Three‐dimensional shape variation of talar surface morphology in hominoid primates

The hominoid foot is of particular interest to biological anthropologists, as changes in its anatomy through time reflect the adoption of terrestrial locomotion, particularly in species of Australopithecus and Homo. Understanding the osteological morphology associated with changes in whole foot function and the development of the plantar medial longitudinal foot arch are key to understanding the transition through habitual bipedalism in australopithecines to obligate bipedalism and long‐distance running in Homo. The talus is ideal for studying relationships between morphology and function in this context, as it is a major contributor to the adduction–abduction, plantar–dorsal flexion and inversion–eversion of the foot, and transmits all forces encountered from the foot to the leg. The talar surface is predominantly covered by articular facets, which have different quantifiable morphological characters, including surface area, surface curvature and orientation. The talus also presents challenges to the investigator, as its globular shape is very difficult to quantify accurately and reproducibly. Here we apply a three‐dimensional approach using type 3 landmarks (slid semilandmarks) that are geometrically homologous to determine overall talar shape variations in a range of living and fossil hominoid taxa. Additionally, we use novel approaches to quantify the relative orientations and curvatures of talar articular facets by determining the principal vectors of facet orientation and fitting spheres to articular facets. The resulting metrics are analysed using phylogenetic regressions and principal components analyses. Our results suggest that articular surface curvatures reflect locomotor specialisations with, in particular, orang‐utans having more highly curved facets in all but the calcaneal facet. Similarly, our approach to quantifying articular facet orientation appears to be effective in discriminating between extant hominoid species, and may therefore provide a sound basis for the study of fossil taxa and evolution of bipedalism in Australopithecus and Homo.     

Exploring Third Metacarpal Capitate Facet Shape in Early Hominins

The joint between the capitate and third metacarpal plays an important role in stabilizing the manus during hand use in great apes and humans. Researchers have examined the morphology of this region in humans, our fossil relatives, and other extant primates to try to understand the importance of this joint in human evolution. The first goal of our research was to explore shape variation of the third metacarpal capitate facet across extant anthropoids, including hominoids, cercopithecoids, and platyrrhines. This analysis allowed us to examine the range of variation in the capitate facet and the degree to which locomotor behavior, phylogeny, and size explained shape variation. We also examined capitate facet shape in the early hominin fossil record in order to explore how the shape of this articular surface has changed during early hominin evolution. We captured six landmark coordinates on the edge of the capitate facet in extant anthropoids and fossil specimens to quantify and visualize shape variation in this region. We used principal components analysis, Procrustes distances, and multivariate regression analysis to investigate different possible influences on shape variation. We found that shape variation corresponded to function, phylogeny, and size. With the exception of brachiation, shape variation did not clearly correspond with any specific locomotor behavior. However, we identified a shift in the relative mediolateral breadth of the capitate facet during early hominin evolution, which is most likely one of several adaptations for a more stable joint surface. Anat Rec, 2013. © 2012 Wiley Periodicals, Inc.     

Spatial distribution of human arachnoid trabeculae

Traumatic brain injury (TBI) is a common injury modality affecting a diverse patient population. Axonal injury occurs when the brain experiences excessive deformation as a result of head impact. Previous studies have shown that the arachnoid trabeculae (AT) in the subarachnoid space significantly influence the magnitude and distribution of brain deformation during impact. However, the quantity and spatial distribution of cranial AT in humans is unknown. Quantification of these microstructural features will improve understanding of force transfer during TBI, and may be a valuable dataset for microneurosurgical procedures. In this study, we quantify the spatial distribution of cranial AT in seven post-mortem human subjects. Optical coherence tomography (OCT) was used to conduct in situ imaging of AT microstructure across the surface of the human brain. OCT images were segmented to quantify the relative amounts of trabecular structures through a volume fraction (VF) measurement. The average VF for each brain ranged from 22.0% to 29.2%. Across all brains, there was a positive spatial correlation, with VF significantly greater by 12% near the superior aspect of the brain (p < .005), and significantly greater by 5%−10% in the frontal lobes (p < .005). These findings suggest that the distribution of AT between the brain and skull is heterogeneous, region-dependent, and likely contributes to brain deformation patterns. This study is the first to image and quantify human AT across the cerebrum and identify region-dependencies. Incorporation of this spatial heterogeneity may improve the accuracy of computational models of human TBI and enhance understanding of brain dynamics.     

