Submyotodon latirostris ( Kishida, 1932 )

Ruedi, Manuel, Csorba, Gábor, Lin, Liang- Kong & Chou, Cheng-Han, 2015, Molecular phylogeny and morphological revision of Myotis bats (Chiroptera: Vespertilionidae) from Taiwan and adjacent China, Zootaxa 3920 (1), pp. 301-342 : 319-321

Submyotodon latirostris ( Kishida, 1932)

Synonymy. Myotis latirostris Kishida, 1932 . Type locality C Taiwan. Myotis muricola orii Kuroda, 1935 . Type locality Taihezon, Taihokusiu, N Taiwan. Myotis mystacinus latirostris: Tate 1941 . Name combination.

Myotis mystacinus orii: Tate 1941 . Name combination.

Myotis mystacinus latirostris: Ellerman & Morrison-Scott 1966 . Name combination. Myotis muricola latirostris: Findley 1972 . Name combination.

Myotis muricola orii: Corbet and Hill 1992 . Name combination.

Myotis latirostris: Lin et al. 2004 . Name combination.

Myotis muricola latirostris: Simmons 2005 . Name combination.

Myotis latirostris: Stadelmann et al. 2007 . Name combination. Myotis latirostris: Cheng et al. 2010 . Name combination. Myotis latirostris: Lack et al. 2010 . Name combination.

Myotis latirostris: Ruedi et al. 2013 . Name combination.

Taxonomic remarks. Kishida (1932) described a small species of Myotis from Taiwan and named it M. latirostris . Shortly after this description and also based on small specimens caught in Taiwan, Kuroda (1935) described another taxon, M. muricola orii . The very small forearm dimensions of both taxa (FA 33–34 mm), their tiny hind feet (6.5 mm), blackish fur and their small second upper premolars that are clearly visible laterally, are all morphological characters found in no other Myotis from Taiwan. Hence, despite the fact that the type specimens of latirostris and orii are not available for direct comparisons ( Imaizumi 1962; Kaneko & Maeda 2002), there is no doubt that both taxa belong to the same species, but its systematic position is more contentious. Classical accounts variously treated latirostris (and orii) as a subspecies of M. mystacinus or of M. muricola , ( Tate 1941; Findley 1972; Corbet & Hill 1992; Simmons 2005), but recent molecular reconstructions suggest that none of these species share a common ancestor ( Stadelmann et al. 2007; Lack et al. 2010; Ruedi et al. 2013). The molecular data, whether issued from mitochondrial ( Stadelmann et al. 2007; Fig. 3) or nuclear genes ( Lack et al. 2010; Ruedi et al. 2013), rather show that the phylogenetic position of the latirostris lineage is very peculiar, being basal to all recent Myotis species tested so far. In addition to these molecular reconstructions, specimens of the latirostris lineage show that their first two lower molars have a nyctalodont configuration (i.e., where the postcristid is linking to the hypoconulid; Menu & Sigé 1971), whereas most species of Myotis have myotodont lower molars (i.e., where the postcristid is linking to the entoconid; Menu & Sigé 1971). The only exceptions are the small Myotis of the siligorensis-alticraniatus group ( Tiunov et al. 2011; Ruedi et al. 2013), that can be easily recognized by their distinctly raised frontal part of the braincase and crowded premolars ( Borisenko et al. 2008); these features are very different in latirostris skulls (Fig. 4a). Multiple independent evidences therefore support that bats from the latirostris lineage belong to a distinct genus within the Myotinae radiation ( Ruedi et al. 2013). In fact, while checking all relevant type material currently assigned to Asian Myotinae , we found that the very peculiar skull shape and dental characteristics of this latirostris lineage are typical of three further taxa described from continental Asia, namely Vespertilio caliginosus ( Tomes 1859; type locality India), V. blanfordi ( Dobson 1871; type locality northern India) and V. moupinensis ( Milne-Edwards 1872; type locality Moupin, Szechuan, China). We therefore consider these four taxa as congeners, but their distinction at the species level is beyond the scope of the present study. More remarkably, we also examined the paleontological literature and found that these four species also perfectly fit the diagnosis of the Upper Miocene genus Submyotodon described by Ziegler (2003). In particular, the Miocene fossils and recent material of the latirostris lineage share not only the nyctalodont condition of the first two lower molars, but also several other dental traits (such as four-cusped third lower incisors, unreduced length of third upper molar, uncrowded premolars, etc.), a peculiar skull shape (i.e., long bony bridge between lachrymal and infraorbital foramina; ascending ramus of mandible standing nearly perpendicular to the horizontal ramus; low articular process, etc.), and very small overall dimensions (see Ziegler 2003). As the paleontological material is fragmentary, it is not possible to compare the upraised shape of posterior parts of the neurocranium, nor the elongated, relatively flattened rostrum typical of latirostris (Fig. 4a), but as we cannot find any marked difference in other characters between the diagnosis of the Miocene Submyotodon and recent material, we propose to assign the four species of the latirostris lineage to that genus. Previous molecular dating further support this assignment, as the estimated age of the divergence time between the latirostris linage and other Myotis (credibility interval 23–20 million years ago, Ruedi et al. 2013 or 18 mya, Lack et al. 2010), indeed predates the paleontological age of Submyotodon (which is dated from the MN 7/8 stratum, i.e., 13.5–11 mya, Ziegler 2003). The divergence of the unrelated nyctalodont Myotis of the siligorensis – alticraniatus group is much more recent (mean 2.2 mya, Ruedi et al. 2013) and is not compatible with a Miocene divergence.

