Fundamental Adaptations in the Lacertilian Hind Limb: A Partial Analysis of the Sprawling Limb Posture and Gait

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Abstract
Lizards lacking extreme locomotor adaptations exhibit a type of limb posture and locomotion termed sprawling. Two major mechanical problems inherent in this type of posture can be identified, one concerning the support of the body between laterally projecting limbs, the other focusing on the efficiency of the limb in producing effective locomotor thrust. Analysis of distinct morphological features of the hind limb, including knee and mesotarsal joints and the geometry of the pes, reveals an integrated set of adaptations which maximize the effective participation of all limb segments in locomotion. The lacertilian pes probably represents a key innovation potentiating the exploitation of new locomotor niches. Functional demands stimulating the early evolutionary development of the reptilian pes may have preadapted that of lizards for a new role. The prime potential of the sprawling limb posture probably is in scansorial or arboreal locomotion. [The account is based on the following species: Iguanidae: Iguana iguana, Basiliscus basiliscus, B. plumifrons, Crotaphytus collaris; Agamidae: Uromastyx spinipes, Sitana ponticeriana; Teiidae: Tupinambis nigropunctatus, T. teguixin; Lacertidae: Lacerta lepida, L. viridis; Helodermatidae: Heloderma suspectum; Varanidae: Varanus salvator, V. bengalensis, V. griseus, V. timorensis, V. prasinus, V. komodoensis.].