Fig. 1.

Target and model systems for understanding the role of body undulation in the lizard body-elongation and limb-reduction continuum. (Left, from top to bottom) Fully limbed lizards (U. scoparia and S. olivaceus) in comparison with extant short-limbed, elongate lizards (B. kadwa, B. taylori, and B. muntingkamay) and limbless/almost limbless species (L. praepedita and C. occipitalis). (Scale bars: 5 cm.) (Right) An illustrative diagram of force generation in short-limbed, elongate lizards: The force generated by limb retraction is labeled in red arrows; the forces generated by body undulation is labeled in yellow arrows.