Scientific rotoscoping: a morphology-based method of 3-D motion analysis and visualization

The Kinematics of Proal Chewing in Rats

Chewing kinematics are well-documented in several mammal species with fused mandibular symphyses, but relatively understudied in mammals with an unfused symphysis, despite the fact that more than half of extant Mammalia have an unfused mandibular symphysis. The Wistar brown rat (Rattus norvegicus) is widely used in human health research, including studies of mastication or neurological studies where mastication is the output behavior. These animals are known to have unfused mandibular symphyses and proal jaw (rostrocaudal) motion during occlusion, but the lack of high resolution, 3-dimensional analysis of rat chewing leaves the functional significance of symphyseal mobility unknown. We used biplanar fluoroscopy and the X-ray reconstruction of moving morphology workflow to quantify chewing kinematics in 3 brown rats, quantifying overall jaw kinematics, including motions about the temporomandibular joint and unfused mandibular symphysis. During occlusion, the teeth and the mandibular condyle translate almost exclusively anteriorly (proal) during occlusion, with little motion in any other degrees of freedom. At the symphysis, we observed minimal flexion throughout the chew cycle. Overall, there are fundamental differences in jaw kinematics between rats and other mammals and therefore rats are not an appropriate proxy for ancestral mammal jaw mechanics. Additionally, differences between humans and rat chewing kinematics must be considered when using rats as a clinical model for pathological feeding research.

The "elongate chelicera problem": A virtual approach in an extinct pterygotid sea scorpion from a 3D kinematic point of view

Chelicerae, distinctive feeding appendages in chelicerates, such as spiders, scorpions, or horseshoe crabs, can be classified based on their orientation relative to the body axis simplified as either orthognathous (parallel) or labidognathous (inclined), exhibiting considerable diversity across various taxa. Among extinct chelicerates, sea scorpions belonging to the Pterygotidae represent the only chelicerates possessing markedly elongated chelicerae relative to body length. Despite various hypotheses regarding the potential ecological functions and feeding movements of these structures, no comprehensive 3D kinematic investigation has been conducted yet to test these ideas. In this study, we generated a comprehensive 3D model of the pterygotid Acutiramus, making the elongated right chelicera movable by equipping it with virtual joint axes for conducting Range of Motion analyses. Due to the absence in the fossil record of a clear indication of the chelicerae orientation and their potential lateral or ventral movements (vertical or horizontal insertion of joint axis 1), we explored the Range of Motion analyses under four distinct kinematic settings with two orientation modes (euthygnathous, klinogathous) analogous to the terminology of the terrestrial relatives. The most plausible kinematic setting involved euthygnathous chelicerae being folded ventrally over a horizontal joint axis. This configuration positioned the chelicera closest to the oral opening. Concerning the maximum excursion angle, our analysis revealed that the chela could open up to 70°, while it could be retracted against the basal element to a maximum of 145°. The maximum excursion in the proximal joint varied between 55° and 120° based on the insertion and orientation. Our findings underscore the utility of applying 3D kinematics to fossilized arthropods for addressing inquiries on functional ecology such as prey capture and handling, enabling insights into their possible behavioral patterns. Pterygotidae likely captured and processed their prey using the chelicerae, subsequently transporting it to the oral opening with the assistance of other prosomal appendages.

Articular surface interactions distinguish dinosaurian locomotor joint poses

Our knowledge of vertebrate functional evolution depends on inferences about joint function in extinct taxa. Without rigorous criteria for evaluating joint articulation, however, such analyses risk misleading reconstructions of vertebrate animal motion. Here we propose an approach for synthesizing raycast-based measurements of 3-D articular overlap, symmetry, and congruence into a quantitative "articulation score" for any non-interpenetrating six-degree-of-freedom joint configuration. We apply our methodology to bicondylar hindlimb joints of two extant dinosaurs (guineafowl, emu) and, through comparison with in vivo kinematics, find that locomotor joint poses consistently have high articulation scores. We then exploit this relationship to constrain reconstruction of a pedal walking stride cycle for the extinct dinosaur Deinonychus antirrhopus, demonstrating the utility of our approach. As joint articulation is investigated in more living animals, the framework we establish here can be expanded to accommodate additional joints and clades, facilitating improved understanding of vertebrate animal motion and its evolution.

Modulation of limb mechanics in alligators moving across varying grades

Graded substrates require legged animals to modulate their limb mechanics to meet locomotor demands. Previous work has elucidated strategies used by cursorial animals with upright limb posture, but it remains unclear how sprawling species such as alligators transition between grades. We measured individual limb forces and 3D kinematics as alligators walked steadily across level, 15 deg incline and 15 deg decline conditions. We compared our results with the literature to determine how limb posture alters strategies for managing the energetic variation that accompanies shifts in grade. We found that juvenile alligators maintain spatiotemporal characteristics of gait and locomotor speed while selectively modulating craniocaudal impulses (relative to level) when transitioning between grades. Alligators seem to accomplish this using a variety of kinematic strategies, but consistently sprawl both limb pairs outside of the parasagittal plane during decline walking. This latter result suggests alligators and other sprawling species may use movements outside of the parasagittal plane as an axis of variation to modulate limb mechanics when transitioning between graded substrates. We conclude that limb mechanics during graded locomotion are fairly predictable across quadrupedal species, regardless of body plan and limb posture, with hindlimbs playing a more propulsive role and forelimbs functioning to dissipate energy. Future work will elucidate how shifts in muscle properties or function underlie such shifts in limb kinematics.

Beam theory predicts muscle deformation and vertebral curvature during feeding in rainbow trout (Oncorhynchus mykiss)

Muscle shortening underpins most skeletal motion and ultimately animal performance. Most animal muscle generates its greatest mechanical output over a small, homogeneous range of shortening magnitudes and speeds. However, homogeneous muscle shortening is difficult to achieve for swimming fish because the whole body deforms like a bending beam: as the vertebral column flexes laterally, longitudinal muscle strain increases along a medio-lateral gradient. Similar dorsoventral strain gradients have been identified as the vertebral column flexes dorsally during feeding in at least one body location in one fish. If fish bodies also deform like beams during dorsoventral feeding motions, this would suggest the dorsal body (epaxial) muscles must homogenize both dorsoventral and mediolateral strain gradients. We tested this hypothesis by measuring curvature of the anterior vertebral column with XROMM and muscle shortening in 14 epaxial subregions with fluoromicrometry during feeding in rainbow trout (Oncorhynchus mykiss). We compared measured strain with the predicted strain based on beam theory's curvature-strain relationship. Trout flexed the vertebrae dorsally and laterally during feeding strikes, yet when flexion in both planes was included, the strain predicted by beam theory was strongly and significantly correlated with measured strain (P<0.01, R2=0.60). Beam theory accurately predicted strain (slope=1.15, compared with ideal slope=1) across most muscle subregions, confirming that epaxial muscles experience dorsoventral and mediolateral gradients in longitudinal strain. Establishing this deformation-curvature relationship is a crucial step to understanding how these muscles overcome orthogonal strain gradients to produce powerful feeding and swimming behaviours.

Emerging biological insights enabled by high-resolution 3D motion data: promises, perspectives and pitfalls

Deconstructing motion to better understand it is a key prerequisite in the field of comparative biomechanics. Since Marey and Muybridge's work, technical constraints have been the largest limitation to motion capture and analysis, which, in turn, limited what kinds of questions biologists could ask or answer. Throughout the history of our field, conceptual leaps and significant technical advances have generally worked hand in hand. Recently, high-resolution, three-dimensional (3D) motion data have become easier to acquire, providing new opportunities for comparative biomechanics. We describe how adding a third dimension of information has fuelled major paradigm shifts, not only leading to a reinterpretation of long-standing scientific questions but also allowing new questions to be asked. In this paper, we highlight recent work published in Journal of Experimental Biology and influenced by these studies, demonstrating the biological breakthroughs made with 3D data. Although amazing opportunities emerge from these technical and conceptual advances, high-resolution data often come with a price. Here, we discuss challenges of 3D data, including low-throughput methodology, costly equipment, low sample sizes, and complex analyses and presentation. Therefore, we propose guidelines for how and when to pursue 3D high-resolution data. We also suggest research areas that are poised for major new biological advances through emerging 3D data collection.

Joint mobility as a bridge between form and function

Joints enable nearly all vertebrate animal motion, from feeding to locomotion. However, despite well over a century of arthrological research, we still understand very little about how the structure of joints relates to the kinematics they exhibit in life. This Commentary discusses the value of joint mobility as a lens through which to study articular form and function. By independently exploring form-mobility and mobility-function relationships and integrating the insights gained, we can develop a deep understanding of the strength and causality of articular form-function relationships. In turn, we will better illuminate the basics of 'how joints work' and be well positioned to tackle comparative investigations of the diverse repertoire of vertebrate animal motion.

