Neogobius bettinae, Bratishko, Schwarzhans & Kovalchuk, 2017

Bratishko, Andriy, Kovalchuk, Oleksandr & Schwarzhans, Werner, 2017, Bessarabian (Tortonian, Late Miocene) fish otoliths from a transitional freshwater-brackish environment of Mykhailivka, Southern Ukraine, Palaeontologia Electronica 17 (9), pp. 1-13 : 7-9

Neogobius bettinae n. sp.

Figure 4.1 -9

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Etymology. In honour of Bettina Reichenbacher (Munich, Germany) for her great contribution to the knowledge of fossil fish faunas, particularly freshwater fishes and gobioids.

Type material. Holotype: NMNHU-P 33 /1496 ( Figure 4.5 -6) . Paratypes: seven specimens NMNHUP 33/1497-1503 ( Figures 4.1-4, 4.7 -9), Mykhailivka 1.

Type locality. Mykhailivka village , Mykolaiv region, Southern Ukraine .

Diagnosis. Compact otoliths with low anterodorsal rim and posteriorly elevated, rounded dorsal rim. Posterodorsal projection short, wide and rounded. Anteroventral projection weak or lacking. Sulcus with characteristic tip positioned just anterior to the junction of ostium and cauda. Otoliths rather thick (OH:OT = 2.0-2.2).

Description. The thick massive otoliths range from 1.5 to 4.5 mm in length. OL:OH = 1.16-1.23; 1.07 (in juveniles). The anterior rim is short with a weak or absent anteroventral projection. The posterior rim is vertical and can be incised beneath the posterodorsal projection. The dorsal rim is highly elevated posteriorly, curved and slightly undulating; the anterodorsal angle is very low. These otoliths have a broad, rounded posterodorsal projection, which gently bends outwards. The ventral rim is smooth and straight with a rounded posterodorsal angle. The inner face is gently convex. The deep sulcus is inclined and sole-shaped. The tips of the sulcus are rounded. The ostium is wider than the cauda and displays a distinct and often pointed lobe at the dorsal rim. Some specimens ( Figures 4.1, 4.3, 4.5 ) have a faint and narrow subcaudal iugum, but in most instances it is missing. The crista superior is more pronounced than the crista inferior. The ventral line is distinct. The dorsal depression is broad, distinct and rather deep in several specimens (e.g., Figures 4.5, 4.9 ). The outer face is slightly convex, with the greatest convexity at the long axis.

Comparison. Similar otoliths, showing the same characteristic tip of the ostial lobe, have been described from the middle Sarmatian of Azerbaijan as Gobius pricaspicus Pobedina, 1956 (see Pobedina et al., 1956, pl. 23, figure 4). Otoliths from the Mykhailivka locality are clearly different from those by having less crenulated rims, a depressed anterodorsal angle, and a distinctly longer sulcus. The faint or absent subcaudal iugum and the rather compressed shape with a low OL:OH index resembles Recent otoliths of the genus Neogobius . Otoliths of all extant species are figured here ( Figure 5 ) for comparison [ Neogobius caspius ( Eichwald, 1831) ( Figure 5.7 -9), N. fluviatilis ( Pallas, 1814) ( Figure 5.5 -6), N. melanostomus ( Pallas, 1814) ( Figure 5.1-2 ) and N. pallasi ( Berg, 1916) ( Figure 5.3-4 )]. In the Recent species, N. melanostomus exhibits a clear subcaudal iugum, whereas in the other species it is either totally lacking or occasionally faint and indistinct as in N. bettinae . Neogobius fluviatilis and N. pallasi most closely resemble N. bettinae . However, N. bettinae is distinguished from the Recent species as well as the two fossil ones so far known ( N. rhachis Rückert-Ülkümen, 1993 in Rückert-Ülkümen et al., 1993 and N. udovichenkoi Bratishko, Schwarzhans and Reichenbacher, 2015 [in Bratishko et al., 2015]) by the high postdorsal rim, the relatively short and broad postdorsal projection and the rather thick appearance (OH:OT = 2.0-2.2). Otoliths of extant Gobius species all show a distinct and broad subcaudal iugum except faint in Gobius cobitis and G. paganellus , which however have very slender otoliths. Neogobius bettinae differs from N. rhachis by the low anterodorsal angle and curved dorsal rim (vs. rather flat). Both species occur together in Mykhailivka, indicating an already advanced speciation of the genus in the Ponto-Caspian Basin, possibly including extinct lineages (see also Schwarzhans et al., 2017c).

