Muscle Attachment Sites Research Articles

Expression of distal limb patterning genes in Hypsibius exemplaris indicate regionalization and suggest distal identity of tardigrade legs

BackgroundPanarthropods, a major group of invertebrate animals comprised of arthropods, onychophorans, and tardigrades, are the only limb-bearing members of Ecdysozoa. The complexity and versatility of panarthropod paired limbs has prompted great interest in their development to better understand the formation of these structures and the genes involved in this process. However, studies of limb patterning and development are overwhelmingly focused on arthropods, followed by select work on onychophorans but almost entirely lacking for tardigrades. This model organism bias is inherently limited and precludes a comparative analysis of how panarthropod legs originated, have evolved, and the likely limb patterning genes present in the earliest panarthropod ancestors. In this study, we investigated tardigrade homologs of seven arthropod distal limb patterning genes (apterous, aristaless, BarH1, clawless, Lim1, rotund, and spineless) to better characterize tardigrade limb development in a comparative context.ResultsWe detected homologs of all seven genes in the eutardigrade Hypsibius exemplaris and heterotardigrade Echiniscoides cf. sigismundi suggesting their conservation in both tardigrade lineages. Hybridization chain reaction experiments in H. exemplaris reveal a regionalized expression pattern for the genes aristaless, BarH1, clawless, rotund and spineless.ConclusionThe observed regionalized expression of the distal limb patterning genes in H. exemplaris might reflect the external morphological features of tardigrade legs, such as the distal claws, sensory organs in the proximal region, and specific muscle attachment sites. The comparison between the expression of these limb patterning genes in H. exemplaris relative to other panarthropods suggests their conserved role in the last common panarthropod ancestor, such as establishing the distal limb end and the distribution of sensory structures. Our results support the hypothesis that tardigrade legs are homologous to the distal region of other panarthropod limbs, as suggested by previous work on the expression of leg gap genes in H. exemplaris.

Actin-driven nanotopography promotes stable integrin adhesion formation in developing tissue

Morphogenesis requires building stable macromolecular structures from highly dynamic proteins. Muscles are anchored by long-lasting integrin adhesions to resist contractile force. However, the mechanisms governing integrin diffusion, immobilization, and activation within developing tissues remain elusive. Here, we show that actin polymerization-driven membrane protrusions form nanotopographies that enable strong adhesion at Drosophila muscle attachment sites (MASs). Super-resolution microscopy reveals that integrins assemble adhesive belts around Arp2/3-dependent actin protrusions, forming invadosome-like structures with membrane nanotopographies. Single protein tracking shows that, during MAS development, integrins become immobile and confined within diffusion traps formed by the membrane nanotopographies. Actin filaments also display restricted motion and confinement, indicating strong mechanical connection with integrins. Using isolated muscle cells, we show that substrate nanotopography, rather than rigidity, drives adhesion maturation by regulating actin protrusion, integrin diffusion and immobilization. These results thus demonstrate that actin-polymerization-driven membrane protrusions are essential for the formation of strong integrin adhesions sites in the developing embryo, and highlight the important contribution of geometry to morphogenesis.

Humanlike manual activities in Australopithecus

The evolution of the human hand is a topic of great interest in paleoanthropology. As the hand can be involved in a vast array of activities, knowledge regarding how it was used by early hominins can yield crucial information on the factors driving biocultural evolution. Previous research on early hominin hands focused on the overall bone shape. However, while such approaches can inform on mechanical abilities and the evolved efficiency of manipulation, they cannot be used as a definite proxy for individual habitual activity. Accordingly, it is crucial to examine bone structures more responsive to lifetime biomechanical loading, such as muscle attachment sites or internal bone architecture. In this study, we investigate the manual entheseal patterns of Australopithecus afarensis, Australopithecus africanus, and Australopithecus sediba through the application of the validated entheses-based reconstruction of activity method. Using a comparative sample of later Homo and three great ape genera, we analyze the muscle attachment site proportions on the thumb, fifth ray, and third intermediate phalanx to gain insight into the habitual hand use of Australopithecus. We use a novel statistical procedure to account for the effects of interspecies variation in overall size and ray proportions. Our results highlight the importance of certain muscles of the first and fifth digits for humanlike hand use. In humans, these muscles are required for variable in-hand manipulation and are activated during stone-tool production. The entheses of A. sediba suggest muscle activation patterns consistent with a similar suite of habitual manual activities as in later Homo. In contrast, A. africanus and A. afarensis display a mosaic entheseal pattern that combines indications of both humanlike and apelike manipulation. Overall, these findings provide new evidence that some australopith species were already habitually engaging in humanlike manipulation, even if their manual dexterity was likely not as high as in later Homo.

