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Session Schedule & Abstracts

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Thursday 30th June, 2016

Locomotion 2

Room: Salon G   11:30 am–1:00 pm

Moderator(s): Lees JL, Miyake T
LOC2-1  11:30 am  The transition to adhesion in geckos: evidence from Gonatodes (Gekkota: Sphaerodactylidae). Russell A.P.*, University of Calgary; Higham T.E., University of California Riverside; Gamble T., Marquette University
Abstract: The adhesive system originated in at least 11 separate gekkotan lineages, but taxa representing transitional phases are poorly known. Comparative studies led us to the "padless" sphaerodacyline genus Gonatodes to investigate this transition. We examined the macroscopic and microscopic digital anatomy of Gonatodes (about 27 species displaying considerable variety in digit form and locomotor substrate preferences). One species, Gonatodes humeralis, bears enlarged proximal subdigital scales that are candidate incipient pads. We investigated digit proportions, shape, scalation and skeletal form throughout the genus, and correlated these with the patterns of micro-ornamentation encountered on the subdigital surfaces. We then measured the ability to generate adhesive force in key taxa, and examined locomotor capabilities on low-friction surfaces. We found that G. humeralis generates adhesive force that is only slightly less than that for Anolis (when normalized for body mass). It thus has feet that are functionally adhesive, even though it lacks the manifold anatomical modifications typical of pad-bearing geckos. Indeed, its digital anatomy is even more basic than that of Anolis. Despite this it can scale vertical Plexiglas® sheets. As in Anolis, release of adhesion is achieved through passive digital hyperextension, with the digits rolling off the substratum at the end of pedal plantarflexion (rather than being actively disengaged by muscular action prior to raising the heel, as is typical of geckos with a more derived adhesive system). G. humeralis thus exhibits a very basic rendition of the gekkotan adhesive system. Field observations provide evidence of circumstances in which adhesive capabilities are selectively advantageous, and which are unavailable to species of Gonatodes lacking adhesive capabilities. The enormous geographic range of G. humeralis relative to its congeners suggests that its adhesive capabilities are associated with ecological release.

LOC2-2  11:45 am  The coordinated motion control model of tetrapod limbs with mono- and bi-articular muscles: Model, application, and evolutionary origin. Miyake T.*, Graduate School of Science and Technology, Keio University, Japan; Iwata M., Aquamarine Fukushima, Marine Science Museum, Japan; Sato R., Instutite of Biomechanical Control Systems, Kanazawa Institute of Technology, Japan; Tsuji T., Department of Electrical and Electronic Systems, Saitama University, Japan; Tajima T., Honda R&D Co., Ltd., Japan; Koie H., Department of Veterinary Medicine, Nihon University, Japan; Umemura A., Department of Electrical and Electronic Engineering, Kitami Institute of Technology, Japan; Yoshimura K., Aquamarine Fukushima, Marine Science Museum, Japan; Abe Y., Aquamarine Fukushima, Marine Science Museum, Japan; Kumamoto M., Kyoto University, Japan
Abstract: The presence of bi-articular muscles in tetrapod limbs has created an enigmatic paradox. When the rectus femoris acts alone, the knee is extended but the hip is flexed. When the hamstring acts alone, the knee is flexed but the hip is extended. When both muscles act together, however, they act as a braking against each other for one joint whereas they act coordinately for another joint. To solve this paradox and examine functional roles of and motion control over mono- and bi-articular muscles in human limbs, the coordinated motion control model has been established based on human biomechanics and robotics. The model has demonstrated that three antagonistic pairs of six mono- and bi-articular muscles control coordinated output force and force direction at the wrist or ankle, perform weight-bearing motion, and maintain stable posture. These antagonistic muscles are defined as functionally different effective muscular system (FEMS) of the two-joint link mechanism. Using robotics, the model has also been shown to achieve the contact task without slippage. Recently, some of the results have led to practical applications for automotive engineering and robotics, i.e., Twin Lever Steering (TLS) system and an amphioxus robot, respectively. Since the model was proposed for biomechanics of human limbs, we have investigated morphology, evolutionary origin, and biomechanics of FEMS in vertebrates by examining the pectoral fin musculature of extant sarcopterygians, the African coelacanth Latimeria chalumane and two lungfish species, Neoceratodus forsteri and Protopterus aethiopicus. Since terrestrial locomotion necessitates solving contact tasks and achieving weight-bearing motions and stable posture on the ground against gravity, we will discuss the model and present our results, particularly by focusing our discussions on the fin-to-limb transition and the subsequent evolution of tetrapods.

LOC2-3  12:00 pm  Rachis morphology cannot accurately predict the mechanical performance of primary feathers in extant (and therefore fossil) birds. Lees J*, University of Manchester; Garner T, University of Manchester; Cooper G, University of Manchester; Nudds R, University of Manchester
Abstract: It was previously suggested that the flight ability of feathered fossils could be hypothesized from the diameter of their feather rachises. Central to the idea is the unvalidated assumption that the strength of a primary flight feather (i.e., its material and structural properties) may be consistently calculated from the external diameter of the feather rachis, which is the only dimension that is likely to relate to structural properties available from fossils. Here, using three-point bending tests, the relationship between feather structural properties (maximum bending moment, Mmax and Young’s modulus, Ebend) and external morphological parameters (primary feather rachis length, diameter and second moment of area at the calamus) in 180 primary feathers from 4 species of bird of differing flight style was investigated. Intraspecifically, both Ebend and Mmax were strongly correlated with morphology, decreasing and increasing, respectively, with all three morphological measures. Without accounting for species, however, external morphology was a poor predictor of rachis structural properties, meaning that precise determination of aerial performance in extinct, feathered species from external rachis dimensions alone is not possible. Even if you could calculate the second moment of area of the rachis, our data suggest that you could still not reliably estimate feather strength.

