Cancellous bone and theropod dinosaur locomotion. Part III—Inferring posture and locomotor biomechanics in extinct theropods, and its evolution on the line to birds

This paper is the last of a three-part series that investigates the architecture of cancellous bone in the main hindlimb bones of theropod dinosaurs, and uses cancellous bone architectural patterns to infer locomotor biomechanics in extinct non-avian species. Cancellous bone is highly sensitive to its prevailing mechanical environment, and may therefore help further understanding of locomotor biomechanics in extinct tetrapod vertebrates such as dinosaurs. Here in Part III, the biomechanical modelling approach derived previously was applied to two species of extinct, non-avian theropods, Daspletosaurus torosus and Troodon formosus. Observed cancellous bone architectural patterns were linked with quasi-static, three-dimensional musculoskeletal and finite element models of the hindlimb of both species, and used to derive characteristic postures that best aligned continuum-level principal stresses with cancellous bone fabric. The posture identified for Daspletosaurus was largely upright, with a subvertical femoral orientation, whilst that identified for Troodon was more crouched, but not to the degree observed in extant birds. In addition to providing new insight on posture and limb articulation, this study also tested previous hypotheses of limb bone loading mechanics and muscular control strategies in non-avian theropods, and how these aspects evolved on the line to birds. The results support the hypothesis that an upright femoral posture is correlated with bending-dominant bone loading and abduction-based muscular support of the hip, whereas a crouched femoral posture is correlated with torsion-dominant bone loading and long-axis rotation-based muscular support. Moreover, the results of this study also support the inference that hindlimb posture, bone loading mechanics and muscular support strategies evolved in a gradual fashion along the line to extant birds

TACR Shorts: College Accommodations Comic

This comic is designed to help young adults with mental health conditions find out that accommodations in college are available and where to go to learn more about them and request them. It also offers additional resources such as these tip sheets: Getting Accommodations at College: Tools for School [English and Spanish versions]: https://escholarship.umassmed.edu/pib/vol8/iss16/1/ Outside-The-Box College Accommodations: Real Support for Real Students: Tools for School II [English and Spanish versions]: https://escholarship.umassmed.edu/pib/vol14/iss3/1

A preliminary case study of the effect of shoe-wearing on the biomechanics of a horse’s foot

Horse racing is a multi-billion-dollar industry that has raised welfare concerns due to injured and euthanized animals. Whilst the cause of musculoskeletal injuries that lead to horse morbidity and mortality is multifactorial, pre-existing pathologies, increased speeds and substrate of the racecourse are likely contributors to foot disease. Horse hooves have the ability to naturally deform during locomotion and dissipate locomotor stresses, yet farriery approaches are utilised to increase performance and protect hooves from wear. Previous studies have assessed the effect of different shoe designs on locomotor performance; however, no biomechanical study has hitherto measured the effect of horseshoes on the stresses of the foot skeleton in vivo. This preliminary study introduces a novel methodology combining three-dimensional data from biplanar radiography with inverse dynamics methods and finite element analysis (FEA) to evaluate the effect of a stainless steel shoe on the function of a Thoroughbred horse's forefoot during walking. Our preliminary results suggest that the stainless steel shoe shifts craniocaudal, mediolateral and vertical GRFs at mid-stance. We document a similar pattern of flexion-extension in the PIP (pastern) and DIP (coffin) joints between the unshod and shod conditions, with slight variation in rotation angles throughout the stance phase. For both conditions, the PIP and DIP joints begin in a flexed posture and extend over the entire stance phase. At mid-stance, small differences in joint angle are observed in the PIP joint, with the shod condition being more extended than the unshod horse, whereas the DIP joint is extended more in the unshod than the shod condition. We also document that the DIP joint extends more than the PIP after midstance and until the end of the stance in both conditions. Our FEA analysis, conducted solely on the bones, shows increased von Mises and Maximum principal stresses on the forefoot phalanges in the shod condition at mid-stance, consistent with the tentative conclusion that a steel shoe might increase mechanical loading. However, because of our limited sample size none of these apparent differences have been tested for statistical significance. Our preliminary study illustrates how the shoe may influence the dynamics and mechanics of a Thoroughbred horse's forefoot during slow walking, but more research is needed to quantify the effect of the shoe on the equine forefoot during the whole stance phase, at faster speeds/gaits and with more individuals as well as with a similar focus on the hind feet. We anticipate that our preliminary analysis using advanced methodological approaches will pave the way for new directions in research on the form/function relationship of the equine foot, with the ultimate goal to minimise foot injuries and improve animal health and welfare

New antelope fossils from Awash, Ethiopia, and phylogenetic analysis of Hippotragini (Bovidae, Mammalia)

New hippotragine antelope fossils from the Middle Awash, Ethiopia, include a new species Praedamalis howelli from Maka, an early species of Oryx from Matabaietu, and Hippotragus gigas from Gamedah. Our comparisons of these fossils with all other known fossil and Recent Hippotragini includes a cladistic analysis. The results suggest that the two major lineages in the monophyletic Hippotragini are Hippotragus including taxa from the Siwaliks previously ascribed to Sivatragus, and a Praedamalis - Oryx sister-group. Some evolutionary and biogeographic implications of the new fossils from the Middle A wash deposits are discussed

Gearing effects of the patella (knee extensor muscle sesamoid) of the helmeted guineafowl during terrestrial locomotion

