No abstract

The influence of different substrate inclinations on gaits and metric gait parameters (relative forelimb and hind limb protraction, relative forelimb, and hind limb retraction, stride length, stance, and swing phase duration) of cotton-top tamarin locomotion was studied using high-speed video films and evaluated by descriptive and analytical statistical methods. As previously shown, lateral sequence gaits predominantly occurred on descending arboreal substrates (branchlike pole with a smaller diameter than the animal's body). Gait sequence patterns display significant dependency on substrate inclination. Cotton-top tamarins utilize lower diagonality values the more the substrate declines. This tendency leads to a greater use of lateral sequence gaits on steeply declined substrates. Conversely, these primates display the tendency to utilize higher diagonality values the more the substrate inclines leading to the predominant occurrence of diagonal sequence (DS) gaits. Duty factor index, extent of relative protraction, and relative retraction of both limb pairs as well as the relation of forelimb stance phase duration to hind limb stance phase duration is also correlated to the inclination of the substrate. Stride length and swing phase duration display no significant dependence on inclination, but are determined by the speed of the moving animal. The relevant duty factor is approximately constant at all inclinations. Integrating our results with results of other authors we propose a hypothesis for the functional relevance of a utilization of lateral sequence gaits in downward locomotion and DS gaits in upward locomotion. Our data support the notion of a wide ranging behavioral plasticity as a general primate locomotor characteristic.

In contrast to the upright trunk in humans, trunk orientation in most birds is almost horizontal (pronograde). It is conceivable that the orientation of the heavy trunk strongly influences the dynamics of bipedal terrestrial locomotion. Here, we analyse for the first time the effects of a pronograde trunk orientation on leg function and stability during bipedal locomotion. For this, we first inferred the leg function and trunk control strategy applied by a generalized small bird during terrestrial locomotion by analysing synchronously recorded kinematic (three-dimensional X-ray videography) and kinetic (three-dimensional force measurement) quail locomotion data. Then, by simulating quail gaits using a simplistic bioinspired numerical model which made use of parameters obtained in in vivo experiments with real quail, we show that the observed asymmetric leg function (left-skewed ground reaction force and longer leg at touchdown than at lift-off) is necessary for pronograde steady-state locomotion. In addition, steady-state locomotion becomes stable for specific morphological parameters. For quail-like parameters, the most common stable solution is grounded running, a gait preferred by quail and most of the other small birds. We hypothesize that stability of bipedal locomotion is a functional demand that, depending on trunk orientation and centre of mass location, constrains basic hind limb morphology and function, such as leg length, leg stiffness and leg damping.

No abstract

BackgroundOwls possess an extraordinary neck and head mobility. To understand this mobility it is necessary to have an anatomical description of cervical vertebrae with an emphasis on those criteria that are relevant for head positioning. No functional description specific to owls is available.Methodology/Principal findingsX-ray films and micro-CT scans were recorded from American barn owls (Tyto furcata pratincola) and used to obtain three-dimensional head movements and three-dimensional models of the 14 cervical vertebrae (C1−C14). The diameter of the vertebral canal, the zygapophyseal protrusion, the distance between joint centers, and the pitching angle were quantified. Whereas the first two variables are purely osteological characteristics of single vertebrae, the latter two take into account interactions between vertebrae. These variables change in characteristic ways from cranial to caudal. The vertebral canal is wide in the cranial and caudal neck regions, but narrow in the middle, where both the zygapophyseal protrusion and the distance between joint centers are large. Pitching angles are more negative in the cranial and caudal neck regions than in the middle region. Cluster analysis suggested a complex regionalization. Whereas the borders (C1 and C13/C14) formed stable clusters, the other cervical vertebrae were sorted into 4 or 5 additional clusters. The borders of the clusters were influenced by the variables analyzed.Conclusions/SignificanceA statistical analysis was used to evaluate the regionalization of the cervical spine in the barn owl. While earlier measurements have shown that there appear to be three regions of flexibility of the neck, our indicators suggest 3–7 regions. These many regions allow a high degree of flexibility, potentially facilitating the large head turns that barn owls are able to make. The cervical vertebral series of other species should also be investigated using statistical criteria to further characterize morphology and the potential movements associated with it.