New evidence for five cephalic appendages in trilobites and implications for segmentation of the trilobite head

AbstractHead segments play a critical role in revealing the relationships within major arthropod groups but the accurate determination of their number and relationship is challenging because of the decoupling of dorsal tergites and ventral appendages. In recent decades, trilobites have been considered to have four pairs of cephalic appendages and, commonly, five dorsal segments, which has served as the basis for understanding euarthropod cephalic evolution. Based on multiple analytical techniques applied to well‐preserved soft‐bodied specimens of the Upper Ordovician olenid Triarthrus eatoni and middle Cambrian corynexochid Olenoides serratus, we argue that an additional pair of cephalic biramous appendages occurred just behind the antennae, indicating that trilobites had five pairs of cephalic appendages and six dorsally expressed segments. We propose that the mismatch between the four dorsal furrows and five ventral appendages in Olenoides may be reconciled by considering the morphology of the hypostome that marks the position of the antenna and the bifurcation of the first glabellar furrow that has two muscle attachment sites fused. The fusion of clustered attachment sites of the cephalic biramous appendages may have aided feeding ability by gathering the limb bases close to the mouth.

The semispinalis capitis muscle skull attachment as a superficial external landmark for the location of the transverse dural venous sinuses

IntroductionIdentifiable superficial external landmarks can be used to determine the exact location of the internally located dural venous sinuses, for neurosurgical procedures. Several studies have been conducted to determine a standard method or a consistent reliable landmark, but all reported variations and inconsistencies with the examined landmarks. This study evaluated the relationship between the attachment site of the semispinalis capitis muscles on the external aspect of the skull and the internally located transverse dural venous sinuses. MethodsFifty-one South African skulls were used in this study. The Micro-focus X-ray Radiography and Tomography (MIXRAD) system at Necsa (Nuclear Energy Corporation South Africa) was used to scan and create three-dimensional images of each skull specimen. Pre-determined reference points were placed on the reconstructed images with the VGStudio Max volume rendering software. The relevant distances and locations of the reference points were measured and documented. ResultsThe muscle attachment site was located inferior to the transverse sinuses in all the skulls with a mean distance of 15.99 mm (left side) and 19.43 mm (right side). A statistically significant difference was found between all the measurements comparing the left- and right sides, however, no such difference was found between males and females. ConclusionThe apical attachment of the semispinalis capitis muscle is a good indicator for the internally located transverse dural venous sinus. This study indicates that a point of entry 8–10 mm inferior to this muscle attachment site be used, for safe access to the internal aspect of the posterior cranium.

The Biological Crystals in Chamid Bivalve Shells: Diversity in Morphology and Crystal Arrangement Pattern