Human patellae (kneecaps) are thought to act as gears, altering the mechanical advantage of knee extensor muscles during running. Similar sesamoids have evolved in the knee extensor tendon independently in birds, but it is unknown if these also affect the mechanical advantage of knee extensors. Here, we examine the mechanics of the patellofemoral joint in the helmeted guineafowl Numida meleagris using a method based on muscle and tendon moment arms taken about the patella's rotation centre around the distal femur. Moment arms were estimated from a computer model representing hindlimb anatomy, using hip, knee and patellar kinematics acquired via marker‐based biplanar fluoroscopy from a subject running at 1.6 ms−1 on a treadmill. Our results support the inference that the patella of Numida does alter knee extensor leverage during running, but with a mechanical advantage generally greater than that seen in humans, implying relatively greater extension force but relatively lesser extension velocity

Dynamics of Human Walking

The problem of biped locomotion at steady speeds is discussed through a Lagrangian formulation developed for velocity-dependent, body driving forces. Human walking on a level surface is analyzed in terms of the data on the resultant ground-reaction force and the external work. It is shown that the trajectory of the center of mass is due to a superposition of its rectilinear motion with a given speed and a backward rotation along a shortened hypocycloid. A stiff-to-compliant crossover between walking gaits is described and the maximum speed for human walking, given by an instability of the trajectory, is predicted. Key words: locomotion, integrative biology, muscles, bipedalism, human walking, biomechanics.Comment: 9 pages, 4 figure

Three-Dimensional, High-Resolution Skeletal Kinematics of the Avian Wing and Shoulder During Ascending Flapping Flight and Uphill Flap-Running

Past studies have shown that birds use their wings not only for flight, but also when ascending steep inclines. Uphill flap-running or wing-assisted incline running (WAIR) is used by both flight-incapable fledglings and flight-capable adults to retreat to an elevated refuge. Despite the broadly varying direction of travel during WAIR, level, and descending flight, recent studies have found that the basic wing path remains relatively invariant with reference to gravity. If so, joints undergo disparate motions to maintain a consistent wing path during those specific flapping modes. The underlying skeletal motions, however, are masked by feathers and skin. To improve our understanding of the form-functional relationship of the skeletal apparatus and joint morphology with a corresponding locomotor behavior, we used XROMM (X-ray Reconstruction of Moving Morphology) to quantify 3-D skeletal kinematics in chukars (Alectoris chukar) during WAIR (ascending with legs and wings) and ascending flight (AF, ascending with wings only) along comparable trajectories. Evidence here from the wing joints demonstrates that the glenohumeral joint controls the vast majority of wing movements. More distal joints are primarily involved in modifying wing shape. All bones are in relatively similar orientations at the top of upstroke during both behaviors, but then diverge through downstroke. Total excursion of the wing is much smaller during WAIR and the tip of the manus follows a more vertical path. The WAIR stroke appears truncated relative to ascending flight, primarily stemming from ca. 50% reduction in humeral depression. Additionally, the elbow and wrist exhibit reduced ranges of angular excursions during WAIR. The glenohumeral joint moves in a pattern congruent with being constrained by the acrocoracohumeral ligament. Finally, we found pronounced lateral bending of the furcula during the wingbeat cycle during ascending flight only, though the phasic pattern in chukars is opposite of that observed in starlings (Sturnus vulgaris)

A quantitative evaluation of physical and digital approaches to centre of mass estimation

Centre of mass is a fundamental anatomical and biomechanical parameter. Knowledge of centre of mass is essential to inform studies investigating locomotion and other behaviours, through its implications for segment movements, and on whole body factors such as posture. Previous studies have estimated centre of mass position for a range of organisms, using various methodologies. However, few studies assess the accuracy of the methods that they employ, and often provide only brief details on their methodologies. As such, no rigorous, detailed comparisons of accuracy and repeatability within and between methods currently exist. This paper therefore seeks to apply three methods common in the literature (suspension, scales and digital modelling) to three 'calibration objects' in the form of bricks, as well as three birds to determine centre of mass position. Application to bricks enables conclusions to be drawn on the absolute accuracy of each method, in addition to comparing these results to assess the relative value of these methodologies. Application to birds provided insights into the logistical challenges of applying these methods to biological specimens. For bricks, we found that, provided appropriate repeats were conducted, the scales method yielded the most accurate predictions of centre of mass (within 1.49 mm), closely followed by digital modelling (within 2.39 mm), with results from suspension being the most distant (within 38.5 mm). Scales and digital methods both also displayed low variability between centre of mass estimates, suggesting they can accurately and consistently predict centre of mass position. Our suspension method resulted not only in high margins of error, but also substantial variability, highlighting problems with this method

Phylogeny and adaptive evolution of the brain-development gene microcephalin (MCPH1) in cetaceans.

BACKGROUND: Representatives of Cetacea have the greatest absolute brain size among animals, and the largest relative brain size aside from humans. Despite this, genes implicated in the evolution of large brain size in primates have yet to be surveyed in cetaceans. RESULTS: We sequenced ~1240 basepairs of the brain development gene microcephalin (MCPH1) in 38 cetacean species. Alignments of these data and a published complete sequence from Tursiops truncatus with primate MCPH1 were utilized in phylogenetic analyses and to estimate ω (rate of nonsynonymous substitution/rate of synonymous substitution) using site and branch models of molecular evolution. We also tested the hypothesis that selection on MCPH1 was correlated with brain size in cetaceans using a continuous regression analysis that accounted for phylogenetic history. Our analyses revealed widespread signals of adaptive evolution in the MCPH1 of Cetacea and in other subclades of Mammalia, however, there was not a significant positive association between ω and brain size within Cetacea. CONCLUSION: In conjunction with a recent study of Primates, we find no evidence to support an association between MCPH1 evolution and the evolution of brain size in highly encephalized mammalian species. Our finding of significant positive selection in MCPH1 may be linked to other functions of the gene.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are