BackgroundSciuromorpha (squirrels and close relatives) are diverse in terms of body size and locomotor behavior. Individual species are specialized to perform climbing, gliding or digging behavior, the latter being the result of multiple independent evolutionary acquisitions. Each lifestyle involves characteristic loading patterns acting on the bones of sciuromorphs. Trabecular bone, as part of the bone inner structure, adapts to such loading patterns. This network of thin bony struts is subject to bone modeling, and therefore reflects habitual loading throughout lifetime. The present study investigates the effect of body size and lifestyle on trabecular structure in Sciuromorpha.MethodsBased upon high-resolution computed tomography scans, the femoral head 3D inner microstructure of 69 sciuromorph species was analyzed. Species were assigned to one of the following lifestyle categories: arboreal, aerial, fossorial and semifossorial. A cubic volume of interest was selected in the center of each femoral head and analyzed by extraction of various parameters that characterize trabecular architecture (degree of anisotropy, bone volume fraction, connectivity density, trabecular thickness, trabecular separation, bone surface density and main trabecular orientation). Our analysis included evaluation of the allometric signals and lifestyle-related adaptation in the trabecular parameters.ResultsWe show that bone surface density, bone volume fraction, and connectivity density are subject to positive allometry, and degree of anisotropy, trabecular thickness, and trabecular separation to negative allometry. The parameters connectivity density, bone surface density, trabecular thickness, and trabecular separation show functional signals which are related to locomotor behavior. Aerial species are distinguished from fossorial ones by a higher trabecular thickness, lower connectivity density and lower bone surface density. Arboreal species are distinguished from semifossorial ones by a higher trabecular separation.ConclusionThis study on sciuromorph trabeculae supplements the few non-primate studies on lifestyle-related functional adaptation of trabecular bone. We show that the architecture of the femoral head trabeculae in Sciuromorpha correlates with body mass and locomotor habits. Our findings provide a new basis for experimental research focused on functional significance of bone inner microstructure.Electronic supplementary materialThe online version of this article (10.1186/s40851-018-0093-z) contains supplementary material, which is available to authorized users.

Recent phylogenetic analyses imply a distant relationship and long separated evolution of two-toed sloths (Choloepus) and three-toed sloths (Bradypus). No known fossil sloth is interpreted to have been suspensory. As a consequence, the suspensory posture and locomotion of the extant genera likely evolved convergently in both lineages, forming a new framework for the analysis of functional aspects of the locomotor apparatus of extant tree sloths. The suspensory posture and locomotion has altered functional demands from the phylogenetically plesiomorphic nonsuspensory pronograde situation. Here, anatomical traits that have been argued to be of adaptive significance for quadrupedal suspensory locomotion are reviewed and the evolution of these traits is discussed in light of the new framework. Experimental data are largely limited to Choloepus, but help to deduce functional aspects of the anatomy in Bradypus as well. The most important adaptive traits are hands and feet modified into relatively rigid hooklike appendages, great mobility of all joints proximal to the midcarpal and transverse tarsal joints, relatively long arms with a relatively short scapula, a rounded thorax with a small diameter, a highly mobile sterno-clavicular articulation, and emphasis on powerful flexion in the proximal limb joints via advantageous lever arms. Despite these changes, patterns of limb kinematics remained conservative during the course of evolution in the lineages leading to extant tree sloths, and it is suggested here that this also applies to the pattern of neuromuscular control of limb movements during locomotion. Morphological 'solutions'to altered functional demands posed by inversed orientation of the body differ in the two genera of extant tree sloths, thereby corroborating the proposed diphyly. Convergent evolution in tree sloths may be attributed to functional constraints posed by fossorial adaptations in early Xenarthra that canalized sloths to adopt a suspensory posture and locomotion in the arboreal habitat.

The reconstruction of a joint's maximum range of mobility (ROM) often is a first step when trying to understand the locomotion of fossil tetrapods. But previous studies suggest that the ROM of a joint is restricted by soft tissues surrounding the joint. To expand the limited informative value of ROM studies for the reconstruction of a fossil species' locomotor characteristics, it is moreover necessary to better understand the relationship of ex vivo ROM with the actual in vivo joint movement. To gain insight into the relationship between ex vivo mobility and in vivo movement, we systematically tested for the influence of soft tissues on joint ROM in the hip of the modern lizard Iguana iguana. Then, we compared the ex vivo mobility to in vivo kinematics of the hip joint in the same specimens using X-ray sequences of steady-state treadmill locomotion previously recorded. With stepwise removal of soft tissues and a repeated-measurement protocol, we show that soft tissues surrounding the hip joint considerably limit ROM, highlighting the problems when joint ROM is deduced from bare bones only. We found the integument to have the largest effect on the range of long-axis rotation, pro-and retraction. Importantly, during locomotion the iguana used only a fragment of the ROM that was measured in our least restrictive dissection situation (i.e. pelvis and femur only conjoined by ligaments), demonstrating the discrepancy between hip joint ROM and actual in vivo movement. Our study emphasizes the necessity for caution when attempting to reconstruct joint ROM or even locomotor kinematics from fossil bones only, as actual in vivo movement cannot be deduced directly from any condition of cadaver mobility in Iguana and likely in other tetrapods.