Effective locomotion is critical for animal survival and has driven the evolution of specialized morphological structures. The evolution of morphological novelties likely leads to key innovations facilitating adaptive radiations. But to fully understand the evolution of complex morphological structures, it is important to study intermediate forms in morphological series, e.g. species having evolved some, but not all traits forming the complex structure in question.
The adhesive toepads of geckos (and other lizards), which have attracted much research interest from biologists and engineers alike, are complex morphological structures, consisting of multiple, laterally expanded scales, supported by specialised muscles and tendons, and covered with adhesive microstructures (setae). These facilitate the use of complex three-dimensional microhabitats through friction and adhesion. But toepad evolution is poorly understood, partially due to the scarcity of studies on morphologically intermediate forms.