Snake and Snake Robot Locomotion in Complex, 3-D Terrain

Snakes are able to traverse almost all types of environments by bending their elongate bodies in three dimensions to interact with the terrain. Similarly, a snake robot is a promising platform to perform critical tasks in various environments. Understanding how 3-D body bending effectively interacts with the terrain for propulsion and stability can not only inform how snakes move through natural environments, but also inspire snake robots to achieve similar performance to facilitate humans. How snakes and snake robots move on flat surfaces has been understood relatively well in previous studies. However, such ideal terrain is rare in natural environments and little was understood about how to generate propulsion and maintain stability when large height variations occur, except for some qualitative descriptions of arboreal snake locomotion and a few robots using geometric planning. To bridge this knowledge gap, in this dissertation research we integrated animal experiments and robotic studies in three representative environments: a large smooth step, an uneven arena of blocks of large height variation, and large bumps. We discovered that vertical body bending induces stability challenges but can generate large propulsion. When traversing a large smooth step, a snake robot is challenged by roll instability that increases with larger vertical body bending because of a higher center of mass. The instability can be reduced by body compliance that statistically increases surface contact. Despite the stability challenge, vertical body bending can potentially allow snakes to push against terrain for propulsion similar to lateral body bending, as demonstrated by corn snakes traversing an uneven arena. This ability to generate large propulsion was confirmed on a robot if body-terrain contact is well maintained. Contact feedback control can help the strategy accommodate perturbations such as novel terrain geometry or excessive external forces by helping the body regain lost contact. Our findings provide insights into how snakes and snake robots can use vertical body bending for efficient and versatile traversal of the three-dimensional world while maintaining stability

Design and control of amphibious robots with multiple degrees of freedom

This thesis presents the design and realization of two generations of robot elements that can be assembled together to construct amphibious mobile robots. These elements, designed to be individually waterproof and having their own battery, motor controller, and motor, have been used to actually construct a snake, a boxfish and a salamander robot. Central pattern generator (CPG) models inspired from those found in vertebrates have been used for online trajectory generation on these robots and implemented on their onboard locomotion controllers. CPGs proved to be an interesting way of controlling complex robots, providing a simple interface which hides the complexity of the robot to the end user. Online learning algorithms that can be used to dynamically adapt the locomotion parameters to the environment have been implemented. Finally, this work also shows how robotics can be a useful tool to verify biological hypotheses. For instance, the salamander robot has been used to test a model of CPG for salamander locomotion

Modeling, Control and Energy Efficiency of Underwater Snake Robots

This thesis is mainly motivated by the attribute of the snake robots that they are able to move over land as well as underwater while the physiology of the robot remains the same. This adaptability to different motion demands depending on the environment is one of the main characteristics of the snake robots. In particular, this thesis targets several interesting aspects regarding the modeling, control and energy efficiency of the underwater snake robots. This thesis addresses the problem of modeling the hydrodynamic effects with an analytical perspective and a primary objective to conclude in a closed-form solution for the dynamic model of an underwater snake robot. Two mathematical models of the kinematics and dynamics of underwater snake robots swimming in virtual horizontal and vertical planes aimed at control design are presented. The presented models are derived in a closed-form and can be utilized in modern modelbased control schemes. In addition, these proposed models comprise snake robots moving both on land and in water which makes the model applicable for unified control methods for amphibious snake robots moving both on land and in water. The third model presented in this thesis is based on simplifying assumptions in order to derive a control-oriented model of an underwater snake robot moving in a virtual horizontal plane that is well-suited for control design and stability analysis. The models are analysed using several techniques. An extensive analysis of the model of a fully immersed underwater snake robot moving in a virtual horizontal plane is conducted. Based on this analysis, a set of essential properties that characterize the overall motion of underwater snake robots is derived. An averaging analysis reveals new fundamental properties of underwater snake robot locomotion that are useful from a motion planning perspective. In this thesis, both the motion analysis and control strategies are conducted based on a general sinusoidal motion pattern which can be used for a broad class of motion patterns including lateral undulation and eel-like motion. This thesis proposes and experimentally validates solutions to the path following control problem for biologically inspired swimming snake robots. In particular, line-of-sight (LOS) and integral line-of-sight (I-LOS) guidance laws, which are combined with a sinusoidal gait pattern and a directional controller that steers the robot towards and along the desired path are proposed. An I-LOS path following controller for steering an underwater snake robot along a straight line path in the presence of ocean currents of unknown direction and magnitude is presented and by using a Poincaré map, it is shown that all state variables of an underwater snake robot, except for the position along the desired path, trace out an exponentially stable periodic orbit. Moreover, this thesis presents the combined use of an artificial potential fields-based path planner with a new waypoint guidance strategy for steering an underwater snake robot along a path defined by waypoints interconnected by straight lines. The waypoints are derived by using a path planner based on the artificial potential field method in order to also address the obstacle avoidance problem. Furthermore, this thesis considers the energy efficiency of underwater snake robots. In particular, the relationship between the parameters of the gait patterns, the forward velocity and the energy consumption for the different motion patterns for underwater snake robots is investigated. Based on simulation results, this thesis presents empirical rules to choose the values for the parameters of the motion gait pattern of underwater snake robots. The experimental results support the derived properties regarding the relationship between the gait parameters and the power consumption both for lateral undulation and eel-like motion patterns. Moreover, comparison results are obtained for the total energy consumption and the cost of transportation of underwater snake robots and remotely operated vehicles (ROVs). Furthermore, in this thesis a multi-objective optimization problem is developed with the aim of maximizing the achieved forward velocity of the robot and minimizing the corresponding average power consumption of the system

