P2.204 Thursday, Jan. 5 The ontogeny of quadrupedal walking in squirrel monkeys (Saimiri boliviensis) YOUNG, J.W.; Northeast Ohio Medical University (NEOMED) email@example.com
For more than 120 years, locomotor researchers have known that adult primates employ a unique footfall sequence during walking. Most quadrupedal mammals use lateral sequence (LS) gaits, in which hind foot touchdowns are followed by an ipsilateral forefoot touchdown. In contrast, most quadrupedal primates use diagonal sequence (DS) gaits, in which hind foot touchdowns are followed by a contralateral forefoot touchdown. However, gait selection in immature primates is more variable, with infants and juveniles frequently using LS gaits either exclusively or in addition to DS gaits. I explored the developmental bases for this phenomenon by examining the ontogeny of gait selection in growing squirrel monkeys walking on flat and simulated arboreal substrates (i.e., a raised pole). Results showed that although DS gaits predominated throughout development, immature squirrel monkeys nonetheless utilized LS gaits in more than one-third of the ground strides and in nearly one-sixth of pole strides. Gait selection was not significantly associated with either age or body mass per se, arguing against the oft-cited argument that general neuromuscular maturation is responsible for ontogenetic changes in preferred footfall sequence. Rather, lower-level biomechanical variables, specifically the position of the whole-body center of mass and the potential for interference between ipsilateral fore- and hind limbs, best explained variation in footfall patterns. Overall, results demonstrate the promise of developmental studies of growth and locomotor development to serve as “natural experiments”, testing how morphology is, or is not, associated with locomotor behavior – perhaps offering new insight into primate locomotor adaptation. Research supported by the Leakey Foundation, Stony Brook University and NEOMED.