Neogobius rhachis Rückert-Ülkümen, 1993 in

Rückert-Ülkümen et al., 1993

Figure 4.10 -19

1993 Neogobius rhachis n. sp.; Rückert-Ülkümen et al., pl. 5, figs. 4-9.

2009 Neogobius rhachis Rückert-Ülkümen, 1993 ;

Çevik Üner and Özkar Öngen, pl. 4, fig. 3.

Material. Eight otoliths ( NMNHU-P 33/1504-1511, Mykhailivka 1).

Description. These otoliths have a slightly tilted rectangular shape, and range in length from 2.0 to 3.5 mm. OL:OH = 1.1-1.26; OH:OT = 3.3-3.4. The anterior and posterior rims are oblique and almost parallel to each other. The posterior rim is steep and has a slightly rounded posteroventral edge. The dorsal rim is slightly curved; the wide, nearly triangular posterodorsal projection is somewhat bent outwards. The ventral rim is smooth and flat or slightly curved.

The inner face is only slightly bent, primarily along the postdorsal projection. The sulcus is moderately deep. It is sole-shaped and usually shows no subcaudal iugum or only a very narrow and small one. The ostial tip is rather angled, the caudal tip rounded. The ventral furrow is distinct. The dorsal depression is broad and shallow.

The outer face is slightly concave, particularly at the outwardly bent postdorsal projection, and has short radial furrows near the rims. The otoliths are thinner along the dorsal part and increase in thickness towards the ventral part. The postdorsal projection is supported by a ridge on the outer face.

Comparison. Neogobius rhachis differs from N. udovichenkoi Bratishko, Schwarzhans, and Reichenbacher, 2015 from the Konkian of Mangyshlak ( Kazakhstan) in having a more compressed outline expressed in the smaller index of OL:OH (1.10-1.26 vs 1.2-1.4) and shorter preventral and posterodorsal projections. The slightly oblique, parallel anterior and posterior rims represent a characteristic feature for N. rhachis as well as the ridge on the outer face supporting the postdorsal projection. Furthermore, N. rhachis is very similar to otoliths of the extant N. fluviatilis ( Pallas, 1814) ( Figure 5.5 -6), which is common in the rivers flowing to the Azov and Black Seas ( Froese and Pauly, 2016). Nevertheless, otoliths of the fossil species are thinner and have a more pronounced and bent posterodorsal projection.

Figures

FIGURE 4. Otoliths from the Sarmatian s.l. of the Mykhailivka 1. 1-9, Neogobius bettinae n. sp.: NMNHU-P 33/1497 (paratype), inner face (1); NMNHU-P 33/1498 (paratype), inner face (2); NMNHU-P 33/1499 (paratype), inner face (3), ventral view (4); NMNHU-P 33/1496 (holotype), inner face (5), ventral view (6); NMNHU-P 33/1500 (paratype), inner face (7), ventral view (8); NMNHU-P 33/1501 (paratype), inner face (9). 10-19, Neogobius rhachis Rückert-Ülkümen, 1993 in Rückert-Ülkümen et al., 1993: NMNHU-P 33/1504, inner face (10), ventral view (11); NMNHU-P 33/1505, inner face (12), ventral view (13); NMNHU-P 33/1506, inner face (14), ventral view (15); NMNHU-P 33/1507, inner face (16), ventral view (17); NMNHU-P 33/1508, inner face (18); NMNHU-P 33/1509, inner face (19). Scale bars equal 1 mm. 5- 8, 10, 11, 14, 15, 18 are mirrored.

FIGURE 5. Recent otoliths of the genus Neogobius. 1-2, Neogobius melanostomus (Pallas, 1814): ZMMU, P.23515 3, SL91, 43°38'N-51°08'E, inner face (1), dorsal view (2). 3-4, Neogobius pallasi (Berg, 1916): ZMMU, P.23514, SL93, 43°28'N-51°18'E., inner face (3), dorsal view (4). 5-6, Neogobius fluviatilis (Pallas, 1814): ZMMU, P.22433, SL81, 45°20'N-28°57'E, inner face (5), dorsal view (6). 7-9, Neogobius caspius (Eichwald, 1831): 7-8, ZMMU, P.22622 1, SL90, 51°25'N-46°03'E, inner face (7), dorsal view (8); 9, ZMMU, P.22622 2, SL105, 51°25'N-46°03'E, inner face.