The epaxial muscles in snakes are responsible for locomotion and as such can be expected to show adaptations in species living in different environments. Here, we tested whether the structural units that comprise the superficial epaxial muscles (semispinalis‐spinalis, SSP; longissimus dorsi, LD; iliocostalis, IC) were different in animals occupying similar habitats. To do so, we analyzed and compared the muscle architecture (mass, fiber length, and physiological cross‐sectional area) of the superficial epaxial muscle segments in snakes that differ in their habitat use (e.g., arboreal, terrestrial, and aquatic). Our results showed that arboreal species have on average longer muscles and tendons spanning more segments likely important during gap bridging. Moreover, aquatic snakes show relatively heavier semispinalis‐spinalis muscles with a greater cross‐sectional area. The longissimus dorsi muscles also showed a greater cross‐sectional area compared with terrestrial and especially arboreal snakes. Whereas the more strongly developed muscles in aquatic snakes are likely associated with the dense and viscous environment through which they move, the lighter muscles in arboreal snakes may provide an advantage when climbing. Future studies comparing other ecologies (e.g., burrowing snakes) and additional muscle units (e.g., multifidus; hypaxial muscles) are needed to better understand the structural features driving variation in locomotor performance and efficiency in snakes.

Diet and habitat use impose mechanical constraints that may impact head morphology and bite force. Skinks (Scincidae) comprise the largest family of lizards with ~1700 species currently described. They also show an important morphological and ecological diversity. Using phylogenetically informed analyses, we studied the interrelationships between ecology (diet, habitat use), head morphology and bite force in these lizards. Our results show a strong link between body size, bite force and diet, with herbivorous species being larger and biting harder than species from other dietary groups. Despite a lack of differences in body size and head morphology, omnivorous species bite harder than insectivorous species, in order to process the fibrous plant material that is part of their diet. Overall, lineages that evolved greater bite forces also showed an increase in relative head height allowing for more vertically oriented jaw muscles. Moreover, we find evidence for correlated evolution between bite force and head length: skinks that bite harder tend to have shorter jaws that likely provide a greater mechanical advantage when biting at the tip of the jaw. Surprisingly, habitat use does not appear to be correlated with morphological traits or bite force, but this needs to explored further.

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