Estimation of skeletal kinematics in freely moving rodents

Forming a complete picture of the relationship between neural activity and skeletal kinematics requires quantification of skeletal joint biomechanics during free behavior; however, without detailed knowledge of the underlying skeletal motion, inferring limb kinematics using surface-tracking approaches is difficult, especially for animals where the relationship between the surface and underlying skeleton changes during motion. Here we developed a videography-based method enabling detailed three-dimensional kinematic quantification of an anatomically defined skeleton in untethered freely behaving rats and mice. This skeleton-based model was constrained using anatomical principles and joint motion limits and provided skeletal pose estimates for a range of body sizes, even when limbs were occluded. Model-inferred limb positions and joint kinematics during gait and gap-crossing behaviors were verified by direct measurement of either limb placement or limb kinematics using inertial measurement units. Together we show that complex decision-making behaviors can be accurately reconstructed at the level of skeletal kinematics using our anatomically constrained model.

In Vivo Analysis of the Dynamic Motion Stability Characteristics of Geese’s Neck

The goose’s neck is an excellent stabilizing organ with its graceful neck curves and flexible movements. However, the stabilizing mechanism of the goose’s neck remains unclear. This study adopts a dynamic in vivo experimental method to obtain continuous and accurate stable motion characteristics of the goose’s cervical vertebra. Firstly, the results showed that when the body of a goose was separately moved back and forth along the Y direction (front and back) and Z direction (up and down), the goose’s neck can significantly stabilize the head. Then, because of the limitation of the X-ray imaging area, the three-dimensional intervertebral rotational displacements for vertebrae C4–C8 were obtained, and the role that these five segments play in the stabilization of the bird’s neck was analyzed. This study reveals that the largest range of the adjacent vertebral rotational movement is around the X-axis, the second is around the Y-axis, and the smallest is around the Z-axis. This kinematic feature is accord with the kinematic feature of the saddle joint, which allows the flexion/around X-axis and lateral bending/around Y-axis, and prevents axial rotation/around Z-axis.

Color in motion: Generating 3-dimensional multispectral models to study dynamic visual signals in animals

Analyzing color and pattern in the context of motion is a central and ongoing challenge in the quantification of animal coloration. Many animal signals are spatially and temporally variable, but traditional methods fail to capture this dynamism because they use stationary animals in fixed positions. To investigate dynamic visual displays and to understand the evolutionary forces that shape dynamic colorful signals, we require cross-disciplinary methods that combine measurements of color, pattern, 3-dimensional (3D) shape, and motion. Here, we outline a workflow for producing digital 3D models with objective color information from museum specimens with diffuse colors. The workflow combines multispectral imaging with photogrammetry to produce digital 3D models that contain calibrated ultraviolet (UV) and human-visible (VIS) color information and incorporate pattern and 3D shape. These “3D multispectral models” can subsequently be animated to incorporate both signaler and receiver movement and analyzed in silico using a variety of receiver-specific visual models. This approach—which can be flexibly integrated with other tools and methods—represents a key first step toward analyzing visual signals in motion. We describe several timely applications of this workflow and next steps for multispectral 3D photogrammetry and animation techniques.

Automatic landmark detection and mapping for 2D/3D registration with BoneNet

The 3D musculoskeletal motion of animals is of interest for various biological studies and can be derived from X-ray fluoroscopy acquisitions by means of image matching or manual landmark annotation and mapping. While the image matching method requires a robust similarity measure (intensity-based) or an expensive computation (tomographic reconstruction-based), the manual annotation method depends on the experience of operators. In this paper, we tackle these challenges by a strategic approach that consists of two building blocks: an automated 3D landmark extraction technique and a deep neural network for 2D landmarks detection. For 3D landmark extraction, we propose a technique based on the shortest voxel coordinate variance to extract the 3D landmarks from the 3D tomographic reconstruction of an object. For 2D landmark detection, we propose a customized ResNet18-based neural network, BoneNet, to automatically detect geometrical landmarks on X-ray fluoroscopy images. With a deeper network architecture in comparison to the original ResNet18 model, BoneNet can extract and propagate feature vectors for accurate 2D landmark inference. The 3D poses of the animal are then reconstructed by aligning the extracted 2D landmarks from X-ray radiographs and the corresponding 3D landmarks in a 3D object reference model. Our proposed method is validated on X-ray images, simulated from a real piglet hindlimb 3D computed tomography scan and does not require manual annotation of landmark positions. The simulation results show that BoneNet is able to accurately detect the 2D landmarks in simulated, noisy 2D X-ray images, resulting in promising rigid and articulated parameter estimations.

DeepLabCut increases markerless tracking efficiency in X-Ray video analysis of rodent locomotion

Despite the prevalence of rat models to study human disease and injury, existing methods for quantifying behavior through skeletal movements are problematic due to skin movement inaccuracies associated with optical video analysis; or, require invasive implanted markers or time consuming manual rotoscoping for x-ray video approaches. We examined the use of a machine learning tool, DeepLabCut, to perform automated, markerless tracking in bi-planar x-ray videos of locomoting rats. Models were trained on 590 pairs of video frames to identify 19 unique skeletal landmarks of the pelvic limb. Accuracy, precision, and time savings were assessed. Machine-identified landmarks deviated from manually labeled counterparts by 2.4±0.2 mm (n=1,710 landmarks). DeepLabCut decreased analysis time by over three orders of magnitude (1,627x) compared to manual labeling. Distribution of these models may enable the processing of a large volume of accurate x-ray kinematics locomotion data in a fraction of the time without requiring surgically implanted markers.

A therian mammal with sprawling kinematics? Gait and 3D forelimb X-ray motion analysis in tamanduas

Therian mammals are known to move their forelimbs in a parasagittal plane, retracting the mobilised scapula during stance phase. Non-cursorial therian mammals often abduct the elbow out of the shoulder-hip parasagittal plane. This is especially prominent in Tamandua (Xenarthra), which suggests they employ aspects of sprawling (e.g., lizard-like-) locomotion. Here, we test if tamanduas use sprawling forelimb kinematics, i.e., a largely immobile scapula with pronounced lateral spine bending and long-axis rotation of the humerus. We analyse high speed videos and use X-ray motion analysis of tamanduas walking and balancing on branches of varying inclinations and provide a quantitative characterization of gaits and forelimb kinematics. Tamanduas displayed lateral sequence lateral-couplets gaits on flat ground and horizontal branches, but increased diagonality on steeper in- and declines, resulting in lateral sequence diagonal-couplets gaits. This result provides further evidence for high diagonality in arboreal species, likely maximising stability in arboreal environments. Further, the results reveal a mosaic of sprawling and parasagittal kinematic characteristics. The abducted elbow results from a constantly internally rotated scapula about its long axis and a retracted humerus. Scapula retraction contributes considerably to stride length. However, lateral rotation in the pectoral region of the spine (range: 21°) is higher than reported for other therian mammals. Instead, it is similar to skinks and alligators, indicating an aspect generally associated with sprawling locomotion is characteristic for forelimb kinematics of tamanduas. Our study contributes to a growing body of evidence of highly variable non-cursorial therian mammal locomotor kinematics.

Modular lung ventilation in Boa constrictor

The evolution of constriction and of large prey ingestion within snakes are key innovations that may explain the remarkable diversity, distribution and ecological scope of this clade, relative to other elongate vertebrates. However, these behaviors may have simultaneously hindered lung ventilation such that early snakes may have had to circumvent these mechanical constraints before those behaviors could evolve. Here, we demonstrate that Boa constrictor can modulate which specific segments of ribs are used to ventilate the lung in response to physically hindered body wall motions. We show that the modular actuation of specific segments of ribs likely results from active recruitment or quiescence of derived accessory musculature. We hypothesize that constriction and large prey ingestion were unlikely to have evolved without modular lung ventilation because of their interference with lung ventilation, high metabolic demands and reliance on sustained lung convection. This study provides a new perspective on snake evolution and suggests that modular lung ventilation evolved during or prior to constriction and large prey ingestion, facilitating snakes' remarkable radiation relative to other elongate vertebrates.

