57.

Yok Don Helmeted Bat

Cassistrellus yokdonensis

French: Vespertilion du Yok Don / German: Yok-Don-Helmfledermaus / Spanish: Casistrelo de Yok Don

Taxonomy. Cassistrellus yokdonensis Ruedi et al., 2017,

“ Vietnam, Dak Lak province; Yok Don National Park, Dak Ken River (tributary of the Serepok River), base of Yok Mt. Geographic coordinates 12.8672°N, 107.7075°E, at 194 m asl in dry, open dipterocarp forest.”

Until this species was described formally in 2017 it waslisted in the DNA molecular phylogenetic study by C. M. Francis and colleagues in 2010 as Eptesicus sp. A JLE-2010, a form very distantly related to any other Eptesicus . It is sister to C. dimissus, the pair being most closely related to Tylonycteris and Philetor . Monotypic.

Distribution. Known only from the type locality in Yok Don National Park, SC Vietnam.

Descriptive notes. Head—body 61-66 mm, tail 46-52 mm, ear 14-6-15-2 mm, hindfoot 12 mm, forearm 43-47-5 mm; weight 12-15 g. The Yok Don Helmeted Bat is characterized by pointed, narrow wings similar in shape to those of Nyctalus, but less narrow. It has sparse fur, with short hairs; dorsally it is clove-brown; underparts are beige, being cream-colored on throat; there is no glossy tinge to the fur. Wing membranes and otherskin parts are blackish brown. Wing membranes attach to distal end of metatarsus. Calcar extends less than halfway to tail and has no visible lobe. Yok Don Helmeted Bat exceeds the largest Surat Helmeted Bat (C. dimissus) in measurements. Skull is rather large, but the characteristic helmet present in the Surat Helmeted Bat is less apparent. Skull possesses a pair of deep, well-defined basisphenoid pits and prominent preorbital processes that are also present in the Surat Helmeted Bat. Dental formula for both species of Cassistrellusis12/3,C1/1,P1/2,M 3/3 (x2) = 32. This species has substantially larger and much stronger dentition in general than its congener, with subequal small lower premolars, longer more curved C', and procumbent upper incisors. Condylo-canine length 15:7-16-5 mm; maxillary tooth row 6-3-6-6 mm.

Habitat. Dry open dipterocarp forest in lowlands.

Food and Feeding. No information.

Breeding. No information.

Activity patterns. The two Yok Don Helmeted Bat specimens were caught as they flew into large canopy nets (set 10 m aboveground) in dry open dipterocarp forest in lowlands.

Movements, Home range and Social organization. Other bats caught in the same nets included Taphozous, Pipistrellus, Murina, Cynopterus, Megaerops, and Rhinolophus species; several Hylopetes flying squirrels and a flying gecko (Ptychozoon trinotaterra) were also caught.

Status and Conservation. Not assessed on The [UCN Red List, due to its recent recognition as a species. Known only from a subadult male and a juvenile female. Additional studies are needed into the distribution, abundance, general ecology, and threats to this species. It occurs within the Yok Don National Park, the second largest in Vietnam, and the only one to conserve dry deciduous dipterocarp forests in Vietnam.

Bibliography. Francis et al. (2010), Gorfol et al. (2019), Ruedi, Eger et al. (2017).