Biology subjects

van Bijlert, P. A.

Publications and source records attributed to van Bijlert, P. A..

4 recordsLinked to original sources

bioRxiv2026

Biomechanics of the extremely elongated neck of the Triassic archosauromorph Tanystropheus

Extremely elongate necks have convergently evolved in several amniote lineages, including both aquatic and terrestrial forms (Fig. 1). The development of such a feature brings with it advantages in obtaining food items, but also biomechanical challenges, such as flexibility, stability, lift, and inertia. In Tanystropheus, a particularly long-necked Triassic archosauromorph, the neck is composed of only 13, mostly extraordinarily elongated and slender cervical vertebrae and accompanying rod-like, overlapping ribs, making it arguably the most extreme example of neck elongation in tetrapod evolution (Fig. 1;1-6). Understanding the function of this remarkable neck provides insights into the limits of neck elongation in amniotes and the evolution of morphological novelties in Triassic reptiles. Here we present the first quantitative biomechanical analysis of the Tanystropheus neck using a digital model based on three-dimensionally preserved bones. We assessed its range of motion (ROM) and performed finite element analysis (FEA) on the individual cervical ribs and the neck model in different configurations. Our results indicate that the neck of Tanystropheus was not extremely stiff, as previously postulated, and the ribs likely did not impair its movements. They transferred tensile forces towards the base of the neck, similar to what hypothesized for sauropods7. This study elucidates the bauplan of an extremely specialized animal and brings us closer to understanding the patterns of achieving neck elongation in vertebrates. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=186 SRC="FIGDIR/small/735087v1_fig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@6732a3org.highwire.dtl.DTLVardef@12d9dcdorg.highwire.dtl.DTLVardef@1d331a0org.highwire.dtl.DTLVardef@5f0a91_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOFigure 1.C_FLOATNO Comparison of the cervical vertebral column anatomy of some long-necked tetrapods. Reconstructions not to scale. Based on: Tanystropheus conspicuus - Rytel6; Dinocephalosaurus orientalis - Spiekman et al.8; Mamenchisaurus youngi - Pi et al.9, Ouyang and Ye10; Struthio camelus - Mivart11; Quetzalcoatlus - Padian et al.12; Chelodina longicollis - Herrel et al.13; Albertonecte vanderveldei - Kubo et al.14, Sachs et al.15; Giraffa camelopardalis - Badlangana et al.16. The numbered nodes correspond to the following taxa: 1. Tetrapoda; 2. Diapsida; 3. Archosauromorpha; 4. Tanysauria; 5. Avemetatarsalia; and 6. Saurischia. C_FIG

paleontology↗

bioRxiv2025

Scaling contact force parameters across body size, limb count, and number of contact spheres

A popular way to model contact interactions in musculoskeletal simulations uses Hertz theory applied to contact spheres, with Hunt Crossley based dissipation. Suitable contact parameters for dynamic simulations will be highly dependent on the morphology, scale, materials, and movement in question. Inappropriate parameter choices can manifest in unpredictable ways during simulations, potentially resulting in misinterpretations or failed simulations. Here, I demonstrate that both the plane strain modulus and the dissipation parameters are not scale invariant. I derive equations to scale the contact parameters in dimensionless form, which allows accounting for differences in body size, number of legs, contact sphere radius, and number of spheres per foot. As a demonstration of this scaling approach, I scale the contact parameters of a 62 kg human to a 500 kg human, a mouse (0.02 kg), an emu (37.8 kg), a horse (545 kg), and a giraffe (1190 kg), and demonstrate that geometrically and dynamically similar contact behaviour is achieved in all cases. The scaling approach presented here can be used to scale parameters known to work for one model to a completely different model, which is particularly useful in studies that simulate the effects of allometric scaling. I also provide equations to estimate suitable contact parameters for a model directly, without using a different model as a starting point. The limitations of Hertz Hunt Crossley contact models in biomechanical simulations are discussed. Lastly, I derive dimensionless expressions and scaling guidelines for the smoothed contact force implementation "SmoothSphereHalfSpaceForce" in the popular biomechanical simulator OpenSim.

biophysics↗

bioRxiv2024

MuSkeMo: Open-source software to construct, analyze, and visualize human and animal musculoskeletal models and movements in Blender

Musculoskeletal models for multibody dynamic analysis provide unique insights into human and animal movement. Although some biomechanical simulators provide model-building tools, these presuppose substantial preprocessing by the user, and resulting models are generally not cross-platform compatible. Thus, the workflow from anatomical 3D scans to musculoskeletal model is time-consuming, requiring numerous processing and conversions steps between software packages, and the process differs between simulators. Despite the popularity of musculoskeletal modelling within biomechanics, no cross-platform, open source software package exists for constructing musculoskeletal models. Here, I introduce MuSkeMo: A software suite for defining 3D musculoskeletal models entirely within Blender (open-source 3D computer graphics software). MuSkeMo provides a visual interface, enabling users to interactively define all aspects of a musculoskeletal model (including rigid bodies, skeletal geometry, joint centres, muscles, landmarks, and body-fixed reference frames). MuSkeMo can calculate 3D inertial tensors from arbitrary meshes (e.g., from CT scans), and also implements automated convex-hull based mass-estimation approaches from the literature. Joints can be defined using shape-fitting of bony surfaces, and muscles can wrap around primitive shapes. Models can be analyzed within MuSkeMo using popular pose-sampling procedures, or exported to multiple text-based formats for use in biomechanical simulators. A conversion script to OpenSim is included. MuSkeMo is compatible with models created for popular biomechanical simulators (OpenSim and Gaitsym). MuSkeMo can import these models and simulation trajectories, enabling users to create publication-ready stills and animations with Blenders ray tracing. These visualisations include volumetric muscles based on the contractile parameters, which can be more visually intuitive than traditional constant-diameter tube segments. Whether the end goal is a highly-detailed subject-specific human model, or a simplified animal model, MuSkeMo includes features that can aid this process. By consolidating many elements of common model construction workflows into a cohesive package, MuSkeMo substantially simplifies musculoskeletal modelling.

biophysics↗

bioRxiv2024

Muscle-controlled physics simulations of the emu (a large running bird) resolve the grounded running paradox

Humans and birds utilize very different running styles. Unlike humans, birds adopt "grounded running" at intermediate speeds - a running gait where at least one foot is always in contact with the ground. Avian grounded running is paradoxical: animals tend to minimize locomotor energy expenditure, but birds prefer grounded running despite incurring higher energy costs. Using predictive gait simulations of the emu (Dromaius novaehollandiae), we resolve this paradox by demonstrating that grounded running represents an energetic optimum for birds. Our virtual experiments decoupled biomechanically relevant anatomical features that cannot be isolated in a real bird. The avian body plan prevents (near) vertical leg postures while running, making the running style used by humans impossible. Under this anatomical constraint, grounded running is optimal if the muscles produce the highest forces in crouched postures, as is true in most birds. Anatomical similarities between birds and non-avian dinosaurs suggest that, as a behavior, avian grounded running first evolved within non-avian theropods.

zoology↗