Ischnacanthiformes, Berg, 1940
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publication ID |
https://doi.org/ 10.4202/app.00456.2018 |
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persistent identifier |
https://treatment.plazi.org/id/9F0087B5-4034-1A3B-FFD2-C2FC218FBCF2 |
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treatment provided by |
Felipe |
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scientific name |
Ischnacanthiformes |
| status |
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Ischnacanthiformes fam., gen. et sp. indet.
Fig. 8 View Fig .
Material.— SMNH BP.1586/4, a jaw bone fragment, 3.4 mm long, with three teeth of the lateral tooth row in different states of preservation (the smallest has a complete but erased tip, though lacks a side tooth part, the two other teeth have lost their tips); right bank of the Dniester River , opposite Zalishchyky , Zastavna (Chernivtsi) region ( Podolia ), Ukraine ( Fig. 1C View Fig : point 1); upper part of Ivanie Horizon of the Tyver Series, Lower Devonian ( Fig. 2 View Fig : point 6) .
Description.—The teeth are triangular in profile view with their tips slightly inclined backwards. The teeth seem to be heavy, massive and probably have no tooth cavity as, at least, the smallest of them ( Fig. 8D, E View Fig ). The broken tip of the largest tooth also does not reveal the tooth cavity ( Fig. 8D, E View Fig ). All broken zones show only vascular canals 20–30 μm in diameter ( Fig. 8B, E View Fig ). There are no clearly visible anterior or posterior flanges on the teeth. The largest of the preserved teeth has a crown-base border on the medial side, which comprises the lower third of the overall tooth height ( Fig. 8B, E View Fig ). The lingual tooth side forms a buttress that juts out in a medial-posterior direction ( Fig. 8A–C View Fig ). Thus, a parabasal section of the tooth looks like an “arrow” directed forward. The tooth size increases forward rapidly. The teeth have a smooth surface with no tooth side dentition visible. The width/height tooth ratio can be estimated as 1. The teeth are relatively tight. The linear size of the teeth in their base plane is much bigger than size of the inter-tooth pits on this level. Inter-tooth pits are funnel-shaped with a narrow lingual outlet ( Fig. 8A, C, E View Fig ). The lingual ridge is poorly preserved ( Fig. 6C View Fig ) and is weakly developed along the two smaller teeth of the jaw bone fragment and slightly marked out by pores of the vascular canal system near the largest ( Fig. 8B View Fig ). Pores of about 30 μm in diameter appear in the second lingual outlet, while those along the base of the largest tooth are 50–70 μm in diameter ( Fig. 8A, B View Fig ). No pores are present around the two smaller teeth and in the inter-tooth pit between them. Small pores are randomly distributed on the lateral/labial side of the jaw bone ( Fig. 8D View Fig ) and there are no inter-tooth denticles between the first two teeth of the jaw bone fragment. They are possibly broken off between the second and the third (the largest) tooth. One or two broken inter-tooth denticles appear immediately ahead the third tooth ( Fig. 8A, C View Fig ). The inter-tooth walls are slightly curved outwards and, together with the curved lateral side of the teeth, form a sinusoidal contour of the lateral tooth row ( Fig. 8A View Fig ).
Remarks.—The new form can be distinguished by massive solid teeth which have a smooth surface, prominent lingual buttress and arrow-like parabasal section. The specimen evidently represents a mature jaw bone. We leave this form in open nomenclature as only one jaw bone fragment is known.
| SMNH |
Department of Paleozoology, Swedish Museum of Natural History |
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