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Powerful digital grasping is essential for primates navigating arboreal environments and is often regarded as a defining characteristic of the order. However,in vivodata on primate grip strength are limited. In this study, we collected grasping data from the hands and feet of eleven strepsirrhine species to assess how ecomorphological variables—such as autopodial shape, laterality, body mass and locomotor mode—influence grasping performance. Additionally, we derived anatomical estimates of grip force from cadaveric material to determine whetherin vivoandex vivogrip strength measurements follow similar scaling relationships and how they correlate. Results show that bothin vivoand anatomical grip strength scale positively with body mass, though anatomical measures may overestimatein vivoperformance. Species with wider autopodia tend to exhibit higher grip forces, and forelimb grip forces exceed those of the hindlimbs. No lateralization in grip strength was observed. While strepsirrhine grip forces relative to their body weight are comparable to those of other primates and slightly exceed those of humans, they are not exceptional compared to other arboreal mammals or birds, suggesting that claims of extraordinary primate grasping abilities require further investigation. 

Abstract Access to high‐quality outreach programs is crucial for preparing students for STEM careers, yet traditional classrooms often lack diverse, hands‐on learning opportunities, particularly in anatomy and evolutionary biology. We present Are You Stronger Than a Lemur?—an interactive STEM activity that introduces K‐12 students to fundamental concepts in anatomy, evolution, physics, and data analysis through real‐world applications. Participants formulate hypotheses, collect and analyze data, and engage with age‐tailored educational materials that support differentiated learning. We assessed the program's effectiveness through pre‐ and post‐program knowledge assessments across 1670 participants (1045 eligible responses) from the United States and Mongolia. Results showed a significant increase in knowledge acquisition in anatomy, evolution, physics, statistics, and zoology. After controlling for confounding variables, we also observed a significant increase in interest in STEM careers. Are You Stronger Than a Lemur? bridges gaps in STEM education, particularly in underrepresented fields like anatomy and evolutionary biology, by providing an adaptable program suited to different age groups, genders, and countries. Its success lies in connecting theoretical concepts to tangible data, fostering critical thinking, problem‐solving, and data interpretation skills. The program not only reinforces core STEM concepts but also offers students a unique, engaging experience that deepens their understanding and enhances their potential for future STEM careers. 

Abstract Analysis of muscle architecture, traditionally conducted via gross dissection, has been used to evaluate adaptive relationships between anatomical form and behavioral function. However, gross dissection cannot preserve three‐dimensional relationships between myological structures for analysis. To analyze such data, we employ diffusible, iodine‐based contrast‐enhanced computed tomography (DiceCT) to explore the relationships between feeding ecology and masticatory muscle microanatomy in eight dietarily diverse strepsirrhines: allowing, for the first time, preservation of three‐dimensional fascicle orientation and tortuosity across a functional comparative sample. We find that fascicle properties derived from these digital analyses generally agree with those measured from gross‐dissected conspecifics. Physiological cross‐sectional area was greatest in species with mechanically challenging diets. Frugivorous taxa and the wood‐gouging species all exhibit long jaw adductor fascicles, while more folivorous species show the shortest relative jaw adductor fascicle lengths. Fascicle orientation in the parasagittal plane also seems to have a clear dietary association: most folivorous taxa have masseter and temporalis muscle vectors that intersect acutely while these vectors intersect obliquely in more frugivorous species. Finally, we observed notably greater magnitudes of fascicle tortuosity, as well as greater interspecific variation in tortuosity, within the jaw adductor musculature than in the jaw abductors. While the use of a single specimen per species precludes analysis of intraspecific variation, our data highlight the diversity of microanatomical variation that exists within the strepsirrhine feeding system and suggest that muscle architectural configurations are evolutionarily labile in response to dietary ecology—an observation to be explored across larger samples in the future. 

