Nikolivia undetermined

Burrow, Carole Jan, Murphy, Michael & Turner, Susan, 2023, Late Silurian to earliest Devonian vertebrate biostratigraphy of the Birch Creek II section, Roberts Mountains, Nevada, U. S. A., PaleoBios 40 (1975), pp. 1-32 : 23

NIKOLIVIA SPP.

( FIG. 7E–J ; TABLE 1; SUPPL. 1, FIGS. 5 , 9 , 20, 25)

Referred material — Rare except for one level; c. 15 specimens from section BC II: one scale AMF97875 from 402’ (122.5 m)– this specimen is missing; c. 11 from 430.5’ (131.2 m), 456.5’ (139.1 m); level 527.25’ (160.7 m); one specimen from level 591.5’ (180.3 m): Roberts Mountains Formation .

Description and comparison —AMF97875 and the other Nikolivia scales from BC II, notably from 430.5’, resemble scales of N. gutta , N. aligera Karatajūtė-Talimaa, 2002 ( Fig. 7 A-E), and N. auriculata Märss et al., 2002 ( Fig. 7F ). These nikoliid taxa are found in the early Lochkovian elsewhere ( Märss et al. 2007). The specimen that Parkes (2005, fig. 22.17, 18; Fig. 7G ) captioned as Amaltheolepis sp. cf. A. winsnesi from 402’ is a typical nikoliviid scale, bilaterally symmetrical, small (0.4 mm long x 0.3 mm wide) and rounded. The central squat teardrop-shaped crown section is smooth and rounded anteriorly and raised slightly, curving to a posterior point with three short anterior ridges that extend less than a quarter scale length. There is a pair of lateral flattened lappets with a simple but slightly imperfect (damaged?) rim with small scallop-shaped concavities, two on one side and one on the other. The central surface of the crown is smooth with a broad middle raised ridge extending from the midpoint near the base to the posterior point. The neck is smooth and low. The anteriorly placed base is a rounded torus: relatively smooth, deep, and mature with a smaller central rounded pulp opening. One possible thelodont specimen (Suppl. 1, fig. 25:?) from level 591.5’ just above the S–D boundary appears typical of Nikolivia gutta Karatajūtė-Talimaa, 1978 with its smooth heart-shaped crown.

Remarks — Parkes (1995) interestingly misidentified scale AMF97875 ( Fig. 7G ) as an amaltheolepid. Here we refer it to Nikolivia sp. But there are not enough scales in the Nevadan material to judge the variation. Nikoliviid scales are typical of the Early Devonian (Lochkovian) in Europe, and elsewhere in North America ( Märss et al. 2007). The small regular concavities on the rim of the lateral lappets of the specimen might be damage made in handling the specimen or a pathological feature as they resemble bite-marks, but this has not been seen elsewhere. Lepidophagy is common in modern bony fishes and it is feasible that the scale was attacked in life or alternatively post-mortem by another fish or even by an unknown invertebrate.

Figures

Figure 5. Funicristata nevadaensis n. gen. n. sp. from the uppermost Silurian of the Birch Creek II section. A–C. UCR 10750-3 (level 456.5') in crown views and magnified view of the crown ridges; D, E. UCR 10750-2 (level 456.5') in crown and lateral views; F, G. UCR 10746-10 (level 430.5') in anterocrown and crown views; H, I. UCR 10746-8 (level 430.5') in anterocrown and laterocrown views; J, K. UCR 10750-10 (level 456.5') vertical longitudinal section; L. UCR 10750-12 (level 456.5') horizontal section through crown. Abbreviations: c=canal; en=enameloid; h=hyphal boring; po=pore openings. Scale bars=0.1 mm in A, B, D–L, 0.01 mm in C; anterior is to left or down, otherwise arrows point to anterior. See Table 1 for meterage.

Figure 7. Thelodont scales from the uppermost Silurian of the Birch Creek II section, all level 430.5' except B, C, G, K, L, P, Q. A. Trimerolepis sp. cf. T. tricava. UCR 10746-43 in crown view. B. Trimerolepis sp. AMF97876 (Parkes 1995, fig. 22.19, 20) from level 503’, base view. C.?Lanarkia sp. UCR 944-20 (level 527.25’) in lateral view. D.?Turinia sp. UCR10746-19, showing taphonomic effects and ultrasculpture, in crown view. E-J. Nikolivia spp. E. UCR 10746-13 with cell pattern on surface in crown view; F, UCR 10746-20 in crown view; G, AMF97875 (Parkes 1995, fig. 22.17, 18) from level 402' with possible bite marks, in crown view; H, UCR 10746-27 in ventral basal view; I, UCR 10746-25 showing taphonomic effects in crown view; J, Nikolivia sp. cf. N. auriculata, UCR 10746-18 in crown view. K, L. Apalolepis sp. AMF97872 (level 503’) (Parkes 2005, fig. 22.11, 12), crown and basal views. M-O. Talivalia sp. cf. T. elongata. M, UCR 10746-17 in crown view; N, UCR 10746-37 in crown view; O, UCR 10746-21 in lateral view. P-S. Barlowodus sp. cf. B. tridens. P,Q, AMF97874 (level 875’) in crown and basal views (Parkes 2005, fig. 22.15, 16). R, S, UCR 944-21 (level 527.25') in laterocrown view, closeup in S showing striated ultrasculpture. Scale bars=0.2 mm; anterior to left or top, otherwise arrow points to anterior. See Table 1 for meterage.

Figure 9. Paleogeographic reconstruction for the late Silurian, base map from Scotese (2014, map 73), showing possible vertebrate dispersal route from the Baltic to the circum-Arctic and thence south to western Laurentia.