Meeting Abstract
Rodent jaw adductor musculature and mandibular mechanics are unique among mammals. In rodents, incisor and molar occlusion are mutually exclusive. Millions of years after the evolution of this unique mandibular system, jaw adductor musculature began to diversify, convergently evolving toward three distinctly different masseter configurations a number of times. Prior work in our lab using 2D lever mechanics modeling across 200 species of rodents has demonstrated that one of these conditions, sciuromorphy, is associated with incisor gnawing adaptions. Hystricomorphy lacks any clear relationship to either gnawing or chewing performance when it exists alone. When hystricomorphy and sciuromorphy are combined, a condition called myomorphy found in 50% of rodent species, both of the novel muscular units of these conditions demonstrate positive covariation with both gnawing and molar chewing performance metrics. However, these relationships are based on comparative data across tens of species in large clades, such as Sciuridae, Ctenohystrica, and Muroidea. Smaller clades that have independently evolved derived masseter configurations are not amendable to this type of comparative analysis, and unfortunately these groups have been neglected in terms of detailed descriptive anatomy. In order to properly model the biomechanics of the adductor musculature in these groups, we’ve conducted diffusible iodine-based contrast enhanced computed tomography (DICE CT) scanning on kangaroo rats (Dipodomys: Heteromyidae) and jerboas (Jaculus jaculus: Dipodidae). These taxa have independently evolved sciuromorphy and hystricomorphy, respectively, however, whether their convergent morphologies are identical to the more well known configurations and will share their biomechanics is an open question.
