Chilonatalus tumidifrons Miller, 1903

Tejedor, Adrian, 2011, Systematics Of Funnel-Eared Bats (Chiroptera: Natalidae), Bulletin of the American Museum of Natural History 2011 (353), pp. 1-140 : 35-39

Chilonatalus tumidifrons Miller, 1903

Figure 17

Chilonatalus tumidifrons Miller, 1903 . Type locality ‘‘Watling Island’’ [5 San Salvador Island], Bahamas.

Natalus (Chilonatalus) tumidifrons: Dalquest, 1950: 443 . New combination.

Natalus micropus tumidifrons: Varona, 1974: 32 . New combination.

Natalus tumidifrons: Ottenwalder and Genoways, 1982: 32 . New combination.

HOLOTYPE: USNM 122024, adult male, skin in alcohol with skull removed, collected by J.H. Riley on 12 July 1903 in a cave near Sandy Point (locality 524 in appendix 1), San Salvador Island, the Bahamas. Skin and skull in good condition.

DISTRIBUTION: The Bahamas (Abaco, Andros, and San Salvador; also, as a fossil, in New Providence, Cat and Great Exuma) ; fig. 11.

DIAGNOSIS: Forearm short (31.7–36.0 mm) relative to skull length; length of tibia (17.8– 20.05 mm); penis short (1.1–2.25 mm); natalid organ long (3.6–7.25 mm); skull long (15.15–15.95 mm) relative to forearm length; least postorbital breadth relatively narrow; lateral margin of ear straight; attachment of wing to tibia on the proximal half of the tibia (at about 1/3 of its length, measured from the knee); in lateral view, braincase rises from rostrum as a softly curving slope dorsal to orbit; ridge between basisphenoid furrows wide; caudal margin of ascending ramus of mandible forming a straight angle with alveolar plane of dentary; lateral sides of basisphenoid pits nearly parallel; p2 crowded; seamless fusion of ribs to sternum. A comparison of diagnostic characters between C. tumidifrons , and other species of Chilonatalus is summarized in table 4.

DESCRIPTION: Small size (forearm length 31.7–36.0 mm; greatest skull length 15.0– 16.0 mm; weight 3–3.5 g); muzzle long and dorsoventrally flattened; nostrils elliptical, opening ventrolaterally at the end of tubelike projections on margin of upper lip; upper lip slightly thickened; lower lip markedly thickened and constricted on dorsal and ventral margin, with numerous transversal grooves; small, smooth central pad on dorsal margin of lower lip; high dermal tubercle on dorsum of rostrum caudal to nostrils; tubercles of ramal vibrissae coalesced into transversal ridge ventral to lower lip; natalid organ very large (up to 1/2 of greatest length of skull), spindle shaped, reaching crown of head; ears relatively long (14.7–17.2 mm); ear pinna very wide and funnel shaped; pinna with moderately pointed tip; lateral and medial margins of pinna straight; three very small ear ridges along lateral margin of distal pinna; ventral region of ear pinna greatly expanded, covering the eye and tragus in lateral view; medial ear margin thin and flexible; tragus markedly short, lanceolate, and twisted into helixlike structure; tibia (17.8–20.1 mm) longer than half the length of the forearm; calcar very long and thin, occupying about 2/3 of the length of the free edge of uropatagium; free margin of uropatagium with sparse fringe of thin hairs; wings relatively long and wide, with 3rd metacarpal (30.3–32.4 mm) longer than 5th metacarpal (27.9–30.5 mm); wings attach to tibia at proximal third of distance between knee and ankle; pelage dense and lax; hairs long (5– 9 mm, dorsally; 4–7 mm, ventrally); pelage color from light brown to orange brown, lighter dorsally; hairs bicolored, with tips darker than bases; dense mustachelike hair tufts along lateral margins of upper lip; mustache formed by dense, tough, parallel, and ventrally curved hairs; natalid organ nearly naked; skull long and narrow with moderate rostral flexion; rostrum long and narrow, with marked sulcus between nasals; moderate palatal emargination; maxilla

convex dorsal to molars; braincase greatly inflated, rising gently from rostrum; sagittal crest moderately developed; postorbital constriction relatively narrow (38 % –41 % of zygomatic breadth); maxillary branch of zygomatic arch thin, less deep than twice the height of crowns of last molars; pterygoids convergent; palate extending caudally to half the length of pterygoids; basisphenoid pit deep and steep sided; longitudinal medial ridge on basisphenoid present; ectotympanic large, covering about half of the periotic; upper incisors long and pointed; occlusal profile of premolars long; upper premolars of similar size and crowded; mesostylar crests on M1 and M2 long and broadly curved, mesostylar crest present on M3; cingular cusp of p4 long and pointed; molars cusps relatively broad; spinous process of humerus much higher than capitulum; thorax relatively short and wide; all ribs fused together and with sternum forming a single bell-shaped structure; vertebrae C7 to T7 fused together and to ribs; vertebrae T11–L5 fused entirely without vestige of sutures; vertebrae L6 free; caudal vertebrae 4 to 7 longer than distance from ischium to iliac crest of sacrum.

COMPARISONS: From species of the genera Natalus and Nyctiellus , Chilonatalus tumidifrons can be distinguished on the basis of generic level characters (for generic-level comparison between Chilonatalus and Natalus and Nyctiellus see account of C. macer ). From Chilonatalus micropus , and Chilonatalus macer , C. tumidifrons can be distinguished using a combination of external and internal characters.