Faster than the blink of an eye

Arboreal snakes such as the amazon tree boa (Corallus hortulanus) are able to cantilever large sections of their body for very long periods of time with seemingly minimal muscular effort. From this cantilevered position they exert quick strikes as well as compensate for any movement of the object from which they cantilever. The mechanisms of muscle coordination required for the dynamic switch between resting and strike have been hypothesized for terrestrial puff adders (Bitis arietans) to result from the vast and unique musculo-tendon arrangement of the snake's epaxial muscles put under pre-strike tension, i.e. a spring-like mechanism where the snake is able to store a large amount of energy in tendons which can then be later quickly released. Furthermore, while muscle activity during gap crossing or extension activities has been described for an arboreal species, it is not clear how the stationary snake's muscles compensate for perturbations of the anchoring object, e.g. as happens in the wild with a branch swaying in the breeze. Using a self-built high-speed 3D tracking system along with a novel method for collecting chronic multi-electrode bipolar electromyography (EMG) information, my data is not only unsupportive of the elastic energy-storing strike hypothesis but provides insights to the muscle coordination required for stabilization in a moving, as well as stationary, environment

Taxonomy, Natural History, and Ecology of Selected Herpetofaunal Species from the Sunda Islands and Adjacent Regions – Synergistic Effects of Fieldwork and Museum Collections for Biodiversity Research

