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Cassistrellus dimissus (Thomas, 1916)
Ruedi, Eger, Lim & Csorba, 2018
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Abstract
Bats belonging to the subfamily Vespertilioninae are diverse and cosmopolitan, but their systematic arrangement remains a challenge. Previous molecular surveys suggested new and unexpected relationships of some members compared to more traditional, morphology-based classifications, and revealed the existence of taxonomically undefined lineages. We describe here a new genus and species corresponding to an enigmatic lineage that was previously identified within the genus Eptesicus in the Indomalayan Region. Phylogenetic reconstructions based on mitochondrial and nuclear genes relate the new taxon to Tylonycteris and Philetor, and show that specimens associated with this new genus represent 2 genetically distinct species. Although little is known about their ecology, locations of capture and wing morphology suggest that members of this new genus are tree-dwelling, open-space aerial insect predators. The new species has only been documented from Yok Don National Park in Vietnam, so its conservation status is uncertain until more surveying methods target the bat fauna of the dipterocarp forest in Southeast Asia.
Key words: eptesicoid bats, phylogeny, systematics, taxonomy, Vespertilionidae
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| Fig. 1. Maximum likelihood (ML) phylogeny of selected Vespertilioninae bats based on a combined alignment of 2 mitochondrial and 1 nuclear gene (2,161 bp in total). Numbers near nodes indicate branch support (left, percent ML bootstrap, right, posterior probability), while solid circles represent nodes recovered in >98% of both resampling methods. The gray box highlights the strongly supported clade comprising species of Cassistrellus gen. nov., Tylonycteris, and Philetor. |
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Fig. 2. Portrait of a live adult male Cassistrellus dimissus captured near the Royal Chitwan National Park in Nepal in March 1990. This specimen was collected as part of the series of vouchers described by Myers et al. (2000b) and conserved at the UMMZ
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Fig. 3. Dorsal, ventral, and lateral views of the skull and mandible of a male Cassistrellus dimissus from Laos (MHNG 1926.053). Notice the deep basisphenoid pits between tympanic bullae, long, cuspidate upper canines, strong lambdoidal and occipital crests, and prominent preorbital processes that are typical morphological features of Cassistrellus gen. nov.
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Cassistrellus gen. nov.
Type species: Eptesicus dimissus Thomas, 1916
Description: Species of Cassistrellus are medium-sized vespertilionids (FA 39–47 mm; body mass 12–17 g) characterized externally by short, chestnut-brown pelage that is paler on the ventral parts, by narrow wings with short and pointed tips, and an especially broad muzzle (Fig. 2). Wing membranes are attached to the middle or distal parts of the metatarsus. The tail is mostly included in the uropatagium and extends by 2–3 mm beyond its posterior margin. The calcar extends less than halfway to the tail and may have a small lobe near the ankle. The skull is robust and angular in profile making an almost straight line between the rostrum and the occipital region. It is characterized by well-developed sagittal and lambdoid crests, which meet near the top of the skull to form an occipital helmet. On its ventral surface, the skull has a pair of deep and well-delimited basisphenoid pits located between the cochleae (Fig. 3). Laterally, the lachrymal region has prominent preorbital processes, but the supraoccipital ridges are weak and barely visible. The dental formula is 2113/3123 = 32 teeth, with the upper canines possessing a distinct secondary cusp along the rear edge (Fig. 3).
Etymology: The name Cassistrellus derives from the Latin noun “cassis”, which means wearer of a helmet, in reference to the shape of the hind parts of the skull. The suggested English vernacular name is helmeted bat.
Geographic distribution: The type specimen of C. dimissus was collected by H. C. Robinson and E. Seimund in Kao Nawng, Bandon (currently within Tai Rom Yen National Park in Surat Thani province of Thailand) at 1,400 feet (= 436 m a.s.l.), in June 1913 (Robinson and Kloss 1915). However, the altitude associated with this specimen was reported by Thomas (1916) as 3,500 feet (= 1,067 m a.s.l.), which would correspond to near the summit of the Khao Nong mountain, where the collectors did not capture bats. As all known localities of Cassistrellus are located in the lowlands at elevation between 190 and 674 m a.s.l., these bats should be indeed regarded as lowland dwellers. The vast area covered by the few scattered records of Cassistrellus suggests that it should be widely distributed from the Isthmus of Kra into mainland Southeast Asia and the foothills of the Himalaya, i.e., across most of the Indo-Burma biodiversity hotspot (Myers et al. 2000a). All capture sites were situated in hilly terrain with mixed deciduous or dipterocarp forests traversed by large rivers.