Externally, Chilonatalus tumidifrons differs from C. micropus in its straight lateral margin of the ear, the attachment of the wing on the proximal half of the tibia, a short penis (1.1–2.25 mm), a long tibia (17.8– 20.05 mm), and a large, elliptical natalid organ (length of natalid organ 3.6–8.5 mm). Chilonatalus micropus , in contrast, is characterized by a deeply notched (concave) lateral ear margin, a wing attaching to the tibia on its distal half, a long penis (3.6–6.5 mm), a short tibia (14.7–17.95), and a small, hemispherical natalid organ (length of natalid organ 3.3–3.7). Cranially, C. tumidifrons and C. micropus can be separated by the dorsal flexion point of the skull (with a well-defined angle in C. micropus and a gently curving slope in C. tumidifrons ), the angle formed by the caudal margin of the ascending ramus of mandible with the alveolar plane of the dentary (straight in C. tumidifrons and about 70u in C. micropus ), the lateral sides of the basisphenoid pits (nearly parallel in C. tumidifrons and caudally divergent in C. micropus ), and by the fusion of the ribs with sternum (without vestige of sutures in C. tumidifrons and retaining sutures in C. micropus ).

Chilonatalus tumidifrons does not differ appreciably from Chilonatalus macer in external characters. The skull of Chilonatalus tumidifrons (greatest skull length 15.15– 15.95 mm), however, is absolutely and proportionately (relative to forearm length) larger than that of C. macer (13.8–14.7 mm). Also, the two species differ in the relative width of the postorbital constriction (38 % – 41 % of zygomatic breadth in C. tumidirostris and 42 % –44 % in C. macer ), in the degree of crowding of P2 (crowded in C. tumidifrons and not crowded in C. macer ), and in the relative width of the ridge between basicranial furrows (narrow in C. tumidifrons and wide in C. macer ).

VARIATION: No significant sexual variation has been detected in the samples available of C. tumidifrons ( Ottenwalder and Genoways, 1982) . Specimens from Abaco had significantly deeper braincases (on average) than those from San Salvador (P, 0.001; fig. 18).

NATURAL HISTORY AND CONSERVATION: Chilonatalus tumidifrons is known from 20 localities (including 8 represented by bone remains only) of which eight are caves, this species’ only known roost type. It has been found in caves both large and small where it often roosts above water, but also in drier areas. Individuals hang regularly spaced, and generally from a single foot ( Miller, 1905). It has been found in caves with two other bat species ( Erophylla sezekorni and Macrotus waterhousii ; Andersen, 1994; Hall et al., 1998). When found sharing caves with Erophylla , C. tumidifrons occupies low areas often under shelves or ledges ( Hall et al., 1998). Roost-site temperatures at one cave (locality 520) ranged from 22.8u to 24.2u C and in a second cave (locality 522) from 23.6 to 23.9u C. Roosting groups have been observed to switch roosting caves set on average 1 km apart, apparently on a daily basis. A colony of about 300 individuals in Abaco was observed to have abandoned a cave entirely, coinciding with the occupation of that cave by 100–200 Erophylla ( Allen, 1905) .

Chilonatalus tumidifrons is associated with deciduous forest habitats of moderate precipitation (1021–1288 mm annual precipitation) and occurs near sea level throughout its range. It is presumably insectivorous, but nothing has been published on the diet of this species.

Chilonatalus tumidifrons is known from at least 123 museum specimens. It has been found in groups ranging from less than 10 to over 500 individuals. The population of San Salvador Island could be relatively large given the high abundance of small, unsurveyed caves on the island that may potentially harbor colonies of this species ( Hall et al., 1998). In Andros, C. tumidifrons is known from a single cave (Bat Cave) and although only four individuals were taken there, many individuals were observed to swarm out of the cave during a feeding exodus ( Andersen, 1994). Chilonatalus tumidifrons has no known predators and reportedly is parasitized by the streblid Trichobious wenzeli ( Hall et al., 1998) .

The reproduction biology of C. tumidifrons is not known. Colonies apparently formed exclusively by males have been found in July ( Allen, 1905), suggesting the sexual segregation pattern that occurs during the period of lactation in other species of the genus. Males have an extremely short penis (1.0– 2.3 mm) relative to other natalids, but the possible implications of this trait in the reproduction and mating system of the species is unknown.

Foraging activity begins around sunset. At Crescent Top Cave (locality 520) emergence has been recorded to extend from 17:33 to 18:05 (January 1996) and from 17:44 to 18:10 (January 1997; Hall et al., 1998). Judging from its limb morphology, the flight of C. tumidifrons must be very slow, having been compared to that of a large moth ( Miller, 1905).

Chilonatalus tumidifrons is listed as vulnerable in the IUCN’s Red List of Threatened Species (IUCN, 2010). The extremely reduced range of this species, fragmented across three islands, is of concern. On Abaco and Andros this species is known from only two caves in each case. It seems most abundant in San Salvador, but further survey work is needed on that island to estimate its population size and conservation status ( Hall et al., 1998).

Figures

Fig. 17. Holotype of Chilonatalus tumidifrons (USNM 122024, male, San Salvador, the Bahamas). Scale bar 5 5 mm.