Lateral bending of the lumbar spine during quadrupedalism in strepsirhines

Much research has been devoted to spinal kinematics of nonmammalian vertebr ates, while comparatively little is known about the locomotor role of spina l movements in mammals, especially primates. This study, conducted at the D uke University Primate Center, examines the function of lateral spinal bend ing during quadrupedal walking among a diverse sample of strepsirhines. The taxa studied include Loris tardigradus (1), Nycticebus coucang (1), N. pyg maeus (1), Cheirogaleus medius (2), Varecia variegata (2), Eulemur fulvus ( 2), and a total sample size of 261 strides. Lateral bending varies among th e taxa with respect to both magnitude and effects of velocity, and does not appear to be correlated with body size. In addition, the timing of lateral bending during a stride appears to differ from that reported for other (no nmammalian) tetrapods. On average, maximum lateral flexion occurs just afte r ipsilateral foot touchdown, which may be functionally associated with tou chdown of the contralateral forelimb during diagonal sequence gait. For som e of the taxa, lateral flexion coincides more closely with foot touchdown a s velocity increases, suggesting a functional role in increasing hindlimb s tride length. Both of these timing patterns contrast with those reported fo r lizards. Finally, although lorids as a group have been described as havin g a "sinuous" gait, this study shows more pronounced lateral flexion in Nyc ticebus than in Loris. (C) 2001 Academic Press.