Hindlimb Skeleton Research Articles

A new abelisaurid dinosaur from the end Cretaceous of Patagonia and evolutionary rates among the Ceratosauria.

Gondwanan dinosaur faunae during the 20 Myr preceding the Cretaceous-Palaeogene (K/Pg) extinction included several lineages that were absent or poorly represented in Laurasian landmasses. Among these, the South American fossil record contains diverse abelisaurids, arguably the most successful groups of carnivorous dinosaurs from Gondwana in the Cretaceous, reaching their highest diversity towards the end of this period. Here we describe Koleken inakayali gen. et sp. n., a new abelisaurid from the La Colonia Formation (Maastrichtian, Upper Cretaceous) of Patagonia. Koleken inakayali is known from several skull bones, an almost complete dorsal series, complete sacrum, several caudal vertebrae, pelvic girdle and almost complete hind limbs. The new abelisaurid shows a unique set of features in the skull and several anatomical differences from Carnotaurus sastrei (the only other abelisaurid known from the La Colonia Formation). Koleken inakayali is retrieved as a brachyrostran abelisaurid, clustered with other South American abelisaurids from the latest Cretaceous (Campanian-Maastrichtian), such as Aucasaurus, Niebla and Carnotaurus. Leveraging our phylogeny estimates, we explore rates of morphological evolution across ceratosaurian lineages, finding them to be particularly high for elaphrosaurine noasaurids and around the base of Abelisauridae, before the Early Cretaceous radiation of the latter clade. The Noasauridae and their sister clade show contrasting patterns of morphological evolution, with noasaurids undergoing an early phase of accelerated evolution of the axial and hind limb skeleton in the Jurassic, and the abelisaurids exhibiting sustained high rates of cranial evolution during the Early Cretaceous. These results provide much needed context for the evolutionary dynamics of ceratosaurian theropods, contributing to broader understanding of macroevolutionary patterns across dinosaurs.

Endochondral ossification of hindlimbs in embryonic development of Japanese Quail (Coturnix japonica)

The endochondral ossification of hindlimb is essential to a bird's ability to stand, walk and fly. Most hindlimb is ossified in the embryos before hatching in precocial birds. However, the molecular mechanisms of hindlimb ossification in birds is still unclear. Therefore, we tried to examine the process of hindlimb ossification and its molecular regulation by using an animal model—Japanese Quail (Coturnix japonica). We selected four critical stages (Embryo Day: E6, E8, E12 and E16) of skeletal development of embryonic quails for hindlimb skeleton staining to show the process of endochondral ossification and to examine the molecular regulation of endochondral osteogenesis by RNA-Seq analysis. The results showed that ossification became increased with embryonic development and most hindlimb was ossified before hatching. RNA-Seq analysis revealed that various signaling pathways were involved with endochondral ossification with thyroid hormone signaling and WNT signaling pathway particularly enriched. Moreover, the expression levels of 42 genes were continuously upregulated and 14 genes were continuously downregulated from E6 to E16. The present study might provide new insights into complex molecular mechanisms in regulation of endochondral ossification.

The fossil record of appendicular muscle evolution in Synapsida on the line to mammals: Part II-Hindlimb.

This paper is the second in a two-part series that charts the evolution of appendicular musculature along the mammalian stem lineage, drawing upon the exceptional fossil record of extinct synapsids. Here, attention is focused on muscles of the hindlimb. Although the hindlimb skeleton did not undergo as marked a transformation on the line to mammals as did the forelimb skeleton, the anatomy of extant tetrapods indicates that major changes to musculature have nonetheless occurred. To better understand these changes, this study surveyed the osteological evidence for muscular attachments in extinct mammalian and nonmammalian synapsids, two extinct amniote outgroups, and a large selection of extant mammals, saurians, and salamanders. Observations were integrated into an explicit phylogenetic framework, comprising 80 character-state complexes covering all muscles crossing the hip, knee, and ankle joints. These were coded for 33 operational taxonomic units spanning >330 Ma of tetrapod evolution, and ancestral state reconstruction was used to evaluate the sequence of muscular evolution along the stem lineage from Amniota to Theria. The evolutionary history of mammalian hindlimb musculature was complex, nonlinear, and protracted, with several instances of convergence and pulses of anatomical transformation that continued well into the crown group. Numerous traits typically regarded as characteristically "mammalian" have much greater antiquity than previously recognized, and for some traits, most synapsids are probably more reflective of the ancestral amniote condition than are extant saurians. More broadly, this study highlights the utility of the fossil record in interpreting the evolutionary appearance of distinctive anatomies.

