Fig. 14. A in Carnassiform notches improve the functional efficiency of bat molar shearing crests

Fig. 14. A. Diagram of a bat M2 and m2 in posterolingual view showing the relationship of the shearing crests (postparacrista of M2 with cristid obliqua of m2) of tribosphenic bat molars during occlusion. Dotted line indicates portion of m2 hidden by M2; dashed line indicates metacone "removed" to reveal the paracone and postparacrista of M2; thin arrow indicates trajectory of hypoconid into the protofossa (not visible) of M2 during occlusion; boldest line on M2 is edge of postparacrista; boldest line on m2 is tip of hypoconid and cristid obliqua. B. Outline representations of the hypoconid and cristid obliqua observed in this study, without and with in-crest carnassiform notches. Types 1–4 without carnassiform notches: 1 and 2 are seen for example, in Hipposideridae, Rhinolophidae, Rhinopomatidae, Emballonuridae, Mormoopidae, Phyllostomidae, Molossidae, Vespertilionidae; 3 in Miniopteridae, Murininae; 4 in Phoniscus. Types 5–8 with carnassiform notches: 5 in Megadermatidae; 6 in Nycteridae; 7 in Natalidae; 8 in Mystacinidae, Furipteridae, Thyropteridae, Phyllostomidae, Kerivoulinae. C. Evans model showing effect of approach angles of two occluding blades on point cutting: With both blades at 0° and both at 10° no point cutting occurs; with one blade at 10° and one blade at 0°, one point cutting is enabled (Evans 2006: fig. 5.1c). Our application of Evans model to bat postparacrista and cristid obliqua as the upper and lower blades, respectively: with two curved blades without carnassiform notches, two point cutting occurs at opposite end of blades until center is reached and approach angles reach 0°; with emplacement of a carnassiform notch in lower blade at the point at which changing blade angles approach 0°, notch enables a second change in approach angles.