Fluid Dynamics of Feeding Behaviour in White-Spotted Bamboo Sharks

Although the motor control of feeding is presumed to be generally conserved, some fishes are capable of modulating the feeding behaviour in response to prey type and or prey size. This led to the ʻfeeding modulation hypothesisʼ, which states that rapid suction strikes are pre-programmed stereotyped events that proceed to completion once initiated regardless of sensory input. If this hypothesis holds true, successful strikes should be indistinguishable from unsuccessful strikes owing to a lack of feedback control in specialized suction feeding fishes. The hydrodynamics of suction feeding in white-spotted bamboo sharks (Chiloscyllium plagiosum) was studied in three behaviours: successful strikes, intraoral transports of prey and unsuccessful strikes. The area of the fluid velocity region around the head of feeding sharks was quantified using time-resolved digital particle image velocimetry (DPIV). The maximal size of the fluid velocity region is 56% larger in successful strikes than unsuccessful strikes (10.79cm2 vs 6.90cm2), but they do not differ in duration, indicating that strikes are modulated based on some aspect of the prey or simply as a result of decreased effort on the part of the predator. The hydrodynamic profiles of successful and unsuccessful strikes differ after 21 ms, a period probably too short to provide time to react through feedback control. The predator-to-prey distance is larger in missed strikes compared with successful strikes, indicating that insufficient suction is generated to compensate for the increased distance. An accuracy index distinguishes unsuccessful strikes (–0.26) from successful strikes (0.45 to 0.61). Successful strikes occur primarily between the horizontal axis of the mouth and the dorsal boundary of the ingested parcel of water, and missed prey are closer to the boundary or beyond. Suction transports are shorter in duration than suction strikes but have similar maximal fluid velocity areas to move the prey through the oropharyngeal cavity into the oesophagus (54ms vs 67ms)

Orientation and location of the finite helical axis of the equine forelimb joints

To reduce anatomically unrealistic limb postures in a virtual musculoskeletal model of a horse's forelimb, accurate knowledge on forelimb joint constraints is essential. The aim of this cadaver study is to report all orientation and position changes of the finite helical axes (FHA) as a function of joint angle for different equine forelimb joints. Five horse cadaver forelimbs with standardized cuts at the midlevel of each segment were used. Bone pins with reflective marker triads were drilled into the forelimb bones. Unless joint angles were anatomically coupled, each joint was manually moved independently in all three rotational degrees of freedom (flexion-extension, abduction-adduction, internal-external rotation). The 3D coordinates of the marker triads were recorded using a six infra-red camera system. The FHA and its orientational and positional properties were calculated and expressed against joint angle over the entire range of motion using a finite helical axis method. When coupled, joint angles and FHA were expressed in function of flexion-extension angle. Flexion-extension movement was substantial in all forelimb joints, the shoulder allowed additional considerable motion in all three rotational degrees of freedoms. The position of the FHA was constant in the fetlock and elbow and a constant orientation of the FHA was found in the shoulder. Orientation and position changes of the FHA over the entire range of motion were observed in the carpus and the interphalangeal joints. We report FHA position and orientation changes as a function of flexion-extension angle to allow for inclusion in a musculoskeletal model of a horse to minimize calculation errors caused by incorrect location of the FHA. [Abstract copyright: © 2019 Wiley Periodicals, Inc.

Sagittal plane fore hoof unevenness is associated with fore and hindlimb asymmetrical force vectors in the sagittal and frontal planes

Asymmetry in forelimb dorsal hoof wall angles, termed unevenness, is associated with forelimb gait asymmetries, but compensatory mechanisms and out of plane ground reaction forces (GRFs) due to unevenness have yet to be documented. The aim of this study was therefore to investigate the effects of fore hoof unevenness on contralateral fore and hind limb force vectors patterns, in both sagittal and frontal planes. A group of n = 34 riding horses were classified into four groups: hoof angle difference of more than 1.5 degrees (UNEVEN; n = 27), including higher left fore (HIGH-LF; n = 12), higher right fore (HIGH-RF; n = 15), and hoof angle difference of less than 1.5 degrees (EVEN; n = 7). Three dimensional ground reaction forces GRFs were collected during trotting. GRF summary vectors representing the magnitude (VecMag) and angular direction (VecAng) of the entire stance phase in the sagittal and the frontal plane were calculated. The effects of unevenness on GRF production were explored using linear regression, repeated measures ANOVA and statistical parametric mapping (SPM) with significance at (P0.05) were found between hindlimb pairs in the EVEN group. Unbalanced sagittal and increased frontal plane GRFs in uneven horses suggest that they have greater locomotory challenges, as the equine musculoskeletal system is not constructed to withstand movement and loading in the frontal plane as effectively as it is in the sagittal plane

Metacarpophalangeal joint loads during bonobo locomotion: model predictions vs. proxies

