Three-dimensional mandibular kinematics of mastication in the marsupial Didelphis virginiana

Didelphis virginiana (the Virginia opossum) is often used as an extant
model for understanding feeding behavior in Mesozoic mammaliaforms,
primarily due to their morphological similarities, including an unfused
mandibular symphysis and tribosphenic molars. However, the 3D jaw
kinematics of opossum chewing have not yet been fully quantified. We used
biplanar videofluoroscopy and the X-Ray Reconstruction of Moving
Morphology workflow to quantify mandibular kinematics in four wild-caught
opossums feeding on hard (almonds) and soft (cheese cubes) foods. These
data were used to test hypotheses regarding the importance of roll versus
yaw in chewing by early mammals, and the impact of food material
properties (FMPs) on jaw kinematics. The magnitude of roll exceeds that of
yaw, but both are necessary for tooth-tooth or tooth-food-tooth contact
between complex occlusal surfaces. We confirmed the utility of the four
vertical kinematic gape cycle phases identified in tetrapods but we
further defined two more in order to capture non-vertical kinematics.
Statistical tests support the separation of chew cycle phases into two
functional groups: occlusal and non-occlusal phases. The separation of
slow close into two (occlusal) phases gives quantitative kinematic support
for the long-hypothesized multifunctionality of the tribosphenic molar.