Cone beam computed tomography and cross-sectional anatomy of the region of the fetlock in the horse (Equus caballus).

This study aimed to delineate the detailed anatomy of the metacarpophalangeal (MCP) and metatarsophalangeal (MTP) joints in healthy horses using cone beam computed tomography (CBCT). The fetlock region of 15 cadaveric forelimbs and 14 cadaveric hindlimbs from nine adult horses without orthopaedic disease underwent CBCT scanning. Additionally, arthrography CBCT scans were conducted following intra-articular injection of a radiopaque contrast medium containing blue epoxy resin dye. Subsequently, limbs were frozen and sectioned to visualize anatomical structures in sectional planes corresponding to selected CBCT images. CBCT proved suitable for detailed visualization of the bony components of the fetlock region. Furthermore, the common digital extensor tendon, superficial and deep digital flexor tendons, suspensory ligament, and straight and oblique sesamoidean ligaments were identifiable on CBCT images. However, certain ligaments, such as the collateral sesamoidean ligaments and intersesamoidean ligaments, were not clearly identified. The hyaline cartilage of the MCP and MTP joint facets was assessable on the post-contrast sequence. In cases where a radiographic or ultrasound examination cannot provide a definitive diagnosis and determine the extent of disease, CBCT can provide additional valuable data on the equine MCP and MTP joint. The images obtained in this study can serve as a reference for CBCT examination of the equine MCP and MTP joint.

Radiographic evaluation of the forelimb bone development in maned wolves (Chrysocyon brachyurus).

This study aimed to assess the fusion of growth plates and the development of secondary ossification centres in the forelimb bones of maned wolves (Chrysocyon brachyurus), contrasting the findings with established data from domestic dogs. Three maned wolves, comprising one male and two females, initially aged between 3 and 4 months, were subjected to monthly radiographic evaluations until 10-11 months of age, followed by bimonthly assessments until 18-19 months of age, encompassing both forelimbs. The closure times of growth plates were observed as follows: supraglenoid tubercle (7-8 months), proximal humerus (17-19 months), distal humerus (8-9 months), medial epicondyle of the humerus (8-9 months), proximal ulna (9-10 months), proximal radius (13-15 months), distal ulna (13-15 months) and distal radius (17-19 months). Statistical analysis revealed significant differences in the areas of secondary ossification centres in the proximal epiphyses of the humerus and radius, respectively, observed from the initial evaluation at 8-9 months and 6-7 months. Conversely, the epiphyses of the supraglenoid tubercle, distal humerus, proximal ulna, distal ulna, medial epicondyle of the humerus and distal radius did not exhibit significant area differences between 3-4 months and 4-5 months, yet notable distinctions emerged at 5-6 months. In summary, while the radiographic appearance of epiphyseal growth plates and secondary ossification centres in maned wolves resembles that of domestic dogs, closure times vary. These findings contribute to understanding the dynamics of epiphyseal growth plates in this species.

Distal forelimb radiographic bone morphology in Thoroughbred foals during the first 10 months post-partum. Part 1: Carpus.

BACKGROUND: The risk of carpal injury in racehorses may be related to the morphology, yet whether carpal morphologies are set from birth or change through growth remains unclear. OBJECTIVE: To quantify carpal bone changes through growth. METHOD: Twenty privately owned Thoroughbred foals born between January 2022 and May 2023 were radiographed bimonthly from birth to 10 months of age. Imprint training was used to take radiographs safely without chemical restraints. Fifteen individual and 11 relative angular carpal parameters were measured using ImageJ on dorsopalmar radiographs of the carpus at zero degrees of vertical and horizontal rotation. Associations with age (growth), sex and the differences between left and right limbs were analysed separately using a linear mixed effects model. RESULTS: Six individual carpal parameters changed with age (radial carpal joint [RCJ], Prx.dor. radial carpal [Cr], Prx.Cu, Dis.dor. third carpal [C3], Dis.pal.C3 and Dis.pal. intermediate carpal), and one was influenced by side, that is higher in the left carpus (Dis.pal.Cr). Seven relative parameters changed with age, and one relative parameter was influenced by side, that is higher in the left (Ra.met-RCJ). The proximo-dorsal bone surface angle of Cr and disto-dorsal bone surface angle of C3 became flatter over time, which may be associated with the re-direction of the load towards the sagittal carpal plane. Sex did not influence any of the carpal parameters, nor did the combined effect of age, side of the limb and sex. CONCLUSION: Specific individual and relative angular carpal parameters changed significantly over time and some differed between the left and right limb, whereas other parameters did not change. The steeper carpal bone angles achieved proximally with the parameters that did change may improve stability by redirecting the load more medially through the carpus and the proximal and distal bones.