In this cumulative thesis (papers 1–13) I investigated the taxonomy, natural history, and ecology of selected species of amphibians and reptiles from the Sunda Islands and adjacent regions, and highlighted the importance of natural history collections for biodiversity research. Several Sundaic species provided unexpected challenges, primarily because of significant problems stemming from their taxonomic history. Only the synergy of fieldwork and collection-based studies, allowed me to resolve some of these issues, as outlined below. Herpetological surveys in all districts of Timor-Leste (except the Oecusse exclave), including its offshore islands, contributed towards a comprehensive inventory of the amphibians and reptiles of this country at the southern border of the Wallacea Biodiversity Hotspot. New distribution records of amphibians and reptiles for 11 of the country’s 12 contiguous districts, along with natural history data were presented. Results of the survey work increased the number of amphibian and reptile species known to occur in Timor-Leste to > 60, including > 20 candidate species. Many of the recorded species appear to be endemic to Timor Island, including the frog Kaloula sp. nov., several bent-toed gecko species of the genus Cyrtodactylus, and the agamid Draco timoriensis. Notable reptile discoveries included at least seven undescribed Cyrtodactylus species, a genus previously not recorded from Timor, the first records of the gecko Hemidactylus garnotii and of the gecko genus Hemiphyllodactylus for Timor-Leste, and several undescribed skinks (chapter 4, papers 1 & 2). Revisions of the genus Cyrtodactylus, and the skink genus Eremiascincus on Timor and adjacent islands, including the description of new species, are currently in preparation together with colleagues from the USA and the UK. A revision of Timorese Cyrtodactylus is not possible without resolving the tangled taxonomy of some extralimital species. The taxonomy of selected non-Timorese Cyrtodactylus geckos was investigated accordingly, in three papers (chapter 5, papers 3–5). A new species of Cyrtodactylus, originally catalogued as C. fumosus in the herpetological collection of the Senckenberg Naturmuseum Frankfurt, Germany, was described from Klakah, Lumajang Regency, Jawa Timur Province, Indonesia. The new species differs from all other congeners by a combination of seven characters (paper 3). The Cyrtodactylus fauna of Java had been underestimated for centuries with four out of the five endemic species described as late as during the 2000s. Cyrtodactylus fumosus, hitherto considered widespread in the Sunda Archipelago, including the islands of Sumatra, Java, Bali, Sulawesi, and Halmahera, was redescribed and confirmed to possess a precloacal groove in males. Examination of the type specimen and additional vouchers from Rurukan and Mount Masarang, North Sulawesi Province, Indonesia, revealed that this population was distinct from other forms heretofore called ‘fumosus’ by a combination of unique morphological characters. Cyrtodactylus fumosus was identified as the most distinctive species among the six bent-toed geckos recorded from Sulawesi, differing from Sulawesi congeners by four striking characters (paper 5). Since there was also much taxonomic confusion of C. fumosus with C. marmoratus, the type series of the latter taxon was described for the first time. I was able to demonstrate that the type series actually comprises two sets of specimens, and that examination of specimens from only one set or the other was responsible for some confusion surrounding these vouchers. Owing to the inconsistent naming and application of terms for some key characters (e.g., groove, sulcus, pit, hollow, depression) used in the diagnoses of Cyrtodactylus species, a set of novel and useful definitions was proposed. A comparative table for the bent-toad geckos of the Sunda Islands and Sulawesi was provided for the first time (paper 4). Cyrtodactylus throughout the Lesser Sundas, the Moluccas, and Sulawesi will be further investigated in future studies. Several museum vouchers will be described as new species. The discovery of snakes of the genus Cylindrophis in Timor-Leste led to an investigation of the taxon C. ruffus, which is widely distributed in Maritime Southeast Asia. A new species of Cylindrophis, originally catalogued as C. ruffus in the herpetological collections of the Naturalis Biodiversity Center, Leiden, The Netherlands and the Naturhistorisches Museum Wien, Austria, was described from Grabag, Purworejo Regency, Jawa Tengah Province, Java, Indonesia. The new species can be distinguished from all congeners by several, distinct morphological features. A detailed account of the tangled taxonomic history of the similar and only putatively wide-ranging C. ruffus was provided, Scytale scheuchzeri (name referring to a colubroid taxon) was removed from the synonymy of C. ruffus, C. rufa var. javanica (a taxon originally described from Borneo) was listed as species inquirenda, and the recently described C. mirzae was synonymized with C. ruffus. Evidence was provided that the type locality of C. ruffus is Java. The discovery of C. subocularis and the bent-toed gecko Cyrtodacytlus klakahensis on Java highlights how little we know about the diversity of an island, on which herpetological research in Indonesia began two centuries ago (paper 6). The systematic relationships within Cylindrophis are being investigated in an ongoing study utilizing both molecular and morphological methods. Based on specimens discovered in the collection of The Natural History Museum, London, UK, a new distribution record for the skink Sphenomorphus oligolepis was made for Seram Island, Maluku Province, Indonesia. The find constituted the westernmost record for this species and extended the distribution of this Papuan lizard well into Wallacea (paper 7). The Asian toad, Duttaphrynus melanostictus, which was recently introduced to Madagascar (paper 8), is the main research focus of chapter 6. During field work in Timor-Leste, an Asian toad that had consumed a brahminy blindsnake, Indotyphlops braminus, was discovered. This indicated that indiscriminate foraging by this recently introduced toad species could endanger small vertebrates (paper 9). Timor shows an exceptionally high level of endemism in a wide range of faunal groups, and concerns that D. melanostictus may have a negative impact on this diversity, including vertebrates, through direct predation, had been raised by scientists. To evaluate the potential impact the feeding by D. melanostictus might have on the local fauna, gut contents of > 80 preserved toad specimens from five habitat types in Timor-Leste were examined and almost 6000 prey items identified. All prey items were invertebrates, with small eusocial insects comprising the major component of the diet. The wide prey spectrum demonstrated that D. melanostictus is a generalist invertebrate feeder. Although the Asian toad seems to not generally prey on vertebrates, vertebrate species that are morphologically similar to invertebrates in their overall appearance (worm-like gestalt) may be consumed. Data on intestinal parasites occuring in D. melanostictus were presented alongside the food spectrum analysis (paper 11). Whereas information on the diet and internal parasites of anurans based on internal examinations have been published by numerous researchers, details of the incision method used to open the abdominal cavity of preserved specimens are rarely explained. An optimal incision into the pleuroperitoneal cavity of liquid-preserved anuran specimens to gain access to and permit easy removal of parts of the digestive tract in preparation for food spectrum analyses was formally proposed. This U-shaped cut is easy to perform and teach, and it has already been adopted in lab manuals. It provides better access to the pleuroperitoneal cavity than a small ventrolateral incision, and is less destructive than the classic textbook medial “double T-incision” routinely listed in dissection protocols. This new method may encourage other researchers to use preserved anurans for the purpose of food spectrum analyses and other examinations of internal morphology (paper 10). An instance of captive breeding in a species of Timorese night skink (genus Eremiascincus) was reported, and the taxon demonstrated to be viviparous. A summary of information pertaining to the reproductive biology of other members of the genus Eremiascincus was provided (paper 12). Increased knowledge on the reproductive biology of Eremiascincus taxa will contribute to revisions of the group carried out by morphological and molecular analyses. The type of the skink Anomalopus leuckartii was rediscovered in the herpetological collection of the Museum für Tierkunde, Dresden, Germany, together with other specimens from the original collection of Karl Georg Friedrich Rudolf Leuckart, who was one of zoology’s leading scientists during the second half of the 19th century and the founder of modern parasitology. This rediscovery serves as an excellent example to highlight the importance of maintaining natural history collections, not merely as static archives but rather as valuable dynamic and lively databases. This, in combination with optimal taxonomic expertise as a bedrock, guarantees an environment, in which new discoveries, like the ones presented in this dissertation, are actively promoted, thereby inevitably advancing modern biodiversity research (paper 13). In a general conclusions section (chapter 8), the effects resulting from the combination and coordination of field work and collection-based studies are elaborated and illustrated in a diagram. The value of the studies presented in this thesis is primarily derived from specific interactions, synergistic effects, and an iterative process that connects them. Finally, the benefit for decision-makers dealing with conservation and species management is assessed

