Vesper and evening bats (Family Verspertilionidae) are a diverse group (about 350 living species) that has a nearly global distribution (being absent only in polar regions, on some oceanic islands and in harsher desert climates). Vespertilionids often have been included with molossids, mystacinids, myzopodids, thyropterids, furipterids and natalids in the superfamily Vespertilionoidea (Koopman, 1994), but many other variations of the superfamily exist (e.g., Simmons, 1998; Jones et al., 2002; Hoofer and Van Den Bussche, 2003; Hoofer et al., 2003; Horáček et al., 2006; Miller-Butterworth et al., 2007). Our prime focus in this chapter is on two subfamilies of the Vespertilionidae, Vespertilioninae and Myotinae, as defined by Simmons (2005).
Osteologically, the basic dichotomy between myotines and vespertilionines can be typified by differing patterns of dental morphology. All myotines share myotodont lower molar morphology, in which the postcristid extends to the entoconid and isolates the hypoconulid (as opposed to nyctalodonty where the postcristid extends to the hypoconulid and does not reach the entoconid). Myotines also share the presence of three premolars, with the middle premolar being reduced. Some vespertilionines have myotodont lower molars, but only a few exhibit both myotodonty and the retention of three premolars (e.g., Plecotus and Idionycteris). No vespertilionines have the middle premolar reduced. Recent phylogenetic analyses suggest that all vespertilionines are far removed from myotines (e.g., Hoofer and Van Den Bussche, 2003), implying that any shared morphological similarities are likely to be convergences.