Intraspecific variation in the pterosaur Rhamphorhynchus muensteri-implications for flight and socio-sexual signaling.

Pterosaurs were the first powered flying vertebrates, with a fossil record that stretches back to about 230 million years before present. Most species are only known from one to three specimens, which are most often fragmentary. However, Rhamphorhynchus muensteri is known from numerous excellent specimens, including multiple specimens with soft tissue preservation. As such, Rhamphorhynchus muensteri is one of the only pterosaurs amenable to analysis for intraspecific variation. It has been previously predicted that elements directly involved in the flight apparatus, such as those of the forelimb, will be more highly constrained in their proportions than other parts of the skeleton. We investigated the degree of variation seen in elements and body parts of Rhamphorhynchus, which represents the best model system among pterosaurs for testing these expectations of intraspecific variation. We recover evidence for high levels of constraint throughout the appendicular and axial elements (head, neck, torso, tail, forelimbs, hindlimbs), suggesting that all were important for flight. We further find that tail variation increases among the largest specimens, suggesting reduced constraint and/or stronger sexual selection on the tail in more mature individuals.

A hyaena on stilts: comparison of the limb morphology of Ictitherium ebu (Mammalia: Hyaenidae) from the Late Miocene of Lothagam, Turkana Basin, Kenya with extant Canidae and Hyaenidae.

The long, gracile morphology of the limb bones of the Late Miocene hyaenid Ictitherium ebu has led to the hypothesis that this animal was cursorial. The forelimb and femur of the holotype were compared with specimens of extant Hyaenidae and Canidae. Two morphometric methods were used. The first used measurements to calculate indices of different morphological characters. The second method involved capturing photographs of the anterior distal humerus of each specimen, mapping six landmarks on them, and calculating truss distances. These distances represent a schematic reproduction of the elbow. Multivariate statistical analysis primarily separated the data based on taxonomy, yet locomotor and habitat categories were also considered. Ictitherium ebu has an overall morphology similar to that of the maned wolf and a distal humerus reminiscent of that of the aardwolf. The long, gracile limb bones of I. ebu are suggested to be adaptations for pouncing on prey, for locomotor efficiency, and for looking over the tall grass of the open environments the animal lived in, much like the present-day maned wolf.

Estimation of the forces exerted on the limb long bones of a white rhinoceros (Ceratotherium simum) using musculoskeletal modelling and simulation.

Heavy animals incur large forces on their limb bones, due to the transmission of body weight and ground reaction forces, and the contractions of the various muscles of the limbs. This is particularly true for rhinoceroses, the heaviest extant animals capable of galloping. Several studies have examined their musculoskeletal system and the forces their bones incur, but no detailed quantification has ever been attempted. Such quantification could help understand better the link between form and function in giant land animals. Here we constructed three-dimensional musculoskeletal models of the forelimb and hindlimb of Ceratotherium simum, the heaviest extant rhino species, and used static optimisation (inverse) simulations to estimate the forces applied on the bones when standing at rest, including magnitudes and directions. Overall, unsurprisingly, the most active muscles were antigravity muscles, which generate moments opposing body weight (thereby incurring the ground reaction force), and thus keep the joints extended, avoiding joint collapse via flexion. Some muscles have an antigravity action around several joints, and thus were found to be highly active, likely specialised in body weight support (ulnaris lateralis; digital flexors). The humerus was subjected to the greatest amount of forces in terms of total magnitude; forces on the humerus furthermore came from a great variety of directions. The radius was mainly subject to high-magnitude compressive joint reaction forces, but to little muscular tension, whereas the opposite pattern was observed for the ulna. The femur had a pattern similar to that of the humerus, and the tibia's pattern was intermediate, being subject to great compression in its caudal side but to great tension in its cranial side (i.e. bending). The fibula was subject to by far the lowest force magnitude. Overall, the forces estimated were consistent with the documented morphofunctional adaptations of C. simum's long bones, which have larger insertion areas for several muscles and a greater robusticity overall than those of lighter rhinos, likely reflecting the intense forces we estimated here. Our estimates of muscle and bone (joint) loading regimes for this giant tetrapod improve the understanding of the links between form and function in supportive tissues and could be extended to other aspects of bone morphology, such as microanatomy.

