Rhinolophidae, Gray, 1825

Harrison, David L. & Hooker, Jeremy J., 2010, Late Middle Eocene bats from the Creechbarrow Limestone Formation, Dorset, southern England with description of a new species of Archaeonycteris (Chiroptera: Archaeonycteridae), Acta Chiropterologica 12 (1), pp. 1-18 : 10-11

Rhinolophidae gen. et sp. indet.

v. 1986. Microchiroptera gen. et sp. indet. 2 Hooker: 244–245, fig. 17a–d.

Material

HZM 1.31222 left M 1/2: CL 1.95 ; TRI W 1.09; TRI L 1.15; TAL W 1.15 (e) ; TAL L 0.77 ( Figs . 4G–J, 7F–H). HZM 2.38159 trigonid fragment of right lower molar TRI W 1.47 ; TRI L 1.15 ; PH 1.63 ( Fig. 8 D–F). BMNH M35711 trigonid fragment left lower molar TRI W 1.17 ( Fig. 8 A–C) .

Description

The left M 1/2 (HZM 1.31222) clearly belongs to a different taxon from the specimens here referred to Pseudorhinolophus schlosseri . It has a more elongated and narrower outline, with the cusps and crests more gracile. The paraconid is directed more mesially, thus lacking the subrectangular outline of P. schlosseri M 1/2. It is a well preserved tooth, intact except for slight erosion of the basal crown edge especially below the entoconid. The trigonid is longer than the talonid, measured by the method of Sigé (1968).

The cusp tips are lightly worn; the cusps of the trigonid are prominent, the protoconid dominant, the metaconid just higher than the upturned paraconid. The cristids are sharply angulated at the protoconid. Beneath the more widely open trigonid basin there is a distinct short lingual cingulum, which is absent in the specimen of P. schlosseri . The distal wall of the trigonid is vertical and high. The talonid is judged wider than the trigonid despite basal erosion. The hypoconulid is prominent, its cusp directed upwards and it is situated slightly buccally to the entoconid, but closer to this cusp than the hypoconid. The preentocristid declines steeply to form a rounded talonid notch extending below the level of the cristid obliqua, contrasting strongly with Stehlinia in this respect. It is lingually concave, thus conforming with Vaylatsia prisca ( Revilliod, 1920) . The unworn cristid obliqua is attached more buccally to the posterior trigonid wall than in P. schlosseri and close to the midline. The buccal cingulum was continuous from its origin just distal to the base of the paraconid to the base of the hypoconulid, but is partly eroded. It is attached closer to the tip of the paraconid than in Stehlinia . It is compatible in size with the M 2 of P. schlosseri described above, but the two teeth do not occlude well with each other, supporting the conclusion that this M 1/2 belongs to a different taxon.

HZM 2.38159 and M35711 are isolated trigonids similar in size and morphology to HZM 1.31222 described above. Their mesial cingulum extends across the trigonid notch. These trigonids are slightly less open than in the intact specimen, perhaps indicating that they are M 2 ’s and the intact specimen is an M 1.

Discussion

In the absence of complete mandibular and maxillary dentitions considerable difficulty is bound to be encountered in identification of isolated rhinolophoid teeth. The marked morphological similarity of the two specimens here referred to P. schlosseri to the lectotype and other published material has enabled a confident identification of this species. However, this second M 1/2 (HZM 1.31222) is a much more complicated and difficult problem. The genus Palaeophyllophora Revilliod, 1917 can be excluded because the talonid of M 1 –M 2 is much reduced in this genus relative to the trigonid ( Sigé, 1978: 255, plate 1, fig. 4). The hypoconulid is stronger and less closely situated to the entoconid, more nearly median in position. Genus Pseudorhinolophus Schlosser, 1887 has been consider- ed a subgenus of Hipposideros Gray, 1821 by some authors (e.g., Sigé, 1978: 251; 1988: 89). The taxonomic history of P. schlosseri has been reviewed by Sigé (1978). This species is represented by abundant material from the Late Eocene of Ste-Néboule, including 60 specimens of M 1 –M 2 and from the late Middle Eocene of Le Bretou (10 M 1 –M 2) listed by Sigé (1988).

