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First published online October 27, 2003

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Three-dimensional hindlimb kinematics of water running in the plumed basilisk lizard (Basiliscus plumifrons)

S. Tonia Hsieh

Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA

View larger version (28K): [in a new window]   Fig. 1. Kinematic landmarks and calculated angles describing the motion of the hind limb. (A) Eight points marked with reflective paint. The abbreviations are as follows: E, eye, positioned between the eyes in the dorsal aspect; the center of the eye was digitized in the lateral aspect; PC, pectoral, positioned midway between the shoulder joints; M, a point midway between pectoral and pelvis points; PL, pelvis, midpoint between palpated positions of acetabula; H, hip acetabulum; K, knee; A, ankle; MP, foot, positioned over the metatarsal–phalangeal joint of the longest (fourth) digit. Even though all of these points were digitized, only data from the hind limb points are presented in this paper. (B) Three-dimensional angles are labeled as follows: hip, hip angle formed by two planes containing lines PL–H and H–K; knee, knee angle formed by two planes containing lines H–K and K–A; ankle, ankle angle formed by two planes containing lines K–A and A–MP; fw, angle formed between the foot (line MP–A) and the water surface; tw, angle formed by the tibia (line K–A) to the water surface; bw, angle formed between the torso (line PC–PL) and the water surface. Pelvic rotation was measured as a two-dimensional angle, pr, formed by two planes containing lines H–PL and E–PL. All joint angles greater than 90° indicate joint extension, and all joint angles less than 90° indicate joint flexion. Negative values of fw indicate a toe-up foot position, whereas positive values indicate a toe-down foot position. Angles were measured in the counterclockwise direction.

View larger version (63K): [in a new window]   Fig. 2. Simultaneous lateral and dorsal images from high-speed video, illustrating the four phases of a stride. Some kinematic landmarks are visible in the dorsal view. Time for each frame of this run (20.8 g lizard, 1.4 m s–1) is shown in milliseconds in the upper right corner of each lateral view frame. The left foot is highlighted in both the lateral and dorsal images to show foot position at each phase. The blue circle in each lateral frame marks the same grid intersection to serve as a global point of reference that does not move with the lizard. Bars at the top of the figure represent footfall patterns for the right and left feet for this run. Colors of each section indicate stride phase, progressing from black to light gray: slap, stroke, recovery up and recovery down. See text for details on phase determination. The light blue box around the bars indicates when the foot is in the water. Numbers below the left foot footfall pattern indicate mean percent duration of each phase for all analyzed runs, simplified for clarity. Actual values (mean ± S.E.M.) from slap to recovery down averaged for 11 basilisk lizards are: 13.9±5.2%, 17.5±5.1%, 49.1±4.4% and 19.5±6.8%.

View larger version (26K): [in a new window]   Fig. 3. A time series of pelvis and left hind limb point excursions in (A) X-, (B) Y- and (C) Z-axes over one stride for a 20.8 g lizard running at 1.2 m s–1. The foot (MP) point experiences the greatest excursion along all three axes. The left foot footfall pattern is shown above A.

View larger version (17K): [in a new window]   Fig. 4. (A) Lateral (X–Y), (B) dorsal (X–Z) and (C) posterior (Z–Y) views of limb points relative to the hip. Hip position is designated by a cross. Lizard images behind graphs show position of points relative to the lizard at the start of slap. The path of each point is counterclockwise in all three plots, starting with the points outlined in black (foot and ankle) or blue (knee). Solid points indicate stance phase, open points indicate swing (i.e. recovery) phase.

View larger version (26K): [in a new window]   Fig. 5. Three time series of velocities of pelvis and left limb points in the three axes, for the same run as that presented in Fig. 3 (20.8 g, 1.4 m s–1). The left foot footfall pattern is presented above A (see Fig. 3 for phase breakdown). Symbol definitions are as in Fig. 3. (A) Point velocities in the X (fore–aft) direction. All positive values indicate movement in the direction of motion, and all negative values indicate movement opposite the direction of motion. (B) Point velocities in the Y (vertical) direction. All positive values indicate movement upwards, and all negative values indicate movement downwards. (C) Point velocities in the Z (medio-lateral) direction. Positive values indicate medial movements, and negative values indicate lateral movements. Open symbols indicate when the foot is out of water, whereas closed symbols indicate that the foot is submerged.

View larger version (26K): [in a new window]   Fig. 6. Time series of three-dimensional angular excursions of (A) limb joints and (B) body segments relative to the water surface for the identical run presented in Figs 3, 4, 5. The left footfall pattern is indicated above A. All joint angles (A) greater than 90° indicate joint extension, whereas all angles less than 90° indicate flexion. Open symbols indicate when the foot is out of the water, whereas closed symbols indicate that the foot is submerged.

View larger version (76K): [in a new window]   Fig. 7. Limb positions relative to size for juvenile to adult basilisks. The left-hand column shows a series of frames of a basilisk at the start of slap for a size range of lizards. The backgrounds of the frames are all 2 cmx2 cm grids. The central and right-hand columns are two-dimensional overlaid stick figures of limb positions during the support phase of aquatic running for the run represented in the adjacent frame. The hip, knee, ankle and foot (i.e. metatarsal–phalangeal) points are represented in each set of figures, with the hip at the upper end and the foot at the lower end of each stick figure. In all three columns, the basilisk is running from the right to the left. The dotted, horizontal line in the central column represents water level. The right-hand column figure is created from the same trial as the figure in the left-hand column, but with the position of the toe fixed. The highlighted (green) stick figure represents the limb position shown in the left-hand column video frame. Relative velocities were calculated by dividing by snout–vent length (SVL) and are presented as body lengths per second (L s–1). (A) 2.8 g, 0.84 m s–1 or 17.8 L s–1; (B) 11.4 g, 1.6 m s–1 or 21.2 L s–1; (C) 20.8 g, 1.38 m s–1 or 15.2 L s–1; (D) 78.0 g, 1.00 m s–1 or 7.56 L s–1. At comparable speeds (A–C), heavier lizards exhibited greater limb excursions. Also, whereas lighter lizards (weighing <20 g; A,B) usually slapped the water surface toe first or flat-footed, heavier lizards (>20 g; C,D) slapped the water heel first.

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