1 Nose leaf present; tail vertebrae not extending to edge of interfemoral membrane; no diastema in upper incisor series, bony palate complete in front: Family Phyllostomatidae, 2 1' No nose leaf; tail extending at least to edge of interfemoral membrane; diastema in upper incisor row present; if absent, then tail extending well posterior to edge of interfemoral membrane: 3 | |
2 Tail extremely reduced; zygomatic arch complete; two lower incisors on each side: Leptonycteris sanborni. 2' Tail more than 10 mm: zygomatic arch incomplete; no lower incisors: Choeronycteris mexicana. | |
3 Tail extending conspicuously beyond free edge of interfemoral membrane: Family Molossidae, 4 3' Tail extending at most a few mm beyond free edge of interfemoral membrane: Family Vespertilionidae: 7 | |
4 Forearm more than 65 mm; upper lips without deep vertical grooves; palate without anterior emargination: Eumops perotis. 4' Forearm less than 65 mm; upper lips with deep vertical grooves; palate with anterior emargination: 5 | |
5 Forearm less than 45 mm; ears not united at base; second phalanx of fourth finger more than 5 mm; breadth of rostrum markedly greater than interorbital breadth: Tadarida brasiliensis. 5' Forearm greater than 45 mm; ears united at base; second phalanx of fourth finger less than 5 mm; breadth of rostrum little more than interorbital breadth:6 | |
6 Skull longer than 21 mm: Nyctinomops macrotis. 6' Skull less than 21 mm: Nyctinomops femorosaccus. | |
7 One upper incisor on each side: 8 7' Two upper incisors on each side: 11 | |
8 Total teeth, 28; ears long and naked; upper surface of interfemoral membrane largely naked: Antrozous pallidus. 8' Total teeth, 30 to 32; ears short, rounded, and partly furred; upper surface of interfemoral membrane wholly or at least one-half furred: 9 | |
9 One pair of upper premolars: Lasiurus ega. 9' Two pairs of upper premolars (first of which is minute, medially displaced, and not visible in lateral view of tooth-row): 10 | |
10 Skull longer than 15 mm: Lasiurus cinereus. 10' Skull shorter than 15 mm: Lasiurus borealis. | |
11 Interfemoral membrane densely furred dorsally for more than one-half its length; fur black, tipped with white: Lasionycteris noctivagans. 11' Interfemoral membrane furred for, at most, its basal one-third; fur not black tipped with white: 12 | |
12 Cheek teeth (postcanine teeth) 6/6: (Myotis), 17 12' Cheek teeth fewer than 6/6: 13 | |
13 Length of ear more than 25 mm: 14 13' Length of ear less than 25 mm: 16 | |
14 Dorsal color black with three large white spots; postcanine teeth 5-5: Euderma maculatum. 14' Dorsal color not as above; postcanine teeth 5/6: 15 | |
15 A pair of anterior accessory lappets between base of ears: Idionycteris phyllotis. 15' No anterior accessory lappets between bases of ears: Corynorhinus townsendii. | |
16 One pair of upper premolars: Eptesicus fuscus. 16' Two pairs of upper premolars: Pipistrellus hesperus. | |
17 Calcar with well-marked keel: 18 17' Calcar without well-marked keel: 20 | |
18 Ventral surface of plagiopatagium furred to elbow: Myotis volans. 18' Ventral surface of plagiopatagium not furred to elbow: 19 | |
19 Rostral breadth less than 5.1 mm; skull length less than 13.5 mm: Myotis californicus. 19' Rostral breadth more than 5.1 mm; skull length more than 13.5 mm: Myotis ciliolabrum. | |
20 Free edge of uropatagium with distinct fringe of macroscopically visible short hairs: Myotis thysanodes. 20' Free edge of uropatagium without a distinct fringe of macroscopically visible hairs: 21 | |
21 Well-developed sagittal crest present: Myotis velifer. 21' No well-developed sagittal crest: 22 | |
22 Ears more than 16 mm: 23 22' Ears less than 16 mm: 24 | |
23 Ears black: Myotis evotis. 23' Ears brownish (may be dark, but not black): Myotis auriculus. | |
24 Dorsal fur usually with a slight sheen; mastoid breadth usually 7.5 mm or more: Myotis lucifugus. 24' Dorsal fur usually lacking a sheen; mastoid breadth generally 7.4 mm or less: Myotis yumanensis. |
Key modified from Findley et al. (1975).
Last Update: 20 Jul 2005