Morphological differences from HZM 3.38170 have been noted above, which suggest that HZM 1.31222 from Creechbarrow may belong to a different genus from Pseudorhinolophus . Le Bretou has also yielded an unidentified rhinolophoid taxon, Rhinolophoidea sp. indet. of Sigé (1988: 93). This form also has morphological features suggestive of Rhinolophus . It is clear however, that the Creechbarrow tooth cannot belong to the same taxon, as that from Le Bretou, since the Le Bretou material of M 1 –M 2 is smaller CL 1.39–1.67 (m = 1.57); CW 1.02–1.39 (m = 1.20). It is also clear from Sigé’s (1988: 94, fig. 32) description that the M 1/2 of Le Bretou is less narrow in relation to its length and does not have the pre-entocristid so steeply declining. The possibility therefore exists that the Creechbarrow Rhinolophidae indet. could be referable to genus Rhinolophus Lacépède, 1799 or Vaylatsia Sigé, 1995 . The latter genus is represented in the Eocene by V. prisca ( Revilliod, 1920) , which is similar in size to P. schlosseri ( Sigé, 1978: 261) and morphologically rather similar. Unfortunately the exact provenance of much of the material of the two species attributed to Rhinolophus by Revilliod (1920), and hence their age is unknown. Hooker and Weidmann (2000: fig. 38a–c) have selected and illustrated the lectotype of Rhinolophus priscus , a left dentary with P 4 –M 3, slightly distorted and alveoli of C 1, P 2 –P 3 (NMB Mt992) from Entreroches. It is the only specimen from Revilliod’s (1920) syntypes with a precise locality.

Comparison of HZM 1.31222 with a cast of the lectotype reveals considerable similarities. However, the molars of the lectotype are not in good condition making identification problematic. Rhinolophus pumilio Revilliod, 1920 is a smaller species, similar in size to Pseudorhinolophus morloti , of uncertain stratigraphic origin in Le Quercy. Sigé (1995) considered the genus Vaylatsia to belong to the Hipposideridae . Dentally the genus resembles Rhinolophus but with distal humeri like hipposiderids. Hooker and Weidmann (2000: 60) have, however, pointed out that the hipposiderid humeral structure is primitive for the Rhinolophoidea and that Vaylatsia may therefore be better placed in the Rhinolophidae . HZM 1.31222 certainly exhibits some distinct similarities to Recent Rhinolophus as exemplified by R. rouxii (HZM 72.36548 from Tirunelveli, Tamil Nadu, India). This species also has gracile cusps and crests, a rather mesially directed paraconid, a small cingular ledge below the trigonid basin opening and a steeply sloping preentocristid. Comparison of a variety of Recent species of Rhinolophus and Hipposideros suggests that the dental differences of HZM 1.31222 listed above are distributed in both genera in a random manner partly related to size. It is, however, clear that a relatively narrow M 1/ 2 in relation to its length, especially with gracile crests and cusps as in this specimen is much more likely to be rhinolophid than a hipposiderid. Unequivocal identification as rhinolophid would require the finding of a jaw with the alveolus of a small vestigial, labially situated P 3 ( Sigé, 1988: 93). This vestigial tooth is, however, not always present in Rhinolophus .

Figures

FIG. 8. Trigonids of lower molars, Creechbarrow bats. Rhinolophidae gen. et sp. indet. M35711. Trigonid left lower molar in A — occlusal, B — buccal and C — lingual views. HZM 2.38159. Trigonid right lower molar in D — occlusal, E — buccal and F — lingual views. Microchiroptera gen. et sp. indet. HZM 22.34774. Trigonid right lower molar in G — occlusal, H — buccal