Podoliacanthus sp. 2

Voichyshyn, Victor & Szaniawski, Hubert, 2012, Acanthodian jaw bones from Lower Devonian marine deposits of Podolia, Ukraine, Acta Palaeontologica Polonica 57 (4), pp. 879-896 : 890

Podoliacanthus sp. 2

Figs. 7C, 8A.

Material.— ZPAL P.14/7.3, jaw bone fragment 2.5 mm long lacking the anterior half; right bank of Dniester River (locality Zalishchyky−1; Fig. 2), opposite to Zalishchyky , in fact, Horodenka Rayon , Ivano−Frankivs’k Oblast’ (Podolia), Ukraine; upper part of Ivanie Horizon of the Tyver Series , about 5–15 m below the boundary with the Dniester Series, Lower Devonian .

Description.—The specimen is the posterior half of a jaw bone, with five teeth of the lateral tooth row. The jaw bone is rather deep. The teeth of the lateral tooth row are robust and more blunt than in P. zychi sp. nov., even taking into consideration that they are worn ( Figs. 7C 1, 8A). Their maximal width (diameter of the parabasal section) is almost equal to their height. The teeth are slightly inclined posteriorly and have posterior and anterior flanges. The inter−tooth denticles, probably about five in number, are poorly preserved. The first three teeth of the lateral row have one medial side denticle, but the subsequent ones have two horizontally arranged side denticles ( Figs. 7C 3, 8A). A small ridge rises up on the tooth medial side above each side denticle. The inter−tooth pits are shallow and have no vascular canal pores ( Figs. 7C 2, 8A). No lingual ridge is developed. The lateral and lingual tooth rows are closely arranged ( Figs. 7C 1, C 2, 8A). The lingual tooth row, beginning near the second tooth of the lateral row, forms a single line of relatively large denticle groups composed of three denticles with the largest central one ( Fig. 7C 2), typical for the genus. There are numerous pores of vascular canals on the surface of posterior part and medial side of the jaw bone ( Figs. 7C, 8A). On the lateral jaw bone side such pores probably are lacking ( Fig. 7C 4). The posterior jaw bone part has a large postero−lateral process and barely visible posterior projection, but lacks the postero−medial process ( Figs. 7C 1, 8C 3).

Remarks.—In contrast to Podoliacanthus zychi sp. nov. and P. sp. 1 this form has a robust (thicker in cross section) jaw bone with well developed postero−lateral process, but lacks a postero−medial one. It also differs from the type species by the presence of numerous vascular canal pores on the medial side of the jaw bone and lacks such pores in the inter−tooth pits. Moreover it differs in width/height tooth ratio (about 1.0 against 0.65 in P. zychi sp. nov. and 0.73 in P. sp. 1) and in having two denticles on the medial side of teeth in the main tooth row. The specimen could belong to a separate species, which can be established if additional material will be found.