Hucho sp.

Kovalchuk, О. М., 2015, The First Appearance Of Hucho (Salmonidae) In The Fossil Record Of Eastern Europe, Vestnik Zoologii 49 (5), pp. 413-420 : 415-416

Hucho sp.

D e s c r i p t i o n. The opercular bone ( fig. 2 , 3 , a, a 1 ) is high, dorsally narrowed and ventrally expanded. The maximum width at the straight ventral edge is about 1.2–1.3 of the bone height. Oval articular facet (fovea articularis) is slightly elongated. From its upper part the dorsal edge of the bone is curved dorsocaudally and breaks off vertically. There is a noticeable bulge in the articular part of the bone. The anterior opercular edge is almost vertical, extends slightly forward below the ventral edge of articular facet and forms a shallow ventral caudal incurvity. The ventral border of the opercular is somewhat convex and longer than the dorsal border, while the upper part of the posterior border is gently concave. Posterior ventral angle is straight, anterior ventral angle is about 80°. The outer surface of the bone is sculptured by weak radial grooves directing ventrocaudally from the articular facet area. There are numerous shallow furrows at the inner surface of the opercular bone diverging radially from the articular facet and reaching in a length of about 2–2.5 of its height. Measurements are presented in the table 1. Elongated jaw canine teeth ( fig. 3 , b, c) are conical, with slightly curved crowns, rounded thickened bases and sharpened tops. Height of the teeth is 7.0 and 5.0 mm, diameter of the crowns — 2.6 and 2.1 mm, respectively.

C o m p a r i s o n. Presented bones are the most similar in morphology with those in representatives of the genus Hucho Günther, 1866 . Hucho sp. from the late Miocene of Ukraine, in comparison to extant Hucho hucho and H. taimen , is characterized by smaller, slightly higher and narrower opercular bones. Specimens from Kubanka 2 and Cherevychnoe 3 have most as twice shorter articular process and significantly smaller diameter of the articular facet. Described opercular bones are comparable in size and completely similar to those in Hucho sp. from the late Oligocene — middle Miocene of Russia ( Sytchevskaya, 1989) except the presence of well-visible weak radial grooves at the inner surface. Although jaw teeth are similar to those of Hucho , I only tentatively identify them as belonging to this genus because of the significant resemblance of teeth in salmonid taxa and the lack of reliable diagnostic features for this kind of remains.

Figures

Fig.2. Left opercular bone of Hucho sp., NMNHU-P 41/3079, Tretya Krucha:a — medial view; b — lateral view. Scale bar 5 mm.

Fig. 3. Remains of Hucho sp. from the late Miocene localities of southern Ukraine:a, a 1 — fragment of left opercular bone, NMNHU-P 41/3746, Kubanka 2 (a— medial view; a1— lateral view).Scale bar 5 mm; b, c — isolated jaw teeth, NMNHU-P 45/5699–5700, Cherevychnoe 3. Scale bar 2 mm.

Fig. 1. Localities of the late Miocene huchen remains in Ukraine: 1 — Kubanka 2; 2 — Cherevychnoe 3; 3 — Tretya Krucha.