Comparative Anatomy of Bat Jaw Musculature via Diffusible Iodine‐Based Contrast‐Enhanced Computed Tomography

Abstract

Noctilionoid bats exhibit an extraordinary array of cranial specializations that match diverse diets, including variation in jaw musculature physiological cross-sectional areas (PCSA), lever arms, and relative contribution to bite force. Although previous research in this group has linked variation in skull shape and muscle mechanics to biting performance, there are still important gaps about the anatomical underpinnings of noctilionoid dietary adaptations, including the degree of compartmentalization of the jaw musculature, and whether and how muscle attachment sites have evolved across noctilionoid species that specialize on derived diets. Here, we paired dissections with Diffusible Iodine-based Contrast-Enhanced Computed Tomography (diceCT) scanning in a comparative anatomical study of the jaw musculature of 12 noctilionoid species that span all diets found within the clade. We evaluated changes in jaw muscle attachments across species, identified differences in muscle compartments, examined scaling relationships, and compared the power of diceCT and dissections to generate morphological data. We found that diceCT enables more detailed investigation of muscle compartments and generates greater PCSA values, but these are strongly correlated with estimates from dissections. Jaw muscle origin and insertion sites are relatively conserved across noctilionoids when compared to other species-rich and ecologically-diverse mammalian groups. However, we found interspecific differences in the degree of separation of the m. masseter, and in the scaling relationships of different jaw muscles with body mass, both of which might be associated with diet and feeding behavior specialization. Our study highlights an unexplored diversity in the compartmentalization and fiber architecture of bat jaw muscles. Anat Rec, 301:267-278, 2018. © 2018 Wiley Periodicals, Inc.

Correlation of skull morphology and bite force in a bird-eating bat (Ia io; Vespertilionidae)

“…Additionally, muscle types, fiber length and orientation are also important in bite force production by affecting muscle force [75]. In other animals, fiber length may constrain the gape angles at which force can be optimally produced, and changes in fiber orientation has an effect on pennation angle that may either change the bite force and provide an advantage for jaw opening or closing [76].…”

“…In other animals, fiber length may constrain the gape angles at which force can be optimally produced, and changes in fiber orientation has an effect on pennation angle that may either change the bite force and provide an advantage for jaw opening or closing [76]. Temporalis muscle attachment (volume) and physiological cross-sectional area are related to body size and also affect the bite force [75,77], in that species with a larger cranium, a larger temporalis mass, and shorter temporalis fiber lengths bite harder. Thus, larger head size and the features of the skull in I. io such as robust mandibles, high cranial sagittal crests, and wider zygomatic arches allow for more jaw adductors (temporalis) and specific muscle fiber length and orientation, which may lead to elevated bite force to help I. io withstand the high biomechanical loads imposed by their prey (i.e., birds).…”

The Ontogeny of Masticatory Muscle Architecture in Microcebus murinus

“…The arrangement of muscle fascicles within the masticatory apparatus has been shown to correlate with dietary adaptations in both primates (Perry and Wall, ; Eng et al, ; Taylor and Vinyard, ; Perry and Hartstone‐Rose, ; Perry et al, ; Perry et al, ; Hartstone‐Rose et al, ) and other mammals (Taylor et al, ; Herrel et al, ; Hartstone‐Rose et al, ; Santana and Cheung, ; Fabre et al, ; Curtis and Santana, ; Santana, ). Despite our understanding of the relationship between fascicular architecture and masticatory function, however, few studies have considered how this architecture changes throughout the lifetime of an animal (Huhov et al, ; Langenbach and Weijs, ; Pfaller et al, ; Pfaller et al, ), especially within the primate order (though see Dickinson et al, ).…”

Behavioral Correlates of Cranial Muscle Functional Morphology

“…Next, we include one of our own papers (Santana, 2018): a comparative study of the masticatory muscles of bats. In line with much of her previous work, Santana conducts a detailed analysis of the correlates of cranial morphology across a broad sample of dietarily diverse species.…”