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First published online February 6, 2004
Journal of Experimental Biology 207, 1027-1042 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00863

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Stabilization and mobility of the head and trunk in wild monkeys during terrestrial and flat-surface walks and gallops

Donald C. Dunbar^1,*, Gyani L. Badam^2,, Benedikt Hallgrímsson³ and Stéphane Vieilledent⁴

¹ Department of Anatomy and Caribbean Primate Research Center, University of Puerto Rico Medical School, PO Box 365067, San Juan, PR 00936-5067, USA
² Department of Archaeology, Deccan College Post-graduate and Research Institute, Pune 411006 (Maharashtra), India
³ Department of Cell Biology & Anatomy, University of Calgary, 3330 University Drive NW, Calgary, AB T2N 4N1, Canada
⁴ Département STAPS, Centre Universitaire de Recherche en Activités Physiques et Sportives (CURAPS), Université de La Réunion, Site du Tampon, 117 rue du Général Ailleret, 97430 Le Tampon, France

View larger version (10K): [in a new window]   Fig. 1. Measured axes and angles in the pitch plane. Head axis was a line passing through the external auditory meatus and the apex of the prognathous mouth. Trunk axis was a line passing through the hip and shoulder joints. Head angle relative to space () and trunk angle relative to space (ß) were measured in reference to earth horizontal. Head-to-trunk angle () was calculated from the head-to-space and trunk-to-space angles.

View larger version (26K): [in a new window]   Fig. 2. Cine film tracing of diagonal-sequence walks by (A) a hanuman langur and (B) a bonnet macaque. Note the large yaw rotations of the head as the hanuman looks to its right (A3) and left (A5).

View larger version (11K): [in a new window]   Fig. 3. Range of head (triangles) and trunk (circles) excursions in the pitch plane during walks and gallops (N=10 cycles/gait/species). For both (A) hanumans and (B) bonnets, the clusters of symbols to the left (lower velocities) are for walks, whereas the clusters to the right (higher velocities) are for gallops. Note that the head usually pitches through more degrees than the trunk during walks. By contrast, the trunk usually pitches through more degrees than the head during gallops. These basic patterns are seen in both species but are more extreme in hanumans.

View larger version (12K): [in a new window]   Fig. 4. Graphs of vertical translations (dotted lines) and pitch rotations (solid lines) of the head during single representative cycles of (A,B) walks and (C,D) gallops by (A,C) hanumans and (B,D) bonnets. Horizontal lines below each graph depict the support phases of the left hind limb (LH), left forelimb (LF), right forelimb (RF) and right hind limb (RH). Note that the phase relationship between head translation and head rotation is variable during the walk cycle, ranging from nearly 180° out of phase to more closely in phase. By contrast, head translation and rotation are nearly in phase over most of the gallop cycle, with small counter rotations occurring primarily when the head reaches maximal heights and depths of translation. Also note that in the depicted hanuman walk cycle (A), the head pitched downward (>20°) throughout the cycle as the monkey looked down at the support surface. In the remaining three cycles depicted (B–D), by contrast, the monkeys rotationally stabilized (<20°) their heads.

View larger version (31K): [in a new window]   Fig. 5. Segmental angular displacements and instantaneous angular velocities during single representative cycles by a hanuman walking at 0.9 m s–1 (left column) and a bonnet walking at 1.0 m s–1 (right column). (A) The segmental displacement graphs depict changes in head-to-space (H-S), trunk-to-space (T-S) and head-to-trunk (H-T) angles. Earth horizontal is indicated by 0° (broken horizontal line), and negative values indicate a nose-down angle of the head axis and a shoulders-down angle of the trunk axis. The horizontal lines depict the support phases of the left hind limb (LH), left forelimb (LF), right forelimb (RF) and right hind limb (RH). The remaining graphs depict instantaneous angular velocity changes of (B) the head relative to space, (C) the trunk relative to space and (D) the head relative to the trunk. In B, the head-to-space velocity graphs, the solid horizontal lines indicate 350 deg. s–1, which, at least in humans, is the saturation velocity for the vestibulo-ocular (VOR) reflex (Pulaski et al., 1981). Note that the pitch velocities of the head-to-space angular displacements are greater than those of the trunk-to-space angular displacements and that head angular velocities remain below 350 deg. s–1 throughout the cycle duration.

View larger version (13K): [in a new window]   Fig. 6. Mean angular positions of the (A,C) head (triangles) and (B,D) trunk (circles) segments in the pitch plane during walks and gallops by (A,B) hanumans and (C,D) bonnets (N=10 cycles/gait/species). Within each graph, the clusters of symbols to the left (lower velocities) are for walks, whereas the clusters to the right (higher velocities) are for gallops. Note that in both species, the range of mean positions for each segment is very similar during both walks and gallops.

View larger version (26K): [in a new window]   Fig. 7. Cine film tracing of (A) a rotary gallop by a hanuman langur and (B) a transverse gallop by a bonnet macaque. Note the minimal rotations of the head in any plane by both species. Airborne or flight phases occur at the end of the cycles by both (A5,A10) hanumans and (B5) bonnets. Note also that two rotary gallop cycles are depicted for the hanuman: a clockwise touchdown sequence (A1–A5) followed by a counterclockwise sequence (A6–A10).

View larger version (27K): [in a new window]   Fig. 8. Segmental angular displacements and instantaneous velocities during single representative cycles by a hanuman galloping at 3.2 m s–1 (left column) and a bonnet galloping at 2.1 m s–1 (right column). (A) The segmental displacement graphs depict changes in head-to-space (H-S), trunk-to-space (T-S) and head-to-trunk (H-T) angles. Earth horizontal is indicated by 0° (broken horizontal line), and negative values indicate a nose-down angle of the head axis and a shoulders-down angle of the trunk axis. Positive values, seen in T-S, indicate a shoulders-up angle. The horizontal lines depict the support phases of the left hind limb (LH), left forelimb (LF), right forelimb (RF) and right hind limb (RH). The remaining graphs depict instantaneous angular velocity changes of (B) the head relative to space, (C) the trunk relative to space and (D) the head relative to the trunk. In B, the head-to-space velocity graphs, the solid horizontal lines indicate 350 deg. s–1, which, at least in humans, is the saturation velocity for the vestibulo-ocular (VOR) reflex (Pulaski et al., 1981). Note that head angular velocities remain below 350 deg. s–1 throughout the cycle duration and that the pitch velocities of the head-to-space angular displacements are similar to those during walking. The pitch velocities of the trunk, however, increase to or surpass the levels of the head.