Position of the Proximal Manica Flexoria under different grades of fetlock joint extension - A biomechanical observational study in the equine fore- and hindlimb.

OBJECTIVE: The aim of this study was to examine the position of the proximal manica flexoria and the proximal scutum under different grades of fetlock joint extension and to describe measurements and compare findings between equine fore- and hindlimbs. STUDY DESIGN: It was an observational study. RESULTS: During fetlock joint extension, the proximal manica flexoria and the proximal scutum displace distally relative to the palmar/plantar extent of the sagittal ridge of the cannon bone. The proximal manica flexoria is further displaced distal to the proximal scutum within the fetlock canal. No significant differences were identified between fore- and hindlimbs at different levels of fetlock joint extension. The proximal scutum was observed to be longer and thicker and the tendinous part of the manica flexoria was longer in forelimbs compared with hindlimbs. CONCLUSION AND CLINICAL RELEVANCE: The described findings contribute to the understanding of the pathogenesis of manica flexoria tearing. The fact that the proximal scutum and the tendinous part of the manica flexoria are shorter in the hindlimb might explain why the manica flexoria is more likely to get caught on the proximal aspect of the scutum and develop a tear in the equine hindlimb.

Forelimb muscle activation patterns in American alligators: Insights into the evolution of limb posture and powered flight in archosaurs.

The evolution of archosaurs provides an important context for understanding the mechanisms behind major functional transformations in vertebrates, such as shifts from sprawling to erect limb posture and the acquisition of powered flight. While comparative anatomy and ichnology of extinct archosaurs have offered insights into musculoskeletal and gait changes associated with locomotor transitions, reconstructing the evolution of motor control requires data from extant species. However, the scarcity of electromyography (EMG) data from the forelimb, especially of crocodylians, has hindered understanding of neuromuscular evolution in archosaurs. Here, we present EMG data for nine forelimb muscles from American alligators during terrestrial locomotion. Our aim was to investigate the modulation of motor control across different limb postures and examine variations in motor control across phylogeny and locomotor modes. Among the nine muscles examined, m. pectoralis, the largest forelimb muscle and primary shoulder adductor, exhibited significantly smaller mean EMG amplitudes for steps in which the shoulder was more adducted (i.e., upright). This suggests that using a more adducted limb posture helps to reduce forelimb muscle force and work during stance. As larger alligators use a more adducted shoulder and hip posture, the sprawling to erect postural transition that occurred in the Triassic could be either the cause or consequence of the evolution of larger body size in archosaurs. Comparisons of EMG burst phases among tetrapods revealed that a bird and turtle, which have experienced major musculoskeletal transformations, displayed distinctive burst phases in comparison to those from an alligator and lizard. These results support the notion that major shifts in body plan and locomotor modes among sauropsid lineages were associated with significant changes in muscle activation patterns.

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

This paper is the first 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 forelimb. Understanding forelimb muscular anatomy in extinct synapsids, and how this changed on the line to mammals, can provide important perspective for interpreting skeletal and functional evolution in this lineage, and how the diversity of forelimb functions in extant mammals arose. 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 73 character-state complexes covering all muscles crossing the shoulder, elbow, and wrist 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. In addition to producing a comprehensive documentation of osteological evidence for muscle attachments in extinct synapsids, this work has clarified homology hypotheses across disparate taxa and helped resolve competing hypotheses of muscular anatomy in extinct species. The evolutionary history of mammalian forelimb musculature was a complex and nonlinear narrative, punctuated by multiple instances of convergence and concentrated phases of anatomical transformation. More broadly, this study highlights the great insight that a fossil-based perspective can provide for understanding the assembly of novel body plans.

