pedal evolution. For these purposes we filmed wild-caught Dendrogale murina from Vietnam and analyzed their foot mechanisms. Our observations showed that hallucal grasp was moderately used and was mainly associated with small and horizontal substrates. Convergent grasp was frequently used on medium-sized and horizontal substrates whereas claws were related to large and vertical substrates. In addition, the foot was frequently inverted and mainly placed in a semiplantigrade position. Inversion and semiplantigrady dominated on small, mediumsized and horizontal substrates but decreased on larger substrates with increased inclinations. The observed pedal mechanism probably represents a derived condition, where hallucal grasping tends to become slightly restrained, compared to the primitive euarchontan (and scandentian) pedal grasping mechanism. Furthermore, it hallmarks an early stage in tupaiid evolution towards a more constrained pedal grasping. This further substantiates pedal grasping plasticity within euarchontan mammals and highlights the strong relation between a hallucal grasping mechanism and the frequent and primary use of small slender substrates.
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