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Fig. 4. Lateral view of skull of A) Cassistrellus yokdonensis sp. nov. (holotype, ROM 107751) and B) C. dimissus (holotype, BM(NH) 16.4.21.1.). The scale bar at the bottom represents 5 mm.
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| Fig. 4. Lateral view of skull of C) C. dimissus from Laos (MHNG 1926.053), and D) C. dimissus from Nepal (UMMZ 172218). The scale bar at the bottom represents 5 mm. |
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Fig. 4. Lateral view of skull of A) Cassistrellus yokdonensis sp. nov. (holotype, ROM 107751), B) C. dimissus (holotype, BM(NH) 16.4.21.1.), C) C. dimissus from Laos (MHNG 1926.053), and D) C. dimissus from Nepal (UMMZ 172218).
The scale bar at the bottom represents 5 mm.
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Cassistrellus yokdonensis sp. nov.
Yok Don helmeted bat
Eptesicus sp. A JLE-2010: Francis et al., 2010
Holotype: Male ROM 107751 (field number 42734) collected on 6 June 1997 by B. K. Lim and M. Theberge. Preserved as a skin, skull, and partial skeleton. Epiphyses almost completely fused, indicating that this bat was a subadult.
Type locality: Vietnam: Dak Lak province; Yok Don National Park, Dak Ken River (tributary of the Serepok River), base of Yok Mt. ..., at 194 m a.s.l. in dry, open dipterocarp forest.
Diagnosis: Cassistrellus yokdonensis sp. nov. is a medium-sized vespertilionid bat (body mass about 15 g) characterized by pointed, narrow wings similar in shape to those of Nyctalus species, but not as narrow. The fur is sparse with short hairs, clove brown (Ridgway 1912) dorsally, lighter beige ventrally, and cream colored at the throat. There is no glossy tinge to the fur. The color of the wings and other skin parts is blackish brown. The wing membranes attach to the distal end of the metatarsus. The calcar extends less than halfway to the tail and has no visible lobe.
Although the dental formula is identical to that of Eptesicus species, the skull possesses a pair of deep and well-defined basisphenoid pits and prominent preorbital processes that are otherwise absent from the latter genus. C. yokdonensis sp. nov. is morphologically similar to C. dimissus, but—in spite of the fact that the known individuals are not fully grown adults—is substantially larger, both externally (e.g., FA 47 mm versus 39–42 mm; Table 1), and cranially (e.g., maxillary toothrow length over 6.5 mm versus less than 6.4 mm). C. yokdonensis sp. nov. has also a much stronger dentition in general, and subequal small lower premolars, longer more curved upper canines, and procumbent upper incisors compared to its congener. Genetically, C. yokdonensis sp. nov. has unique mitochondrial (Cytb, Co1) and nuclear (Rag2) sequences compared to C. dimissus from Laos.
Etymology: We propose the name C. yokdonensis after the national park where it has been found, in recognition of the importance of protected areas in conserving species and their habitats.
Geographic distribution: Currently known only from Yok Don National Park, Dak Lak Province of Vietnam. The 2 specimens were caught shortly after 2100 h as they flew into large (30 m long by 10 m high) canopy nets deployed in a dry, open dipterocarp forest of lowland regions. Other species of mammals caught in the same nets included Taphozous, Pipistrellus, Murina, Cynopterus, Megaerops, and Rhinolophus bats and several Hylopetes flying squirrels. In addition, a paratype specimen of a new species of parachute gecko (Ptychozoon trinitaterra) was caught in this net (Brown 1999).
Manuel Ruedi, Judith L. Eger, Burton K. Lim and Gábor Csorba. 2017. A New Genus and Species of Vespertilionid Bat from the Indomalayan Region.
Journal of Mammalogy. gyx156. DOI:
10.1093/jmammal/gyx156