Chamid bivalves are marine organisms that live in high-energy environments and are cemented to hard substrates. To avoid shell damage, the organisms form thick, densely ornamented shells. Shell material consists of aragonite, and the ornamentation may be either aragonitic or calcitic. The latter can be developed as scaly spines, rows of blades, or comarginal, radial arched lamellae. We investigated biological crystal morphology and mode of assembly of Chama arcana and Chama gryphoides shells. Structural characteristics were obtained from electron backscatter diffraction (EBSD) measurements, complemented with laser confocal and BSE imaging. We found a wide range of crystal morphologies and sizes, ranging from irregularly shaped calcite and/or aragonite prisms to tiny and thin aragonite laths. We observed four different modes of crystal assembly patterns: 1. strongly interlocked dendritic calcite units forming the ornamentation blades; 2. aragonite laths arranged to lamellae forming the outer shell layer, the layer adjacent to the calcite; 3. aragonite laths arranged into blocks comprising inner shell layers or aragonitic ornamentations; and 4. shell portions consisting of aragonite prisms, structured in size and crystal orientation, at muscle attachment sites. These four different types of crystal arrangements were observed for the shells of the investigated chamid species; however, they had slightly different strengths of structuring and slight variations in crystal organisation. Additionally, we observed unique microstructural features in Chama shells: We report ornamentation crystals resembling idiomorphic calcite and novel, twinned entities found at the changeover between the aragonitic layers. We highlight and discuss these differences and anomalies in this contribution.

Dendrite intercalation between epidermal cells tunes nociceptor sensitivity to mechanical stimuli in Drosophila larvae.

An animal's skin provides a first point of contact with the sensory environment, including noxious cues that elicit protective behavioral responses. Nociceptive somatosensory neurons densely innervate and intimately interact with epidermal cells to receive these cues, however the mechanisms by which epidermal interactions shape processing of noxious inputs is still poorly understood. Here, we identify a role for dendrite intercalation between epidermal cells in tuning sensitivity of Drosophila larvae to noxious mechanical stimuli. In wild-type larvae, dendrites of nociceptive class IV da neurons intercalate between epidermal cells at apodemes, which function as body wall muscle attachment sites, but not at other sites in the epidermis. From a genetic screen we identified miR-14 as a regulator of dendrite positioning in the epidermis: miR-14 is expressed broadly in the epidermis but not in apodemes, and miR-14 inactivation leads to excessive apical dendrite intercalation between epidermal cells. We found that miR-14 regulates expression and distribution of the epidermal Innexins ogre and Inx2 and that these epidermal gap junction proteins restrict epidermal dendrite intercalation. Finally, we found that altering the extent of epidermal dendrite intercalation had corresponding effects on nociception: increasing epidermal intercalation sensitized larvae to noxious mechanical inputs and increased mechanically evoked calcium responses in nociceptive neurons, whereas reducing epidermal dendrite intercalation had the opposite effects. Altogether, these studies identify epidermal dendrite intercalation as a mechanism for mechanical coupling of nociceptive neurons to the epidermis, with nociceptive sensitivity tuned by the extent of intercalation.

Reconstructing patterns of domestication in reindeer using 3D muscle attachment areas

The use of reindeer has been a crucial element in the subsistence strategies of past Arctic and Subarctic populations. However, the spatiotemporal occurrence of systematic herding practices has been difficult to identify in the bioarchaeological record. To address this research gap, this study proposes a new virtual anthropological approach for reconstructing habitual physical activity in reindeer, relying on the protocols of the “Validated Entheses based Reconstruction of Activity” (VERA) method. Following blind analytical procedures, we focused on eight muscle attachment sites (“entheses”) in 36 reindeer free ranging in the wild, 21 specimens in captivity (zoo), and eight racing reindeer (habitual runners). Importantly, our analyses accounted for the effects of variation by subspecies, sex, age, and estimated body size. Our results showed clear differences across activity groups, leading to the development of discriminant function equations with cross-validated accuracies ranging from approximately 88 to 100%. The reliability of our functions was additionally confirmed using a blind test involving six zoo individuals not included in the initial dataset. Our findings support the use of the proposed approach for identifying domestication-related activities in zooarchaeological contexts, introducing a valuable tool for locating suspected domestication hotspots and elucidating the nature of past human-reindeer interactions.

Looking back over the shoulder: New insights on the unique scapular anatomy of the tapir (Perissodactyla: Tapiridae).