Low morphological disparity and decelerated rate of limb size evolution close to the origin of birds.

The origin of birds from theropod dinosaurs involves many changes in musculoskeletal anatomy and epidermal structures, including multiple instances of convergence and homology-related traits that contribute to the refinement of flight capability. Changes in limb sizes and proportions are important for locomotion (for example, the forelimb for bird flight); thus, understanding these patterns is central to investigating the transition from terrestrial to volant theropods. Here we analyse the patterns of morphological disparity and the evolutionary rate of appendicular limbs along avialan stem lineages using phylogenetic comparative approaches. Contrary to the traditional wisdom that an evolutionary innovation like flight would promote and accelerate evolvability, our results show a shift to low disparity and decelerated rate near the origin of avialans that is largely ascribed to the evolutionarily constrained forelimb. These results suggest that natural selection shaped patterns of limb evolution close to the origin of avialans in a way that may reflect the winged forelimb 'blueprint' associated with powered flight.

[Anatomical observation and CT three-dimensional reconstruction of Five-shu acupoints of Shaoyin Heart Meridian in rabbit's forelimb].

OBJECTIVE: To investigate the location and anatomical structure of "Shaochong"(HT9), "Shaofu"(HT8), "Shenmen"(HT7), "Lingdao"(HT4) and "Shaohai"(HT3) in the rabbit's forelimb. METHODS: Sixteen rabbits (half male and half female) were used in the present study. By referring to the national standards on the location of acupoints in the human body and the literature about the location of acupoints in the rabbit, and by using the method of comparative anatomy, the location and needling operation of the Five-shu acupoints of Shaoyin Heart Meridian on the rabbit's forelimb were defined, and these acupoints were needled and CT three-dimensional reconstruction were conducted. Then, the rabbits were killed, and intravascular perfusion was performed, followed by inserting acupuncture needles into these five acupoints for observing the anatomical relationship between the inserted acupuncture needle and the structure of surrounding tissues. RESULTS: HT9 is located at the medial side of the little finger of forelimb, about 1 mm beside the nail root, and is adjacent to the superficial flexor tendon of the finger, the dorsal branches of the proper palmar digital artery and vein, and the endings of dorsal branch of palmar digital proper nerve of the ulnar nerve on the fifth finger side. HT8 is located at the palm side of the forelimb, horizontally parallel to the proximal end of the 5th metacarpophalangeal joint and between the 4th and 5th metacarpal bones, and is adjacent to the lumbricalis, the 4th and 5th interossei, and common palmar digital artery and vein and the palmar digital proper nerve of the ulnar nerve. HT7 is located at the medial margin of the extensor carpal tendon on the ulnar side, between the distal end of the ulna and the ulnar carpal bone, and is adjacent to the tendons of flexor carpi ulnaris and extensor carpi ulnaris, ulnar artery, ulnar vein and ulnar nerve. HT4 is located at the medial border of the ulnar flexor tendon, about 1.5 cun superior to HT7, and is adjacent to extensor carpi ulnaris, flexor carpi ulnaris, flexor digitorum superficialis, flexor digitorum profundus, ulnar artery, vein and ulnar nerve. HT3 is located at the depression, medial to the condyle of humerus when the elbow is bent at 90°, its neighbor structure is composed of pronator teres, biceps brachii, brachial artery and vein, radial collateral artery, radial collateral vein, medial antebrachial cutaneous nerve and median nerve. CONCLUSION: In the rabbit, there is a close relationship between HT9, HT8, HT7, HT4 and HT3 regions and brachial vascular and its branches, cephalic vein and its branches, medial antebrachial cutaneous nerve, median nerve and ulnar nerve, which is the morphological basis of the Five-shu acupoints of Shaoyin Heart Meridian for treating some related clinical disorders.

Magnetic resonance imaging, computed tomography, and gross anatomy of forelimb joints in New Zealand rabbit (Oryctolagus cuniculus L.).

