Raw data accompanying: Ground reaction forces in monitor lizards (Varanidae) and the scaling of locomotion in sprawling tetrapods

Geometric scaling predicts a major challenge for legged, terrestrial
locomotion. Locomotor support requirements scale identically with body
mass (α M1), while force generation capacity should scale α M2/3 as it
depends on muscle cross-sectional area. Mammals compensate with more
upright limb postures at larger sizes, but it remains unknown how
sprawling tetrapods deal with this challenge. Varanid lizards are an ideal
group to address this question because they cover an enormous body size
range while maintaining a similar bent-limb posture and body proportions.
This study reports the scaling of ground reaction forces and duty factor
for varanid lizards ranging from 7 g 37 kg. Impulses (force x time) scaled
roughly as predicted by the inverted pendulum model (α M0.99-1.34) while
peak forces (α M0.73-1.00) scaled higher than expected. Duty factor scaled
α M0.04 and was higher for the hindlimb than the forelimb. The proportion
of vertical impulse to total impulse increased with body size, and
impulses decreased while peak forces increased with speed. These results
provide valuable data into how locomotor forces vary with body size and
suggest how other, extinct, sprawling tetrapods may have dealt with the
biomechanical challenges associated with generating sufficient locomotor
forces at larger body sizes.