A new conceptual framework for the musculoskeletal biomechanics and physiology of ray-finned fishes

Suction feeding in ray-finned fishes requires substantial muscle power for fast and forceful prey capture. The axial musculature located immediately behind the head has been long known to contribute some power for suction feeding, but recent XROMM and fluoromicrometry studies found nearly all the axial musculature (over 80%) provides effectively all (90–99%) of the power for high-performance suction feeding. The dominance of axial power suggests a new framework for studying the musculoskeletal biomechanics of fishes: the form and function of axial muscles and bones should be analysed for power production in feeding (or at least as a compromise between swimming and feeding), and cranial muscles and bones should be analysed for their role in transmitting axial power and coordinating buccal expansion. This new framework is already yielding novel insights, as demonstrated in four species for which suction power has now been measured. Interspecific comparisons suggest high suction power can be achieved in different ways: increasing the magnitude of suction pressure or the rate of buccal volume change, or both (as observed in the most powerful of these species). Our framework suggests that mechanical and evolutionary interactions between the head and the body, and between the swimming and feeding roles of axial structures, may be fruitful areas for continued study.

Summary: The recent discovery that some fish use their whole bodies for high-performance suction feeding prompts a reappraisal of cranial and axial biomechanics and overall body shape in ray-finned fishes.

In vivo intraoral waterflow quantification reveals hidden mechanisms of suction feeding in fish

Virtually all fishes rely on flows of water to transport food to the back of their pharynx. While external flows that draw food into the mouth are well described, how intra-oral water flows manage to deposit food at the esophagus entrance remains unknown. In theory, the posteriorly moving water must, at some point, curve laterally and/or ventrally to exit through the gill slits. Such flows would eventually carry food away from the esophagus instead of toward it. This apparent paradox calls for a filtration mechanism to deviate food from the suction-feeding streamlines. To study this gap in our fundamental understanding of how fishes feed, we developed and applied a new technique to quantify three-dimensional patterns of intra-oral water flows in vivo. We combined stereoscopic high-speed x-ray videos to quantify skeletal motion (XROMM) with 3D x-ray particle tracking (XPT) of neutrally buoyant spheres of 1.4 mm in diameter. We show, for carp (Cyprinus carpio) and tilapia (Oreochromis niloticus), that water tracers displayed higher curvatures than food tracers, indicating an inertia-driven filtration. In addition, tilapia also exhibited a 'central jet' flow pattern, which aids in quickly carrying food to the pharyngeal jaw region. When the food was trapped at the branchial basket, it was resuspended and carried more centrally by periodical bidirectional waterflows, synchronized with head-bone motions. By providing a complete picture of the suction-feeding process and revealing fundamental differences in food transport mechanisms among species, this novel technique opens a new area of investigation to fully understand how most aquatic vertebrates feed.

Spines and baskets in apex predatory sea scorpions uncover unique feeding strategies using 3D-kinematics

Megalograptidae and Mixopteridae with elongate, spinose prosomal appendages are unique early Palaeozoic sea scorpions (Eurypterida). These features were presumably used for hunting, an untested hypothesis. Here, we present 3D model-based kinematic range of motion (ROM) analyses of Megalograptus ohioensis and Mixopterus kiaeri and compare these to modern analogs. This comparison confirms that the eurypterid appendages were likely raptorial, used in grabbing and holding prey for consumption. The Megalograptus ohioensis model illustrates notable Appendage III flexibility, indicating hypertrophied spines on Appendage III may have held prey, while Appendage II likely ripped immobilized prey. Mixopterus kiaeri, conversely, constructed a capture basket with Appendage III, and impaled prey with Appendage II elongated spines. Thus, megalograptid and mixopterid frontalmost appendages constructed a double basket system prior to moving dismembered prey to the chelicerae. Such 3D kinematic modeling presents a more complete understanding of these peculiar euchelicerates and highlights their possible position within past ecosystems.

Virtual and augmented reality: New tools for visualizing, analyzing, and communicating complex morphology

Virtual and augmented reality (VR/AR) are new technologies with the power to revolutionize the study of morphology. Modern imaging approaches such as computed tomography, laser scanning, and photogrammetry have opened up a new digital world, enabling researchers to share and analyze morphological data electronically and in great detail. Because this digital data exists on a computer screen, however, it can remain difficult to understand and unintuitive to interact with. VR/AR technologies bridge the analog-to-digital divide by presenting 3D data to users in a very similar way to how they would interact with actual anatomy, while also providing a more immersive experience and greater possibilities for exploration. This manuscript describes VR/AR hardware, software, and techniques, and is designed to give practicing morphologists and educators a primer on using these technologies in their research, pedagogy, and communication to a wide variety of audiences. We also include a series of case studies from the presentations and workshop given at the 2019 International Congress of Vertebrate Morphology, and suggest best practices for the use of VR/AR in comparative morphology.

Three-Dimensional Kinematics of the Pelvis and Caudal Lumbar Spine in German Shepherd Dogs

Lumbosacral vertebral motion is thought to be a factor in the development of degenerative lumbosacral stenosis in German shepherd dogs. So far, few studies exist describing natural canine lumbosacral movement in vivo. Therefore, this investigation aims to achieve a detailed in vivo analysis of bone movement of the lumbosacral region to gain a better understanding of the origin of degenerative lumbosacral stenosis using three-dimensional non-invasive in vivo analysis of canine pelvic and caudal lumbar motion (at L6 and L7). Biplanar cineradiography of the pelvis and caudal lumbar spine of four clinically sound German shepherd dogs at a walk and at a trot on a treadmill was recorded. Pelvic and intervertebral motion was virtually reconstructed and analyzed with scientific rotoscoping. The use of this technique made possible non-invasive measurement of physiological vertebral motion in dogs with high accuracy. Furthermore, the gait patterns of the dogs revealed a wide variation both between individual steps and between dogs. Pelvic motion showed a common basic pattern throughout the stride cycle. Motion at L6 and L7, except for sagittal rotation at a trot, was largely asynchronous with the stride cycle. Intervertebral motion in all dogs was small with approximately 2–3° rotation and translations of approximately 1–2 mm. The predominant motion of the pelvis was axial rotation at a walk, whereas lateral rotation was predominant at a trot. L7 showed a predominance of sagittal rotation (with up to 5.1° at a trot), whereas lateral rotation was the main component of the movement at L6 (about 2.3° in both gaits). During trotting, a coupling of various motions was detected: axial rotation of L7 and the pelvis was inverse and was coupled with craniocaudal translation of L7. In addition, a certain degree of compensation of abnormal pelvic movements during walking and trotting by the caudal lumbar spine was evident.

Biomechanics of the Canine Elbow Joint

The canine elbow joint is a complex joint, whose musculoskeletal anatomy is well investigated. During the last 30 years kinematic analysis has gained importance in veterinary research and kinematics of the healthy and medial coronoid disease affected canine elbow joint are progressively investigated. Video-kinematographic analysis represents the most commonly used technique and multiple studies have investigated the range of motion, angular velocity, duration of swing and stance phase, stride length and other kinematic parameters, mostly in the sagittal plane only. However, this technique is more error-prone and data gained by video-kinematography represent the kinematics of the whole limb including the soft tissue envelope. A more precise evaluation of the in vivo bone and joint movement can only been achieved using fluoroscopic kinematography. Based on recent studies significant differences in the motion pattern between healthy joints and elbows with medial coronoid disease could be detected. Thereby not only adaptive changes, caused by pain and lameness, could be described, but primary changes in the micromotion of the joint forming bones could be found, which potentially represent new factors in the pathogenesis of medial coronoid disease. This chapter gives a review of current literature on elbow joint kinematics, with particular focus onto pathologic biomechanics in dysplastic canine elbows.

Three-Dimensional Kinematic Motion of the Craniocervical Junction of Chihuahuas and Labrador Retrievers

All vertebrate species have a distinct morphology and movement pattern, which reflect the adaption of the animal to its habitat. Yet, our knowledge of motion patterns of the craniocervical junction of dogs is very limited. The aim of this prospective study is to perform a detailed analysis and description of three-dimensional craniocervical motion during locomotion in clinically sound Chihuahuas and Labrador retrievers. This study presents the first in vivo recorded motions of the craniocervical junction of clinically sound Chihuahuas (n = 8) and clinically sound Labrador retrievers (n = 3) using biplanar fluoroscopy. Scientific rotoscoping was used to reconstruct three-dimensional kinematics during locomotion. The same basic motion patterns were found in Chihuahuas and Labrador retrievers during walking. Sagittal, lateral, and axial rotation could be observed in both the atlantoaxial and the atlantooccipital joints during head motion and locomotion. Lateral and axial rotation occurred as a coupled motion pattern. The amplitudes of axial and lateral rotation of the total upper cervical motion and the atlantoaxial joint were higher in Labrador retrievers than in Chihuahuas. The range of motion (ROM) maxima were 20°, 26°, and 24° in the sagittal, lateral, and axial planes, respectively, of the atlantoaxial joint. ROM maxima of 30°, 16°, and 18° in the sagittal, lateral, and axial planes, respectively, were found at the atlantooccipital joint. The average absolute sagittal rotation of the atlas was slightly higher in Chihuahuas (between 9.1 ± 6.8° and 18.7 ± 9.9°) as compared with that of Labrador retrievers (between 5.7 ± 4.6° and 14.5 ± 2.6°), which corresponds to the more acute angle of the atlas in Chihuahuas. Individual differences for example, varying in amplitude or time of occurrence are reported.

