Benthosema duanformis, Lin & Wu & Lin & Chien, 2023

Lin, Chien-Hsiang, Wu, Siao-Man, Lin, Chia-Yen & Chien, Chi-Wei, 2023, Early Pliocene otolith assemblages from the outer-shelf environment reveal the establishment of mesopelagic fish fauna over 3 million years ago in southwestern Taiwan, Swiss Journal of Palaeontology (23) 142 (1), pp. 1-40 : 9-13

Benthosema duanformis sp. nov. Lin

Figure 6h–k

?2019 Benthosema aff. fibulatum —van Hinsbergh & Helwerda: pl. 3, Fig. 32, 34 [ Philippines].

2019 Benthosema aff. fibulatum —van Hinsbergh & Helwerda: pl. 3, Fig. 33 [ Philippines].

Holotype ASIZF 0100613 ( Fig. 6h ), Site 5, mud layer, Tianliao (Kaohsiung), Taiwan. Early Pliocene.

Paratypes Tree specimens: two specimens ASIZF 0100614 , 0100616 ( Fig. 6i, k ) , Site 5, mud layer, Tianliao (Kaohsiung), Taiwan; one specimen ASIZF 0100615

( Fig. 6j ), Site 2, Chochen (Tainan), Taiwan. Early Pliocene.

Etymology From duan (Chinese) = short, referring to the compact outline of the otolith.

Diagnosis OL/OH = 1.11–1.16, OL/OT = 4.33–4.44, OsL/ CaL = 1.67–1.42. Rounded otoliths with vertical posterior rim and truncated posterior part of the otolith. Outline very compact. Two strong ventral denticles separated by a smooth gap.

Description Te otoliths are generally characterized by their large, regularly rounded shape, with a vertical posterior rim that results in a truncated appearance of the otoliths. Te dorsal rim is gently curved to flat, while the ventral rim is curved. Tere is a prominent antero-ventral denticle located just before the midline of the otolith, and a much stronger posterior denticle positioned at the postero-ventral corner. Tese two denticles are separated by a smooth gap, and there may be some minute denticles between the rostrum and the antero-ventral denticle

( Fig. 6h, j ). Te antirostrum is slightly smaller than the rostrum, and both are pointed. An angle is present at the postero-dorsal corner. Te sulcus is well-divided, very wide, and centrally positioned on the inner face of the otolith. Te ostium is slightly greater in height and longer than the cauda. Te dorsal and ventral areas of the otolith are similar in size.

Remarks Tis newly described species is characterized by having otoliths with the lowest aspect ratio (OL/ OH = 1.11–1.16) compared to other closely related species in the region ( B. fibulatum : 1.28–1.33; B. pterotum : 1.21–1.26; B. parafibulatum sp. nov.: 1.15–1.26, see below). However, it is likely that the species can only be reliably identified in adult individuals, as the otoliths of juveniles (typically OL <2 mm) may be indistinguishable from those of other closely related species. Te otoliths of B. duanformis are similarly compressed to those of Benthosema minutum Schwarzhans, 2019 from the Early Miocene of New Zealand ( Schwarzhans, 2019a), but B. minutum otoliths are typically small-sized, have nearly equally long ostium and cauda (vs OsL/CaL = 1.67–1.42) and are thicker.

Occurrence Taiwan: Lower Pliocene Gutingkeng Formation in Chochen (Tainan) and Tianliao (Kaohsiung), southwest Taiwan. Philippines: Upper Pliocene–Lower

Pleistocene Santa Cruz Formation in Cabarruyan, northwest Philippines.

Figures

Fig. 6 Fish otoliths from the Lower Pliocene Gutingkeng Formation, southern Taiwan. Scale bars=1 mm. Images are inner views unless otherwise indicated. a–g Benthosema parafibulatum sp. nov., ASIZF 0100606–612, a holotype, Site 5, mud layer, b–g paratypes, b, e–g Site 5, mud layer, c–d Site 5, sand layer. h–k Benthosema duanformis sp. nov., ASIZF 0100613–616,h holotype,Site 5, mud layer, i–k paratypes, i, k Site 5, mud layer, j Site 2. l–n Benthosema pterotum (Alcock, 1890), Site 5, mud layer, ASIZF 0100617–619. 1, ventral view; 2, inner view