Department of Anthropology, Boston University, Boston, Massachusetts.
Department of Evolutionary Anthropology, Duke University, Durham, North Carolina.
Am J Phys Anthropol. 2020 Feb;171(2):182-197. doi: 10.1002/ajpa.23959. Epub 2019 Nov 24.
Documenting the variety of quadrupedal walking gaits in a variety of marsupials (arboreal vs. terrestrial, with and without grasping hind feet), to aid in developing and refining a general theory of gait evolution in primates.
Video records of koalas, ringtail possums, tree kangaroos, sugar gliders, squirrel gliders, wombats, numbats, quolls, a thylacine, and an opossum walking on a variety of substrates were made and analyzed to derive duty factors and diagonalities for symmetrical walking gaits. The resulting distributions of data points were compared with published data and theories.
Terrestrial marsupials' gaits overwhelmingly plot slightly below the theoretical "horse line" (Cartmill et al., Zoological Journal of the Linnean Society. 2002;136:401-420) typical of terrestrial mammals; arboreal marsupials' gaits overwhelmingly plot more decisively above it. Both distributions are roughly parallel to the horse line, but arboreal animals exhibit increased diagonality, so that their higher-speed walking gaits overlap with those of typical primates on the Hildebrand diagram of diagonality against duty factor.
Quadrupeds avoid gaits lying exactly on the (theoretically optimum) horse line, to avoid fore/hind limb interference ("forging"). This can be accomplished by either a slight reduction in diagonality ("downshifting") or a more decisive increase ("upshifting"). Tree-dwellers adopt the second option to eliminate unilateral bipods of support from the gait cycle. The upshifted horse line represents an early phase in the evolution of primate-like diagonal-sequence gaits.
记录各种有袋类动物（树栖与地栖、有抓握后肢与无抓握后肢）的多种四足行走步态，以帮助发展和完善灵长类动物步态进化的一般理论。
对考拉、环尾负鼠、树袋鼠、蜜袋鼯、袋鼯、袋熊、袋貂、袋狼、袋獾和负鼠在各种基质上行走的视频记录进行了制作和分析，以得出对称行走步态的任务因子和对角线。将得到的数据点分布与已发表的数据和理论进行比较。
地栖有袋动物的步态绝大多数明显低于典型地栖哺乳动物的理论“马线”（Cartmill 等人，Zoological Journal of the Linnean Society. 2002;136:401-420）；树栖有袋动物的步态绝大多数则更明显地高于该线。这两种分布大致与马线平行，但树栖动物表现出更高的对角线性，因此它们的高速行走步态在 Hildebrand 对角线性对任务因子图上与典型灵长类动物重叠。
四足动物避免处于（理论上最佳的）马线的步态，以避免前/后肢干扰（“锻造”）。这可以通过稍微降低对角线性（“降档”）或更果断地增加对角线性（“升档”）来实现。树栖动物采用后一种选择来消除步态周期中的单侧支撑双足。上移的马线代表了类似灵长类动物对角线序列步态进化的早期阶段。
