Functional Analysis of the Masticatory Apparatus in Two Species of Myotis

Jaw and skull morphologies were analyzed in two morphologically distinct species of bats, Myotis evotis (substrate gleaner) and Myotis volans (aerial insectivore). Force vector analyses were performed on five major muscle-bone lever systems to compare the relative adductive forces produced at three functional points (the incisors, canines, and protoconids of the lower second molar) during jaw closure. Relative force produced by contraction of a given adductor was approximated using a modified muscle mass value. Seven angles of dentary position were analyzed for changes in mechanical advantage due to changing muscle fiber orientation. Results of the analyses suggest that M. evotis has a more forceful bite than M. volans , but only as the upswinging dentary approaches closure. Moreover, M. evotis has the potential for a quicker jaw closure than M. volans and the ability to produce series of rapid nipping motions. The masticatory apparatus of M. volans appears well suited for capture of insect prey using a wide gape followed by a forceful closure. These results are interpreted in view of available ecological data concerning the foraging behavior of the two species.