A neck-like vertebral motion in fish

Tetrapods use their neck to move the head three-dimensionally, relative to the body and limbs. Fish lack this anatomical neck, yet during feeding many species elevate (dorsally rotate) the head relative to the body. Cranial elevation is hypothesized to result from the craniovertebral and cranial-most intervertebral joints acting as a neck, by dorsally rotating (extending). However, this has never been tested due to the difficulty of visualizing and measuring vertebral motion in vivo. I used X-ray reconstruction of moving morphology to measure three-dimensional vertebral kinematics in rainbow trout (Oncorhynchus mykiss) and Commerson's frogfish (Antennarius commerson) during feeding. Despite dramatically different morphologies, in both species dorsoventral rotations extended far beyond the craniovertebral and cranial intervertebral joints. Trout combine small (most less than 3°) dorsal rotations over up to a third of their intervertebral joints to elevate the neurocranium. Frogfish use extremely large (often 20-30°) rotations of the craniovertebral and first intervertebral joint, but smaller rotations occurred across two-thirds of the vertebral column during cranial elevation. Unlike tetrapods, fish rotate large regions of the vertebral column to rotate the head. This suggests both cranial and more caudal vertebrae should be considered to understand how non-tetrapods control motion at the head-body interface.

Modeling Sprawling Locomotion of the Stem Amniote Orobates: An Examination of Hindlimb Muscle Strains and Validation Using Extant Caiman

The stem amniote Orobates pabsti has been reconstructed to be capable of relatively erect, balanced, and mechanically power-saving terrestrial locomotion. This suggested that the evolution of such advanced locomotor capabilities preceded the origin of crown-group amniotes. We here further investigate plausible body postures and locomotion of Orobates by taking soft tissues into account. Freely available animation software BLENDER is used to first reconstruct the lines of action of hindlimb adductors and retractors for Orobates and then estimate the muscle strain of these muscles. We experimentally varied different body heights in modeled hindlimb stride cycles of Orobates to find the posture that maximizes optimal strains over the course of a stride cycle. To validate our method, we used Caiman crocodilus. We replicated the identical workflow used for the analysis of Orobates and compared the locomotor posture predicted for Caiman based on muscle strain analysis with this species’ actual postural data known from a previously published X-ray motion analysis. Since this validation experiment demonstrated a close match between the modeled posture that maximizes optimal adductor and retractor muscle strain and the in vivo posture employed by Caiman, using the same method for Orobates was justified. Generally, the use of muscle strain analysis for the reconstruction of posture in quadrupedal vertebrate fossils thus appears a promising approach. Nevertheless, results for Orobates remained inconclusive as several postures resulted in similar muscle strains and none of the postures could be entirely excluded. These results are not in conflict with the previously inferred moderately erect locomotor posture of Orobates and suggest considerable variability of posture during locomotion.

On the 3D Nature of the Magpie (Aves: Pica pica) Functional Hindlimb Anatomy During the Take-Off Jump

Take-off is a critical phase of flight, and many birds jump to take to the air. Although the actuation of the hindlimb in terrestrial birds is not limited to the sagittal plane, and considerable non-sagittal plane motion has been observed during take-off jumps, how the spatial arrangement of hindlimb muscles in flying birds facilitates such jumps has received little attention. This study aims to ascertain the 3D hip muscle function in the magpie (Pica pica), a bird known to jump to take-off. A musculoskeletal model of the magpie hindlimb was developed using μCT scans (isotropic resolution of 18.2 μm) to derive bone surfaces, while the 3D muscle path definition was further informed by the literature. Function was robustly characterized by determining the 3D moment-generating capacity of 14 hip muscles over the functional joint range of motion during a take-off leap considering variations across the attachment areas and uncertainty in dynamic muscle geometry. Ratios of peak flexion-extension (FE) to internal-external rotation (IER) and abduction-adduction (ABD) moment-generating capacity were indicators of muscle function. Analyses of 972 variations of the 3D muscle paths showed that 11 of 14 muscles can act as either flexor or extensor, while all 14 muscles demonstrated the capacity to act as internal or external rotators of the hip with the mean ratios of peak FE to IER and ABD moment-generating capacity were 0.89 and 0.31, respectively. Moment-generating capacity in IER approaching levels in the FE moment-generating capacity determined here underline that the avian hip muscle function is not limited to the sagittal plane. Together with previous findings on the 3D nature of hindlimb kinematics, our results suggest that musculoskeletal models to develop a more detailed understanding of how birds orchestrate the use of muscles during a take-off jump cannot be restricted to the sagittal plane.

Alligators employ intermetatarsal reconfiguration to modulate plantigrade ground contact

Feet must mediate substrate interactions across an animal's entire range of limb poses used in life. Metatarsals, the ‘bones of the sole’, are the dominant pedal skeletal elements for most tetrapods. In plantigrade species that walk on the entirety of their sole, such as living crocodylians, intermetatarsal mobility offers the potential for a continuum of reconfiguration within the foot itself. Alligator hindlimbs are capable of postural extremes from a belly sprawl to a high walk to sharp turns – how does the foot morphology dynamically accommodate these diverse demands? We implemented a hybrid combination of marker-based and markerless X-ray reconstruction of moving morphology (XROMM) to measure 3D metatarsal kinematics in three juvenile American alligators (Alligator mississippiensis) across their locomotor and maneuvering repertoire on a motorized treadmill and flat-surfaced arena. We found that alligators adaptively conformed their metatarsals to the ground, maintaining plantigrade contact throughout a spectrum of limb placements with non-planar feet. Deformation of the metatarsus as a whole occurred through variable abduction (twofold range of spread) and differential metatarsal pitching (45 deg arc of skew). Internally, metatarsals also underwent up to 65 deg of long-axis rotation. Such reorientation, which correlated with skew, was constrained by the overlapping arrangement of the obliquely expanded metatarsal bases. Such a proximally overlapping metatarsal morphology is shared by fossil archosaurs and archosaur relatives. In these extinct taxa, we suggest that intermetatarsal mobility likely played a significant role in maintaining ground contact across plantigrade postural extremes.

Summary: We measured 3D metatarsal kinematics in American alligators. Alligator metatarsals conform with the ground across a diversity of high walk and maneuvering postures, providing a context for interpreting the evolutionary history of metatarsals in the fossil record.

Cortical and trabecular bone structure of the hominoid capitate

Morphological variation in the hominoid capitate has been linked to differences in habitual locomotor activity due to its importance in movement and load transfer at the midcarpal joint proximally and carpometacarpal joints distally. Although the shape of bones and their articulations are linked to joint mobility, the internal structure of bones has been shown experimentally to reflect, at least in part, the loading direction and magnitude experienced by the bone. To date, it is uncertain whether locomotor differences among hominoids are reflected in the bone microarchitecture of the capitate. Here, we apply a whole‐bone methodology to quantify the cortical and trabecular architecture (separately and combined) of the capitate across bipedal (modern Homo sapiens), knuckle‐walking (Pan paniscus, Pan troglodytes, Gorilla sp.), and suspensory (Pongo sp.) hominoids (n = 69). It is hypothesized that variation in bone microarchitecture will differentiate these locomotor groups, reflecting differences in habitual postures and presumed loading force and direction. Additionally, it is hypothesized that trabecular and cortical architecture in the proximal and distal regions, as a result of being part of mechanically divergent joints proximally and distally, will differ across these portions of the capitate. Results indicate that the capitate of knuckle‐walking and suspensory hominoids is differentiated from bipedal Homo primarily by significantly thicker distal cortical bone. Knuckle‐walking taxa are further differentiated from suspensory and bipedal taxa by more isotropic trabeculae in the proximal capitate. An allometric analysis indicates that size is not a significant determinate of bone variation across hominoids, although sexual dimorphism may influence some parameters within Gorilla. Results suggest that internal trabecular and cortical bone is subjected to different forces and functional adaptation responses across the capitate (and possibly other short bones). Additionally, while separating trabecular and cortical bone is normal protocol of current whole‐bone methodologies, this study shows that when applied to carpals, removing or studying the cortical bone separately potentially obfuscates functionally relevant signals in bone structure.

