Meeting Abstract
Among terrestrial vertebrates, foot morphology and locomotor function are closely associated. A prominent example of this is the pedally-based adhesive system of geckos. Although the integumentary aspects of this complex are well-studied, its skeletal elements are not. The mesotarsal ankle joint of limbed squamates, situated between the astragalocalcaneum and fourth distal tarsal, is complex and governs the patterns of foot motion during propulsion. Among geckos, pad-bearing taxa have different limb and ankle kinematics from ancestrally padless forms, and we predicted that such kinematic differences are reflected in skeletal anatomy. To explore whether evolutionary changes in the morphology of the ankle joint have accompanied the acquisition of adhesive function, we obtained 3D micro CT images of the hind foot of 28 genera of the Gekkonidae and six outgroups. Our sample represents seven origins of the adhesive apparatus. We used 3D geometric morphometrics and phylogenetic comparative methods to compare shape variation in the ankle joint among ancestrally padless and pad-bearing lineages. Preliminary results suggest that the ankle joint of pad-bearing lineages differs from that of ancestrally padless lineages in having a shallower astragalocalcaneal groove and a shorter ventral peg on the fourth distal tarsal. This is suggestive that flexion and rotation of the crus about the foot are decoupled in pad-bearing lineages. Our results have important implications for the function of the adhesive system and gecko locomotion, and also provide evidence relating to how superficial and deep anatomy change in parallel in association with function.
