Meeting Abstract

79.5  Friday, Jan. 6  Scales Assist Scaling in Lizards: Keeled, Subcaudal Scale Arrays Engage Substrate during Rapid Vertical Climbing JUSUFI, A.*; LIBBY, T.; FULL, R.J.; Univ. of California, Berkeley ardianj@berkeley.edu

To explore substrate interactions between locomotor appendages such as feet and tails, we video recorded lizards Iguana iguana, Acanthosaurus crucigera and Gonocephalus grandis as they scaled substrates of varying traction (tree bark, sandpaper, wire mesh). In addition, we observed how Forest Dragons climb trees in their natural habitats in South-East Asian tropical rainforests and Green Iguanas in Central America. Analysis revealed that lizards are continuously perturbed by natural substrata and frequently experience foot displacement. Lizards held their tail tip in constant contact with the substratum. Previously, using a force platform embedded in wall, we showed that tails pushing against the substrate can stabilize the body against overturning during rapid, vertical running (Jusufi et al., 2008). The lizard species investigated here possess subcaudal scales that are keeled and therefore have the potential to anchor in the substrate. To experimentally determine whether these structures could arrest a fall to avoid climbing failure, we mounted cadaver tails from deceased lizards in a materials testing machine (Instron). We performed friction tests to determine the toughness of the subcaudal structures to a simulated fall by pulling the tail parallel to the substrate. We discovered that engagement of only one or a few caudal scales with the substrate allowed support of 1 to 2 times body weight. Using the passive attachment properties of scales increases fault tolerance from foot slippage and could significantly simplify the control of climbing. Robots could increase the robustness of dynamic climbing by using keeled scale arrays on their tails.