Calcaneum talar facets,its diagnostic and clinical relevance to fracture

Introduction

Calcanei are classified into three to five patterns according to the number of superior articular facets present. As reported earlier the relative distribution of facets pattern varies with race and sex. Study of the calcaneal talar facets variation is important because it influence subtalar joint stability and knowledge of facets is essential while correcting foot deformities and for placing the screw in fracture fixation by orthopaedic surgeons.

Quantifying Mental Foramen Position in Extant Hominoids and Australopithecus: Implications for its Use in Studies of Human Evolution

The location of the mental foramen on the mandibular corpus has figured prominently in debates concerning the taxonomy of fossil hominins and Gorilla gorilla. In this study we quantify the antero/posterior (A/P) position of the mental foramen across great apes, modern humans and Australopithecus. Contrary to most qualitative assessments, we find significant differences between some extant hominoid species in mental foramen A/P position supporting its potential usefulness as a character for taxonomic and phylogenetic analyses of fossil hominoids. Gorilla gorilla, particularly the eastern subspecies, with a comparatively longer dental arcade and fossil and extant hominins with reduced canines and incisors tend to exhibit more anteriorly positioned mental foramina. Conversely, Pan troglodytes exhibits more posteriorly positioned mental foramina. Variation in this character among Gorilla gorilla subspecies supports recent taxonomic assessments that separate eastern and western populations. In all taxa other than Pan troglodytes the A/P position of the mental foramen is positively allometric with respect to dental arcade length. Thus, within each of these species, specimens with longer dental arcades tend to have more posteriorly positioned mental foramina. Those species with greater sexual dimorphism in canine size and dental arcade length (i.e., Gorilla gorilla and Pongo pygmaeus) exhibit more extreme differences between smaller and larger individuals. Moreover, among great apes those individuals with greater anterior convergence of the dental arcade tend to exhibit more posteriorly positioned mental foramina. Dental arcade length, canine crown area and anterior convergence are all significantly associated with mental foramen A/P position, suggesting that these traits may influence taxonomic variation in the A/P position of the mental foramen. Anat Rec 293:1337–1349, 2010. © 2010 Wiley‐Liss, Inc.     

Comparative analysis of femoral biomechanical neck length in primates

The unique abductor capability of the human lesser gluteal muscles among extant hominoids has been suggested to be associated, in part, with biomechanical neck length of the femur. Beyond the hominin lineage, the relationship between biomechanical neck length and locomotor performance remains unclear due, in part, to the limited number of primate taxa directly compared and the need to examine species characterized by a wider range of locomotor diversity. Measurements were taken on the proximal femora of 28 extant taxa, with each species being assigned to a locomotor and phylogenetic category. Pairwise comparisons and phylogenetic generalized least-squares analysis were performed to examine the impact of phylogeny and locomotor adaptation on relative biomechanical neck length. Arboreal quadrupeds that perform varying proportions of climbing/clambering versus leaping were characterized by different biomechanical neck lengths, whereas semi-terrestrial anthropoids that perform either knuckle-walking or palmigrade/digitigrade quadrupedalism were found to have similar relative neck lengths. Samples categorized as either orthograde clamberers or bipeds were distinct from all other anthropoid samples and characterized by the relatively shortest and longest biomechanical neck lengths, respectively. Results of additional analyses that included prosimian primates suggest that relatively long biomechanical necks characterize species adapted to hind limb-dominated forms of locomotion (e.g., vertical clinging and leaping and bipedalism). Thus, biomechanical neck length is useful for signaling reliance on bipedalism (as performed by humans) or leaping, including subtle variation in leaping performance among arboreal quadrupeds. Furthermore, this trait is informative regarding reliance on irregular gait clambering as performed by orangutans.     