The musculoskeletal anatomy of the shoulder of many ungulates has been inferred from veterinary model taxa, with uniformity in muscle arrangements and attachment sites often assumed. In this study, I investigated the muscular and osteological anatomy of tapirs and their relatives (Perissodactyla: Tapiroidea), using a combination of gross dissection and digital imaging (photography and laser surface scanning). Dissections of three modern tapir species revealed that the m. infraspinatus originates from both supraspinous and infraspinous fossae for all species, lying on both sides of the distal scapular spine. The epimysial border between the m. supraspinatus and m. infraspinatus origin sites are marked in all species by an ossified ridge, sometimes extending the length of the scapular spine. This "supraspinous ridge" is clearly visible on the scapular surface of both modern and extinct Tapirus scapulae; however, the ridge does not appear present in any non-Tapirus tapiroids examined (e.g., Helaletes, Nexuotapirus), nor in other perissodactyls or artiodactyls. Moreover, the ridge exhibits a clearly distinct morphology in Tapirus indicus compared to all other Tapirus species examined. Combined, these findings indicate that the presence and position of the "supraspinous ridge" may represent a robust phylogenetic character for reconstructing relationships within tapiroids. Unfortunately, any functional locomotor outcomes or benefits of the m. infraspinatus straddling the scapular spine remains elusive. This study represents a firm reminder for anatomists, veterinarians, and paleontologists to (where possible) look beyond veterinary model systems when inferring musculoskeletal form or function in non-model organisms.

A Recording Method for Sixteen Nonadult Muscle Entheses

ABSTRACT Bioarchaeology lacks a system for recording the morphology of muscle and ligament attachment sites, called entheses, in growing individuals. Such information is useful in investigating factors that affect bone growth and development, including sex, age, puberty, pathology, and activity. This paper presents a standardized recording method for nonadult entheses based on 29 archaeological individuals of archivally known sex and age-at-death, ranging from two to 17 years. This paper (a) assesses the range of osseous changes of 16 entheses in the upper and lower limbs of growing individuals, and (b) presents a scoring method for each enthesis, which is evaluated through inter-and intra-observer comparisons. Nonadult entheses show a wide range of morphological variation. Method reproducibility is established. This method will allow researchers to further investigate factors affecting bone development in nonadult skeletal remains.

Mandibular anatomy of the paracryptodire Glyptops ornatus supports active hunting behavior in a Jurassic turtle.

The mandible of turtles is rich in osteological characters that are relevant for systematic purposes. Shape variation additionally reflects upon various feeding strategies and are thus informative for the palaeoecological interpretation of extinct species based on fossils. The mandibular anatomy of non-baenid paracryptodires has so far been undescribed. Based on digital segmentation of a computed tomography scan, I herein describe the mandible of the pleurosternid paracryptodire Glyptops ornatus. This taxon has a slender and gracile jaw, with weakly developed muscle attachment sites for adductor muscles (i.e., adductor fossa, coronoid process, and retroarticular process) and strongly reduced triturating ridges. These features are typical for suction-feeding aquatic hunters, thereby contrasting with the robust, durophagous-adapted mandibles of many baenid or compsemydid paracryptodires. In addition, the mandible of G. ornatus is characterized by the presence of a large splenial with a dorsal splenial-dentary contact, the presence of a splenial foramen, and the strong reduction of the foramen dentofaciale majus and the absence of a posterior intermandibular foramen.

Comparison of anterior segment optical coherence tomography and ultrasound biomicroscopy in localizing horizontal rectus muscle insertions.