The analysis of internal trabecular and cortical bone has been an informative tool for drawing inferences about behaviour in extant and fossil primate taxa. Within the hand, metacarpal bone architecture has been shown to correlate well with primate locomotion; however, the extent of morphological differences across taxa is unexpectedly small given the variability in hand use. One explanation for this observation is that the activity-related differences in the joint loads acting on the bone are simply smaller than estimated based on commonly used proxies (i.e. external loading and joint posture), which neglect the influence of muscle forces. In this study, experimental data and a musculoskeletal finger model are used to test this hypothesis by comparing differences between climbing and knuckle-walking locomotion of captive bonobos (Pan paniscus) based on (i) joint load magnitude and direction predicted by the models and (ii) proxy estimations. The results showed that the activity-related differences in predicted joint loads are indeed much smaller than the proxies would suggest, with joint load magnitudes being almost identical between the two locomotor modes. Differences in joint load directions were smaller but still evident, indicating that joint load directions might be a more robust indicator of variation in hand use than joint load magnitudes. Overall, this study emphasizes the importance of including muscular forces in the interpretation of skeletal remains and promotes the use of musculoskeletal models for correct functional interpretations

Segmental morphometrics of bonobos (Pan paniscus): are they really different from chimpanzees (Pan troglodytes)?

The inertial properties of body segments reflect performance and locomotor habits in primates. While Pan paniscus is generally described as more gracile, lighter in body mass, and as having relatively longer and heavier hindlimbs than Pan troglodytes, both species exhibit very similar patterns of (quadrupedal and bipedal) kinematics, but show slightly different locomotor repertoires. We used a geometric model to estimate the inertial properties for all body segments (i.e. head, trunk, upper and lower arms, hand, thigh, shank and foot) using external length and diameter measurements of 12 anaesthetized bonobos (eight adults and four immatures). We also calculated whole limb inertial properties. When we compared absolute and relative segment morphometric and inertial variables between bonobos and chimpanzees, we found that adult bonobos are significantly lighter than adult chimpanzees. The bonobo is also shorter in head length, upper and lower arm lengths, and foot length, and is generally lighter in most absolute segment mass values (except head and hand). In contrast, the bonobo has a longer trunk. When scaled relative to body mass, most differences disappear between the two species. Only the longer trunk and the shorter head of the bonobo remain apparent, as well as the lighter thigh compared with the chimpanzee. We found similar values of natural pendular periods of the limbs in both species, despite differences in absolute limb lengths, masses, mass centres (for the hindlimb) and moments of inertia. While our data contradict the commonly accepted view that bonobos have relatively longer and heavier hindlimbs than chimpanzees, they are consistent with the observed similarities in the quadrupedal and bipedal kinematics between these species. The morphological differences between both species are more subtle than those previously described from postcranial osteological materials

Musculoskeletal models of a human and bonobo finger: parameter identification and comparison to in vitro experiments

Introduction: Knowledge of internal finger loading during human and non-human primate activities such as tool use or knuckle-walking has become increasingly important to reconstruct the behaviour of fossil hominins based on bone morphology. Musculoskeletal models have proven useful for predicting these internal loads during human activities, but load predictions for non-human primate activities are missing due to a lack of suitable finger models. The main goal of this study was to implement both a human and a representative non-human primate finger model to facilitate comparative studies on metacarpal bone loading. To ensure that the model predictions are sufficiently accurate, the specific goals were: (1) to identify species-specific model parameters based on in vitro measured fingertip forces resulting from single tendon loading and (2) to evaluate the model accuracy of predicted fingertip forces and net metacarpal bone loading in a different loading scenario. Materials & Methods: Three human and one bonobo (Pan paniscus) fingers were tested in vitro using a previously developed experimental setup. The cadaveric fingers were positioned in four static postures and load was applied by attaching weights to the tendons of the finger muscles. For parameter identification, fingertip forces were measured by loading each tendon individually in each posture. For the evaluation of model accuracy, the extrinsic flexor muscles were loaded simultaneously and both the fingertip force and net metacarpal bone force were measured. The finger models were implemented using custom Python scripts. Initial parameters were taken from literature for the human model and own dissection data for the bonobo model. Optimized model parameters were identified by minimizing the error between predicted and experimentally measured fingertip forces. Fingertip forces and net metacarpal bone loading in the combined loading scenario were predicted using the optimized models and the remaining error with respect to the experimental data was evaluated. Results. The parameter identification procedure led to minor model adjustments but considerably reduced the error in the predicted fingertip forces (root mean square error reduced from 0.53/0.69 N to 0.11/0.20 N for the human/bonobo model). Both models remained physiologically plausible after the parameter identification. In the combined loading scenario, fingertip and net metacarpal forces were predicted with average directional errors below 6◦ and magnitude errors below 12%. Conclusions. This study presents the first attempt to implement both a human and nonhuman primate finger model for comparative palaeoanthropological studies. The good agreement between predicted and experimental forces involving the action of extrinsic flexors—which are most relevant for forceful grasping—shows that the models are likely sufficiently accurate for comparisons of internal loads occurring during human and non-human primate manual activities