Bipartition of the superior articular facets of the first cervical vertebra (atlas or C1): a human variant probably specific among primates

The bipartition of the superior articular facet is one of the classical variants of the human atlas. Rare quantitative data are available in the literature on this possible bipartition in humans and this disposition remains little understood. For non-human primates, there are almost no detailed comparative data in the literature, despite their potential importance in understanding the significance of this pattern in humans and its evolution. The material used in this study consisted of 500 human atlases and of 256 atlases of non-human primates representing 37 genera. In humans, bipartition of one or both of the superior articular facets was observed in 104 individuals out of the 500 (20.8%); bilateral occurrence was observed in 46.2% of the bipartitions and unilateral occurrence in 53.8%; no significant right or left predominance was observed. In non-human primates, no case of bipartition of the superior articular facets of the atlas was found in any of the 256 individuals studied. From a phylogenetic point of view, we suggest that a single superior facet of the atlas is the primitive pattern or plesiomorphy in primates. Modification of this general pattern seems to occur only in some individuals in Homo sapiens within primates, and the bipartition of the facet could thus be interpreted as a derived characteristic restricted to the human species or autapomorphy. The appearance of the bipartition of the superior articular facet of the atlas during human evolution could be the result of functional modifications due to the acquisition of constant erect posture and bipedalism.     

Trabecular Bone Fraction Variation in Modern Humans,Fossil Hominins and Other Primates

Evidence suggests that recent modern humans (Holocene) have low trabecular bone density (i.e., trabecular bone fraction, TBF) compared with other extant primates and fossil hominins. However, the extent to which TBF in recent humans with varying subsistence strategies differs from that of fossil hominins, and in turn, how hominins differ from various extant catarrhines is unclear. This study tests the hypotheses that first, populations with subsistence strategies demanding high physical activity exhibit greater TBF than sedentary populations and are more similar to fossil Homo. Secondly, that, australopiths have TBF that is more similar to nonhuman primates because of the greater mechanical loading on their skeletons. The study quantifies TBF in the limb epiphyses of recent humans, hominoids, cercopithecines, and fossil hominins. The results show overall a significant decrease in TBF among recent humans, whereas hominins, hominoids, and cercopithecines have similar, high TBF values. In addition, active human populations display TBF that is more similar to fossil Homo. The results suggest that this TBF decline reflects a reduction in activity levels among sedentary populations, although a systemic decline cannot be ruled out. These findings support the recent evolution of low trabecular density because of a decline in activity levels and underscore the utility of comparing multiple skeletal elements across a diverse set of recent modern humans when drawing conclusions about changes in trabecular bone in the human skeleton. Anat Rec, 302:288–305, 2019. © 2018 Wiley Periodicals, Inc.     

Trabecular architecture of the great ape and human femoral head

Studies of femoral trabecular structure have shown that the orientation and volume of bone are associated with variation in loading and could be informative about individual joint positioning during locomotion. In this study, we analyse for the first time trabecular bone patterns throughout the femoral head using a whole‐epiphysis approach to investigate how potential trabecular variation in humans and great apes relates to differences in locomotor modes. Trabecular architecture was analysed using microCT scans of Pan troglodytes (n = 20), Gorilla gorilla (n = 14), Pongo sp. (n = 5) and Homo sapiens (n = 12) in medtool 4.1. Our results revealed differences in bone volume fraction (BV/TV) distribution patterns, as well as overall trabecular parameters of the femoral head between great apes and humans. Pan and Gorilla showed two regions of high BV/TV in the femoral head, consistent with hip posture and loading during two discrete locomotor modes: knuckle‐walking and climbing. Most Pongo specimens also displayed two regions of high BV/TV, but these regions were less discrete and there was more variability across the sample. In contrast, Homo showed only one main region of high BV/TV in the femoral head and had the lowest BV/TV, as well as the most anisotropic trabeculae. The Homo trabecular structure is consistent with stereotypical loading with a more extended hip compared with great apes, which is characteristic of modern human bipedalism. Our results suggest that holistic evaluations of femoral head trabecular architecture can reveal previously undetected patterns linked to locomotor behaviour in extant apes and can provide further insight into hip joint loading in fossil hominins and other primates.     

