Rhinolophus Lacepede, 1799

Nishioka, Yuichiro, Nakagawa, Ryohei, Nunami, Shin & Hirasawa, Satoshi, 2016, Small Mammalian Remains from the Late Holocene Deposits on Ishigaki and Yonaguni Islands, Southwestern Japan, Zoological Studies 55 (5), pp. 1-21 : 11-13

Genus Rhinolophus Lacepede, 1799

Material examined: A skull with C, P 4, M 1, M 2, and M 3 (MPM-Fo 2858); a left maxilla with P 4 and M 1 (MPM-Fo 2859); a left P 4 (MPM-Fo 2867); a left M 1 (MPM-Fo 2868); four right M 1 (MPM-Fo 2869-2872); two left M 2 (MPM-Fo 2873-2874); two right M 2 (MPM-Fo 2875-2876); a right M 3 (MPM- Fo 2877); a left mandible with P 4, M 1, M 2, and M 3 (MPM-Fo 2879); a left mandible with P 4 (MPM-Fo 2878); a left mandible with M 1, M 2, and M 3 (MPM- Fo 2880); a left mandible with M 1 and M 2 (MPM- Fo 2881); a left mandible with M 2 (MPM-Fo 2882); a right mandible with C, P 2, P 3, P 4, M 1, M 2, and M 3 (MPM-Fo 2883); a right mandible with P 3, P 4, M 1, M 2, and M 3 (MPM-Fo 2884); a right mandible with P 4, M 1, M 2, and M 3 (MPM-Fo 2885); a left P 4 (MPM- Fo 2888); two right P 4 (MPM-Fo 2889-2890); six left M 1 or M 2 (MPM-Fo 2891-2896); a right M 1 or M 2 (MPM-Fo 2897).

Locality: Sabichi-do Cave, Ishigaki Island.

Measurements: See Tables 2 and 3.

Description: MPM-Fo 2858 is an anterior part of skull, and preserves the nasal bone, orbitals, frontal bone, and maxilla with teeth ( Fig. 9). The skull is slender: the brain-case is antero-posteriorly long. The nasal bone at the nose-leaf region projects strongly upward, like a rhino-horn. The interval between left and right canines is broad. The frontal bone is narrow laterally and becomes depressed deeply (frontal depression) due to large and converging orbitals. The brain-case has a sharp sagittal crest, extending from the frontal depression to the posterior end. The zygomatic arches are thick dorso-ventrally, and curve as an S-letter in the lateral view. The infraorbital foramen is large, whereas a bridge over this foramen is very slender. The choana is broad laterally. The anterior end of the choana is situated as far as the metacone of M 2. There is a small notch at the center of the palatine. The premaxilla and incisors are broken.

The maxilla has a canine, two premolars (a small alveolus and a large tooth), and three molars in each side. The premolar alveolus behind the canine is small but distinct. The other premolar (P 4) forms a quadrate occlusal outline. The paracone of P 4 is sharp, and has a crista extending to the lingual side. The upper molars are similar basically with those of Hipposideros turpis described in this study in terms of occlusal patterns. M 1 has a trapezoidal occlusal outline with a cingulum on the postero-lingual side, while M 2 has a triangular one because the postero-lingual cingulum is very weak. The posterior of M 3 is reduced but somewhat prominent relative to that of H. turpis . M 3 almost lacks the postero-lingual cingulum.

The mandibles, MPM-Fo 2880, 2883, and 2884, are well preserved ( Fig. 10 A-C). The mandibular body is slender and straight. The mental protuberance, with a straight symphysis, is prominently developed below the canine. The mental foramen is situated directly below P 2. The ramus is dorso-ventrally low: the coronoid process reaches as high as the protoconid of M 1. The tip of the coronoid process is rounded, approaching to M 3. The angular process is robust and short.

The lower canine is very sharp and straight, and has a triangular occlusal outline. The crown is surrounded by the basal cingulum on the anterior and lateral surfaces. There are six postcanine teeth (three premolars and three molars). P 2 is unicuspidated, low-crowned, and with the basal cingulum. The occlusal outline shows an equilateral triangle shape. Very small P 3 is present on the buccal side. P 4 is pointed as a canine. The protoconid extends two sharp cristids to the posterior. The basal cingulum of P 4 bends as a V-letter line in the buccal view. The anterior point of P 4 is adjacent to the posterior of P 2. Each P 2 and P 3 has a single root, and P 4 has two roots.

The occlusal structures of lower molars are similar to those of Hipposideros turpis represented by a W-shaped occlusal pattern. M 1 or M 2 has the trigonid bucco-lingually narrower than the talonid. M 3 trigonid and talonid are almost the same in width. The basal cingulums are strong, except on the lingual side. M 1 is almost as large as M 2, but the protoconid of the former is slightly higher than that of the latter. M 3 is smaller than M 1 or M 2, but relatively less reduced than M 3 of H. turpis . Each molar has two roots.

Remarks: Rhinolophus , belonging to Rhinolophidae , is characterized by horseshoeshaped nose (or nose-leaf), and this feature reflects to their nasal bones: Rhinolophus has a horn-like ridge on the nasal bone, as the skull (MPM-Fo 2858) referred in this study. The dental formula of Rhinolophus (1.1.2.3/2.1.3.3) is unique in having P 3. The mandible of Rhinolophus is relatively slender and flat, with small processes on the ramus. These features distinguish Rhinolophus from the other genera of microchiropterans ( Abe 2000).

There are three species of Rhinolophus ( R. cornutus , R. pumilus , and R. perditus ) in the Ryukyu area (or the south of Tokara Gap), and only R. perditus is distributed on Ishigaki Island at the present time. Morphological difference among these species have been discussed in previous studies (e.g., Yoshiyuki 1989; Abe 2000; Hirasawa et al. 2006), but their dental features are similar to one another. Rhinolophus perditus is usually larger than the other species in the maximum length of the skull, and has a relatively large upper premolar (P 3) behind the canine. The tooth row (from upper canine to M 3) of R. perditus is also larger than that of R. cornutus or R. pumilus ( Yoshiyuki 1989) . Based on these differences, all remains of Rhinolophus from Sabichi-do Cave are similar to R. perditus rather than R. cornutus and R. pumilus .

A possible extinct species of Rhinolophus was reported from Miyako Island. This species was originally described as R. cornutus miyakonis ( Kuroda 1924) , and later classified into a subspecies of R. pumilus ( Yoshiyuki 1989) or an independent species on Miyako Island ( Maeda 2001). Hirasawa et al. (2006) preliminarily discussed, based on paleontological analysis, that lower teeth of the Rhinolophus species on Miyako Island could not be distinguished from those of the other species. However, the dental morphology of the fossil specimens from Sabichi-do Cave fit exactly to that of living R. perditus , comparing with the recent remains collected from Ishigaki Island.

Distribution: Ishigaki, Iriomote, Kohama, and Taketomi Islands ( Sano and Armstrong 2009).