Computational modelling of muscle fibre operating ranges in the hindlimb of a small ground bird (Eudromia elegans), with implications for modelling locomotion in extinct species

The arrangement and physiology of muscle fibres can strongly influence musculoskeletal function and whole-organismal performance. However, experimental investigation of muscle function during in vivo activity is typically limited to relatively few muscles in a given system. Computational models and simulations of the musculoskeletal system can partly overcome these limitations, by exploring the dynamics of muscles, tendons and other tissues in a robust and quantitative fashion. Here, a high-fidelity, 26-degree-of-freedom musculoskeletal model was developed of the hindlimb of a small ground bird, the elegant-crested tinamou (Eudromia elegans, ~550 g), including all the major muscles of the limb (36 actuators per leg). The model was integrated with biplanar fluoroscopy (XROMM) and forceplate data for walking and running, where dynamic optimization was used to estimate muscle excitations and fibre length changes throughout both gaits. Following this, a series of static simulations over the total range of physiological limb postures were performed, to circumscribe the bounds of possible variation in fibre length. During gait, fibre lengths for all muscles remained between 0.5 to 1.21 times optimal fibre length, but operated mostly on the ascending limb and plateau of the active force-length curve, a result that parallels previous experimental findings for birds, humans and other species. However, the ranges of fibre length varied considerably among individual muscles, especially when considered across the total possible range of joint excursion. Net length change of muscle-tendon units was mostly less than optimal fibre length, sometimes markedly so, suggesting that approaches that use muscle-tendon length change to estimate optimal fibre length in extinct species are likely underestimating this important parameter for many muscles. The results of this study clarify and broaden understanding of muscle function in extant animals, and can help refine approaches used to study extinct species.

Musculoskeletal modelling of the Nile crocodile (Crocodylus niloticus) hindlimb: Effects of limb posture on leverage during terrestrial locomotion

We developed a three-dimensional, computational biomechanical model of a juvenile Nile crocodile (Crocodylus niloticus) pelvis and hindlimb, composed of 47 pelvic limb muscles, to investigate muscle function. We tested whether crocodiles, which are known to use a variety of limb postures during movement, use limb orientations (joint angles) that optimise the moment arms (leverages) or moment-generating capacities of their muscles during different limb postures ranging from a high walk to a sprawling motion. We also describe the three-dimensional (3D) kinematics of the crocodylian hindlimb during terrestrial locomotion across an instrumented walkway and a treadmill captured via X-ray Reconstruction of Moving Morphology (biplanar fluoroscopy; 'XROMM'). We reconstructed the 3D positions and orientations of each of the hindlimb bones and used dissection data for muscle lines of action to reconstruct a focal, subject-specific 3D musculoskeletal model. Motion data for different styles of walking (a high, crouched, bended and two types of sprawling motion) were fed into the 3D model to identify whether any joints adopted near-optimal poses for leverage across each of the behaviours. We found that (1) the hip adductors and knee extensors had their largest leverages during sprawling postures and (2) more erect postures typically involved greater peak moment arms about the hip (flexion-extension), knee (flexion) and metatarsophalangeal (flexion) joints. The results did not fully support the hypothesis that optimal poses are present during different locomotory behaviours because the peak capacities were not always reached around mid-stance phase. Furthermore, we obtained few clear trends for isometric moment-generating capacities. Therefore, perhaps peak muscular leverage in Nile crocodiles is instead reached either in early/late stance or possibly during swing phase or other locomotory behaviours that were not studied here, such as non-terrestrial movement. Alternatively, our findings could reflect a trade-off between having to execute different postures, meaning that hindlimb muscle leverage is not optimised for any singular posture or behaviour. Our model, however, provides a comprehensive set of 3D estimates of muscle actions in extant crocodiles which can form a basis for investigating muscle function in extinct archosaurs.

A Practical Guide to Measuring Ex vivo Joint Mobility Using XROMM

X-Ray Reconstruction of Moving Morphology (XROMM), though traditionally used for studies of in vivo skeletal kinematics, can also be used to precisely and accurately measure ex vivo range of motion from cadaveric manipulations. The workflow for these studies is holistically similar to the in vivo XROMM workflow but presents several unique challenges. This paper aims to serve as a practical guide by walking through each step of the ex vivo XROMM process: how to acquire and prepare cadaveric specimens, how to manipulate specimens to collect X-ray data, and how to use these data to compute joint rotational mobility. Along the way, it offers recommendations for best practices and for avoiding common pitfalls to ensure a successful study.

3D hindlimb joint mobility of the stem-archosaur Euparkeria capensis with implications for postural evolution within Archosauria

Triassic archosaurs and stem-archosaurs show a remarkable disparity in their ankle and pelvis morphologies. However, the implications of these different morphologies for specific functions are still poorly understood. Here, we present the first quantitative analysis into the locomotor abilities of a stem-archosaur applying 3D modelling techniques. μCT scans of multiple specimens of Euparkeria capensis enabled the reconstruction and three-dimensional articulation of the hindlimb. The joint mobility of the hindlimb was quantified in 3D to address previous qualitative hypotheses regarding the stance of Euparkeria. Our range of motion analysis implies the potential for an erect posture, consistent with the hip morphology, allowing the femur to be fully adducted to position the feet beneath the body. A fully sprawling pose appears unlikely but a wide range of hip abduction remained feasible-the hip appears quite mobile. The oblique mesotarsal ankle joint in Euparkeria implies, however, a more abducted hindlimb. This is consistent with a mosaic of ancestral and derived osteological characters in the hindlimb, and might suggest a moderately adducted posture for Euparkeria. Our results support a single origin of a pillar-erect hip morphology, ancestral to Eucrocopoda that preceded later development of a hinge-like ankle joint and a more erect hindlimb posture.

Fishes can use axial muscles as anchors or motors for powerful suction feeding

Some fishes rely on large regions of the dorsal (epaxial) and ventral (hypaxial) body muscles to power suction feeding. Epaxial and hypaxial muscles are known to act as motors, powering rapid mouth expansion by shortening to elevate the neurocranium and retract the pectoral girdle, respectively. However, some species, like catfishes, use little cranial elevation. Are these fishes instead using the epaxial muscles to forcefully anchor the head, and if so, are they limited to lower-power strikes? We used X-ray imaging to measure epaxial and hypaxial length dynamics (fluoromicrometry) and associated skeletal motions (XROMM) during 24 suction feeding strikes from three channel catfish (Ictalurus punctatus). We also estimated the power required for suction feeding from oral pressure and dynamic endocast volume measurements. Cranial elevation relative to the body was small (<5 deg) and the epaxial muscles did not shorten during peak expansion power. In contrast, the hypaxial muscles consistently shortened by 4–8% to rotate the pectoral girdle 6–11 deg relative to the body. Despite only the hypaxial muscles generating power, catfish strikes were similar in power to those of other species, such as largemouth bass (Micropterus salmoides), that use epaxial and hypaxial muscles to power mouth expansion. These results show that the epaxial muscles are not used as motors in catfish, but suggest they position and stabilize the cranium while the hypaxial muscles power mouth expansion ventrally. Thus, axial muscles can serve fundamentally different mechanical roles in generating and controlling cranial motion during suction feeding in fishes.

Highlighted Article: Channel catfish use their dorsal body muscles to stabilize the head during suction feeding, while the ventral body muscles power mouth expansion.

It's in the loop: shared sub-surface foot kinematics in birds and other dinosaurs shed light on a new dimension of fossil track diversity

The feet of ground-dwelling birds retain many features of their dinosaurian ancestry. Experiments with living species offer insights into the complex interplay among anatomy, kinematics and substrate during the formation of Mesozoic footprints. However, a key aspect of the track-making process, sub-surface foot movement, is hindered by substrate opacity. Here, we use biplanar X-rays to image guineafowl walking through radiolucent substrates of different consistency (solid, dry granular, firm to semi-liquid muds). Despite substantial kinematic variation, the foot consistently moves in a looping pattern below ground. As the foot sinks and then withdraws, the claws of the three main toes create entry and exit paths in different locations. Sampling these paths at incremental horizons captures two-dimensional features just as fossil tracks do, allowing depth-based zones to be characterized by the presence and relative position of digit impressions. Examination of deep, penetrative tracks from the Early Jurassic confirms that bipeds had an equivalent looping response to soft substrates approximately 200 Ma. Our integration of extant and extinct evidence demonstrates the influence of substrate properties on sinking depth and sub-surface foot motion, both of which are significant sources of track variation in the fossil record of dinosaurs.

