Kasperacanthus serratus, Voichyshyn & Szaniawski, 2018

Voichyshyn, Victor & Szaniawski, Hubert, 2018, New ischnacanthiform jaw bones from the Lower Devonian of Podolia, Ukraine, Acta Palaeontologica Polonica 63 (2), pp. 327-339 : 332-335

Kasperacanthus serratus sp. nov.

Figs. 5, 6. Etymology: After the serrated profile of lateral tooth rows and interteeth denticles of the jaw bone.

Holotype: SMNH BP.1595/14, a jaw bone fragment, 1.2 mm long, with three teeth of the lateral tooth row.

Type locality: Left bank of the Seret River near Kasperivtsi, downstream a dam, Zalishchyky (Ternopil) region, Podolia, Ukraine; sample 3/ 11г (Daniel Drygant collection); Fig. 1C : point 3.

Type horizon: Middle part of the Chortkiv Horizon, Tyver Series, Low- er Devonian.

Material.— Aside from the holotype, three other jaw bone fragments: SMNH BP.1601/14, 1.07 mm long, with one preserved tooth of the lateral tooth row and three teeth remnants, ZPAL P.14/5.5, 2.42 mm long with two teeth, and ZPAL P.14/7.6, 2.81 mm long, with one tooth of the lateral tooth row. The last two specimens have been found in the same rock sample taken from the left bank of the Dniester River , on the East of Ivanie Zolote. Its stratigraphic level corresponds to upper part of the Ivanie Horizon of the Tyver

Series , 34 m below the boundary with the Dniester Series , Zalishchyky (Ternopil) region, Podolia, Ukraine ( Fig. 2C ). The SMNH BP.1601/14 was found in the same residuum as the holotype . It is a part of another jaw bone but possibly belongs to the same fish individual as the holotype.

Diagnosis.—Same as for the genus.

Description.—Teeth of the lateral tooth row are conical in shape and smooth. Their parabasal section is from halfmoon to almost circular (Figs. 5A 1, B 1, 6A 1, B 1). No additional dentition on the teeth is found. The teeth are hollow (Figs. 5B 5, 6A 3) and the holotype does not show any ridges on the teeth of the lateral tooth row. However, the teeth of the other specimens, including SMNH BP.1601/14 from the same rock sample as the holotype, have a narrow posterior ridge and traces of an anterior one (Figs. 5B 2, B 3, 6A 2, B 2). The teeth are slightly inclined backwards and inwardly relative to the jaw bone axis (Figs. 5A 1, A 2, B 1, B 2, 6A 1, B 1). They are relatively high; their width/height ratio is 0.5–0.7. In the ZPAL P.14/5.5 rare pores of vascular canals can be observed within the lower third of the medial surface ( Fig. 6A 4 ) but there are no such pores in the other specimens (Figs. 5A 2, A 3, B 2, B 3, 6B 2). As in previously described species, there is a crown-base border on the medial side of the tooth ( Fig. 6A 3 , B 4 ).

There is no continuous inter-tooth wall between the teeth. Instead one can see the gaps which emphasize the complex tooth within the lateral tooth row (Fig. 5A 1, B 1, B 3, B 5). The complex tooth consists of the tooth proper and two denticulated flanges, long posterior and short anterior (Fig. 5A 1, A 2, B 2, B 5). There are 5–9 denticles in the posterior complex

Fig. 5. Ischnacanthiform fish Kasperacanthus serratus gen. et sp. nov., → Seret River near Kasperivtsi , downstream a dam, Zalishchyky (Ternopil) region, Podolia , Ukraine; Middle part of the Chortkiv Horizon , Tyver Series, Lower Devonian; the holotype, SMNH BP.1595/14 (A) and paratype, SMNH BP.1601/14 (B). Jaw bone fragments in occlusal (A 1, B 1, B 5), anterolingual (A 2), lingual (A 3, B 3), lateral (A 4), posterolingual (B 2), and bottom (B 4) views. Arrows indicate rostral direction .

tooth flange (Figs. 5A 3, B 1, B 5, 6A 2) and 1–2 denticle(s) in the anterior flange (Figs. 5A 1, A 3, 6A 1). The denticles are relatively large and, in the posterior flange, increase in size in anterior direction (Figs. 5A 3, 6A 1, B 1, B 2). The biggest have their own posterior and anterior ridges and an even posterior flange ( Fig. 6B 4 ). Tips of the denticles seem to be slightly inclined backwards, in the same manner as the teeth ( Fig. 6B 3 ). Inter-tooth pits are clearly outlined along the lateral tooth row only (Fig. 5A 1, A 2, B 1, B 2).