The present study aimed to define the anatomical structures by comparing the transversal computed tomography (CT) and magnetic resonance (MR) images of the forelimb joints of the rabbits with the cross-sectional plastinated images. A total of 14 (seven females, seven males) one-year-old adult New Zealand rabbits were used in the study. After the CT and MR imaging procedures were completed, the forelimbs were removed from the body. The forelimbs were plastinated using the silicone plastination method and sectioned transversal. Cross-sectional plastinates were evaluated and correlated anatomically with conjugate CT and MR images. Joint and surrounding anatomical structures were defined in sections. Cross-sectional plastinated samples were highly correlated with CT and MR images in terms of bone and soft tissue, respectively. It is thought that the anatomical and radiological data obtained from the forelimb joints of rabbits will provide a basis for scientists who are involved in both experimental surgical interventions and clinical anatomy education.

Fossorial mammals emphasise the forelimb muscle moment arms used for digging: New indices for reconstruction of the digging ability and behaviours in extinct taxa.

Among fossorial mammals, forelimbs are major digging apparatuses for dwelling, sheltering and foraging underground. Forelimb-diggers have independently evolved in many lineages of mammals; thus, the method of digging with forelimbs varies by taxon. Therefore, the reconstruction of digging behaviours in extinct animals leads us to understand the evolutionary process of fossorial adaptation in each lineage. However, no morphological index was found to reconstruct if, or how, extinct taxa dug with forelimbs. In this study, we used the shoulder and elbow muscle moment arms in relation to the out-force lever on the manus as indices of the efficiency of motions. The mechanical advantage of two shoulder motions (medial rotation and retraction) and three elbow motions (extension, flexion and adduction) was measured in 381 extant mammal specimens representing 332 species, 279 genera, 103 families and 24 orders. Assuming that both forelimb-digging and -paddling in water require relatively high-output moment arm efficiency, the studied taxa were categorised into four groups based on the presence or absence of forelimb-digging and -paddling abilities. We found that the efficiencies of all five muscle moment arms in the forelimb-diggers and -paddlers were higher than those of the non-diggers and non-paddlers. Furthermore, among the forelimb-diggers, the taxa that dig compact substrates or frequently burrow tend to emphasise the muscle moment arms compared to the taxa that dig loose substrates or dig less frequently. The comparison among the 53 extant forelimb-diggers revealed that the efficiency marked among the five muscle moment arms reflects the difference in digging strategy: humeral rotation diggers emphasise the shoulder medial rotator and elbow adductor, hook-and-pull diggers emphasise the shoulder retractor and elbow flexor and scratch diggers emphasise the shoulder retractor and elbow extensor. We propose that these indices will be powerful tools for reconstructing the fossorial behaviours of extinct mammals. Applying these indices to extinct taxa, Ceratogaulus, Ernanodon, Metacheiromys and Prozaedyus are capable of more efficient forelimb-digging, and each may have adopted different digging strategies.

Functional space analyses reveal the function and evolution of the most bizarre theropod manual unguals.

Maniraptoran dinosaurs include the ancestors of birds, and most used their hands for grasping and in flight, but early-branching maniraptorans had extraordinary claws of mysterious function. Alvarezsauroids had short, strong arms and hands with a stout, rock-pick-like, single functional finger. Therizinosaurians had elongate fingers with slender and sickle-like unguals, sometimes over one metre long. Here we develop a comprehensive methodological framework to investigate what the functions of these most bizarre bony claws are and how they formed. Our analysis includes finite element analysis and a newly established functional-space analysis and also involves shape and size effects in an assessment of function and evolution. We find a distinct functional divergence among manual unguals of early-branching maniraptorans, and we identify a complex relationship between their structural strength, morphological specialisations, and size changes. Our analysis reveals that efficient digging capabilities only emerged in late-branching alvarezsauroid forelimbs, rejecting the hypothesis of functional vestigial structures like T. rex. Our results also support the statement that most therizinosaurians were herbivores. However, the bizarre, huge Therizinosaurus had sickle-like unguals of such length that no mechanical function has been identified; we suggest they were decorative and lengthened by peramorphic growth linked to increased body size.

Muscle architecture and muscle fibre type composition in the forelimb of two African mole-rat species, Bathyergus suillus and Heterocephalus glaber.

