58.

Surat Helmeted Bat

Cassistrellus dimissus

French: Vespertilion de Surat Thani / German: Surat-Helmfledermaus / Spanish: Casistrelo de Surat Thani

Other common names: Surat Serotine

Taxonomy. Eptesicus dimissus Thomas, 1916,

“ Kao Nawng, Bandon, Malay Peninsula [= Thailand], 3,500’ [= 1067 m].”

Originally treated as an individual of Eptesicus pachyotis by H. C. Robinson and C. B. Kloss in 1915, but O. Thomas described this bat as a distinct but related species. Traditionally associated with species of the Eptesicus serotinus group. It is not closely related to any Eptesicus, and therefore M. Ruedi and colleagues in 201 7 created a new genus, Cassistrellus, for this and its sister species. Recent molecular phylogenetic studies place this dimassus lineage as sister to Tylonycteris, and more distantly related to Philetor . Monotypic.

Distribution. Known only from a single specimen collected in S Thailand (Tai Rom Yen National Park, Surat Thani Province) and eight specimens from S Nepal (in and near Royal Chitwan National Park); recently also a single specimen from N Laos (Ban Naten, Phongsaly Province).

Descriptive notes. Head—body 59-63 mm, tail 40-41 mm, ear 15-4-16 mm, hindfoot 8:8-10 mm, forearm 38-9—-41-8 mm; weight 15 g (single individual). The Surat Helmeted Bat has short (3 mm), sparsely haired chestnut-brown pelage on dorsum, individual hairs having brown tips and pale bases; ventral surface is pale brown; fur extends in a triangle onto base oftail. Short, rounded ears are sparsely furred on anterior surface and naked on posterior; they are triangular and fleshy. Short, round tragus has concave posterior margin and convex anterior margin; posterior edge of tragus and base of anterior edge of pinna appear to be slightly thickened. Muzzle is very broad. Skin on top of the head is loose, sometimes forming a fold running from ear to ear. Dark brown wing membranes are attached on side of foot near ankle; patagial membranes are almost hairless. Calcar with well-developed keel extends less than halfway to tail and may have a small lobe near the ankle. Tail extends 1-3 mm beyond border of uropatagium. Bare parts of skin are pinkish brown. Baculum is tiny and triangular in outline, much like those of Eptesicus serotinus group, but ventral parts have two lateral wings that are not present in Eptesicus . Skull is robust and relatively flat, with a moderately inflated braincase; it has well-developed sagittal and lambdoid crests, which meet near top of skull to form an occipital helmet. Rostrum is relatively short and broad. Bulbous part of lacrimal region has no frontal depression, but bears prominent supraorbital tubercles. On its ventral surface, skull has a pair of deep, well-delimited basisphenoid pits located between the cochleae;this is the most distinctive character of Cassistrellus . Deep basisphenoid pits between tympanic bullae, notably long, cuspidate C!, strong lambdoidal and occipital crests, and prominent preorbital processes are typical morphological features of the genus Cassistrellus . In the dentition, the bifid I’ barely extends beyond the cingulum of the C!. I? is approximately two-thirds the length of I*. P* is less than half the length of the adjacent C'. C! has a pronounced cingulum and a trace of a secondary cusp;it is especially long and slender. Condylo-canine length 14:6-16-5 mm; maxillary tooth row 5:8-6-4 mm.

Habitat. All capture sites were situated in hilly terrain, with mixed deciduous or dipterocarp forests traversed by small streams or large rivers. In Nepal, also caught in a forest, dominated by sal ( Shorea robusta, Dipterocarpaceae) trees. In Laos, the capture site was far from karstic or rocky areas, so presumably the species’ roosting sites are in trees rather than caves. Elevation ranges 190-674 m.

Food and Feeding. Derived from wing morphology, characteristics of ears, thumbs, hindfeet, and weak dentition, Surat Helmeted Bats are likely to be fast-flying that probably catch soft-bodied insects such as moths.

Breeding. No information.

Activity patterns. No information.

Movements, Home range and Social organization. No information.

Status and Conservation. Classified as Data Deficient on The IUCN Red List (as Eptesicus dimissus), as it is only known from three localities, and its ecology is almost entirely unknown. Further studies are needed into the distribution, abundance, natural history and threats to this species. It was not found during a series of recent surveys in forest areas in peninsular Thailand, including some around the type locality of the species.

Bibliography. Boitani et al. (2006), Corbet & Hill (1992), Csorba et al. (2016), Francis (2008a), Gorfol et al. (2019), Hill & Harrison (1987), Koubinova et al. (2013), Lekagul & McNeely (1988), Myers, P. et al. (2000), Pearch & Writer (2009), Robinson & Kloss (1915), Ruedi, Eger et al. (2017), Simmons (2005), Tate (1942b), Thomas (19164).