Figure 1.
Three-dimensional reconstructions of the skull, mandible, deep masseter and zygomatico-mandibularis of three rodents.
(A) sciuromorph (squirrel); (B) hystricomorph (guinea pig); (C) myomorph (rat). adm, anterior deep masseter; iozm, infraorbital part of the zygomatico-mandibularis; pdm, posterior deep masseter. Scale bars = 5 mm.
Figure 2.
Simplified cladogram of the extant rodents showing the distribution of masticatory muscle morphologies.
Topology based on Blanga-Kanfi et al [15]. Silhouettes indicate the position of the rat, guinea pig and squirrel within the Muroidea, Ctenohystrica and Sciuridae respectively.
Figure 3.
Predicted distribution of von Mises stresses across the skull.
Arrows indicate the biting tooth: (A–C) incisor bites; (D–F) unilateral bites on M1; (G–I) unilateral bites on M3; (J–L) maximum von Mises stress experienced by each element across unilateral and bilateral bites on every tooth. (A,D,G,J) squirrel; (B,E,H,K) guinea pig; and (C,F,I,L) rat. Grey areas indicate von Mises stresses exceeding 10 MPa.
Figure 4.
Biting performance of rodents at each tooth.
(A) Median von Mises stresses on the skull and (B) mechanical efficiency of biting (predicted bite force divided by total applied muscle force) in squirrels, guinea pigs and rats. (C) Median von Mises stresses and (D) mechanical efficiency of biting of each of the three models with the squirrel, guinea pig and rat muscle configurations applied in turn. I, incisor; PM, premolar (absent in rats); M, Molar.
Table 1.
Average predicted bite force (N) and mechanical efficiency of biting at each tooth.
Figure 5.
Predicted distribution of von Mises stresses across the skull.
Incisor biting in squirrel (A,D,G), guinea pig (B,E,H) and rat (C,F,I), each loaded with squirrel (A–C), guinea pig (D–F) and rat muscles (G–I). Grey areas indicate von Mises stresses exceeding 10 MPa.
Figure 6.
Predicted distribution of von Mises stresses across the skull.
Unilateral biting on M1 in squirrel (A,D,G), guinea pig (B,E,H) and rat (C,F,I), each loaded with squirrel (A–C), guinea pig (D–F) and rat muscles (G–I). Grey areas indicate von Mises stresses exceeding 10 MPa.
Figure 7.
Contour maps showing the difference in von Mises stresses experienced by each model when loaded with different muscle configurations.
(A) Stress generated by guinea pig muscles subtracted from stress generated by squirrel muscles. (B) Stress generated by rat muscles subtracted from stress generated by squirrel muscles. (C) Stress generated by rat muscles subtracted from stress generated by guinea pig muscles. Positive results represented by hot colours, negative results by cool colours. Dotted pattern in temporal region of the rat (B and C) indicates the nodes from which the temporalis muscle originates and is a result of the large temporalis of the rat. Arrows indicate the biting tooth.
Table 2.
Muscle forces (N) applied to each side of each model.
Table 3.
Material properties of cranial and dental components.
Table 4.
Recalculated muscle forces (N) simulating muscle proportions of each rodent on the other two skulls.