The forearm and hand musculature of semi-terrestrial rhesus macaques (Macaca mulatta) and arboreal gibbons (fam.Hylobatidae). Part II. Quantitative analysis

Nonhuman primates have a highly diverse locomotor repertoire defined by an equally diverse hand use. Based on how primates use their hands during locomotion, we can distinguish between terrestrial and arboreal taxa. The ‘arboreal’ hand is likely adapted towards high wrist mobility and grasping, whereas the ‘terrestrial’ hand will show adaptations to loading. While the morphology of the forearm and hand bones have been studied extensively, functional adaptations in the forearm and hand musculature to locomotor behaviour have been documented only scarcely. In this paper, we investigate the forelimb musculature of the highly arboreal gibbons (including Hylobates lar,Hylobates pileatus,Nomascus leucogenys,Nomascus concolor and Symphalangus syndactylus) and compare this with the musculature of the semi-terrestrial rhesus macaques (Macaca mulatta). Anatomical data from previous dissections on knuckle-walking bonobos (Pan paniscus) and bipedal humans (Homo sapiens) are also included to further integrate the analyses in the scope of catarrhine hand adaptation. This study indicates that the overall configuration of the arm and hand musculature of these primates is very similar but there are some apparent differences in relative size which can be linked to differences in forelimb function and which might be related to their specific locomotor behaviour. In macaques, there is a large development of wrist deviators, wrist and digital flexors, and m. triceps brachii, as these muscles are important during the different phases of palmi- and digitigrade quadrupedal walking to stabilize the wrist and elbow. In addition, their m. flexor carpi ulnaris is the most important contributor to the total force-generating capacity of the wrist flexors and deviators, and is needed to counteract the adducting torque at the elbow joint during quadrupedal walking. Gibbons show a relatively high force-generating capacity in their forearm rotators, wrist and digital flexors, which are important muscles in brachiation to actively regulate forward movement of the body. The results also stress the importance of the digital flexors in bonobos, during climbing and clambering, and in humans, which is likely linked to our advanced manipulation skills.     

High values of alpha (CXCL10) and beta (CCL2) circulating chemokines in patients with psoriatic arthritis,in presence or absence of autoimmune thyroiditis

The possible role of circulating alpha and beta chemokines in psoriatic arthritis is not extensively studied. The aim of the study is to evaluate serum levels of CXCL10, CXCL9 (alpha) and CCL2 (beta) chemokines in a large series of psoriatic arthritis patients, with or without autoimmune thyroid (AT) disorders, and to relate chemokines levels to the clinical phenotype of these patients.

Serum levels of CXCL10 and CCL2 were measured in 37 patients with psoriatic arthritis without AT (PsA) and 28 with AT (PsA+AT), and in gender- and age-matched (1:1) controls without (control 1) or with AT (control 2).

Serum CXCL10 levels were significantly higher in control 2 than in control 1 (p < 0.001) and in PsA than control 1 or 2 (p < 0.0001). PsA+AT patients have CXCL10 higher than controls 1 and 2 (p < 0.0001, for both) and than PsA (p < 0.001). By defining a high CXCL10 level as a value at least 2 SD above the mean value of the control group (>192 pg/ml), 5% of control 1, 19% of control 2, 42% of PsA and 63% of PsA+AT, had high CXCL10 (p < 0.0001; χ²).

Serum CCL2 levels were similar in controls 1 and 2. PsA or PsA+AT patients have serum CCL2 levels significantly (p < 0.01, for both) higher than controls 1 and 2.

Serum CXCL9 was not significantly different in the study groups.

In conclusion, our study demonstrates higher serum levels of CXCL10 and CCL2 chemokines in patients with PsA than in controls. Serum CXCL10 (alpha chemokine) levels in psoriatic arthritis patients are significantly higher in presence of AT.     

