Podoliacanthus sp. 3

Voichyshyn, Victor & Szaniawski, Hubert, 2012, Acanthodian jaw bones from Lower Devonian marine deposits of Podolia, Ukraine, Acta Palaeontologica Polonica 57 (4), pp. 879-896 : 891-894

Podoliacanthus sp. 3

Figs. 7D, 8C.

Material.—ZPAL P.14/12.12, jaw bone fragment lacking the anterior half, 1.8 mm long; right bank of Dniester River

http://dx.doi.org/10.4202/app.2011.0079

(locality Zalishchyky−2; Fig. 2C), opposite to Zalishchyky , in fact, Horodenka Rayon , Ivano−Frankivs’k Oblast’ (Podolia), Ukraine; upper part of Ivanie Horizon of the Tyver Series, about 6 m below the boundary with the Dniester Series, Lower Devonian .

Description.—The specimen is a jaw bone that lost the anterior half (or more), with five teeth in the lateral tooth row. The first tooth is broken, the second has no traces of the medial side denticle, and the third has at least one such denticle, similar to those in the type species ( Fig. 7D 2, D 3). The remaining two teeth have three medial side denticles, two of them closely placed one above another, and the third situated some distance anterior to them ( Fig. 8C). Perhaps, the first two denticles could be described as multiple growth of the medial side denticle. There are about six inter−tooth denticles between the two largest teeth, but the denticles are insufficiently preserved ( Fig. 8C). The inter−tooth pits are quite deep and clearly defined. Pores of vascular canals concentrate along the pit perimeter but probably are lacking on the rest of the pit surface ( Fig. 8C). The lingual tooth row resembles that in Podoliacanthus zychi sp. nov. The denticle groups are arranged diagonally and sometimes extend onto the lingual slope of the jaw bone ( Fig. 8C). The posterior end of the jaw bone has a clearly expressed small postero−medial process, very large postero−lateral one, and a wide concavity in the posterior−most profile of the bone ( Fig. 7D). Posterior projection is practically invisible. Total jaw bone length of the species is estimated at 3–4 mm.

Remarks.—In comparison with the other Podoliacanthus forms, P. sp. 3 has a smaller jaw bone possessing both the posterior processes (with smallest postero−medial one and a well developed postero−lateral one) and three denticles attached to the medial side of the tooth. The paucity of pores of the vascular canal system along the medial and lateral sides of the jaw, and well defined inter−tooth pits with surrounding pores distinguishes P. sp. 3 from P. sp. 2. As before, we leave this form in open nomenclature as only one jaw bone fragment is known.

Ischnacanthiformes fam., gen. et sp. indet. 1

Fig. 8D.

Material.— ZPAL P.14/10.7, a jaw bone fragment, 1.4 mm long, with two teeth of the lateral tooth row preserved (one tooth with broken tip and one tooth almost completely destroyed); left bank of the Dniester River , opposite to Doroshivtsi , Zastavna Rayon , Chernivtsi Oblast’ (Podolia), Ukraine ( Fig. 2C); upper part of the Chortkiv Horizon of the Tyver Series , about 240 m below the lower boundary of the Dniester Series (Middle Lochkovian), Lower Devonian ( Fig. 1: point 2) .

Description.—The teeth are conical in shape, hollow, and have posterior and anterior flanges which seem wider than in

http://dx.doi.org/10.4202/app.2011.0079

Podoliacanthus gen. nov. The tooth with broken tip is 0.5 mm high, and has a smooth surface. A small salient (not developed into a denticle or ridge) is situated on the medial side of the tooth ( Fig. 8D). The lingual ridge, which is quite distinct from the teeth of the lateral row, is devoid of any denticles. Inter−tooth denticles are damaged. Inter−tooth pits are deep and clearly defined. Large pores of vascular canals are situated at the anterior border of the inter−tooth pits, while elsewhere around the pit the pores are small ( Fig. 8D 2). On the pit surface the pores are also small and very rare.

Remarks.—The specimen is the oldest known ischnacanthiform dentigerous jaw bone from Podolia. Because of its incompleteness, diagnostic features cannot be recognized. Additional specimens are needed to be sure whether the described medial salient of the tooth and lack of the lingual tooth row are its real characteristic features and not an artefact or atypical growth.