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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.

Past research has shown that growth mindset and motivational beliefs have an important role in math and science career interest in adolescence. Drawing on situated expectancy-value theory (SEVT), this study extends these findings by investigating the role of parental motivational beliefs (e.g., expectancy beliefs, utility values) and parent growth mindset in math on adolescent career interest in math-intensive fields (e.g., mathematics, computer science, statistics, and engineering; MCSE) through adolescent motivational beliefs in math. Structural equation modeling was used to test the hypothesized model using data from 290 adolescents (201 girls, 69.3%;M_age= 15.20), who participate in informal STEM (science, technology, engineering, mathematics) youth programs, and their parents (162 parents, 87.7% female) in the United Kingdom and the United States. As hypothesized, adolescent expectancy beliefs, utility values, and growth mindset in math had a significant direct effect on MCSE career interest. Further, there was a significant indirect effect of parental expectancy beliefs in math on MCSE career interest through adolescents’ expectancy beliefs. Similarly, there was a significant indirect effect from parental utility values in math to MCSE career interest through adolescents’ utility values. The findings suggest that parents’ math motivational beliefs play a critical role in adolescent math motivational beliefs and their career interest in math-intensive fields.

Carnivorans represent extreme ecomorphological diversity, encompassing remarkable variation in form, habitat, and diet. The relationship between the masticatory musculature and dietary ecology has been explored in a number of carnivoran lineages, including felids and the superfamily Musteloidea. In this study, we present novel architectural data on two additional carnivoran families—Ursidae and Canidae—and supplement these previous studies with additional felid, musteloid, herpestid, hyaenid, and viverrid taxa (a total of 53 species across 10 families). Gross dissection data were collected following a standardized protocol—sharp dissection followed by chemical digestion. Summed jaw adductor forces were also transformed into bite force estimates (BF) using osteologically calculated leverages. All data were linearized, log‐transformed, and size‐adjusted using two proxies for each taxon—body mass (BM) and cranial geometric mean—to assess relative scaling trends. These architectural data were then analyzed in the context of dietary ecology to examine the impact of dietary size (DS) and dietary mechanical properties (DMP). Muscle mass, physiological cross‐sectional area, and BF scaled with isometry or positive allometry in all cases, whereas fascicle lengths (FLs) scaled with isometry or negative allometry. With respect to diet, BM‐adjusted FLs were strongly correlated with DS in musteloids, but not in any other lineage. The relationship between size‐adjusted BF and DMP was also significant within musteloids, and across the sample as a whole, but not within other individual lineages. This interfamilial trend may reflect the increased morphological and dietary diversity of musteloids relative to other carnivoran groups.

By combining muscle architectural data with biomechanical variables relating to the jaw, we produce anatomically derived maximum bite force estimations for 23 species of catarrhine and platyrrhine primates. We investigate how bite force scales across the sample as a whole (and within each parvorder) relative to two size proxies, body mass and cranial geometric mean, and the effect of diet upon bite force. Bite force is estimated at three representative bite points along the dental row: the first maxillary incisor, canine, and third‐most mesial paracone. We modeled bite force by combining calculated physiological cross‐sectional area of the jaw adductors from Hartstone‐Rose et al. [Anat Rec 301 (2018) 311–324] with osteological measurements of lever‐ and load‐arm lengths from the same specimens [Hartstone‐Rose et al., Anat Rec 295 (2012) 1336–1351]. Bite force scales with positive allometry relative to cranial geometric mean across our entire sample and tends toward positive allometry relative to body mass. Bite force tends toward positive allometry within platyrrhines but scales isometrically within catarrhines. There was no statistically significant scaling difference with diet. Our findings imply an absence of a dietary signal in the scaling of bite force, a result that differs from the scaling of physiological cross‐sectional area alone. That is, although previous studies have found a dietary signal in the muscle fiber architecture in these species, when these are combined with their leverages, that signal is undetectable. On the parvorder level, our data also demonstrate that the platyrrhine masticatory system appears more mechanically advantageous than that of catarrhines. Anat Rec, 2019. © 2019 American Association for Anatomy Anat Rec, 303:2026–2035, 2020. © 2019 American Association for Anatomy

In carnivorans, bite force is a critical and ecologically informative variable that has been correlated with multiple morphological, behavioral, and environmental attributes. Whereas in vivo measures of biting performance are difficult to obtain in many taxa—and impossible in extinct species—numerous osteological proxies exist for estimating masticatory muscle size and force. These proxies include both volumetric approximations of muscle dimensions and direct measurements of muscular attachment sites. In this study, we compare three cranial osteological techniques for estimating muscle size (including 2D‐photographic and 3D‐surface data approaches) against dissection‐derived muscle weights and physiological cross‐sectional area (PCSA) within the jaw adductor musculature of 40 carnivoran taxa spanning eight families, four orders of magnitude in body size, and the full dietary spectrum of the order. Our results indicate that 3D‐approaches provide more accurate estimates of muscle size than do surfaces measured from 2D‐lateral photographs. However, estimates of a muscle's maximum cross‐sectional area are more closely correlated with muscle mass and PCSA than any estimates derived from muscle attachment areas. These findings highlight the importance of accounting for muscle thickness in osteological estimations of the masticatory musculature; as muscles become volumetrically larger, their larger cross‐sectional area does not appear to be associated with a proportional increase in the attachment site area. Though volumetric approaches approximate muscle dimensions well across the order as a whole, caution should be exercised when applying any single method as a predictor across diverse phylogenies.