Functional Locomotor Consequences of Uneven Forefeet for Trot Symmetry in Individual Riding Horses

ABSTRACT: Left-right symmetrical distal limb conformation can be an important prerequisite for a successful performance, and it is often hypothesized that asymmetric or uneven feet are important enhancing factors for the development of lameness. On a population level, it has been demonstrated that uneven footed horses are retiring earlier from elite level competition, but the biomechanical consequences are not yet known. The objectives of this study were to compare the functional locomotor asymmetries of horses with uneven to those with even feet. Hoof kinetics and distal limb kinematics were collected from horses (n = 34) at trot. Dorsal hoof wall angle was used to classify horses as even or uneven (1.5° difference between forefeet respectively) and individual feet as flat (55°). Functional kinetic parameters were compared between even and uneven forefeet using MANOVA followed by ANOVA. The relative influences of differences in hoof angle between the forefeet and of absolute hoof angle on functional parameters were analysed using multiple regression analysis (P<0.05). In horses with uneven feet, the side with the flatter foot showed a significantly larger maximal horizontal braking and vertical ground reaction force, a larger vertical fetlock displacement and a suppler fetlock spring. The foot with a steeper hoof angle was linearly correlated with an earlier braking-propulsion transition. The conformational differences between both forefeet were more important for loading characteristics than the individual foot conformation of each individual horse. The differences in vertical force and braking force between uneven forefeet could imply either an asymmetrical loading pattern without a pathological component or a subclinical lameness as a result of a pathological development in the steeper foot

A horse’s locomotor signature: COP path determined by the individual limb

Introduction Ground reaction forces in sound horses with asymmetric hooves show systematic differences in the horizontal braking force and relative timing of break-over. The Center Of Pressure (COP) path quantifies the dynamic load distribution under the hoof in a moving horse. The objective was to test whether anatomical asymmetry, quantified by the difference in dorsal wall angle between the left and right forelimbs, correlates with asymmetry in the COP path between these limbs. In addition, repeatability of the COP path was investigated. Methods A larger group (n = 31) visually sound horses with various degree of dorsal hoof wall asymmetry trotted three times over a pressure mat. COP path was determined in a hoof-bound coordinate system. A relationship between correlations between left and right COP paths and degree of asymmetry was investigated. Results Using a hoof-bound coordinate system made the COP path highly repeatable and unique for each limb. The craniocaudal patterns are usually highly correlated between left and right, but the mediolateral patterns are not. Some patterns were found between COP path and dorsal wall angle but asymmetry in dorsal wall angle did not necessarily result in asymmetry in COP path and the same could be stated for symmetry. Conclusion This method is a highly sensitive method to quantify the net result of the interaction between all of the forces and torques that occur in the limb and its inertial properties. We argue that changes in motor control, muscle force, inertial properties, kinematics and kinetics can potentially be picked up at an early stage using this method and could therefore be used as an early detection method for changes in the musculoskeletal apparatus

Modern Tapirs as Morphofunctional Analogues for Locomotion in Endemic Eocene European Perissodactyls

Tapirs have historically been considered as ecologically analogous to several groups of extinct perissodactyls based on dental and locomotor morphology. Here, we investigate comparative functional morphology between living tapirs and endemic Eocene European perissodactyls to ascertain whether tapirs represent viable analogues for locomotion in palaeotheres and lophiodontids. Forelimb bones from 20 species of Eocene European perissodactyls were laser scanned and compared to a forelimb dataset of extant Tapirus. Bone shape was quantified using 3D geometric morphometrics; coordinates were Procrustes aligned and compared using Principal Component Analysis and neighbor-joining trees. Functional traits included lever-arm ratios (LARs; proxy for joint angular velocity), long-bone proportions (speed proxy), and estimated body mass. Results suggest that Paralophiodon and Palaeotherium magnum resemble Neotropical tapirs in humeral morphology and LARs. Palaeotheres demonstrate extensive forelimb shape disparity. Despite previous assessments, metacarpal shape analyzes do not support a strong morphological similarity between palaeotheres and tapirs, with Tapirus pinchaque representing the closest analogue for Eocene European equoid manus morphology. Our analyses suggest lophiodontids were not capable of moving as swiftly as tapirs due to greater loading over the manus. We conclude that the variation within modern tapir forelimb morphology confounds the assignment of one living analogue within Tapirus for extinct European equoids, whereas tapirs adapted for greater loading over the manus (e.g., T. bairdii, T. indicus) represent viable locomotor analogues for lophiodontids. This study represents a valuable first step toward locomotor simulation and behavioral inference for both hippomorph and tapiromorph perissodactyls in Eocene faunal communities