LOC2-4  12:15 pm  Estimating scapular positions in extant quadrupedal tetrapods by using two different approaches: implications to forelimb posture reconstructions in extinct taxa. Fujiwara S*, Nagoya University Museum
Abstract: The scapulae have no direct skeletal connection to the rib cage, but are connected to the rib cage via thoracic (e.g., serratus and rhomboideus) muscles. Therefore, the scapular position remains one of the most difficult hurdles in reconstruction of the extinct tetrapod skeletons. In a quadrupedal stance of tetrapods, the presacral portions of the body are lifted upward by pitching torque about the acetabular joint produced by the thoracic muscles, and avoid collapsing on the ground during the locomotion. The thoracic muscles produce roll and yaw torques as well, which disturb stable stance; and compress the rib cage dorsoventrally against the downward body weight, which may cause the bone fracture. Assuming a stance phase supported by left hind- and right forelimbs, 3D musculoskeletal models of Mus, Felis, and Chamaeleo were constructed based on CT-scanned images and dissection to find the 3D scapular positions (1) where the roll and yaw moments of the presacral body produced by the thoracic muscles are minimized, and (2) where the strength against the vertical compression of the rib cage beneath the scapula is maximized. According to the moment analyses model by using SIMM software (Musculographics, Inc.), the distribution of the scapular positions where the muscles minimize yaw and roll torques of the trunk was limited near the median plane and above the cranial-most portion of the rib cage. According the strength analyses model by using Voxelcon software (Quint), the strength of the rib cage against the vertical compression was maximized at above the cranial-most portion of the rib cage. The scapular positions estimated by these two different approaches are consistent with the scapular positions during the stance phase in vivo not only in the studied taxa, but also in most of the extant quadrupedal tetrapods. The scapular positions in extinct quadrupedal tetrapods are expected to be reliably reconstructed by using these two different approaches.

LOC2-5  12:30 pm  Computational and experimental analysis of terrestrial locomotion in fire salamanders: insights into the evolution of walking and running in tetrapods. Rankin JW*, The Royal Veterinary College, UK; Pierce SE, Harvard University, USA; Hutchinson JR, The Royal Veterinary College, UK
Abstract: The water to land transition in stem tetrapods is a key evolutionary event in Earth’s history. However, difficulties arise when using static fossil morphology to rigorously determine how adapted early tetrapods were to dynamically moving through a terrestrial environment. Salamanders are the most commonly used postural model to provide a basis for inferring stem tetrapod movement capacity due to their presumed plesiomorphic morphology and to their specialized life cycle that involves an ontogenetic transition from water to land. Here we present a novel approach that combines experimental data, computational models, and forward dynamics simulations to estimate the maximum terrestrial movement capability of a direct-developing salamander, the fire salamander (Salamandra salamandra). Hindlimb muscle (e.g., mass, pennation angle and musculotendon paths) and segment data (e.g., mass, geometry) were obtained via dissection and microCT scans to create a detailed hindlimb musculoskeletal model. The maximum torque that each hindlimb joint could sustain at each point in its range of motion was then estimated from muscle properties and segment geometry. Torque-driven forward dynamic simulations were then generated to validate the simulation framework and estimate walking capacity. First, a simulation was generated that reproduced collected experimental kinematics (collected using biplanar radiography; XROMM) and ground reaction forces to validate the model. Additional simulations were then generated using different theoretical goals (e.g., maximize forward velocity) to estimate movement capabilities of the fire salamander. We show how we are using this information as a basis for constructing torque-driven models of individual stem tetrapods, thereby inferring their locomotor capabilities in a quantitative way for the first time, without relying on the assumption that they moved just like salamanders.

LOC2-6  12:45 pm  A novel joint-based approach for studying skeletal evolution and motion. Carney Ryan M*, Brown University
Abstract: Understanding skeletal and locomotor evolution – especially across major transitions – is currently hindered by fundamental obstacles to measuring, comparing, and transferring motion between disparate animals. In particular, representations of anatomy and kinematics are often poorly integrated with one another, and lack an evolutionary perspective. This is especially problematic for reconstructing motions in extinct organisms. Here we establish a methodology for representing both bone morphology and motion, based upon the surfaces of articular joints. The anatomical utility of this joint-based approach is illustrated by comparative analysis of humeri from various archosaurs and mammals. Results enabled the discovery of new evolutionary patterns, through the three-dimensional quantification of joint transformations (e.g., humeral torsion, reorientations of individual articular surfaces). The kinematic utility of this approach was also demonstrated, through integration with in vivo kinematics (XROMM) and high-resolution imaging of fossil anatomy, in order to analyze and reconstruct the shoulder motions of extant and extinct archosaur representatives. Compared to current methods, the joint-based approach resulted in greater intra- and interspecific similarity of humeral motion paths, enabling more valid comparisons of alligator and avian locomotion. These kinematic benefits, along with the standardization and repeatability of the joint-based approach, provide a framework for "scientific motion transfer." This in turn provides a testable method for predicting motion in extinct forms, and ultimately a more empirical understanding of locomotor evolution. Additionally, the ability to standardize and compare disparate skeletal systems may also have applications for other disciplines, such as orthopedics, computer animation, and robotics.

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