Sexual Dimorphism in the Limb Bones of Asiatic Toad (Bufo gargarizans) in Relation to Sexual Selection.

Sexual dimorphism is often considered to be the result of differences in the intensity of sexual selection between sexes. From this point of view, the sexual dimorphism of the limb bones of the Bufo gargarizans in southwest China was studied. Results showed that the fore- and hindlimb skeletons of this species were sexually dimorphic in anatomy. The humerus, radioulna, and total lengths of the forelimb skeleton of males were substantially longer than those of females, but the hand length of males was smaller than that of females. Several other features of males, such as deltoid and medial crest areas and humerus and radioulnar weights, were also significantly larger than those of females. The femoris, tibiofibula, talus-calcaneus, and foot lengths; total hindlimb skeleton length; and femoral upper crest areas of males were significantly greater than those of females. However, no significant intersexual difference in femoris and tibiofibular weights was observed. These findings suggested that robust forelimb bones and long hindlimb bones could contribute to the mating success of males; if so, sexual selection promotes the evolution of sexual size and shape dimorphism in the limb bones of the B. gargarizans.

Hindlimb Skeletal Morphology of the Helmeted Guinea Fowl (Numida meleagridis)

Abstract The Guinea fowl (Numida meleagridis) is a semi-domestic bird whose commercial popularity is on the increase. The gross anatomy of the hindlimbs of 8 helmeted Guinea fowls of equal sexes were studied. The pubic shafts were free, thus they did not fuse ventrally to form a symphysis. The ilium had a quadrilateral and roughly triangular pre and post acetabular wings, respectively. A conspicuous renal fossa was observed in the post acetabular wing. An incomplete concentric obturator foramen, lacking a caudal margin, was formed by the ventral border of the ischium and dorsal border of the cranial pubic shaft, while a prominent ischiopubic fissure was formed by the same bones, caudally. The incomplete concentric nature of the obturator foramen created a common space between it and the ischiopubic fissure. The femoral major trochanter was more proximal than the head, while the minor tro-chanter and the head were on the same horizontal level. The femur lacked a visible pneumatic foramen. The tibiotarsus had a prominent cranial cnemial crest. The fibular spine terminated at the tibia mid-shaft, leaving one interosseous space. An intertarsal sesamoid bone was identified, indicative of an adult skeleton. Crests and channels depicted the hypotarsus. Vascular foramen was identified in the distal extremity of the tibiotarsus. Digit I was oriented to the planter direction. These results, and others, were compared with those of other birds in the available literature, and some morpho-functional paradigm of the Guinea fowl hindlimb skeleton was established.

How to make a vampire.

Herein, we compared the developmental maturity of the cranium, limbs, and feeding apparatus in a perinatal common vampire bat relative to its mother. In addition, we introduce a method for combining two computed tomographic imaging techniques to three-dimensionally reconstruct endocasts in poorly ossified crania. The Desmodus specimens were scanned using microcomputed tomography (microCT) and diffusible iodine-based contrast-enhanced CT to image bone and soft tissues. Muscles of the jaw and limbs, and the endocranial cavity were segmented using imaging software. Endocranial volume (ECV) of the perinatal Desmodus is 74% of adult ECV. The facial skeletal is less developed (e.g., palatal length 60% of adult length), but volumes for alveolar crypts/sockets of permanent teeth are nearly identical. The forelimb skeleton is uniformly less ossified than the distal hind limb, with no secondary centers ossified and an entirely cartilaginous carpus. All epiphyseal growth zones are active in the brachium and antebrachium, with the distal radius exhibiting the greatest number of proliferating chondrocytes arranged in columns. The hind limb skeleton is precociously ossified from the knee distally. The musculature of the fore limb, temporalis, and masseter muscles appear weakly developed (6-11% of the adult volume). In contrast, the leg and foot musculature is better developed (23-25% of adult volume), possibly enhancing the newborn's capability to grip the mother's fur. Desmodus is born relatively large, and our results suggest they are born neurally and dentally precocious, with generally underdeveloped limbs, especially the fore limb.