The scratch-digging Cape dune mole-rat (Bathyergus suillus), and the chisel-toothed digging naked mole-rat (Heterocephalus glaber) are African mole-rats that differ in their digging strategy. The aim of this study was to determine if these behavioural differences are reflected in the muscle architecture and fibre-type composition of the forelimb muscles. Muscle architecture parameters of 39 forelimb muscles in both species were compared. Furthermore, muscle fibre type composition of 21 forelimb muscles were analysed using multiple staining protocols. In B. suillus, muscles involved with the power stroke of digging (limb retractors and scapula elevators), showed higher muscle mass percentage, force output and shortening capacity compared to those in H. glaber. Additionally, significantly higher percentages of glycolytic fibres were observed in the scapular elevators and digital flexors of B. suillus compared to H. glaber, suggesting that the forelimb muscles involved in digging in B. suillus provide fast, powerful motions for effective burrowing. In contrast, the m. sternohyoideus a head and neck flexor, had significantly more oxidative fibres in H. glaber compared to B. suillus. In addition, significantly greater physiological cross-sectional area and fascicle length values were seen in the neck flexor, m. sternocleidomastoideus, in H. glaber compared to B. suillus, which indicates a possible adaptation for chisel-tooth digging. While functional demands may play a significant role in muscle morphology, the phylogenetic differences between the two species may play an additional role which needs further study.

Early diversification of avian limb morphology and the role of modularity in the locomotor evolution of crown birds.

High disparity among avian forelimb and hind limb segments in crown birds relative to non-avialan theropod dinosaurs, potentially driven by the origin of separate forelimb and hind limb locomotor modules, has been linked to the evolution of diverse avian locomotor behaviors. However, this hypothesized relationship has rarely been quantitatively investigated in a phylogenetic framework. We assessed the relationship between the evolution of limb morphology and locomotor behavior by comparing a numerical proxy for locomotor disparity to morphospace sizes derived from a dataset of 1,241 extant species. We then estimated how limb disparity accumulated during the crown avian radiation. Lastly, we tested whether limb segments evolved independently between each limb module using phylogenetically informed regressions. Hind limb disparity increased significantly with locomotor disparity after accounting for clade age and species richness. We found that forelimb disparity accumulated rapidly early in avian evolution, whereas hind limb disparity accumulated later, in more recent divergences. We recovered little support for strong correlations between forelimb and hind limb morphology. We posit that these findings support independent evolution of locomotor modules that enabled the striking morphological and behavioral disparity of extant birds.

Reconstruction of the pectoral girdle and forelimb musculature of Megaraptora (Dinosauria: Theropoda).

Megaraptora is a group of enigmatic, carnivorous non-avian theropod dinosaurs from the Cretaceous of Asia, Australia, and especially South America. Perhaps the most striking aspect of megaraptoran morphology is the large, robustly constructed forelimb that, in derived members of the clade, terminates in a greatly enlarged manus with hypertrophied, raptorial unguals on the medialmost two digits and a substantially smaller ungual on digit III. The unique forelimb anatomy of megaraptorans was presumably associated with distinctive functional specializations; nevertheless, its paleobiological significance has not been extensively explored. Here we draw from observations of the pectoral girdle and forelimb skeletons of Megaraptora and myological assessments of other archosaurian taxa to provide a comprehensive reconstruction of the musculature of this anatomical region in these singular theropods. Many muscle attachment sites on megaraptoran forelimb bones are remarkably well developed, which in turn suggests that the muscles themselves were functionally significant and important to the paleobiology of these theropods. Furthermore, many of these attachments became increasingly pronounced through megaraptoran evolutionary history, being substantially better developed in derived taxa such as Australovenator wintonensis and especially Megaraptor namunhuaiquii than in early branching forms such as Fukuiraptor kitadaniensis. When considered alongside previous range of motion hypotheses for Australovenator, our results indicate that megaraptorans possessed a morphologically and functionally specialized forelimb that was capable of complex movements. Notable among these were extensive extension and flexion, particularly in the highly derived manus, as well as enhanced humeral protraction, attributes that very probably aided in prey capture.

