Nikolivia, Karatajute-Talimaa, 1978

Mark-Kurik, Elga, Blieck, Alain, Burrow, Carole J. & Turner, Susan, 2013, Early Devonian fishes from coastal De Long Strait, central Chukotka, Arctic Russia, Geodiversitas 35 (3), pp. 545-578 : 561

Nikolivia ? sp.

( Fig. 7 I-K)

MATERIAL. — Specimen GIT 580-9: scale.

LOCALITY AND STRATIGRAPHIC HORIZON.— Locality (sample) 73, Tonnel’nyj Brook, south of De Long Strait , Chukotka ; Lower Member (1) of Enmakaj Formation, Lochkovian .

DESCRIPTION ħis is an unusual ovoid scale with a wide base, wider than the high, extremely flat and almost featureless crown ( Fig. 7J, K ). ħere is a slight asymmetry to the crown with some curvature to one side. ħe base is also apparently not deep but it is overgrown with a small central pulp hole, denoting a mature state ( Fig. 7I ). ħere is a lateral groove to one side leading to the scale rim.

ħe wide shape of this scale is unlike any Turinia or Nikolivia taxon seen elsewhere. It might be a pathological scale or broken with the crown top sheared off, and/or from the crown flatness it might be a ventral scale on the body. Some cephalopectoral scales of Turinia antarctica Turner & Young, 1992 (Turner & Young1992: figs 4c, l, n, 5m, 7a)show flat tops to the crowns that suggest this explanation.ħe presence of a groove on the base for a large canal is uncommon, and combined with the slight depression to the side of the scale, might indicate that this is a specialized scale associated with a pore-canal or lateral line (see Märss et al. 2007). ħere is a possibility that this is a new form but until further material showing the variation is found, the identification of the taxon for this scale is tentative at best.

COMMENTS ON DISTRIBUTION OF THELODONTS In general the majority of scales are typical of Lower Devonian assemblages around the Old Red Sandstone Continent, with Turinia and Nikolivia type scales. ħe turiniid scales fall within the variation range of the type species and co-occuring taxa such as Turinia composita , T. barentsia and T. polita , all found in the British, Baltic to Arctic localities. As so few scales were recovered from locality73,Tonnel’nyj Brook, Chukotka and possibly the smallest scales were lost, the absence of such expected key taxa as Boreania minima Karatajūtė-Talimaa, 1985 , which typically occur in the earliest Lochkovian (e.g., Talimaa 2000) is not surprising.

Based on published occurrences, there are no identical scales to the two nikoliviid-like scales in the new material from Chukotka. However, they are generally comparable with Nikolivia gutta known from the Lochkovian of Britain, the Baltic and Spitsbergen and perhaps others from Arctic Russia and Podolia ( Ukraine).

Figures

FIG. 7.— Thelodont scales from the Lower Devonian of Chukotka,Arctic far-eastern Russia:A, B, Turinia pagei (Powrie,1870)?,specimens GIT 580-19 (A in antero-lateral view) and 580-16 (B in lateral view); C, D, Turinia sp. cf. T. composita Karatajūtė-Talimaa, 2002,specimens GIT 580-10 (C in crown view) and 580-11 (D in latero-crown view); E, Turinia sp. cf. T. polita Karatajūtė-Talimaa,1978, specimen GIT 580- 17 in lateral view; F, Turinia sp., specimen GIT 580-12 in crown view; G, H, Nikolivia? sp. cf. N. gutta Karatajūtė-Talimaa,1978, specimen GIT 580-13 in crown (G) and basal (H) views;I-K, Nikolivia? sp., specimen GIT 580-9 in basal (I), crown (J) and latero-crown (K) views. All specimens from locality (sample) 73,Tonnel’nyj Brook,Lower Member (1) of Enmakaj Formation,Lochkovian.Scale bars:A-C,F,G, 200 µm; D, 250 µm; E, 300 µm; H-K, 100 µm.