The Reliability of Foot and Ankle Bone and Joint Kinematics Measured With Biplanar Videoradiography and Manual Scientific Rotoscoping

The intricate motion of the small bones of the feet are critical for its diverse function. Accurately measuring the 3-dimensional (3D) motion of these bones has attracted much attention over the years and until recently, was limited to invasive techniques or quantification of functional segments using multi-segment foot models. Biplanar videoradiography and model-based scientific rotoscoping offers an exciting alternative that allows us to focus on the intricate motion of individual bones in the foot. However, scientific rotoscoping, the process of rotating and translating a 3D bone model so that it aligns with the captured x-ray images, is either semi- or completely manual and it is unknown how much human error affects tracking results. Thus, the aim of this study was to quantify the inter- and intra-operator reliability of manually rotoscoping in vivo bone motion of the tibia, talus, and calcaneus during running. Three-dimensional CT bone volumes and high-speed biplanar videoradiography images of the foot were acquired on six participants. The six-degree-of-freedom motions of the tibia, talus, and calcaneus were determined using a manual markerless registration algorithm. Two operators performed the tracking, and additionally, the first operator re-tracked all bones, to test for intra-operator effects. Mean RMS errors were 1.86 mm and 1.90° for intra-operator comparisons and 2.30 mm and 2.60° for inter-operator comparisons across all bones and planes. The moderate to strong similarity values indicate that tracking bones and joint kinematics between sessions and operators is reliable for running. These errors are likely acceptable for defining gross joint angles. However, this magnitude of error may limit the capacity to perform advanced analyses of joint interactions, particularly those that require precise (sub-millimeter) estimates of bone position and orientation. Optimizing the view and image quality of the biplanar videoradiography system as well as the automated tracking algorithms for rotoscoping bones in the foot are required to reduce these errors and the time burden associated with the manual processing.

Effects of treadmill running and limb immobilization on knee cartilage degeneration and locomotor joint kinematics in rats following knee meniscal transection

OBJECTIVE

This study examined the effects of reduced and elevated weight bearing on post-traumatic osteoarthritis (PTOA) development, locomotor joint kinematics, and degree of voluntary activity in rats following medial meniscal transection (MMT).

DESIGN

Twenty-one adult rats were subjected to MMT surgery of the left hindlimb and then assigned to one of three groups: (1) regular (i.e., no intervention), (2) hindlimb immobilization, or (3) treadmill running. Sham surgery was performed in four additional rats. Voluntary wheel run time/distance was measured, and 3D hindlimb kinematics were quantified during treadmill locomotion using biplanar radiography. Rats were euthanized 8 weeks after MMT or sham surgery, and the microstructure of the tibial cartilage and subchondral bone was quantified using contrast enhanced micro-CT.

RESULTS

All three MMT groups showed signs of PTOA (full-thickness lesions and/or increased cartilage volume) compared to the sham group, however the regular and treadmill-running groups had greater osteophyte formation than the immobilization group. For the immobilization group, increased volume was only observed in the anterior region of the cartilage. The treadmill-running group demonstrated a greater knee varus angle at mid-stance than the sham group, while the immobilization group demonstrated greater reduction in voluntary running than all the other groups at 2 weeks post-surgery.

CONCLUSIONS

Elevated weight-bearing via treadmill running at a slow/moderate speed did not accelerate PTOA in MMT rats when compared to regular weight-bearing. Reduced weight-bearing via immobilization may attenuate overall PTOA but still resulted in regional cartilage degeneration. Overall, there were minimal differences in hindlimb kinematics and voluntary running between MMT and sham rats.

Intra-oropharyngeal food transport and swallowing in white-spotted bamboo sharks

Despite the importance of intraoral food transport and swallowing, relatively few studies have examined the biomechanics of these behaviors in non-tetrapods, which lack a muscular tongue. Studies show that elasmobranch and teleost fishes generate water currents as a 'hydrodynamic tongue' that presumably transports food towards and into the esophagus. However, it remains largely unknown how specific musculoskeletal motions during transport correspond to food motion. Previous studies of white-spotted bamboo sharks (Chiloscyllium plagiosum) hypothesized that motions of the hyoid, branchial arches and pectoral girdle, generate caudal motion of the food through the long oropharynx of modern sharks. To test these hypotheses, we measured food and cartilage motion with XROMM during intra-oropharyngeal transport and swallowing (N=3 individuals, 2-3 trials per individual). After entering the mouth, food does not move smoothly toward the esophagus, but rather moves in distinct steps with relatively little retrograde motion. Caudal food motion coincides with hyoid elevation and a closed mouth, supporting earlier studies showing that hyoid motion contributes to intra-oropharyngeal food transport by creating caudally directed water currents. Little correspondence between pectoral girdle and food motion was found, indicating minimal contribution of pectoral girdle motion. Transport speed was fast as food entered the mouth, slower and step-wise through the pharyngeal region and then fast again as it entered the esophagus. The food's static periods in the step-wise motion and its high velocity during swallowing could not be explained by hyoid or girdle motion, suggesting these sharks may also use the branchial arches for intra-oropharyngeal transport and swallowing.

How moles walk; it's all thumbs

A recurring theme in the evolution of tetrapods is the shift from sprawling posture with laterally orientated limbs to erect posture with the limbs extending below the body. However, in order to invade particular locomotor niches, some tetrapods secondarily evolved a sprawled posture. This includes moles, some of the most specialized digging tetrapods. Although their forelimb anatomy and posture facilitates burrowing, moles also walk long distances to forage for and transport food. Here, we use X-ray Reconstruction Of Moving Morphology (XROMM) to determine if the mole humerus rotates around its long axis during walking, as it does when moles burrow and echidnas walk, or alternatively protracts and retracts at the shoulder in the horizontal plane as seen in sprawling reptiles. Our results reject both hypotheses and demonstrate that forelimb kinematics during mole walking are unusual among those described for tetrapods. The humerus is retracted and protracted in the parasagittal plane above, rather than below the shoulder joint and the 'false thumb', a sesamoid bone (os falciforme), supports body weight during the stance phase, which is relatively short. Our findings broaden our understanding of the diversity of tetrapod limb posture and locomotor evolution, demonstrate the importance of X-ray-based techniques for revealing hidden kinematics and highlight the importance of examining locomotor function at the level of individual joint mobility.

A Direct Comparison of Biplanar Videoradiography and Optical Motion Capture for Foot and Ankle Kinematics

Measuring motion of the human foot presents a unique challenge due to the large number of closely packed bones with congruent articulating surfaces. Optical motion capture (OMC) and multi-segment models can be used to infer foot motion, but might be affected by soft tissue artifact (STA). Biplanar videoradiography (BVR) is a relatively new tool that allows direct, non-invasive measurement of bone motion using high-speed, dynamic x-ray images to track individual bones. It is unknown whether OMC and BVR can be used interchangeably to analyse multi-segment foot motion. Therefore, the aim of this study was to determine the agreement in kinematic measures of dynamic activities. Nine healthy participants performed three walking and three running trials while BVR was recorded with synchronous OMC. Bone position and orientation was determined through manual scientific-rotoscoping. The OMC and BVR kinematics were co-registered to the same coordinate system, and BVR tracking was used to create virtual markers for comparison to OMC during dynamic trials. Root mean square (RMS) differences in marker positions and joint angles as well as a linear fit method (LFM) was used to compare the outputs of both methods. When comparing BVR and OMC, sagittal plane angles were in good agreement (ankle: R² = 0.947, 0.939; Medial Longitudinal Arch (MLA) Angle: R² = 0.713, 0.703, walking and running, respectively). When examining the ankle, there was a moderate agreement between the systems in the frontal plane (R² = 0.322, 0.452, walking and running, respectively), with a weak to moderate correlation for the transverse plane (R² = 0.178, 0.326, walking and running, respectively). However, root mean squared error (RMSE) showed angular errors ranging from 1.06 to 8.31° across the planes (frontal: 3.57°, 3.67°, transverse: 4.28°, 4.70°, sagittal: 2.45°, 2.67°, walking and running, respectively). Root mean square (RMS) differences between OMC and BVR marker trajectories were task dependent with the largest differences in the shank (6.0 ± 2.01 mm) for running, and metatarsals (3.97 ± 0.81 mm) for walking. Based on the results, we suggest BVR and OMC provide comparable solutions to foot motion in the sagittal plane, however, interpretations of out-of-plane movement should be made carefully.

Developing Virtual Reality Visualizations for Unsteady Flow Analysis of Dinosaur Track Formation using Scientific Sketching

We present the results of a two-year design study to developing virtual reality (VR) flow visualization tools for the analysis of dinosaur track creation in a malleable substrate. Using Scientific Sketching methodology, we combined input from illustration artists, visualization experts, and domain scientists to create novel visualization methods. By iteratively improving visualization concepts at multiple levels of abstraction we helped domain scientists to gain insights into the relationship between dinosaur foot movements and substrate deformations. We involved over 20 art and computer science students from a VR design course in a rapid visualization sketching cycle, guided by our paleontologist collaborators through multiple critique sessions. This allowed us to explore a wide range of potential visualization methods and select the most promising methods for actual implementation. Our resulting visualization methods provide paleontologists with effective tools to analyze their data through particle, pathline and time surface visualizations. We also introduce a set of visual metaphors to compare foot motion in relation to substrate deformation by using pathsurfaces. This is one of the first large-scale projects using Scientific Sketching as a development methodology. We discuss how the research questions of our collaborators have evolved during the sketching and prototyping phases. Finally, we provide lessons learned and usage considerations for Scientific Sketching based on the experiences gathered during this project.

