Anatomical description of the jaw muscles and theoretical bite force assessment in South American opossums using manual and digital dissection methods

Marsupials (Marsupialia, Mammalia) represent an ecologically diverse clade. This is particularly true for opossums (South American marsupials), which are, however, often difficult to observe and collect. Consequently, few studies have focused on their bite force and the muscles of their masticatory apparatus, and only scant information on the diet of many species exists. Here we describe the masticatory muscles of several previously unstudied opossum species including Caenolestes fuliginosus, Dromiciops gliroides and Monodelphis touan. We calculate the bite force of these species using data from both manual and digital dissections and compare their theoretical bite forces with literature data. Additionally, we explore the differences between manual and digital dissection to determine the muscle PCSA (physiological cross-sectional area). The results highlighted variation in the position of the muscular attachments and muscle size as well as in the distribution of each muscle in the masticatory apparatus, with a larger temporal complex in M. touan and a larger zygomasseteric complex in D. gliroides. The bite forces are coherent with estimates from the literature suggesting that our biomechanical model is reliable. The comparison between manual and digital dissections showed that while digital dissection allows an overall description of the masticatory muscles, it is more complex to accurately describe the different subdivisions of the muscle bundles. The use of digital volumes to calculate the PCSA remains to be evaluated. Digital dissection data can complement manual dissection data, provided that the composite structure of muscles and the physiological changes during impregnation with contrast agents are better understood.