The lingual ridge is weakly expressed (Fig. 5A 1, A 2, B 1, B 2). The denticle groups can be observed on the lingual ridge of SMNH BP.1601/14 (Fig. 5B 1 –B 4) but do not occur in the holotype (Fig. 5A 1 –A 3). Vascular canal pores are situated mainly along the inter-tooth pit perimeter in the specimens from Kasperivtsi. The biggest of them is situated on the posterior part of the base of the teeth (Fig. 5A 3, B 2). Numerous, though mainly smaller vascular canal pores are scattered over the inter-tooth pit area in the other specimens ( Fig. 6A 4 , B 1 ). The labial side of the jaw bone also possesses vascular canal pores (Fig. 5A 4).

The way of growth of the lateral tooth row has engaged our attention. One can see teeth remnants at the posterior (older) part of the SMNH BP.1601/14 (Fig. 5B 1, B 3, B 5). The distance between them at the beginning of the jaw bone growth enlarged significantly but then the growth slowed down. Setting the distance between first two smallest tooth remnants at 1, the next tooth-to-tooth distance ratios are 2.3, 1.9, and 1.2 (the last value is taken from the holotype). The first inter-tooth interval has no denticles. In essence it might be equated to the lateral tooth row gap (Fig. 5B 5). The second shows a relatively large gap and the first three inter-tooth denticles which represent the posterior flange of the first complex tooth (Fig. 5B 3, B 5). At the same time, ZPAL P.14/7.6, which evidently possesses the species’ largest jaw bone has no lateral tooth row gap visible ( Figs. 6B 2 , B 3 ). Possibly, this reflects a change of prey and/or a hunting manner associated with fish size increase.

Remarks.—The described species material resembles the jaw bone of Gomphonchus ( Gross 1971: fig. 9H). Nonetheless, judging by the figure in Gross’ publication, Gomphonchus has very high teeth (the width/height tooth ratio is about 0.36) without teeth ridges.

Stratigraphic and geographic range.—Kasperivtsi and Ivanie Zolote vicinities; upper third of the Chortkiv Horizon to upper part of the Ivanie Horizon of the Tyver Series (late Lochkovian to early Pragian?).

Figures

Fig. 1. A. Location of the study area in Ukraine with position of Podolia. B. Map of the studied region. C. Lower Devonian exposures (modified from Voichyshyn and Szaniawski 2012) with points of sampled sections (triangles 1–4).

Fig. 2. Simplified stratigraphy of the marine Lower Devonian beds in Podolia showing distribution of Ischnacanthiformes jaw bones (modified from Drygant and Szaniawski 2012; Voichyshyn and Szaniawski 2012).

Fig. 6. Ischnacanthiform fish Kasperacanthus serratus gen. et sp. nov., Dniester River, on the East of Ivanie Zolote; upper part of the Ivanie Horizon of the Tyver Series, Lower Devonian; the paratypes ZPAL P.14/5.5 (A) and ZPAL P.14/7.6 (B). Jaw bone fragments in occlusal (A1, B1), lingual (A2, B2, B4), bottom-lingual (A3), top-lingual (A4), and posterolingual (B3) views. Arrows indicate rostral direction.

Fig. 4. Ischnacanthiform fish Drygantacanthus semirotunda gen. et sp. nov., Dniester River, north-west Zalishchyky outskirts, Podolia, Ukraine, Upper Lochkovian, Ivanie Horizon; the paratypes, SMNH BP.1587/3 (A) and SMNH BP.1590/11 (B). Jaw bone fragments in occlusal (A1, B1), lingual (A2, B2), anterior (A3), lateral (A4), and posterior (B3) views. Arrows indicate rostral direction.

Fig. 3. Ischnacanthiform fish Drygantacanthus semirotunda gen. et sp. nov., the holotype, SMNH BP.1581/5, Dniester River opposite Zalishchyky, Zastavna (Chernivtsi) region, Podolia, Ukraine; Upper part of Ivanie Horizon of the Tyver Series, Lower Devonian. Jaw bone fragment in occlusal (A), postero-occlusal (B), lingual (C), lateral (D), and antero-occlusal (E) views. Arrows indicate rostral direction.