The relationship between morphology and behavior reflects evolutionary pressures leading to adaptation and anatomical diversity. We investigated how locomotive behavior influences scapular morphology in Old World monkeys and Great Apes, and how these adaptations may be mediated by body mass, to better understand the morphological evolution of Primates. To do so, we compared scapular length-to-width ratios (LWR), scapular spine depths (SSD), and scapular shapes across 67 specimens (18 species) grouped by locomotion strategy and body mass. We determined scapular shape using landmark-based geometric morphometrics and traditional linear measurements. Seven anatomical landmarks were digitized and analyzed via Generalized Procrustes Analysis (GPA) and Principal Component Analysis to examine shape differences. Maximum LWR was measured using ImageJ, while SSD was measured with calipers. Statistical tests, including Procrustes-based Linear Models (PLM), Analysis of Variance (ANOVA), and phylogenetic ANOVA were used to assess the influence of locomotion strategy and body mass on scapular morphology. We specifically tested the hypothesis that scapular morphology is primarily shaped by locomotion strategy (H1), body mass (H2), or neither (null hypothesis). We found that: (1) scapular shape variation is influenced by factors beyond species and size, with body mass showing a small effect, indicating an allometric relationship; (2) there were significant differences in scapular LWRs and SSDs across locomotion categories, with arboreal species having narrower scapulae and deeper spines compared to terrestrial species; and (3) SSD did not vary significantly between body mass groups while LWR did. The amount of morphological variation was greater in smaller primates than in larger ones, contradicting H2. These results suggest that locomotor habits play a dominant role in shaping scapular morphology, with limited influence from body mass. Our study highlights the interplay between ecological pressures, body size, and skeletal adaptations, offering insights into the evolutionary mechanisms driving morphological variation in primates across diverse habitats.

This study investigates the sensory adaptations of nocturnal and diurnal rodent species, focusing on the relationship between orbital structures and whisker morphology. We hypothesized that nocturnal rodents would exhibit larger orbital dimensions, including maximum orbit length (MOL), due to their need for enhanced light-gathering capabilities in low-light environments. Our analysis of various rodent species, including Peromyscus maniculatus, Rattus norvegicus, and Sciurus carolinensis, revealed significant differences in orbital measurements, with nocturnal species consistently displaying larger orbits (p < 0.001). Our data collection involved taking six linear measurements from skulls (four related to orbit size using ImageJ software and two cranial size proxies using digital calipers) and analyzing whisker morphology, followed by statistical analyses including histograms, boxplots, Pearson correlation test, and phylogenetic analysis to explore relationships among traits in diurnal and nocturnal species. Additionally, while whisker length showed a stronger correlation with body size in diurnal species compared to nocturnal ones, the differences in whisker morphology were less pronounced and not statistically significant. Phylogenetic analyses indicated that certain traits, such as interorbital width, are influenced by evolutionary relationships rather than solely by activity patterns. These findings suggest that while visual adaptations in nocturnal rodents are prominent and likely enhance their survival in dim conditions, the role of tactile sensory structures is more complex and may be shaped by a variety of ecological pressures. Overall, this research contributes to our understanding of how different lifestyles influence sensory system evolution in rodents and has implications for fields such as evolutionary biology and biomimetics.