HETEROSTRACI (Dineley & Loeffler, 1976)

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 : 557

HETEROSTRACI? indet.

( Fig. 6I )

MATERIAL. — Specimen GIT 580-8: isolated tessera or platelet.

LOCALITY AND STRATIGRAPHIC HORIZON. — Same as specimens GIT n°580-1, 2, 3, 4, 6 and 7: locality (sample) 73, Tonnel’nyj Brook, south of De Long Strait, Chukotka; Lower Member (1) of Enmakaj Formation, Lochkovian.

DESCRIPTION ħis specimen is an isolated square-shaped element (either a tessera or platelet), partially broken, and with an altered surface. It bears a single, probably central, star-shaped tubercle ( Fig. 6I ). Because it is larger ( c. 3.2 mm long for its preserved part) than all other tesserae that have been prepared from sample 73 of the Coast section, we suggest that it might correspond to a different taxon. Furthermore, with such a small sample (a single specimen), no thin section has been made, and thus its histology is not confirmed as being of a heterostracan.

Figures

FIG. 6. — Heterostracan microremains from the Lower Devonian of Chukotka,Arctic far-eastern Russia:A, B, Traquairaspididae? gen. et sp. indet., specimen GIT 580-5, from locality (sample) 73, Tonnel’nyj Brook, Lower Member (1) of Enmakaj Formation, Lochkovian; C, Traquairaspididae? gen. et sp. indet., specimen PIN 3845/2, locality 73-4 (74-3), Tonnel’nyj Brook, Lower Member (4) of Pil’hikaj Formation,Lochkovian; D, Lepidaspis? sp., tessera,specimen GIT 580-2,locality 73,same origin as specimen 580-5 (A, B); E, F, Oniscolepis? sp., tesserae, specimens GIT 580-1 (E) and 580-3 (F), locality 73, same origin as specimen 580-5 (A, B); G, H, Poraspididae gen. et sp. indet.,fragments of a scale (G) and of a plate (H), specimens GIT 580-4 (G) and 580-7 (H), locality 73, same origin as specimen 580-5 (A, B); I, Heterostraci? indet., tessera (platelet), specimen GIT 580-8, locality 73, same origin as specimen 580-5 (A, B). Scale bars: A, C, 1 mm; B, 100 µm; D, 300 µm; E, G, 500 µm; F, H, I, 200 µm.