R. KELLY - Snake
Shed skins of snakes have practical applications and can provide information on biodiversity. We examined shed skins or scales stripped from 53 native species of snakes from Taiwan and adjacent islands and 13 foreign species, verified the intraspecific variation of microstructures on the scales, conducted phylogenetic comparative analyses of microdermatoglyphics, and developed a guide and key to identify shed skins by scanning electron microscopy. We examined several microstructural characteristics of scales including the form and dimensions of oberhautchen cells, denticulations, microridges, nanopits, and nanochannels. Furthermore, we noted scale shape and presence or absence of rounded tubercles on the scales. The microstructures of apical (and central) regions of scales were similar to each other, but different from those on basal and lateral margins, the keel, or apical pits. The microdermatoglyphics on cranial scales (cephalic shields) differed from those on scales from other regions of the body. Those from the dorsal and dorsolateral surfaces of the body, and the dorsal surface of the tail were similar, as were those on scales from the ventral surfaces of the body and tail. For adults or juveniles, there was no significant ontogenetic variation in many microdermatoglyphic characteristics. By conducting phylogenetic mapping, we found that symmetrical (dorsal) scales without apical pit organs or rounded tubercles, keelless and rounded scales, flat microdermatoglyphic patterns (without longitudinal microridges), (sub)lamellate oberhautchen cells, cell borders without denticulations or with tiny and keelless denticulations, and relatively small nanopits at denticulation joints or covering cells, are likely to be plesiomorphic character states. We also examined character evolution models based on the microdermatoglyphics and their phylogenetic signals, conducted phylogenetic generalized least-squares regressions to examine the correlations among snake habitat type and the morphological traits on scales, and confirmed a hypothesis that the evolution of scale microstructures is dominated by both phylogenetic and functional (ecological) constraints. This study also indicates that scale microstructure can be used to identify snakeskin products, roadkill specimens and fragmented samples, scale remnants in predator feces, and wild snake sloughs.
R. KELLY - Snake
Despite advances in a diversity of environments, snake robots are still far behind snakes in traversing complex 3-D terrain with large obstacles. This is due to a lack of understanding of how to control 3-D body bending to push against terrain features to generate and control propulsion. Biological studies suggested that generalist snakes use contact force sensing to adjust body bending in real time to do so. However, studying this sensory-modulated force control in snakes is challenging, due to a lack of basic knowledge of how their force sensing organs work. Here, we take a robophysics approach to make progress, starting by developing a snake robot capable of 3-D body bending with contact force sensing to enable systematic locomotion experiments and force measurements. Through two development and testing iterations, we created a 12-segment robot with 36 piezo-resistive sheet sensors distributed on all segments with compliant shells with a sampling frequency of 30 Hz. The robot measured contact forces while traversing a large obstacle using vertical bending with high repeatability, achieving the goal of providing a platform for systematic experiments. Finally, we explored model-based calibration considering the viscoelastic behavior of the piezo-resistive sensor, which will for useful for future studies. 041b061a72