The northern treeshrew (Scandentia: Tupaiidae: Tupaia belangeri) in the context of primate locomotor evolution: A comprehensive analysis of gait, positional, and grasping behavior.

The locomotor behaviors of treeshrews are often reported as scurrying "squirrel-like" movements. As such, treeshrews have received little attention beyond passing remarks in regard to primate locomotor evolution. However, scandentians vary considerably in habitat and substrate use, thus categorizing all treeshrew locomotion based on data collected from a single species is inappropriate. This study presents data on gait characteristics, positional, and grasping behavior of the northern treeshrew (Tupaia belangeri) and compares these findings to the fat-tailed dwarf lemur (Cheirogaleus medius) to assess the role of treeshrews as a model for understanding the origins of primate locomotor and grasping evolution. We found that northern treeshrews were primarily arboreal and shared their activities between quadrupedalism, climbing and leaping in rates similar to fat-tailed dwarf lemurs. During quadrupedal locomotion, they exhibited a mixture of gait characteristics consistent with primates and other small-bodied non-primate mammals and demonstrated a hallucal grasping mode consistent with primates. These data reveal that northern treeshrews show a mosaic of primitive mammalian locomotor characteristics paired with derived primate features. Further, this study raises the possibility that many of the locomotor and grasping characteristics considered to be "uniquely" primate may ultimately be features consistent with Euarchonta.