From sprawling to parasagittal locomotion in Therapsida: A preliminary study of historically collected museum specimens

Therapsids covered the entire spectrum of terrestrial locomotion from sprawling to parasagittal. Switching between sprawling and more erect locomotion may have been possible in earlier taxa. First, the axial skeleton shows little regionalization and allows lateral undulation, evolving then increasingly towards regionalization enabling dorsoventral swinging. During terrestrial locomotion, every step invokes a ground reaction force and functional loadings which the musculoskeletal system needs to accomodate. First insights into the functional loading regime of the fore- and hindlimb skeleton and the body stem of therapsids presented herein are based on the assessment and preliminary measurements of the historical collection of therapsids exhibited in the Paleontological Collection of Eberhard Karls Universität Tübingen, Germany. The specimens included are the archosaurHyperodapedon sanjuanensis, the early synapsidDimetrodon limbatusfor comparison, and the therapsidsKeratocephalus moloch,Sauroctonus parringtoni,Tetragonias njalilus, andBelesodon magnificus. The vertebral columns and ribs of the mounts were carefully assessed for original fossil material and, when preserved, ribs, sacral, and anterior caudal vertebrae were measured. The body of a tetrapod is exposed to forces as well as bending and torsional moments. To resist these functional stresses, certain musculoskeletal specializations evolved. These include: 1) compression resistant plate-like pectoral and pelvic girdle bones, 2) a vertebral column combined with tendinous and muscular structures to withstand compressive and tensile forces and moments, and 3) ribs and intercostal muscles to resist the transverse forces and torsional moments. The legs are compressive stress-resistant, carry the body weight, and support the body against gravity. Tail reduction leads to restructuring of the musculoskeletal system of the pelvic girdle.

Divergence of Tbx4 hindlimb enhancer HLEA underlies the hindlimb loss during cetacean evolution.

The cetacean hindlimb skeleton massively decreased to only vestigial limb elements as cetaceans evolved from land to aquatic lifestyles; however, the molecular mechanism underlying this major morphological transition remains unclear. In this study, four deletions and specific substitutions were detected in cetacean hindlimb enhancer A (HLEA), an enhancer that can regulate Tbx4 expression in hindlimb tissues to control hindlimb development. Transcriptional activation of HLEA was significantly weaker in bottlenose dolphin than mice, and this was found to be closely associated with cetacean-specific deletions. Furthermore, deletions in cetacean HLEA might disrupt HOX and PITX1 binding sites, which are required for enhancer activation. The ancestral state of these deletions was investigated, and all four specific deletions were found to have occurred after the species diverged from their common ancestor, suggesting that the deletion occurred recently, during a secondary aquatic adaptation. Taking these findings together, we suggest that cetacean-specific sequence changes reduced the Tbx4 gene expression pattern, and consequently drove the gradual loss of hindlimb in cetaceans.

Bone structural, biomechanical, and histomorphometric characteristics of the hindlimb skeleton in the marsh rice rat (Oryzomys palustris).

The rice rat (Oryzomys palustris) is a nonconventional laboratory rodent species used to model some human bone disorders. However, no studies have been conducted to characterize the postcranial skeleton. Therefore, we aimed to investigate age- and gender-related features of the hindlimb skeleton of this species. We used femurs and tibiae from 94 rats of both genders aged 4-28 weeks. Bone mineral content (BMC), volumetric bone mineral density (vBMD), and biomechanical properties were determined in femurs. In addition, bone histomorphometry of tibiae was conducted to assess bone cell activities and bone turnover over time. Bone length, total metaphysis BMC and vBMD, mid-diaphyseal BMC and vBMD, cortical thickness, and cortical area progressively augmented with age. Whereas the increase in these parameters plateaued at age 16-22 weeks in female rats, they continued to rise to age 28 weeks in male rats. Furthermore, bone strength parameters increased with age, with few differences between genders. We also observed a rapid decrease in longitudinal growth between age 4 and 16 weeks. Whereas young rats had a greater bone formation rate and bone turnover, older rice rats had greater bone volume and trabecular thickness, with no differences between genders. (a) Sexual dimorphism in the rice rat becomes grossly evident at age 16 weeks; (b) the age-related increases in bone mass, structural cortical parameters, and in some biomechanical property parameters plateau at an older age in male than in female rats; and (c) bone growth and remodeling significantly decreased with age irrespective of the gender.

