HETEROSTRACI

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 (4), pp. 1-32 : 19

HETEROSTRACI LANKESTER, 1868

HETEROSTRACI INDET. GEN. ET SP.

( TABLE 1 ; SUPPL. 1, FIGS. 7 , 11, 12, 14, 18)

Referred specimens —Scale fragments were collected from BC II section at six levels from 430.5’ to 513’ (131.2- 156.4 m): Roberts Mountains Formation.

Remarks —Most remains are conjoined tesserae such as the three small irregular tesserae from level 458.67’ (Suppl. 1, fig. 11). Some (Suppl. 1, figs. 7, 14, 18) resemble traquairaspid remains with slender oak-leaf pattern tubercles: traquairaspids typically range from Přidolí to early Lochkovian. One plate from level 468’ (Suppl. 1, fig. 12) is pteraspid- or poraspid-like, typical of early Lochkovian elsewhere (e.g., Turner et al. 2017). Turner and Murphy (1988, fig. 1.1-6, 8-15, 24) described heterostracan microremains from the Lochkovian Simpson Park section, Nevada. Parkes (1995) also identified heterostracan remains in two levels of BC II (402’, 446’).

As yet, there is no major review of heterostracan dermal scales; a handbook and major description of Cornwallis Island fauna are awaited (D.K. Elliott pers. comm. 2021, Thorsteinsson and Elliott 2022).

Figures

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.