How moles destroy your lawn: the forelimb kinematics of eastern moles in loose and compact substrates

The interplay between morphological specialization and kinematic flexibility is important for organisms that move between habitats within different substrates. Burrowing is energetically expensive and requires substantial interaction with soil to dislodge and transport it. True moles (Talpidae) have extraordinary forelimb morphologies and a unique ability to dig in loose as well as compact soils, yet we know little of how moles coordinate their forelimb joint kinematics when digging in soils of different compactness. Using marker-based X-ray Reconstruction of Moving Morphology (XROMM), we tested the hypothesis that moles burrow using different forelimb kinematics in loose and compact substrates. We predicted that moles raise mounds of loose soil by performing powerful compacting strokes mainly with long-axis rotation of the humerus (i.e. pronation/supination), but shear compact soil away by performing scratching strokes involving amplified elbow extension, similar to most scratching diggers. We also predicted that in both types of substrate, moles displace soil rearward like other mammalian diggers. Our results support our hypothesis but not the predictions. Eastern moles (Scalopus aquaticus) move substrates upward using compacting strokes in loose substrates and outward from the body midline using scratching strokes in compact substrates; unlike the digging strokes of most mammalian forelimb diggers, the power-stroke of moles itself does not displace substrates directly rearward. Compacting and scratching strokes involve similar ranges of humeral pronation and retraction at the scapulohumeral (shoulder) joint, yet the movements at the elbow and carpal joints differ. Our results demonstrate that the combination of stereotypic movements of the shoulder joint, where the largest digging muscles are located, and flexibility in the elbow and carpal joints makes moles extremely effective diggers in both loose and compact substrates.

Assessment of In Vivo Lumbar Inter-Vertebral Motion: Reliability of a Novel Dynamic Weight-Bearing Magnetic Resonance Imaging Technique Using a Side-Bending Task

Study Design

Between-session reliability of a magnetic resonance imaging (MRI) based experimental technique to quantify lumbar inter-vertebral motion in humans.

Purpose

We have developed a novel, dynamic, MRI-based approach for quantifying in vivo lumbar inter-vertebral motion. In this study, we present the protocol’s reliability results to quantify inter-vertebral spine motion.

Overview of Literature

Morphometric studies on intervertebral displacements using static, supine MRI and quantification of dynamic spine motion using different X-ray based radiography techniques are commonly found in the literature. However, reliability testing of techniques assessing real-time lumbar intervertebral motion using weight-bearing MRI has rarely been reported.

Methods

Ten adults without a history of back pain performed a side-bending task on two separate occasions, inside an open-MRI, in a weight-bearing, upright position. The images were acquired during the task using a dynamic magnetic resonance (MR) sequence. The MRI imaging space was externally calibrated before the study to recreate the imaging volume for subsequent use in an animation software. The dynamic MR images were processed to create side-bending movement animations in the virtual environment. Participant-specific three-dimensional models were manually superimposed over vertebral image silhouettes in a sequence of image frames, representing the motion trials. Inter-vertebral axes and translation and rotational displacements of vertebrae were quantified using the animation software.

Results

Quantification of inter-vertebral rotations and translations shows high reliability. Between-session reliability results yielded high values for the intra-class correlation coefficient (0.86–0.93), coefficient of variation (13.3%–16.04%), and Pearson’s correlation coefficients (0.89–0.98).

Conclusions

This technique may be developed further to improve its speed and accuracy for diagnostic applications, to study in vivo spine stability, and to assess outcomes of surgical and non-surgical interventions applied to manage pathological spine motion.

Chewing or not? Intraoral food processing in a salamandrid newt

Food processing refers to any form of food mechanical breakdown prior to swallowing. Variations of this behaviour are found within all major gnathostome groups. Chewing is by far the most commonly used intraoral processing mechanism and involves rhythmic mandibular jaw and hyobranchial (tongue) movements. Chewing occurs in chondrichthyans (sharks and rays), actinopterygians (ray-finned fishes), dipnoi (lungfishes) as well as amniotes and involves similarities in the patterns of muscle activity and movement of the feeding apparatus. It has been suggested that amniote chewing, which involves the interaction of movements of the mandibular jaw and the muscular tongue, has evolved as part of the tetrapod land invasion. However, little is known about food processing mechanisms in lissamphibians, which might have retained many ancestral tetrapod features. Here, we identify a processing mechanism in the salamandrid newt, Triturus carnifex, which after prey capture displays cyclic head bobbing in concert with rhythmic jaw and tongue movements. We use high-speed fluoroscopy, anatomical reconstructions and analyses of stomach content to show that newts, although not using their mandibular jaws, deploy a derived processing mechanism where prey items are rasped rhythmically against the dentition on the mouth-roof, driven by a loop-motion of the tongue. We then compare patterns and coordination of jaw and tongue movements across gnathostomes to conclude that food processing in this newt species shares traits with processing mechanisms in fish as well as amniotes. This discovery casts salamanders as promising models for reconstructing the evolution of intraoral processing mechanisms at the fish-tetrapod split.

Integrating morphology and in vivo skeletal mobility with digital models to infer function in brittle star arms

Brittle stars (Phylum Echinodermata, Class Ophiuroidea) have evolved rapid locomotion employing muscle and skeletal elements within their (usually) five arms to apply forces in a manner analogous to that of vertebrates. Inferring the inner workings of the arm has been difficult as the skeleton is internal and many of the ossicles are sub-millimeter in size. Advances in 3D visualization and technology have made the study of movement in ophiuroids possible. We developed six virtual 3D skeletal models to demonstrate the potential range of motion of the main arm ossicles, known as vertebrae, and six virtual 3D skeletal models of non-vertebral ossicles. These models revealed the joint center and relative position of the arm ossicles during near-maximal range of motion. The models also provide a platform for the comparative evaluation of functional capabilities between disparate ophiuroid arm morphologies. We made observations on specimens of Ophioderma brevispina and Ophiothrix angulata. As these two taxa exemplify two major morphological categories of ophiuroid vertebrae, they provide a basis for an initial assessment of the functional consequences of these disparate vertebral morphologies. These models suggest potential differences in the structure of the intervertebral articulations in these two species, implying disparities in arm flexion mechanics. We also evaluated the differences in the range of motion between segments in the proximal and distal halves of the arm length in a specimen of O. brevispina, and found that the morphology of vertebrae in the distal portion of the arm allows for higher mobility than in the proximal portion. Our models of non-vertebral ossicles show that they rotate further in the direction of movement than the vertebrae themselves in order to accommodate arm flexion. These findings raise doubts over previous hypotheses regarding the functional consequences of ophiuroid arm disparity. Our study demonstrates the value of integrating experimental data and visualization of articulated structures when making functional interpretations instead of relying on observations of vertebral or segmental morphology alone. This methodological framework can be applied to other ophiuroid taxa to enable comparative functional analyses. It will also facilitate biomechanical analyses of other invertebrate groups to illuminate how appendage or locomotor function evolved.

Three-dimensional kinematics of canine hind limbs: in vivo, biplanar, high-frequency fluoroscopic analysis of four breeds during walking and trotting

The first high-precision 3D in vivo hindlimb kinematic data to be recorded in normal dogs of four different breeds (Beagle, French bulldog, Malinois, Whippet) using biplanar, high-frequency fluoroscopy combined with a 3D optoelectric system followed by a markerless XROMM analysis (Scientific Rotoscoping, SR or 3D-2D registration process) reveal a) 3D hindlimb kinematics to an unprecedented degree of precision and b) substantial limitations to the use of skin marker-based data. We expected hindlimb kinematics to differ in relation to body shape. But, a comparison of the four breeds sets the French bulldog aside from the others in terms of trajectories in the frontal plane (abduction/adduction) and long axis rotation of the femur. French bulldogs translate extensive femoral long axis rotation (>30°) into a strong lateral displacement and rotations about the craniocaudal (roll) and the distal-proximal (yaw) axes of the pelvis in order to compensate for a highly abducted hindlimb position from the beginning of stance. We assume that breeds which exhibit unusual kinematics, especially high femoral abduction, might be susceptible to a higher long-term loading of the cruciate ligaments.

