KORFF, W.K.; Univ. of California, Berkeley: Leapin’ Lizards!: A novel locomotor strategy utilized by lizards on sand?

Terrestrial animals typically locomote on natural, compliant, substrates, a factor often overlooked in laboratory studies. Dune-dwelling lizards are an informative system for studying locomotion on natural substrates, because life on sand presents unique biomechanical obstacles that may produce evolutionary specializations. Using digital high speed imaging (500 frames per second, three cameras), I studied the locomotor behavior of three closely related species as they ran in the field on sand: Callisaurus draconoides crinitus in the Viscaino Desert, Baja California Sur Mexico, Callisaurus draconoides and Uma scoparia in the Mojave Desert of California. When animals were induced to sprint from a resting position, animals frequently exhibited a locomotor start like that of a swimming frog with symmetrical and simultaneous extension of all limbs that lasted up to 48ms. Once airborne, lizards postured their limbs for the characteristic diagonal gait and used an alternating diagonal gait while continuing to accelerate. Given the propensity of granular materials like sand to fluidize when rapidly sheared, it appears that lizards utilize a swimming-like gait to generate thrust using their feet as paddles during the initial impulse when accelerations are high and sand behaves more like a fluid. Then, they transition to a standard diagonal gait when the sand behaves more like a solid. This locomotor behavior may provide new insights into the interactions between locomotor strategies and the compliant behavior of natural substrates.