To evaluate the viability and precision of measuring the distance from the limbus to extraocular muscle insertion using anterior segment optical coherence tomography (AS-OCT) and panoramic ultrasound biomicroscopy (UBM) before and after strabismus surgery. We recruited primary strabismus patients and measured the limbus-insertion distance by AS-OCT and UBM preoperatively, 2 weeks, and 1, 3, and 6 months postoperatively. Values were also measured using callipers intraoperatively before and after the planned procedures. Preoperative AS-OCT and UBM values were compared to intraoperative calliper measurements as the gold standard. Postoperative AS-OCT and UBM values were compared to the new postoperative limbus-insertion distance. The limit of agreement deemed clinically acceptable was defined as 1 mm. A total of 85 horizontal muscles of 40 patients, including 48 lateral rectus muscles and 37 medial rectus muscles, were analysed. Primary muscles could be successfully detected by AS-OCT (95%) and UBM (100%). At 2 weeks and 1, 3, and 6 months postoperatively, the new rectus muscle attachment site detection rate by AS-OCT was 6%, 32%, 80%, and 89%, respectively, and that by UBM was 24%, 60%, 85%, and 93%, respectively. The Bland-Altman plots revealed better consistency in pairs of AS-OCT, UBM, and calliper measurements of primary muscles than postoperative muscles. For primary muscles, 89% of AS-OCT measurements fell within the permissible range of surgical measurements (1 mm), but this dropped to 67% at 6 months postoperatively (P < 0.001). The accuracy of UBM measurements of primary muscles was 81%, and this decreased to 59% at 6 months postoperatively (P = 0.001). AS-OCT and UBM performed well in terms of imaging primary horizontal rectus muscles, but showed decreased accuracy and reproducibility in postoperative muscle measures.

Bilateral dislocation of the hip joint and associated pathological changes in the ossa coxae and femora of a European roe deer (Capreolus capreolus).

We describe a bilateral craniodorsal dislocation of the hip joint in a free-ranging young roe buck and the associated pathological changes in the ossa coxae and femora of the animal. The highly symmetrical dislocation, which is considered to have developed secondary to hip dysplasia, caused the formation of two false acetabula that each consist of several, partially fused bone portions. The femora exhibit symmetrical outgrowths that extend from the greater trochanter along the intertrochanteric crest to the lesser trochanter. Formation of these outgrowths is attributed to abnormal traction at muscle attachment sites due to the displacement of the femora. On radiographic examination, both femora show signs of avascular necrosis in their head regions and of fatty marrow necrosis in their shafts, which is attributed to the damage of the arterial blood supply of the femora that was associated with the dislocation. The fact that, according to the hunter who shot the buck, the animal's locomotion was inconspicuous suggests that the false hip joints functioned quite well, thereby demonstrating a remarkable capacity of the musculoskeletal system for functional recovery.

Beyond sex, gender, and other dilemmas: Human pelvic morphology from an integrative context.

Recent research on the pelvis has clarified the flexibility of pelvic bones to manage nearly infinite possibilities in terms of selection and drift, while still maintaining excellent bipedalism. Despite this work, and the studies outlining the diversity of pelvic morphology across the hominin lineage, conversations continue to be stymied by distractions related to purported trade-offs that the different functions the pelvis must either allow for (e.g., parturition)or directly perform (e.g., attachment sites of muscles). Here we show that tight constraints on morphology are not evident in the pelvic variation of multiple human populations. We thus provide further evidence that human pelves are not geometrically similar and that pelvic morphology successfully balances the intersection of population history, active selective, and drift.

Puberty in a Mesozoic reptile.

The histology of bone can be preserved virtually unaltered for hundreds of millions of years in fossils from all environments and all vertebrate taxa, giving rise to the flourishing field of paleohistology.1 The shafts of long bones are formed by the apposition of periosteal bone tissue, similar to the growth of wood, and preserve, an often cyclical, record of the growth of the individual and events in its life history. One such event is sexual maturation or puberty, during which hormonal changes transform the juvenile into a sexually mature adult. Puberty has been well studied in humans and some other living vertebrates. Here, we describe puberty in Keichousaurus, a small sexually dimorphic and live-bearing marine reptile from Middle Triassic rocks of SW China, about 240 million years old. Using a combination of bone histology and morphology, we detected puberty2 as one of the four life stages (the others being fetus, juvenile, and adult). Adult Keichousaurus males have a more robust humerus than females, with pronounced muscle attachment sites and a triangular shaft cross section. Midshaft sections of the humeri of the males show the transition from the rounded juvenile cross section to the triangular adult cross section, as reflected in the contour of the growth marks. This shape change is produced by differential bone apposition of the periosteum, presumably triggered by sex hormones, as in humans,3 and influenced by changes in loading regime during puberty. This is the first report of puberty in a fossil amniote.