Breathing with floating ribs: XROMM analysis of lung ventilation in savannah monitor lizards

The structures and functions of the vertebrate lung and trunk are linked through the act of ventilation, but the connections between these structures and functions are poorly understood. We used X-ray reconstruction of moving morphology (XROMM) to measure rib kinematics during lung ventilation in three savannah monitor lizards (Varanus exanthematicus). All of the dorsal ribs, including the floating ribs, contributed to ventilation; the magnitude and kinematic pattern showed no detectable cranial-to-caudal gradient. The true ribs acted as two rigid bodies connected by flexible cartilage, with the vertebral rib and ventromedial shaft of each sternal rib remaining rigid and the cartilage between them forming a flexible intracostal joint. Rib rotations can be decomposed into bucket handle rotation around a dorsoventral axis, pump handle rotation around a mediolateral axis and caliper motion around a craniocaudal axis. Dorsal rib motion was dominated by roughly equal contributions of bucket and pump rotation in two individuals and by bucket rotation in the third individual. The recruitment of floating ribs during ventilation in monitor lizards is strikingly different from the situation in iguanas, where only the first few true ribs contribute to breathing. This difference may be related to the design of the pulmonary system and life history traits in these two species. Motion of the floating ribs may maximize ventilation of the caudally and ventrolaterally positioned compliant saccular chambers in the lungs of varanids, while restriction of ventilation to a few true ribs may maximize crypsis in iguanas.

Building a Bird: Musculoskeletal Modeling and Simulation of Wing-Assisted Incline Running During Avian Ontogeny

Flapping flight is the most power-demanding mode of locomotion, associated with a suite of anatomical specializations in extant adult birds. In contrast, many developing birds use their forelimbs to negotiate environments long before acquiring "flight adaptations," recruiting their developing wings to continuously enhance leg performance and, in some cases, fly. How does anatomical development influence these locomotor behaviors? Isolating morphological contributions to wing performance is extremely challenging using purely empirical approaches. However, musculoskeletal modeling and simulation techniques can incorporate empirical data to explicitly examine the functional consequences of changing morphology by manipulating anatomical parameters individually and estimating their effects on locomotion. To assess how ontogenetic changes in anatomy affect locomotor capacity, we combined existing empirical data on muscle morphology, skeletal kinematics, and aerodynamic force production with advanced biomechanical modeling and simulation techniques to analyze the ontogeny of pectoral limb function in a precocial ground bird (Alectoris chukar). Simulations of wing-assisted incline running (WAIR) using these newly developed musculoskeletal models collectively suggest that immature birds have excess muscle capacity and are limited more by feather morphology, possibly because feathers grow more quickly and have a different style of growth than bones and muscles. These results provide critical information about the ontogeny and evolution of avian locomotion by (i) establishing how muscular and aerodynamic forces interface with the skeletal system to generate movement in morphing juvenile birds, and (ii) providing a benchmark to inform biomechanical modeling and simulation of other locomotor behaviors, both across extant species and among extinct theropod dinosaurs.

Waddle and shuffle: gait alterations associated with domestication in turkeys

Domestication has altered turkey morphology by artificially selecting for increased muscle mass and breast meat. Artificial selection has resulted in birds that weigh up to 3 times more than their wild counterparts, with relatively little change in the length of their bones and limbs. Considering these structural changes, it seems probable that domestic turkey locomotor kinematics and kinetics would also be altered. To examine the locomotor dynamics of wild and domestic turkeys, we had both strains walk down a runway with a force plate at the center to measure their ground reaction forces and gait parameters. The location of their center of mass was also quantified using a force plate and bi-planar x-ray and found to be further anterior in the domestic strain. The domestic turkeys locomoted across a lower range of speeds (0.25-1.64 ms^-1) than the wild turkeys (0.26-3.26 ms^-1) and increased their stride frequency at a higher rate. They also displayed large lateral oscillations, i.e. waddling, during walking that translated into relatively high medio-lateral ground reaction forces and lateral kinetic energy (3.5 times higher than that of wild turkeys). The results indicate that domestic turkey locomotion is not simply a slowed down version of wild turkey locomotion. The changes in gait observed are similar to the shuffling gait present in some human populations, such as Parkinson's patients, which serves to increase stability. The domestic turkey's increased body mass and more anterior center of mass position may require these kinematic and kinetic gait differences.

Anatomy of the forelimb musculature and ligaments of Psittacus erithacus (Aves: Psittaciformes)

Parrots (order Psittaciformes) are a rather homogeneous group of birds that can be easily distinguished by the notably modified morphology of the skull and hindlimb. Detailed description of the forelimb morphology in these birds has never been provided, though parrots are often used as model objects in flight studies. Parrots are also considered the closest living relatives of the perching birds (Passeriformes), and thus knowledge of the wing morphology in Psittaciformes is important for understanding the evolution of the locomotor apparatus on the way to the most speciose group of birds. Here we provide a comprehensive illustrated description of the wing morphology (musculature and ligaments) of the African grey parrot (Psittacus erithacus) and compare it with several closely related taxa of the high clade Eufalconimorphae and more distantly related outgroups (based on personal dissections and literature data). We note a general similarity of the wing musculature between P. erithacus and Falconidae. A number of features common with the outgroup Columbidae supports a generally plesiomorphic structure of the forelimb in parrots as compared with the Passeriformes. Nevertheless, the wing of the Psittaciformes displays a series of structural (likely autapomorphic) modifications, which can be explained in terms of adaptations for flight with vertical body. An analysis of the anatomical data for parrots (ratio of wing elevators and highly unusual development of the M. supracoracoideus), which is based on the current experiment-based knowledge of the flapping flight in birds, allows us to hypothesize that parrots are able to produce useful aerodynamic force during the upstroke, which is also known for pigeons and hummingbirds. This supposed ability of vertical flight and the zygodactyl foot together link the origin of parrots with the dense (likely tropical) forests.

Bluegill sunfish use high power outputs from axial muscles to generate powerful suction-feeding strikes

Suction-feeding fish rapidly expand the mouth cavity to generate high-velocity fluid flows that accelerate food into the mouth. Such fast and forceful suction expansion poses a challenge, as muscle power is limited by muscle mass and the muscles in fish heads are relatively small. The largemouth bass powers expansion with its large body muscles, with negligible power produced by the head muscles (including the sternohyoideus). However, bluegill sunfish - with powerful strikes but different morphology and feeding behavior - may use a different balance of cranial and axial musculature to power feeding and different power outputs from these muscles. We estimated the power required for suction expansion in sunfish from measurements of intraoral pressure and rate of volume change, and measured muscle length and velocity. Unlike largemouth bass, the sternohyoideus did shorten to generate power, but it and other head muscles were too small to contribute more than 5-10% of peak expansion power in sunfish. We found no evidence of catapult-style power amplification. Instead, sunfish powered suction feeding by generating high power outputs (up to 438 W kg^-1) from their axial muscles. These muscles shortened across the cranial half of the body as in bass, but at faster speeds that may be nearer the optimum for power production. Sunfish were able to generate strikes of the same absolute power as bass, but with 30-40% of the axial muscle mass. Thus, species may use the body and head muscles differently to meet the requirements of suction feeding, depending on their morphology and behavior.

Rib kinematics during lung ventilation in the American alligator (Alligator mississippiensis): an XROMM analysis

The current hypothesis regarding the mechanics of breathing in crocodylians is that the double-headed ribs, with both a capitulum and tuberculum, rotate about a constrained axis passing through the two articulations; moreover, this axis shifts in the caudal thoracic ribs, as the vertebral parapophysis moves from the centrum to the transverse process. Additionally, the ventral ribcage in crocodylians is thought to possess additional degrees of freedom through mobile intermediate ribs. In this study, X-ray reconstruction of moving morphology (XROMM) was used to quantify rib rotation during breathing in American alligators. Whilst costovertebral joint anatomy predicted overall patterns of motion across the ribcage (decreased bucket handle motion and increased calliper motion), there were significant deviations: anatomical axes overestimated pump handle motion and, generally, ribs in vivo rotate about all three body axes more equally than predicted. The intermediate ribs are mobile, with a high degree of rotation measured about the dorsal intracostal joints, especially in the more caudal ribs. Motion of the sternal ribs became increasingly complex caudally, owing to a combination of the movements of the vertebral and intermediate segments. As the crocodylian ribcage is sometimes used as a model for the ancestral archosaur, these results have important implications for how rib motion is reconstructed in fossil taxa, and illustrate the difficulties in reconstructing rib movement based on osteology alone.

Summary: Using XROMM to test how well joint anatomy predicts rib motion during breathing in crocodylians, our best living model for the earliest archosaurs.