3D geometric morphometric analysis of the proximal epiphysis of the hominoid humerus

In this study we perform a three‐dimensional geometric morphometric (3D GM) analysis of the proximal epiphysis of the humerus in extant great apes, including humans, in order to accurately describe the functional anatomical differences between these taxa. In addition, a fossil hominin specimen of Australopithecus afarensis was included in a multivariate GM analysis in order to test the potential of this methodological approach for making locomotor inferences from fossil remains. The results obtained show significant differences in proximal humeral morphology among the taxa studied, which had thus far largely remained unnoticed. Based on morphofunctional considerations, these anatomical differences can be correlated to differences in the locomotor repertoires of the taxa, thus confirming that the proximal humerus is suitable for constructing paleobiological inferences about locomotion. Modern humans display markedly divergent features, which set them apart from both the extant great apes and the fossil hominin A. afarensis. The morphology of the proximal epiphysis of the humerus of the latter more closely resembles that of the orangutans, thus suggesting that despite hindlimb adaptations to bipedalism, the forelimb of this taxon was still functionally involved in arboreal behaviors, such as climbing or suspension.     

Of Mice,Monkeys, And Men: Physiological And Morphological Evidence For Evolutionary Divergence Of Function In Mimetic Musculature

Facial expression is a universal means of visual communication in humans and many other primates. Humans have the most complex facial display repertoire among primates; however, gross morphological studies have not found greater complexity in human mimetic musculature. This study examines the microanatomical aspects of mimetic musculature to test the hypotheses related to human mimetic musculature physiology, function, and evolutionary morphology. Samples from the orbicularis oris muscle (OOM) and the zygomaticus major (ZM) muscle in laboratory mice (N = 3), rhesus macaques (N = 3), and humans (N = 3) were collected. Fiber type proportions (slow‐twitch and fast‐twitch), fiber cross‐sectional area, diameter, and length were calculated, and means were statistically compared among groups. Results showed that macaques had the greatest percentage of fast fibers in both muscles (followed by humans) and that humans had the greatest percentage of slow fibers in both muscles. Macaques and humans typically did not differ from one another in morphometrics except for fiber length where humans had longer fibers. Although sample sizes are low, results from this study may indicate that the rhesus macaque OOM and ZM muscle are specialized primarily to assist with maintenance of the rigid dominance hierarchy via rapid facial displays of submission and aggression, whereas human musculature may have evolved not only under pressure to work in facial expressions but also in development of speech. Anat Rec, 297:1250–1261, 2014. © 2014 Wiley Periodicals, Inc.     

Structure of the Achilles tendon at the insertion on the calcaneal tuberosity

Findings on the twisting structure and insertional location of the AT on the calcaneal tuberosity are inconsistent. Therefore, to obtain a better understanding of the mechanisms underlying insertional Achilles tendinopathy, clarification of the anatomy of the twisting structure and location of the AT insertion onto the calcaneal tuberosity is important. The purpose of this study was to reveal the twisted structure of the AT and the location of its insertion onto the calcaneal tuberosity using Japanese cadavers. The study was conducted using 132 legs from 74 cadavers (mean age at death, 78.3 ± 11.1 years; 87 sides from men, 45 from women). Only soleus (Sol) attached to the deep layer of the calcaneal tuberosity was classified as least twist (Type I), both the lateral head of the gastrocnemius (LG) and Sol attached to the deep layer of the calcaneal tuberosity were classified as moderate twist (Type II), and only LG attached to the deep layer of the calcaneal tuberosity was classified as extreme twist (Type III). The Achilles tendon insertion onto the calcaneal tuberosity was classified as a superior, middle or inferior facet. Twist structure was Type I (least) in 31 legs (24%), Type II (moderate) in 87 legs (67%), and Type III (extreme) in 12 legs (9%). A comparison between males and females revealed that among men, 20 legs (24%) were Type I, 57 legs (67%) Type II, and eight legs (9%) Type III. Among women, 11 legs (24%) were Type I, 30 legs (67%) Type II, and four legs (9%) Type III. No significant differences were apparent between sexes. The fascicles of the Achilles tendon attach mainly in the middle facet. Anterior fibers of the Achilles tendon, where insertional Achilles tendinopathy is most likely, are Sol in Type I, LG and Sol in Type II, and LG only in Type III. This suggests the possibility that a different strain is produced in the anterior fibers of the Achilles tendon (calcaneal side) where insertional Achilles tendinopathy is most likely to occur in each type. We look forward to elucidating the mechanisms generating insertional Achilles tendinopathy in future biomedical studies based on the present results.     

