ИСТИНА

One of the key features of primates is a foot specialized for powerful grasping with a divergent opposable hallux, which can facilitate fine branch use in tree peripheries and shrubs enabling the exploitation of angiosperm products and/or invertebrates. In fact, the evolution of pedal grasping in archontan mammals is of great importance as it bears on the adaptive significance of specialized grasping and associated behaviors within this group and more particularly primates. In this context, extant non-primate arboreal mammals, with their pedal grasping diversity, constitute good models for testing putative evolutionary stages. Treeshrews, especially basal arboreal tupaids, are very suitable for testing pedal grasping modes and associated substrate correlates. For these purposes, we filmed and analyzed foot positioning and pedal grasping in three wild-caught treeshrews Dendrogale murina from Vietnam. Our observations showed that convergent and claw grasping were the more frequent pedal modes in treeshrews. Nevertheless, hallucal grasp was mainly associated with small and vertical substrates, convergent grasp with medium sized and horizontal substrates, whereas claws dominated on large vertical substrates. In addition, the foot was commonly inverted and mainly placed in a semi-plantigrade position. Inversion and semiplantigrady dominated on small, medium-sized and horizontal substrates but decreased on larger substrates with increased inclinations. These results demonstrate that basal treeshrews do not frequently employ hallucal grasping but invert their foot and place it in a semiplantigrade manner. Even if treeshrews have not yet evolved powerful opposable pedal grasping, incipient hallucal grasping was used on small and inclined substrates, underscoring the significance of a grasping hallux for fine branch use. Powerful hallucal grasping did not evolve early in archontan evolution but was pivotal for the evolution and diversification of the groups that subsequently led to primates.