Letters from Michigan Herpetology

http://deepblue.lib.umich.edu/bitstream/2027.42/170907/4/Letters_from_Michigan_Herpetology-Text.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/170907/5/Letters_from_Michigan_Herpetology- Cover.pdfSEL

Reading Prehistoric Human Tracks

This Open Access book explains that after long periods of prehistoric research in which the importance of the archaeological as well as the natural context of rock art has been constantly underestimated, research has now begun to take this context into focus for documentation, analysis, interpretation and understanding. Human footprints are prominent among the long-time under-researched features of the context in caves with rock art. In order to compensate for this neglect an innovative research program has been established several years ago that focuses on the merging of indigenous knowledge and western archaeological science for the benefit of both sides. The book gathers first the methodological diversity in the analysis of human tracks. Here major representatives of anthropological, statistical and traditional approaches feature the multi-layered methods available for the analysis of human tracks. Second it compiles case studies from around the globe of prehistoric human tracks. For the first time, the most important sites which have been found worldwide are published in a single publication. The third focus of this book is on firsthand experiences of researchers with indigenous tracking experts from around the globe, expounding on how archaeological sciencecan benefit from the ancestral knowledge. This book will be of interest to professional archaeologists, graduate students, ecologists, cultural anthropologists and laypeople, especially those focussing on hunting-gathering and pastoralist communities and who appreciate indigenous knowledge