Scleraxis-lineage cells are required for correct muscle patterning.

Movement of the vertebrate body is supported by the connection of muscle, tendon and bone. Each skeletal muscle in the vertebrate body has a unique shape and attachment site; however, the mechanism that ensures reproducible muscle patterning is incompletely understood. In this study, we conducted targeted cell ablation using scleraxis (Scx)-Cre to examine the role of Scx-lineage cells in muscle morphogenesis and attachment in mouse embryos. We found that muscle bundle shapes and attachment sites were significantly altered in embryos with Scx-lineage cell ablation. Muscles in the forelimb showed impaired bundle separation and limb girdle muscles distally dislocated from their insertion sites. Scx-lineage cells were required for post-fusion myofiber morphology, but not for the initial segregation of myoblasts in the limb bud. Furthermore, muscles could change their attachment site, even after formation of the insertion. Lineage tracing suggested that the muscle patterning defect was primarily attributed to the reduction of tendon/ligament cells. Our study demonstrates an essential role of Scx-lineage cells in the reproducibility of skeletal muscle attachment, in turn revealing a previously unappreciated tissue-tissue interaction in musculoskeletal morphogenesis.

Quantitatively biomechanical response analysis of posterior musculature reconstruction in cervical single-door laminoplasty

Background and objectiveThe current trend of laminoplasty is developing toward the goal of muscle preservation and minimum tissue damage. Given this, muscle-preserving techniques in cervical single-door laminoplasty have been modified with protecting the spinous processes at the sites of C2 and/or C7 muscle attachment and reconstruct the posterior musculature in recent years. To date, no study has reported the effect of preserving the posterior musculature during the reconstruction. The purpose of this study is to quantitatively evaluate the biomechanical effect of multiple modified single-door laminoplasty procedures for restoring stability and reducing response level on the cervical spine. MethodsDifferent cervical laminoplasty models were established for evaluating kinematics and response simulations based on a detailed finite element (FE) head-neck active model (HNAM), including ① C3 – C7 laminoplasty (LP_C37), ② C3 – C6 laminoplasty with C7 spinous process preservation (LP_C36), ③ C3 laminectomy hybrid decompression with C4 – C6 laminoplasty (LT_C3 + LP_C46) and ④ C3 – C7 laminoplasty with unilateral musculature preservation (LP_C37 + UMP). The laminoplasty model was validated by the global range of motion (ROM) and percentage changes relative to the intact state. The C2 – T1 ROM, axial muscle tensile force, and stress/strain levels of functional spinal units were compared among the different laminoplasty groups. The obtained effects were further analysed by comparison with a review of clinical data on cervical laminoplasty scenarios. ResultsAnalysis of the locations of concentration of muscle load showed that the C2 muscle attachment sustained more tensile loading than the C7 muscle attachment, primarily in flexion-extension (FE) and in lateral bending (LB) and axial rotation (AR), respectively. Simulated results further quantified that LP_C36 primarily produced 10% decreases in LB and AR modes relative to LP_C37. Compared with LP_C36, LT_C3 + LP_C46 resulted in approximately 30% decreases in FE motion; LP C37 + UMP also showed a similar trend. Additionally, when compared to LP_C37, LT_C3 + LP_C46 and LP C37 + UMP reduced the peak stress level at the intervertebral disc by at most 2-fold as well as the peak strain level of the facet joint capsule by 2–3-fold. All these findings were well correlated with the result of clinical studies comparing modified laminoplasty and classic laminoplasty. ConclusionsModified muscle-preserving laminoplasty is superior to classic laminoplasty due to the biomechanical effect of the posterior musculature reconstruction, with a retained postoperative ROM and loading response levels of the functional spinal units. More motion-sparing is beneficial for increasing cervical stability, which probably accelerates the recovery of postoperative neck movement and reduces the risk of the complication for eventual kyphosis and axial pain. Surgeons are encouraged to make every effort to preserve the attachment of the C2 whenever feasible in laminoplasty.