Elbow-joint morphology in the North American 'cheetah-like' cat Miracinonyx trumani.

The North American cheetah-like cat Miracinonyx trumani is an extinct species that roamed the Pleistocene prairies 13 000 years ago. Although M. trumani is more closely related to the cougar (Puma concolor) than to the living cheetah (Acinonyx jubatus), it is believed that both A. jubatus and M. trumani possess a highly specialized skeleton for fast-running, including limbs adapted for speed at the expense of restricting the ability of prey grappling. However, forelimb dexterity of M. trumani has not been yet investigated. Here, we quantify the 3D-shape of the humerus distal epiphysis as a proxy for elbow-joint morphology in a sample of living cats to determine whether the extinct M. trumani was specialized to kill open-country prey using predatory behaviour based on fast running across the prairies and steppe terrains of the North American Pleistocene. We show that M. trumani had an elbow morphology intermediate to that of P. concolor and A. jubatus, suggesting that M. trumani had a less specialized pursuit predatory behaviour than A. jubatus. We propose that M. trumani probably deployed a unique predatory behaviour without modern analogues. Our results bring into question the degree of ecomorphological convergence between M. trumani and its Old World vicar A. jubatus.

Reversibility of digit loss revisited: Limb diversification in Bachia lizards (gymnophthalmidae).

Strict interpretations of the Dollo's Law lead to postulation that trait loss is irreversible and organisms never recover ancestral phenotypes. Dollo, however, admitted the possibility of reversals in trait loss when predicted differences between reversed (derived) and ancestral forms. Phenotypic signatures from reversals are expected, as the historical context of a reversal in trait loss differs from the initial setting where the trait originally evolved. This article combines morphological and molecular information for Bachia scolecoides to discuss phenotypic and genetic patterns established during processes that reversed digit loss in Gymnophthalmidae (also termed microteiid lizards). Results suggest that pathways leading to the derived tetradactyl state of B. scolecoides comprise particularities in their origin and associated processes. Autopodial bones of B. scolecoides lack digit identity, and muscle anatomy is very similar between manus and pes. Gymnophthalmidae sequence patterns in the limb-specific sonic hedgehog enhancer (ZRS) suggest that regulation of shh expression did not degenerate in Bachia, given the prediction of similar motifs despite mutations specific to Bachia. Persistence of developmental mechanisms might explain intermittent character expression leading to reversals of digit loss, as ZRS signaling pathways remain active during the development of at least one pair of appendices in Bachia, especially if some precursors persisted at early stages. Patterns of ZRS sequences suggest that irreversibility of trait loss might be lineage-specific (restricted to Gymnophthalmini) and contingent to the type of signature established. These results provide insights regarding possible mechanisms that may allow reactivation of developmental programs in specific regions of the embryo.

Osteology and radiographic anatomy of the thoracic limb of the greater cane rat (Thryonomys swinderianus).

The greater cane rat (Thryonomys swinderianus) is mainly distributed in the humid and sub-humid regions of the sub-Saharan Africa. It is believed to be the second largest African rodent. The aim of this study was to describe the normal osteology and radiographic anatomy of the thoracic limb of the greater cane rat as a reference for teaching, clinical use, anatomical studies and biomedical research. Five intact dead greater cane rats were used for radiographic examination. Radiographic findings were correlated with bone specimens. The clavicle was seen in all animals. The scapula was wide with well-developed acromion and coracoid process. The major and minor tubercles did not extend higher than the head of the humerus. The deltoid tuberosity was very prominent. The medial epicondyle was larger than its lateral counterpart, and the supratrochlear foramen was present. The radial tuberosity was further distally located. The ulnar head was well-developed, and the olecranon tuber was square-shaped. The distal physes for the radius and ulna appeared transverse. The carpus had eight bones. The manus presented with five widely spread digits. The first digit was reduced in size and placed such that the dorsal and palmar surfaces face almost medial and lateral, respectively. Additionally, two rudimentary digits were seen. Variations exist in the normal osteology and radiographic anatomy of the thoracic limb in different species. Knowledge of the normal osteology and radiographic anatomy of the thoracic limb of individual species is important for species identification and diagnosis of musculoskeletal diseases involving the thoracic limb.