Differing limb functions and their potential influence upon the diversification of the mustelid hindlimb skeleton

Abstract Though form-function relationships of the mammalian locomotor system have been investigated for over a century, recent models of trait evolution have hitherto been seldom used to identify likely evolutionary processes underlying the locomotor system’s morphological diversity. Using mustelids, an ecologically diverse carnivoran lineage, I investigated whether variation in hindlimb skeletal morphology functionally coincides with climbing, digging, swimming and generalized locomotor habits by using 15 linear traits of the femur, tibia, fibula, calcaneum and metatarsal III across 44 species in a principal component analysis. I subsequently fit different models of Brownian motion and adaptive trait diversification individually to each trait. Climbing, digging and swimming mustelids occupy distinct regions of phenotypic space characterized by differences in bone robustness. Models of adaptive and neutral evolution are, respectively, the best fits for long bone lengths and muscle in-levers, suggesting that different kinds of traits may be associated with different evolutionary processes. However, simulations based upon models of best fit reveal low statistical power to rank the models. Though differences in mustelid hindlimb skeletal morphology appear to coincide with locomotor habits, further study, with sampling expanded beyond the Mustelidae, is necessary to better understand to what degree adaptive evolution shapes morphological diversity of the locomotor system.

Evolution of the Unique Anuran Pelvic and Hind limb Skeleton in Relation to Microhabitat, Locomotor Mode, and Jump Performance.

Anurans (frogs and toads) have a unique pelvic and hind limb skeleton among tetrapods. Although their distinct body plan is primarily associated with saltation, anuran species vary in their primary locomotor mode (e.g., walkers, hoppers, jumpers, and swimmers) and are found in a wide array of microhabitats (e.g., burrowing, terrestrial, arboreal, and aquatic) with varying functional demands. Given their largely conserved body plan, morphological adaptation to these diverse niches likely results from more fine-scale morphological change. Our study determines how shape differences in Anura's unique pelvic and hind limb skeletal structures vary with microhabitat, locomotor mode, and jumping ability. Using microCT scans of preserved specimens from museum collections, we added 3D landmarks to the pelvic and hind limb skeleton of 230 anuran species. In addition, we compiled microhabitat and locomotor data from the literature for these species that span 52 of the 55 families of frogs and ∼210 million years of anuran evolution. Using this robust dataset, we examine the relationship between pelvic and hind limb morphology and phylogenetic history, allometry, microhabitat, and locomotor mode. We find pelvic and hind limb changes associated with shifts in microhabitat ("ecomorphs") and locomotor mode ("locomorphs") and directly relate those morphological changes to the jumping ability of individual species. We also reveal how individual bones vary in evolutionary rate and their association with phylogeny, body size, microhabitat, and locomotor mode. Our findings uncover previously undocumented morphological variation related to anuran ecological and locomotor diversification and link that variation to differences in jumping ability among species.

Expression of a Constitutively Active Form of Hck in Chondrocytes Activates Wnt and Hedgehog Signaling Pathways, and Induces Chondrocyte Proliferation in Mice.

Runx2 is required for chondrocyte proliferation and maturation. In the search of Runx2 target genes in chondrocytes, we found that Runx2 up-regulated the expression of hematopoietic cell kinase (Hck), which is a member of the Src tyrosine kinase family, in chondrocytes, that Hck expression was high in cartilaginous limb skeletons of wild-type mice but low in those of Runx2–/– mice, and that Runx2 bound the promoter region of Hck. To investigate the functions of Hck in chondrocytes, transgenic mice expressing a constitutively active form of Hck (HckCA) were generated using the Col2a1 promoter/enhancer. The hind limb skeletons were fused, the tibia became a large, round mass, and the growth plate was markedly disorganized. Chondrocyte maturation was delayed until E16.5 but accelerated thereafter. BrdU-labeled, but not terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)-positive, chondrocytes were increased. Furthermore, Hck knock-down reduced the proliferation of primary chondrocytes. In microarray and real-time RT-PCR analyses using hind limb RNA from HckCA transgenic mice, the expression of Wnt (Wnt10b, Tcf7, Lef1, Dkk1) and hedgehog (Ihh, Ptch1, and Gli1) signaling pathway genes was upregulated. These findings indicated that Hck, whose expression is regulated by Runx2, is highly expressed in chondrocytes, and that HckCA activates Wnt and hedgehog signaling pathways, and promotes chondrocyte proliferation without increasing apoptosis.