Distribution. Submyotodon latirostris has been found so far only in Taiwan, where it is widespread and relatively common.

Measurements. See Table 4.

External morphology. The combination of very small body size (i.e., forearm about 31–34 mm) and small feet (5–7 mm), sharp notch to the outer edge of the ears and attachment of wing membranes to the outer toe, easily distinguish S. latirostris from any other species found in Taiwan and adjacent mainland China. The dorsal fur is dark slaty brown, long and shaggy, with lighter brown tips. Ventrally the fur is also dark brown with lighter, golden tips of hairs and is particularly long in the posterior parts. Ears nearly reach the nose tip when laid forward, are pointed, and have a sharp notch at the rear edge of the conch ( Cheng et al. 2010). The tip of the relatively short tragus is spatulated, and bent forwards, while the basal parts have more parallel sides. The face is dark and hairy, but there is an area of bare, flesh-colored skin around the eyes. Thumbs are short (4–5 mm) and delicate, with small claws (1–1.5 mm). The feet are almost bare and very small, with small claws and are less than half the tibia length. The dark wing and tail membranes are sparsely haired below and close to the body, with short, whitish hairs extending along the uropatagium near the tibia. Wing membranes are attached to the outer toe. The calcar has a clearly keeled lobe, and extends along half of the rear edge of uropatagium. The penis is short and slightly clubshaped.

Skull morphology. One immediate peculiarity of the skull profile of S. latirostris is the raised occipital part of the braincase (Fig. 4a). The skull is delicate and smooth (with no visible crests), with a narrow and elongated rostrum, and thin zygomatic arches. Due to the elongated rostrum, the foramen lacrymale is relegated to the level of first molars, instead of premolars in Myotis . The toothrow shows a clear diastema between the second incisor and the canine, and premolars are not crowded and are all visible in lateral view. There are three upper and lower premolars and a well-pronounced paraconule to the first upper premolar. The upper canines are relatively large, clearly higher than last premolars; the lower ones weaker and are only slightly larger than third lower premolars. The nyctalodont first and second lower molars are unique to this Taiwanese species; the third lower molar is submyotodont, where the postcristid is bifurcated, one arm joining the hypoconulid, the other the entoconid ( Ziegler 2003). Such dental characteristics only exist in other extant and fossil Submyotodon species and in few other Asian species of Myotis (see taxonomic remarks).

Natural history. Although this forest species appears to be relatively common in Taiwan, it is mainly found in mountain areas above 1000m, up to at least 2200 m. It occurs in lower areas as well, but apparently only during the winter period and is active throughout the year. Based on our observations, lactating females were recorded from April to June, and male with enlarged testis from August to March.