Gait Dynamics of Cebus apella During Quadrupedalism on Different Substrates

摘要

Primates are distinguished from manynmammals by emphasizing arboreal lifestyles. Primate ar-nboreal adaptations include specializations for enhancingnbalance and manipulative skills. Compliant gait and di-nagonal sequence (DS) footfalls are hypothesized mecha-nnisms for improving balance during arboreal quadruped-nalism (AQ), while simultaneously permitting verticalnpeak force reductions sustained by limbs, particularlynforelimbs (FLs). Capuchin monkeys (Cebus apella) arenarboreally-adapted quadrupeds that use both lateralnsequence (LS) and DS footfalls. As tool-users, capuchinsnexperience selective pressures for FL manipulative capa-nbilities, which seemingly conflict with encountering sub-nstantial locomotor stresses. We evaluate kinetic and 3-Dnkinematic data from 172 limb contacts of two adultnmales on terrestrial and arboreal substrates to addressnquestions about C. apella gait compliancy, kinematics ofnLS and DS footfalls during quadrupedalism on differentnsubstrates, and whether capuchins reduce FL verticalnpeak forces relative to hind limb (HL) forces more thannother primates that use tools or those that do not. Lowernvertical peak forces during AQ are consistent with com-npliant gait, but mixed kinematic results obscure how thenreduction occurs. Forearm adduction angle is one con-nsistent kinematic difference between terrestrial and ar-nboreal quadrupedalism, which may implicate frontalnplane movements in gait compliancy. Major differencesnbetween DS and LS gaits were not observed in kinetic ornkinematic comparisons. Capuchins exhibit low FL/HLnvertical peak force ratios like several anthropoids,nincluding tool-users (e.g., chimpanzees), and species notnconsidered tool-users in free-ranging conditions (e.g., spi-nder monkeys). Additional selective pressures besidesnsimply tool use appear responsible for the relative reduc-ntion in primate forelimb forces.