Artificial Selection for Increased Voluntary Wheel Running Alters Limb Skeleton Shape and Exercise Plasticity in Mice

Individual skeletal morphology is determined by genetic effects and within‐generation phenotypic plasticity in response to mechanical loading. Changes in limb bone morphology associated with locomotor activity through ontogeny and across evolutionary time can provide insight into adaptation in locomotor systems. Here, we investigate the effects of long‐term selection for locomotor activity on the gross morphology and exercise response of the hind limb skeleton using a mouse model. A founding population of Hsd:ICR outbred mouse stock was divided into closed lines of “high runner” (HR) and control (C) animals. HR mice were bred for increased voluntary wheel‐running distance by breeding animals (n=10 pairs per generation) with the highest average wheel revolutions on days 5 and 6 of a 6‐day wheel exposure protocol. Control animals were also wheel‐tested but were randomly paired. Male HR and C mice from experimental generation 82 were randomly assigned at 5 weeks of age to be permitted or denied wheel access for 4 weeks, resulting in 4 experimental groups: C wheel (n=12), C no wheel (n=12), HR wheel (n=10), and HR no wheel (n= 10). Following wheel access, mice were euthanized and right hind limbs were micro‐CT scanned (~20 um voxel size). Three‐dimensional shapes of the os coxa, femur, and tibia were defined by digitizing 18, 23, and 18 landmarks, respectively, on each specimen. To adjust for size, individual bones were scaled to the geometric mean of all possible linear distances among landmarks. Between‐group differences were analyzed using canonical variates analysis (CVA) and localized using the Euclidean distance matrix analysis (EDMA) Form procedure. EDMA Growth procedure was used to compare the trajectories of exercise‐induced skeletal plasticity between HR and C animals. Differences ≥3% were considered substantial for both EDMA methods. Shape analyses revealed differences in morphological lability among the three limb bones examined and in subsections within each bone. More specifically, the mean hind limb skeletal morphology, especially of the pelvis and proximal femur, substantially differed between HR and C mice. Plastic bony responses to exercise also differed, most substantially in the iliac blade, ischial tuberosity, and proximal femur. Finally, throughout the hind limb, the baseline skeletal morphology of HR mice did not resemble the exercise response of C animals, indicating that genetic assimilation of plastic bone responses did not occur in this model. The results suggest regional sensitivity of the hind limb skeleton to plastic and evolved morphological change, provide further evidence of genetic influence on bone functional adaptation, and inform our understanding of the evolutionary lability of the musculoskeletal system over evolutionary timescales.Support or Funding InformationUniversity of Missouri School of Medicine, University of Missouri Dissertation Research Travel AwardThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

A three dimensional multiplane kinematic model for bilateral hind limb gait analysis in cats.

BackgroundKinematic gait analysis is an important noninvasive technique used for quantitative evaluation and description of locomotion and other movements in healthy and injured populations. Three dimensional (3D) kinematic analysis offers additional outcome measures including internal-external rotation not characterized using sagittal plane (2D) analysis techniques.MethodsThe objectives of this study were to 1) develop and evaluate a 3D hind limb multiplane kinematic model for gait analysis in cats using joint coordinate systems, 2) implement and compare two 3D stifle (knee) prediction techniques, and 3) compare flexion-extension determined using the multiplane model to a sagittal plane model. Walking gait was recorded in 3 female adult cats (age = 2.9 years, weight = 3.5 ± 0.2 kg). Kinematic outcomes included flexion-extension, internal-external rotation, and abduction-adduction of the hip, stifle, and tarsal (ankle) joints.ResultsEach multiplane stifle prediction technique yielded similar findings. Joint angles determined using markers placed on skin above bony landmarks in vivo were similar to joint angles determined using a feline hind limb skeleton in which markers were placed directly on landmarks ex vivo. Differences in hip, stifle, and tarsal joint flexion-extension were demonstrated when comparing the multiplane model to the sagittal plane model.ConclusionsThis multiplane cat kinematic model can predict joint rotational kinematics as a tool that can quantify frontal, transverse, and sagittal plane motion. This model has multiple advantages given its ability to characterize joint internal-external rotation and abduction-adduction. A further, important benefit is greater accuracy in representing joint flexion-extension movements.

