Deltentosteus aff. telleri ( Schubert, 1906)

Schwarzhans, Werner, Klots, Oleksandr, Ryabokon, Tamara & Kovalchuk, Oleksandr, 2022, A rare window into a back-reef fish community from the middle Miocene (late Badenian) Medobory Hills barrier reef in western Ukraine, reconstructed mostly by means of otoliths, Swiss Journal of Palaeontology (18) 141 (1), pp. 1-35 : 17

Deltentosteus aff. telleri ( Schubert, 1906)

Figure 7a–e

2020a Deltentosteus aff. telleri ( Schubert, 1906) —Schwarzhans, Brzobohatý & Radwańska: pl. 8, figs. 17–21 (and references therein).

Material 8 otoliths: 3 specimens, Kozatskyi Yar, NMNHU-P PI 2552 ; 2 specimens, Mlyntsi, NMB P1209 ; 3 specimens, Shydlivshchyna, NMNHU-P PI 2553 .

Discussion Deltentosteus telleri was a widely distributed and common species in the middle Miocene of the Tethys and Paratethys and the late Miocene of the Tethys. Te otoliths are easily recognizable by their smooth, convex inner face with a shallow sulcus, which has a much widened ostial region and ostial lobe, and narrowed caudal tip. Te otolith outline does not usually show preventral or postdorsal projections.

Otoliths of D. telleri show a certain degree of variability and considerable allometric ontogenetic growth. Morphological variations of large specimens have been observed by Radwańska (1992) and Schwarzhans et. al. (2020a), particularly in the locality Niskowa in Poland; these variations have been tentatively attributed to alterations that may have resulted “from temporary fluctuations in salinity of the coastal waters” that may occur in a marginal marine environment with varying freshwater influx ( Radwańska, 1992). Among the observed alterations in the otoliths from Niskowa were the reduction of the colliculum from the tapering cauda, reduction of the ostial lobe, and differences in otolith shape and thickness. Te largest specimen now available from the Medobory back-reef environment ( Fig. 7a ) shares most of the characteristics observed in the specimens from Niskowa but stems from a completely different environments (reef-associated vs. marginal marine with freshwater influx). Terefore, it now seems possible that these morphotypes actually represent a different species. However, a wider review of otoliths attributed to D. telleri is necessary before a conclusive assessment can be made.

Te otoliths of Deltentosteus aff. telleri described here from the Medobory back reef are also remarkable in that they represent a rather complete ontogenetic sequence, which has thus far rarely been observed in the species, where the fossil record is dominated by adult specimens. Te ontogenetic sequence shows a distinct allometry, with small specimens being much more compressed than large ones. Te ratio OL:OH ranges from 1.02 to 1.07 in specimens of 1.0– 1.4 mm in length ( Fig. 7c–e ); the ratio is about 1.15 in a specimen of 1.8 mm in length ( Fig. 7b ) and about 1.25 in a specimen of 2.1 mm in length ( Fig. 7a ). Likewise, the crenulation of the dorsal rim, albeit weak, is only evident in specimens of about 1.2 to 1.8 mm in length ( Fig. 7b, c ). Te characteristic reduction of the colliculum in the cauda, however, is a stable trait in all sizes observed and could possibly represent a diagnostically valuable feature.

Figures

Fig. 7 Otoliths of Gobionellidae: a–e Deltentosteus aff. telleri (Schubert, 1906), 7a Shydlivshchyna, NMNHU-P PI 2553, b (reversed),d Kozatskyi Yar, NMNHU-P PI 2552,c (reversed), e Mlyntsi, NMB P1209.f, g Economidichthys triangularis (Weiler, 1943), f (reversed) Shydlivshchyna, NMB P1210, g (reversed) Mlyntsi, NMNHU-P PI 2554.h, i Knipowitschia polonica Schwarzhans et al., 2020a, 2020b, h Shydlivshchyna, NMNHU-P PI 2562, i Kozatskyi Yar,NMB P1213. j, k Pomatoschistus elegans (Procházka, 1900), j (reversed) Kozatskyi Yar, NMNHU-P PI 2576, k (reversed) Shydlivshchyna, NMB P1222