The microevolution of modern human cranial variation: implications for hominin and primate evolution

Context: Reconstructing the evolutionary history of fossil human taxa is heavily reliant on the ability to extract phylogenetic information from patterns of morphological variability. However, attempts to reconstruct phylogenetic relationships from craniodental data in extant primates have yielded inconsistent and inconclusive results.

Objective: To critically evaluate a recent body of research, conducted within an explicitly quantitative genetics framework, which investigates the extent to which human cranial variation reflects past population history. Possible ways in which to extrapolate these human-specific insights to higher taxonomic levels will also be assessed.

Results: A consensus is emerging confirming a largely neutral model for the human cranium, although specific instances of climatic and dietary adaptation have also been uncovered. Also, specific regions of the cranium, delineated according to particular criteria, differ in their relative genetic congruence. However, the genetic congruence patterns identified in modern humans are not replicated in other extant primates, calling their generality into question.

Conclusions: Developing a clearer understanding of the evolution of morphological diversity in extinct taxa requires a different inference approach that focuses on assessing the evolutionary forces that shape these patterns, rather than the identification of particular morphological regions that correlate with genetic relatedness across all primates.     

Evolution of arboreality and fossoriality in squirrels and aplodontid rodents: Insights from the semicircular canals of fossil rodents

Reconstructing locomotor behaviour for fossil animals is typically done with postcranial elements. However, for species only known from cranial material, locomotor behaviour is difficult to reconstruct. The semicircular canals (SCCs) in the inner ear provide insight into an animal's locomotor agility. A relationship exists between the size of the SCCs relative to body mass and the jerkiness of an animal's locomotion. Additionally, studies have also demonstrated a relationship between SCC orthogonality and angular head velocity. Here, we employ two metrics for reconstructing locomotor agility, radius of curvature dimensions and SCC orthogonality, in a sample of twelve fossil rodents from the families Ischyromyidae, Sciuridae and Aplodontidae. The method utilizing radius of curvature dimensions provided a reconstruction of fossil rodent locomotor behaviour that is more consistent with previous studies assessing fossil rodent locomotor behaviour compared to the method based on SCC orthogonality. Previous work on ischyromyids suggests that this group displayed a variety of locomotor modes. Members of Paramyinae and Ischyromyinae have relatively smaller SCCs and are reconstructed to be relatively slower compared to members of Reithroparamyinae. Early members of the Sciuroidea clade including the sciurid Cedromus wilsoni and the aplodontid Prosciurus relictus are reconstructed to be more agile than ischyromyids, in the range of extant arboreal squirrels. This reconstruction supports previous inferences that arboreality was likely an ancestral trait for this group. Derived members of Sciuridae and Aplodontidae vary in agility scores. The fossil squirrel Protosciurus cf. rachelae is inferred from postcranial material as arboreal, which is in agreement with its high agility, in the range of extant arboreal squirrels. In contrast, the fossil aplodontid Mesogaulus paniensis has a relatively low agility score, similar to the fossorial Aplodontia rufa, the only living aplodontid rodent. This result is in agreement with its postcranial reconstruction as fossorial and with previous indications that early aplodontids were more arboreal than their burrowing descendants.     

Interspecific scaling patterns of talar articular surfaces within primates and their closest living relatives