Radiological and Histological Assessment of the Ossification Centers of Hind Limb after Hatching in Pigeon

Objective- The aim of this study was to determine the age of physical maturity and evaluation of radiology and histology of hind limb ossification centers in pigeon. Design- Fundamental study. Animals- 14 pigeons. Procedures- These pigeons were cultivated in identical and standard conditions and radiological and histological tests performed every 7 days to 91 days. Results- Based on the results of radiology and histology, the hind limb skeletal differentiation in pigeons with the appearance of centers of immature cartilages in diaphyses of the femur, tibiotarsus and tarsometatarsus at the end of the first week and the fibula bone at the end of the third week began. Growth sequences in the femur, tibiotarsus, fibula, tarsometatarsus and digits were observed during different stages. The maximum growth of these bones was related to the periods of maximum cartilage activity and their bone formation, and the femur holds steady its growth relation to the length of the skeletal body of the hind limb, although at the end of the fifth week its growth slowed down. The histological findings were based on the examination of the proximal extremity of the femur. The tissue samples at one day were lack of bone marrow and the bone marrow begins to form at the end of the first week. The presence of epiphyseal growth plate in samples and its bone formation was confirmed on the basis of radiology early in the fifth week. Conclusion and Clinical Relevance- According to this study, the best time to complete the development of bone formation and the formation of all parts of the hind limb skeleton of the pigeon is probably 35 days after the hatch.

Anatomical integration of the sacral-hindlimb unit coordinated by GDF11 underlies variation in hindlimb positioning in tetrapods.

Elucidating how body parts from different primordia are integrated during development is essential for understanding the nature of morphological evolution. In tetrapod evolution, while the position of the hindlimb has diversified along with the vertebral formula, the mechanism responsible for this coordination has not been well understood. However, this synchronization suggests the presence of an evolutionarily conserved developmental mechanism that coordinates the positioning of the hindlimb skeleton derived from the lateral plate mesoderm with that of the sacral vertebrae derived from the somites. Here we show that GDF11 secreted from the posterior axial mesoderm is a key factor in the integration of sacral vertebrae and hindlimb positioning by inducing Hox gene expression in two different primordia. Manipulating the onset of GDF11 activity altered the position of the hindlimb in chicken embryos, indicating that the onset of Gdf11 expression is responsible for the coordinated positioning of the sacral vertebrae and hindlimbs. Through comparative analysis with other vertebrate embryos, we also show that each tetrapod species has a unique onset timing of Gdf11 expression, which is tightly correlated with the anteroposterior levels of the hindlimb bud. We conclude that the evolutionary diversity of hindlimb positioning resulted from heterochronic shifts in Gdf11 expression, which led to coordinated shifts in the sacral-hindlimb unit along the anteroposterior axis.

Comparing Femur Cross‐sectional Morphology in Young Outbred Mice Following Daily Exposure to Muscle‐, Impact‐, or Combined Loading of the Hind Limb Skeleton

Limb bones are exposed to a multitude of intrinsic and extrinsic loading forces which they must resist in order to prevent fracture and maintain function. Bone is a plastic tissue which can adapt to encountered loads by increasing cortical thickness in areas of high strain and resorbing cortex in areas of low strain, thereby optimizing strength, weight, and metabolic requirements. While exercises such as running and jumping are known to induce changes in the cross‐sectional dimensions of limb bones, the relative contributions of muscular contractions and extrinsic ground reaction forces (GRF) in altering bone morphology are not fully understood. We compared femur gross and cross‐sectional morphology in mice exposed to four loading environments that differ in the source of forces imposed on the skeleton: swimming (muscle‐dominated), impact loading via falling (GRF‐dominated), running (combined muscle and GRF characteristic of natural locomotion), and sedentary controls. Four‐week‐old male Hsd:ICR mice were randomly assigned to treatment groups and completed loading exercises daily for 20 days. Mice were injected twice with fluorochrome labels during the final week of treatment to allow measurement of mineral apposition rates and regionalization. Undecalcified femoral mid‐diaphyseal sections were photographed using light and fluorescent microscopy and analyzed for cross‐sectional properties and mineral apposition patterns. We found that the falling impact group had the greatest distal femoral width, but the swim group had the greatest width at the mid‐diaphysis. The jump impact group demonstrated significantly greater cross‐sectional area and moments of inertia than controls, indicating increased resistance to torsion and bending compared to other loading regimes. Examination of mineral apposition patterns showed that mineral apposition was greatest posterolaterally in all groups, with additional medial or posterior cortical drift characterizing each loading treatment. These results indicate regional sensitivity of the growth and morphology of the femur to muscle‐ and GRF‐derived loads and suggest that impact loading induces the growth of stronger bones than other forms of exercise. Future analyses will use 3D geometric morphometrics to examine overall shape differences in femur, tibia, and pelvis following loading treatment.Support or Funding InformationUniversity of Missouri School of Medicine

