MAMMALIAN SPECIES No. 291, pp. 1-5, 4 figs. Choeronycteris mexicana, By Joaquin Arroyo-Cabrales, Robert R. Hollander, and J. Knox Jones, Jr. Published 12 August 1987 by The American Society of Mammalogists Choeronycteris Tschudi., 1844 Choeronycteris Tschudi, 1844:70. Type species Choeronycteris mexicana Tschudi. CONTEXT AND CONTENT. Order Chiroptera, Suborder Microchiroptera, Superfamily Phyllostomoidea, Family Phyllostom- idae, Subfamily Glossophaginae. Choeronycteris is treated herein as a monotypic genus distinct from the later-named Musonycteris Schaldach and McLaughlin, 1960, but there is controversy on this point. The two were regarded as congeneric by Handley (1966), Hall (1981), and Koopman (1984). Musonycteris was recognized as a valid genus by Phillips (1971), Jones and Carter (1976), Honacki et aL (1982), and Webster et al. (1982). Choeronycteris mexicona Tschudi., 1844 Mexican Long-tongued Bat Choeronycteris mexicana Tschudi, 1844:72. Type locality Mexico. CONTEXT AND CONTENT. Context as in the generic account above. No subspecies are recognized. DIAGNOSIS. Choeronycteris mexicana is a medium-sized phyllostomid with generally grayish to brownish pelage and an elon- gate muzzle (Fig. 1). The tail is relatively short, about a third the length of the naked uropatagium and about half the length of the femur. Diagnostic cranial and dental characteristics (Fig. 2) include: rostrum elongate, accounting for 40 to 50% of length of cranium; zygomata incomplete; pterygoid processes long, concave on inner surfaces, hamulae expanded and in contact (or nearly so) with auditory bullae and mandibular fossae; teeth, except canines, much reduced in size; evident gaps between cheekteeth; lower incisors absent in adults (Hall, 1981; Miller, 1907; Phillips, 1971). From Musonycteris, its nearest relative, Choeronycteris differs principally as follows:rostrum shorter and relatively broader, lacking evident dome; cheekteeth, although reduced, relatively larger and with shorter gaps between them; basisphenoidal ridge much less well developed; braincase larger; M3 reduced and lacking a distinct metastyle; second upper incisor only slightly larger than first (as opposed to noticeably larger in Musonycteris); pterygoid processes concave inwardly rather than evenly rounded; posterior palatine emargination broadly V-shaped rather than broadly U-shaped; fun- damental number of chromosomes 24 instead of 22 (Schaldach and McLaughlin, 1960; Webster et al., 1982). GENERAL CHARACTERS. Ranges in external and cranial measurements (in mm) in a series (three males, 10 females) of adults from Coahuila (Baker, 1956) are as follows: total length, 81 to 103; length of tail, 6 to 10; length of hind foot, 10 to 13; length of ear, 15 to 18; length of forearm 43.2 to 47.8; greatest length of skull, 29.2 to 30.4; condylobasal length, 28.2 to 29.3; postorbital con- striction, 3.6 to 4.1; palatal length, 17.6 to 18.8; mastoid breadth, 9.9 to 10.5; breadth of braincase, 9.4 to 10.1; depth of braincase, 7.3 to 7.9; length of maxillary toothrow, 8.6 to 9.3. Weight ranges from about 10 to 20 g, up to 25 g in pregnant females. The dorsal pelage varies from buffy brown to relatively dark grayish brown, palest on shoulders; the venter is paler than the dorsum; the ears are pale brownish gray but the membranes are darker, a dark shade of grayish brown (paler at the wing tips); the uropatagium is essentially hairless. Middorsally, the pelage is about 7 mm long in specimens we have examined. As in other glosso- phagines, the tongue is long and extensible. The noseleaf is broad at the base, pointed at the tip, and about 5 mm high. The dental formula of C. mexicana is i 2/0, c Ill, p 2/3, m 3/3, total 30. Upper incisors are small and do not fill the space betwen the canines; there is a gap between those of the inner pair. There are no permanent lower incisors, but one to four deciduous teeth may persist in adults. Upper canines are stout, with a narrow anterolingual cingulum and small posterior cingular style. Lower canines are slender and simple. Upper premolars are long and nar- row, nearly the same size, and differ only in that the second has a posterolingual cingular shelf. Lower premolars also are long and narrow and all three are of approximately the same size except that the second and third are narrower than the first; the first lacks anterior and posterior cingular styles present in the other two. All three upper molars are roughly oval in occlusal outline and are so reduced that a W-shaped ectoloph is lacking; the third differs from the others in being slightly smaller and lacking a distinct metastyle; in all the labial edge consists of a raised lip with an anterior parastyle and posterior metacone. The three lower molars are long and narrow, and of approximately the same size except the third is slightly smaller. Phillips (1971) and Phillips et al. (1977) provided a more detailed description of teeth and dental variation. DISTRIBUTION. The distribution of this long-tongued species (Fig. 3) extends from southern California, southern Arizona, and southwestern New Mexico southward through much of northern and central Mexico (including Baja California and the Tres Marias Is- lands) to EI Salvador and Honduras (Hall, 1981). There is a sight record, complete with photographs (LaVal and Shifflett, 1971), of an individual, possibly a straggler, from the lower Rio Grande Valley of Texas. The usual altitudinal range is from about 300 to 2,400 m. We know of no reported fossils of Choeronycteris. FORM AND FUNCTION. McDaniel (1976) described the anatomy of the brain, characterized by relatively elongate, vertically shallow cerebral hemispheres; a cerebellum with only primary folia- tions; large olfactory bulbs; a shallow but definite cingulate sulcus; and a dense layer of cells along the margin of the interhemispheric sulcus above the superior colliculi. According to Phillips (1971), the deciduous dental formula is i 2/2, c1I 1, P 3/2, total 22. Six deciduous teeth (all four lower incisors and the first upper premolars) are not replaced by permanent counterparts. Conversely, the first lower permanant premolars have no known deciduous precursors. The deciduous upper incisors are FIG. 1. Adult Choeronycteris mexicana from the San Carlos Mountains, Tamaulipas. Photograph by R. R. Hollander. Downloaded from https://academic.oup.com/mspecies/article/doi/10.2307/3503823/2600303 by guest on 05 April 2022