Myctophum murbani (Weinfurter, 1952)

Schwarzhans, Werner, Ohe, Fumio, Tsuchiya, Yuki & Ujihara, Atsushi, 2022, Lanternfish otoliths (Myctophidae, Teleostei) from the Miocene of Japan, Zitteliana 96, pp. 103-134 : 103

Myctophum murbani (Weinfurter, 1952)

Fig. 5D-L

Scopelus tenuis murbani 1952 Scopelus tenuis murbani - Weinfurter: pl. 2, figs 1, 2.

Myctophum 1976 Myctophum sp. - Takahashi: pl. 17, fig. 4.

Hygophum murbani 1994 Hygophum murbani (Weinfurter, 1952) - Brzobohatý: pl. 2, figs 10-15.

Myctophum murbani 2013 Myctophum murbani (Weinfurter, 1952) - Schwarzhans and Aguilera: pl. 4, figs 5-8 (see there for further synonymies).

Material.

21 specimens: 20 specimens (figured specimens SMF PO 101.113), Miya River at Numa, Tsuyama City, Okayama Prefecture, Takakura FM, levels MS 07, MS 15, MS 27, MS 36, MS 52, MS 70, MS 80, d, gh and h, late Burdigalian, diatom zone 3A-3B ; 1 specimen, SMF PO 101.114, Okuna, Mizunami City, Gifu Prefecture, Oidawara FM, early Langhian, diatom zone 4A.

Description.

Delicate, moderately large otoliths reaching up to 3.2 mm length (Fig. 5H ). OL:OH = 1.15-1.25; OH:OT = 4.0-4.3. Ventral rim well rounded, deep, very regularly curved; dorsal rim much shallower, likewise regularly curved, sometimes with very mild obliquely cut postdorsal section. Rostrum and antirostrum short, of equal length, with very small excisura in between; posterior rim regularly curved. Rostral tip and posterior tip positioned at lower margin of sulcus and distinctly supramedian. All rims delicately crenulated, ventral rim usually more intensely than dorsal rim.

Inner face distinctly convex, smooth, with distinctly supramedian, long, narrow sulcus. OL:SuL = 1.2; OCL:CCL = 1.9-2.5. Dorsal margin of ostium slightly oscillating; cauda slightly bent upwards, with angular upper-posterior termination. Caudal colliculum narrower than ostial colliculum but of equal width when incorporating underlying pseudocolliculum. Dorsal depression shallow, indistinct; ventral furrow indistinct, far from ventral rim of otolith. Outer face flat to slightly convex, less than inner face, with short radial furrows near rims and smooth central portion.

Discussion.

Myctophum murbani belongs to a group of Myctophum species with oval otoliths that usually also show a strong marginal ornamentation. This group contains the extant species M. lychnobium Bolin, 1946, M. obtusirostre Tåning, 1928, M. orientale (Gilbert, 1913), and M. spinosum (Steindachner, 1867) (see Ohe 1985 and Schwarzhans and Aguilera 2013 for figures). Myctophum murbani is the only fossil representative of this group and differs from all of them in the more gently curving ventral rim (vs. pronounced mid-ventral angle or expansion) and the more regularly curved dorsal rim. In addition, the postdorsal termination of the cauda is less strongly bent upwards and at a less sharp angle than in the extant species. Myctophum murbani (Weinfurter, 1952) is a widely distributed tropical to subtropical species that occurred in the late Burdigalian to Langhian in the Caribbean, the Mediterranean, the Paratethys, and now also in Japan. Thus far, no coeval Myctophum otoliths are known from the southern hemisphere (i.e., New Zealand or Chile; see Schwarzhans 2019 and Schwarzhans and Nielsen 2021).

Figures

Figure 5. A-C: Diogenichthys aguilerai Schwarzhans, 2013, SMF PO 101.112, Tsuyama City, Takakura Formation, level MS 04.5; D-L: Myctophum murbani (Weinfurter, 1952); D-I, K-L; SMF PO 101.113, Tsuyama City, Takakura Formation, levels MS 15, MS 27, MS 52, h, J) SMF PO 101.114 Mizunami City, Oidawara Formation; M-O: Myctophum sp., col. Tsuchiya, Ichishi Group; P-Z: Protomyctophum ahunga Schwarzhans, 2019, SMF PO 101.115, Tsuyama City, Takakura Formation, levels MS 15, MS 22, MS 36, h.