Abstract Physiological cross-sectional area (PCSA), an important biomechanical variable, is an estimate of a muscle’s contractile force potential and is derived from dividing muscle mass by the product of a muscle’s average fascicle length and a theoretical constant representing the density of mammalian skeletal muscle. This density constant is usually taken from experimental studies of small samples of several model taxa using tissues collected predominantly from the lower limbs of adult animals. The generalized application of this constant to broader analyses of mammalian myology assumes that muscle density (1) is consistent across anatomical regions and (2) is unaffected by the aging process. To investigate the validity of these assumptions, we studied muscles of rabbits (Oryctolagus cuniculus) in the largest sample heretofore investigated explicitly for these variables, and we did so from numerous anatomical regions and from three different age-cohorts. Differences in muscle density and histology as a consequence of age and anatomical region were evaluated using Tukey’s HSD tests. Overall, we observed that older individuals tend to have denser muscles than younger individuals. Our findings also demonstrated significant differences in muscle density between anatomic regions within the older cohorts, though none in the youngest cohort. Approximately 50% of the variation in muscle density can be explained histologically by the average muscle fiber area and the average percent fiber area. That is, muscles with larger average fiber areas and a higher proportion of fiber area tend to be denser. Importantly, using the age and region dependent measurements of muscle density that we provide may increase the accuracy of PCSA estimations. Although we found statistically significant differences related to ontogeny and anatomical region, if density cannot be measured directly, the specific values presented herein should be used to improve accuracy. If a single muscle density constant that has been better validated than the ones presented in the previous literature is preferred, then 1.0558 and 1.0502 g/cm³would be reasonable constants to use across all adult and juvenile muscles respectively. 

Abstract Echolocation is the primary sense used by most bats to navigate their environment. However, the influence of echolocating behaviors upon the morphology of the auditory apparatus remains largely uninvestigated. While it is known that middle ear ossicle size scales positively with body mass across mammals, and that peak call frequency scales negatively with body mass among bats, there are still large gaps in our understanding of the degree to which allometry or ecology influences the morphology of the chiropteran auditory apparatus. To investigate this, we used μCT datasets to quantify three morphological components of the inner and middle ear: ossicle size, ossicle shape, and cochlear spirality. These data were collected across 27 phyllostomid species, spanning a broad range of body sizes, habitats, and dietary categories, and the relationships between these variables and ear morphology were assessed using a comparative phylogenetic approach. Ossicle size consistently scaled with strong negative allometry relative to body mass. Cochlear spirality was significantly (p = .025) associated with wing aspect ratio (a proxy for habitat use) but was not associated with body mass. From a morphological perspective, the malleus and incus exhibited some variation in kind with diet and call frequency, while stapes morphology is more closely tied to body size. Future work will assess these relationships within other chiropteran lineages, and investigate potential morphological differences in the middle and inner ear of echolocating‐vs‐non‐echolocating taxa. 

Abstract While theadductormusculature of the primate jaw has been extensively analyzed within the context of dietary and social ecology, little is known about the corresponding muscles of jawabduction. Nonetheless, these muscles significantly contribute to a species' maximum gape potential, and thus might constrain dietary niche diversity and impact social display behaviors. In this study, we quantify the architectural properties of the digastric (a jaw abductor) and lateral pterygoid (a jaw abductor and anterior translator) across a broad sample of male and female anthropoid primates. We test the hypothesis that the abductor musculature reflects specialization to dietary and behavioral ecology. Our sample comprises 14 catarrhine and 13 platyrrhine species spanning a wide range of dietary and social categories. All specimens were sharp dissected and muscles subsequently chemically digested using a standardized protocol. Our findings demonstrate that relative fascicle lengths within the lateral pterygoid (but not the digastric) are significantly greater within species that habitually consume larger food items. Meanwhile, canine length is more strongly associated with fascicle lengths in the digastric than in the lateral pterygoid, particularly within males. Neither dietary mechanical resistance nor the intensity of social competition relates to the size or architectural properties of the jaw abductors. These findings suggest that dietary—and to a lesser extent, socioecological—aspects of a primate's life history may be reflected in the architecture of these muscles, albeit to varying degrees. This underlines the importance of considering the complete masticatory apparatus when interpreting the evolution of the primate jaw.