Oniscolepis, Pander, 1856

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 : 556

Oniscolepis ? sp.

( Fig. 6E, F )

MATERIAL. — Specimens GIT 580-1 and 580-3: isolated tesserae with a central tubercle.

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

DESCRIPTION ħese are two small bony elements, partly fractured, but corresponding to isolated tesserae. Specimen GIT580-1 ( Fig. 6E ) is c. 1.8 mm long, with a single central, denticulated tubercle which shows a thin longitudinal crest. Specimen GIT 580-3 ( Fig. 6F ) is c. 1.5 mm long with a single central, bigger, denticulated tubercle.Both tesserae have a very thin base which corresponds to the cancellous layer with rather wide chambers. ħey may be compared to “juvenile scales” of Strosipherus Pander, 1856 (sensu Karatajūtė- Talimaa & Märss 2008), recently synonymized with Oniscolepis by Märss & Karatajūtė-Talimaa (2009: fig. 4A). Both specimens can also be compared with broken portions of the superficial layer of traquairaspid elements (e.g., Fig. 4C ), but in traquairaspids the base is usually much thicker than in GIT 580-1 and 3. So, affinities with Oniscolepis (senior synonym of Strosipherus ) seem more likely.

DISCUSSION

Strosipherus and Oniscolepis , now synonymized under the name Oniscolepis (Märss & Karatajūtė-Talimaa 2009) , are representatives of tessellated heterostracans, the taxonomic status of which is still uncertain (see the discussion/comparison section in Märss & Karatajūtė-Talimaa [2009: 58-60]; see also Elliott & Loeffler[1989]). ħe family Oniscolepididae Märss & Karatajūtė-Talimaa, 2009 , including Oniscolepis and Kallostrakon Lankester,1870 , is considered by Märss & Karatajūtė-Talimaa (2009) as belonging to the eriptychiid heterostracans(order Eriptychiida Ørvig,1958 ; seealsoObruchev1964];EriptychiiformesTarlo,1962). However, the phylogenetic relationships of eriptychiids to heterostracans are still in debate. Eriptychiids proper (family Eriptychiidae Tarlo, 1962 ) are either considered as the sister-group of Heterostraci (e.g., Janvier 1996), or as an order of the subclass Heterostraci (e.g., Märss 1986;Märss & Karatajūtė-Talimaa 2009). So, the phylogenetic relationships of oniscolepidids, eriptychiids and heterostracans may be considered as unsolved, and we keep here Oniscolepididae at an uncertain ordinal rank within heterostracans.

ħe occurrence of oniscolepidid remains in the Lochkovian of Chukotka, if confirmed, would fit the presently known stratigraphical distribution of Oniscolepididae , which ranges from the Upper Silurian (Pridoli) to Lower Devonian (Lochkovian) (Märss & Karatajūtė-Talimaa 2009).

Incerti ordinis

Incertae familiae

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.

FIG. 4.— Details of superficial ornamentation of specimen PIN 3845/4.A, B, C, refer to the three areas indicated on Figure 3[4A,4B, 4C].