title: The impact of gape on the performance of the skull in chisel-tooth digging and scratch digging mole-rats (Rodentia: Bathyergidae).
abstract: The African mole-rats (Bathyergidae) are a family of rodents highly adapted for life underground. Previous research has shown that chisel-tooth digging mole-rats (which use their incisors to dig burrows) are clearly distinguishable from scratch diggers (which only use the forelimbs to tunnel) on the basis of morphology of the skull, and that the differences are linked to the production of high bite forces and wide gapes. We hypothesized that the skull of a chisel-tooth digging mole-rat would perform better at wider gapes than that of a scratch digging mole-rat during incisor biting. To test this hypothesis, we created finite-element models of the cranium of the scratch diggingBathyergus suillusand the chisel-tooth diggingFukomys mechowii, and loaded them to simulate incisor bites at different gapes. Muscle loads were scaled such that the ratio of force to surface area was the same in both models. We measured three performance variables: overall stress across the cranium, mechanical efficiency of biting and degree of deformation across the skull. TheFukomysmodel had a more efficient incisor bite at all gapes, despite having greater average stress across the skull. In addition, theFukomysmodel deformed less at wider gapes, whereas theBathyergusmodel deformed less at narrower gapes. These properties of the cranial morphology ofFukomysandBathyergusare congruent with their respective chisel-tooth and scratch digging behaviours and, all other factors being equal, would enable the more efficient production of bite force at wider gapes inFukomys. However,in vivomeasurements of muscle forces and activation patterns are needed to fully understand the complex biomechanics of tooth digging.
authors.affiliation: Centre for Anatomical and Human Sciences, Hull York Medical School , University of Hull , Hull , UK.
authors.forename: Andrew F
authors.initials: AF
authors.lastname: McIntosh
authors.affiliation: Centre for Anatomical and Human Sciences, Hull York Medical School, University of York, York, UK; Department of Archaeology, University of York, York, UK.
authors.forename: Philip G
authors.identifier: 0000-0001-9782-2358
authors.initials: PG
authors.lastname: Cox
keywords: Bathyergidae; chisel-tooth digging; cranial biomechanics; finite-element analysis; scratch digging