Mechanical regulation of vinculin conformations and interactions.

Vinculin, as an essential mechanosensitive protein, transmits intracellular tension initiated from the cell-cell and the cell-matrix interfaces, to modulate cellular and tissue functions. However, the tension-dependent conformations and interactions of vinculin are largely unknown. Vinculin provides the mechanical linkages between talin and actin at Focal adhesions, or alpha-catenin and actin at Adherens junctions. In drosophila, vinculin also functions at the muscle attachment sites with Cbl-associated proteins (CAPs) to regulate the cytoskeletal organization and membrane morphology. In this work, we combined single-molecule manipulation, AlphaFold2-based structural prediction, molecular dynamic (MD) simulation and theoretical modelling to understand the tension-dependent conformational changes of drosophila vinculin domains and its interaction with drosophila CAP isoform E (dCAP-E). We reveal that vinculin domains unfold in discrete steps, within 5-15 pN at a physiologically relevant tension loading rate. Based on the structural conformations predicted by AlphaFold2 and confirmed by MD simulation, a theoretical model is developed which predicts a tension-dependent binding affinity between the drosophila vinculin linker and dCAP-E within the physiologically relevant tension range. Together, the results suggest two roles of vinculin, as a tension buffering structure via tension-dependent unfolding and refolding of domains and as a mechanosensor via tension-dependent binding with its binding partners.

Climbing influences entheseal morphology in the humerus of mice: An experimental application of the VERA methodology

AbstractObjectivesWhen studying hominin skeletal remains, anthropologists commonly assume that the morphology of entheses (muscle and tendon attachment sites) is influenced by physical activity patterns during life. Here, we use samples of mice from a prior experiment (Siegel &amp; Jones [1975] American Journal of Physical Anthropology 42:141–144) to test this assumption. Specifically, we investigate the effects of habitual climbing on entheses of the humerus using a recently developed protocol for analyzing entheseal morphology called the “Validated Entheses‐based Reconstruction of Activity” (VERA) method.Materials and MethodsIn the original experiment, young mice were raised for approximately 9 weeks in one of two experimental conditions: a cage designed to limit locomotion to terrestrial quadrupedalism over a flat surface (n = 22), or a cage designed to impel animals to cling to a suspended wire mesh apparatus and limit their locomotion to climbing (n = 21). We μCT‐scanned the humeri of these mice and used the VERA method to assess the morphology of the deltoid tuberosity, greater tubercle, lesser tubercle, and supinator crest.ResultsSignificant differences in entheseal morphology were detected between climbers and non‐climbers when using both multivariate statistics to assess all entheses simultaneously and univariate statistics to assess each enthesis individually.DiscussionOur results provide new support for the general use of entheseal morphology for inferring hominin physical activity patterns in the past. Furthermore, based on our results, we propose that analyzing entheseal morphology using the VERA method may be a promising strategy for future research on the importance of climbing in hominin locomotor evolution.

Linking the proximal tibiofibular joint to hominid locomotion: A morphometric study of extant species

AbstractObjectivesWe perform a comparative assessment of shape variation of the proximal fibula in extant humans and great apes, intending to investigate the possible link between proximal fibular shape and locomotor patterns.MethodsOur sample includes 94 fibulae of 37 Homo sapiens, 15 Gorilla, 17 Pongo, and 25 Pan. Fibular morphology was investigated through three‐dimensional (semi)landmark‐based geometric morphometric methods.ResultsWe found unique features of the human fibular head compared to that of great apes (i.e., oblique articular surface, the presence of the styloid process, specific morphology of muscle attachment sites), supporting the functional role of this bone in relation to human obligate bipedalism. Great apes also showed distinctive traits in their proximal fibula morphology, in agreement with differences in locomotor behavior.ConclusionThe morphology of the proximal fibula in extant humans and great apes is indicative of locomotor behavior, offering the potential for the comparative analysis of fossil hominin remains.