Genus Diaphus Eigenmann & Eigenmann, 1890

The otoliths of Diaphus holti Tåning, 1918 are characterised by a large dorsal area with somewhat pointed dorsal rim at mid-point, which makes their overall shape higher than other Diaphus otoliths (see Schwarzhans 2013a: pl. 3, figs 4, 5 for figured Recent specimens). Although somewhat more compact in the posterior part, several of our juvenile Diaphus otoliths (e.g., Fig. 5A) are recognised as D. holti Tåning, 1918, based on the feature mentioned above. Furthermore, they are very similar to the one figured by Brzobohatý & Nolf (2000: pl. 3, fig. 9).

The otoliths of Diaphus aff. rafinesquii (Cocco, 1838) show reasonable similarities with those of Recent (see Schwarzhans 2013a: pl. 3, figs 7–10) and Plio-Pleistocene specimens (Brzobohatý & Nolf 2000: pl. 3, figs 11–13). Our material, however, is poorly preserved, and the dorsal rim of the figured otolith (Fig. 5H) is somewhat higher than that of the Recent ones. Moreover, the Recent specimens have a more gently curved dorsal rim than the Tortonian specimens.

Brzobohatý & Nolf (2000: 192) mentioned that some juvenile otoliths from the Mediterranean Tortonian deposits could possibly be attributed to Diaphus regani Tåning, 1932. This attribution was not convincing, because only juvenile specimens were available. The otoliths of D. regani are characterised by a widely expanded antero-dorsal area and a narrower postero-dorsal area, making their highest point along the dorsal rim before the mid-point (Nolf & Aguilera 1998: pl. 5, figs 1–6; Schwarzhans 2013a: pl. 10, figs 12–16). Our Tortonian specimens (Fig. 5 C–E) are not common at all the localities, but they include both small and large specimens with characteristic features that now allow the attribution to the Recent D. regani.

Schwarzhans & Aguilera (2013) synonymised Diaphus cahuzaci Steurbaut, 1979 (see Steurbaut 1979: pl. 4, figs 1–6) with Diaphus austriacus (Koken, 1891), disregarding the remarks of Nolf (1985, 2013) that the latter species (firstly described as Otolithus (Berycidarum) austriacus) is a doubtful species. The holotype of D. cahuzaci (refigured in Brzobohatý & Nolf 2000: pl. 5, fig. 6) is more rounded if compared to the more elongate similar-sized (ca 2 mm) lectotype of D. austriacus, which was established by Zilch (1965) (see Schwarzhans & Aguilera 2013: pl. 10, fig. 1). The growth series of D. cahuzaci provided by Brzobohatý & Nolf (2000: pl. 5, figs 1–6) clearly shows this consistent rounded outline feature and a stronger rostrum in the larger specimens that are different from the otoliths of D. austriacus figured by Schwarzhans & Aguilera (2013: pl. 10, figs 1–8, the size of the largest specimen, fig. 7 is comparable to the one figured by Brzobohatý & Nolf 2000: pl. 5, figs 4–5). Therefore, we interpret that D. cahuzaci is still a well-defined fossil species, and our Tortonian specimens (Fig. 5J) can be assigned to D. cahuzaci on the basis of the growth series illustrated by Brzobohatý & Nolf (2000: pl. 5, figs 1–6).

The otoliths of D. cahuzaci resemble those of another species, Diaphus taaningi Norman, 1930 (see Brzobohatý & Nolf 2000: pl. 2, figs 7–12 and pl. 5, figs 1–6, respectively); their small size further impedes an offhand distinction. Key features for distinguishing these species are the shape of the posterior and dorsal rims: these are both straight in D. taaningi but more curved in D. cahuzaci. On this basis, otoliths from Montaldo Torinese previously assigned to D. taaningi by Lin et al. (2015: fig. 2(12, 13)) are here attributed to D. cahuzaci. It is also worth mentioning that the stratigraphic range of D. taaningi and D. cahuzaci in Brzobohatý & Nolf (2000: fig. 2) has to be amended: D. taaningi is not represented in the Tortonian and the range of D. cahuzaci in the Serravallian is now shifted to the Tortonian since this record is based on material from the Tortonian deposits at Mondovi, Madonna della Neve, a locality that was incorrectly considered to be Serravallian at the time (see Locality data).