Developmental stages for the divergence of relative limb length between a twig and a trunk-ground Anolis lizard species.

The divergent evolution of niche-related traits can facilitate adaptive radiation, yet identification of the genetic or molecular mechanisms underlying such trait changes remains a major challenge in evolutionary biology. Conducting a detailed morphological comparison along growth trajectories is a powerful method for observing the formation of differences in niche-related traits. Here, we focused on hindlimb length of Anolis lizards, differences in which are related to adaptation for use of different microhabitats. We measured the length of hindlimb skeletons in different ecomorphs of anole lizards (A. sagrei, a trunk-ground ecomorph with long hindlimbs, and A. angusticeps, a twig ecomorph with short hindlimbs) from early embryonic stages to adulthood, to determine which hindlimb elements mainly differentiate the species and the timing of the formation of these differences. With respect to the digit, differences between the species mainly occurred during the embryonic stages of interdigit reduction, when the cartilage of the distal phalanges was simultaneously forming. In addition, we compared the relative length of developing autopods in early embryonic stages using whole-mount in situ hybridization before the formation of the cartilaginous bones, and the results showed that the relative growth rate of the Hoxa11-negative distal region in A. sagrei was greater than that in A. angusticeps. Our results show that there are several important developmental stages for hindlimb length differentiation between A. angusticeps and A. sagrei, depending on which hindlimb element is considered. In particular, the species differences were largely due to variations in digit length, which arose at early embryonic stages.

Mechanical effects of fine‐wire climbing on the hindlimb skeleton of mice

High‐impact exercise (running/jumping) can stimulate multiple anabolic responses (increased trabecular bone volume, BV/TV) in the skeleton, but is also linked to an increased incidence of skeletal fracture. Thus, it is not an appropriate treatment for patients with elevated fracture risks. However, multi‐directional off‐axis mechanical loading can also elicit anabolic responses, even when magnitudes are relatively low. This represents a potential alternative to high‐impact exercise for improving skeletal mechanical properties. To test this hypothesis, we raised twelve weanling female C57BL/6 mice to 4 months of age in custom enclosures that prevent (control) or require (experimental) manual and pedal grasping while balancing and climbing above narrow wire substrates. At sacrifice, we measured whole mouse bone density (DEXA) and performed architectural (μCT) and mechanical (4‐pt bending) analyses of the femur and tibia. Body mass was similar between groups, although exercised mice were leaner (‐35% fat mass). Bone mineral density was also similar, while bone mineral content was increased (+7%) in the exercised mice. Femoral midshaft polar moment of inertia was similar between groups, but exercised mice had lower BV/TV (‐46%) of the distal femur and greater trabecular spacing (+21%). Exercised femora showed more total displacement (+58%) and post yield displacement (+115%) in bending than controls, and increased material toughness (+40%). Patterns were similar for the tibia. Mechanical data are consistent with high‐impact exercise studies, but architectural data are not. Together they suggest that our exercise model may improve bone mechanical properties by redistributing mineral within the skeleton, and not by increasing net bone formation.

Morphoecological Peculiarities of Pelvis in Several Genera of Rails with Some notes On systematic Position Of The Coot, Fulica Atra (Rallidae, Gruiformes)

Abstract Morphoecological Peculiarities of Pelvis in Several Genera of Rails with Some Notes on Systematic Position of the Coot, Fulica atra (Rallidae, Gruiformes). Bogdanovich, I. A. - Some features of pelvic and hindlimb morphology of several ecologically different species of rallids are studied. Adaptive significances of these features are revealed. A special attention is paid to the hindlimb skeleton of the Coot (Fulica atra, Linnaeus, 1758), which retained the locomotor universalism despite adaptations to swimming and diving.