The articular facets of interosseous joints must transmit forces while maintaining relatively low stresses. To prevent overloading, joints that transmit higher forces should therefore have larger facet areas. The relative contributions of body mass and muscle‐induced forces to joint stress are unclear, but generate opposing hypotheses. If mass‐induced forces dominate, facet area should scale with positive allometry to body mass. Alternatively, muscle‐induced forces should cause facets to scale isometrically with body mass. Within primates, both scaling patterns have been reported for articular surfaces of the femoral and humeral heads, but more distal elements are less well studied. Additionally, examination of complex articular surfaces has largely been limited to linear measurements, so that ‘true area’ remains poorly assessed. To re‐assess these scaling relationships, we examine the relationship between body size and articular surface areas of the talus. Area measurements were taken from microCT scan‐generated surfaces of all talar facets from a comprehensive sample of extant euarchontan taxa (primates, treeshrews, and colugos). Log‐transformed data were regressed on literature‐derived log‐body mass using reduced major axis and phylogenetic least squares regressions. We examine the scaling patterns of muscle mass and physiological cross‐sectional area (PCSA) to body mass, as these relationships may complicate each model. Finally, we examine the scaling pattern of hindlimb muscle PCSA to talar articular surface area, a direct test of the effect of mass‐induced forces on joint surfaces. Among most groups, there is an overall trend toward positive allometry for articular surfaces. The ectal (= posterior calcaneal) facet scales with positive allometry among all groups except ‘sundatherians’, strepsirrhines, galagids, and lorisids. The medial tibial facet scales isometrically among all groups except lemuroids. Scaling coefficients are not correlated with sample size, clade inclusivity or behavioral diversity of the sample. Muscle mass scales with slight positive allometry to body mass, and PCSA scales at isometry to body mass. PCSA generally scales with negative allometry to articular surface area, which indicates joint surfaces increase faster than muscles' ability to generate force. We suggest a synthetic model to explain the complex patterns observed for talar articular surface area scaling: whether ‘muscles or mass’ drive articular facet scaling is probably dependent on the body size range of the sample and the biological role of the facet. The relationship between ‘muscle vs. mass’ dominance is likely bone‐ and facet‐specific, meaning that some facets should respond primarily to stresses induced by larger body mass, whereas others primarily reflect muscle forces.     

Comparative and Quantitative Myology of the Forearm and Hand of Prosimian Primates

Associations between the relative development of muscles of the forearm and hand of prosimian primates and locomotor behavior, body size, and grasping specializations have been made on the basis of qualitative observations. These associations are here tested through comparative and quantitative analyses of muscle mass data for a broad sample of prosimian species (i.e., strepsirrhines and tarsiers). The musculature of the forearm and hand of 17 fresh‐frozen specimens representing six families and 12 species was dissected and weighed. Muscle weights were scaled relative to body mass of individual specimens using regression and compared by limb compartment and functional group. Forearm and digital flexor muscle masses are highly correlated with body mass (r = 0.97 and r = 0.96, respectively) and scale isometrically. As a general trend within the prosimian sample, the relative mass of the flexor compartment increases with body size. Interspecific comparisons of functional groups of muscles did not identify any association between larger muscle mass and locomotor adaptations or grasping specializations of the hand. However, compared to other prosimians, the adductor pollicis muscle of Nycticebus is more developed (52% of the intrinsic hand musculature sampled) and the flexor digitorum profundus muscle has two well‐separated heads with more individualized tendons, with the pollex and digit IV receiving tendinous contributions from both muscle heads. These differences that characterize the forearm and hand of Nycticebus correlate with the extreme thumb divergence and pincer‐like grips of lorises. Anat Rec, 2013. © 2013 Wiley Periodicals, Inc.     

Estimating Flight Style of Early Eocene Stem Palaeognath Bird Calciavis grandei (Lithornithidae)

Lithornithids are volant stem palaeognaths from the Paleocene-Eocene. Except for these taxa and the extant neotropical tinamous, all other known extinct and extant palaeognaths are flightless. Investigation of properties of the lithornithid wing and its implications for inference of flight style informs understood locomotor diversity within Palaeognathae and may have implications for estimation of ancestral traits in the clade. Qualitative comparisons with their closest extant volant relatives, the burst-flying tinamous, previously revealed skeletal differences suggesting lithornithids were capable of sustained flight, but quantitative work on wing morphology have been lacking. Until comparatively recently, specimens of lithornithids preserving wing feather remains have been limited. Here, we reconstruct the wing of an exceptionally preserved specimen of the Early Eocene lithornithid Calciavis grandei and estimate body mass, wing surface area, and wing span. We then estimate flight parameters and compare our estimates with representatives from across Aves in a statistical framework. We predict that flight in C. grandei was likely marked by continuous flapping, and that lithornithids were capable of sustained flight and migratory behavior. Our results are consistent with previous hypotheses that the ancestor of extant Palaeognathae may also have been capable of sustained flight. Anat Rec, 303:1035–1042, 2020. © 2019 Wiley Periodicals, Inc.