Podoliacanthidae, 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 : 335-336

Podoliacanthidae gen. et sp. indet.

Fig. 7 .

Material.—The illustrated specimen only, ZPAL P.14/12.10, a fragment of jaw bone, 3.25 mm long, with 2 broken teeth of the lateral tooth row. The specimen was found on the left bank of the Dniester River, on the east outskirts of Ivanie Zolote ( Fig. 1C : point 4) in the deposits belonging to the upper part of the Ivanie Horizon of the Tyver Series, about 6 m below the boundary with the Dniester Series ( Fig. 2 : point 5).

Description.—The fragment, evidently from a middle part of the jaw bone, represents a relatively large and mature jaw bone. It is one of the biggest known specimens within the proposed Podoliacanthidae fam. nov. The jaw bone seems to be narrow. The width of the preserved fragment increases forward from about 0.7–1.0 mm. The height of the jaw bone, except for that of the lateral tooth row, is about 1.5 mm. Both teeth have their lower half preserved, where they have a short vertical ridge on the medial tooth side ( Fig. 7A, B ). The ridge width, in profile view, increases downward ( Fig. 7C ). The teeth are triangular in parabasal section. There is a crown-base border on the medial side, beneath the vertical ridge ( Fig. 7A ). The lingual tooth row resembles that of Podoliacanthus . The denticle groups are arranged diagonally in irregular transversal rows extending far onto the lingual slope of the jaw bone ( Fig. 7A, B ). The degree of their erasure is an evidence of the specimen maturity. The upper groups are somewhat larger than those situated on the slope. In general, it is particularly notable that the size difference between the denticle groups and the teeth of the lateral tooth row is significantly bigger than those known in other podoliacanthid forms. Specifically, along with the degree of erosion of the denticle groups, it likely indicates the maturity of the jaw bone. Nothing is known about posterior/anterior flanges of the teeth. Possibly, there are 3–5 inter-tooth denticles between the teeth of the lateral tooth row, but due to the poor state of preservation their presence can be known from indirect evidence only ( Fig. 7C ). The inter-tooth pits of the lateral tooth row are clearly defined. They are nearly oval in shape and rapidly increase in size forward, are rather deep and have pores of vascular canals mainly along their perimeter ( Fig. 7D ). There is a horizontally-arranged set of pores on the upper half of the lateral jaw bone surface ( Fig. 7B ).

Remarks.—In comparison with other podoliacanthid forms the specimen represents the largest jaw bone and is distinguished by the possession of lingual dentition of the teeth as a short vertical ridge. Additional data are needed for determining its place within the family.

Figures

Fig. 7. Podoliacanthidae fam. nov. gen. et sp. indet., ZPAL P.14/12.10, Dniester River, on the east outskirts of Ivanie Zolote; upper part of the Ivanie Horizon of the Tyver Series, Lower Devonian; jaw bone fragment in lingual (A), occlusal (B), and linguo-occlusal (D) views, postero-lingual view of lateral tooth row (C). Arrows indicate rostral direction.

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).