Barlowodus, SP. CF. B. FLORALIS

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 : 25

BARLOWODUS SP. CF. B. FLORALIS ( FIG. 8A–K ; TABLE 1 ; SUPPL. 1, FIGS. 4 , 5 , 7 )

Referred specimens — Circa 20 specimens from BC II level 430.5' (131.2 m); two from level 453' (138.1 m): Roberts Mountains Formation .

Description and comparison —Small scales with complex crown sculpture, all with fine ribbed ultrasculpture ( Fig. 8A–K ). One possible head or oral scale has a high multi-ridged crown and high neck with a rounded base and large central pulp opening ( Fig. 8A ). One possible cephalopectoral scale has a flattened rhombic crown which rises only slightly to a posterior point; fine ultrasculpture as well as borings can be seen on the surface ( Fig. 8B ). Most scales are trunk scales. The crowns rise gently posteriad with three flat ridges or a system of bifurcating ridges separated by deep or wide grooves. The posterior or posterolateral crown margin is multi-pointed ( Fig. 8A, C–F, H–K ).

Most scales in level 430.5’ seem affected by fungal damage (as noted for other specimens above). Histology was attempted using anise oil but the structure is disrupted and so we cannot verify the apparent “criss-cross aspidine ‘pegs’” noted as characteristic for the genus and separate family by Märss et al. (2006, p. 121). However, a similar criss-cross pattern of Sharpey’s fiber bundle spaces is found in other deep and swollen old bases of other thelodont scale taxa such as Thelodus laevis (e.g., Bystrow 1957, Gross 1967).

Remarks —Most of the scales from Nevada seem closest to B. floralis . The type locality for the latter is at 34.5* m in the same section where it co-occurs with the other two Barlowodus species ( Märss et al. 2006).

Figures

Figure 4. Nostovicina and Nostolepis sp. acanthodian scales from the Siluro-Devonian boundary levels of the Birch Creek II section. A. Nostovicina sp. cf. N. elegans: UCR 10755-1 (level 470.2’) in crown view (from Supplement 1, fig. 13). B–D, J. Nostovicina laticristata: B. UCR 10768-10 (level 518.3') in crown view; C, D. UCR 10768-6 (level 518.3') in anterocrown and crown views; J. UCR 10768-11 (level 518.3') horizontal thin section through crown. E–I, K, L. Nostovicina sp. cf. N. guangxiensis; E. UCR 5443-1 (level 562.6') in anterocrown view; F, G. UCR 5443-3 (level 562.6') in crown and lateral views; H. UCR 5443-4 (level 562.6') in posterocrown view; I. UCR 5443-6 (level 562.6') in crown view; K, L. UCR 5443-7 (level 562.6') vertical transverse section, magnified view of crown structure in L. M–P. Nostovicina sp. cf. N. lacrima: M. UCR 5439-8 in lateral view; N. UCR 5439-6 in posterior view; O. UCR 5439-4 (level 549') in lateral view; P. UCR 10768-1 (level 518.3') in anterior view. Q–T. Nostolepis matukhini: Q, R. UCR 5443-2 (level 562.6') in crown and laterocrown views; S, T. UCR 5443-5 (level 562.6') in crown and anterocrown views. Abbreviations: cgz=crown growth zones; h=hyphal borings; Sf=Sharpey’s fiber bundles. Scale bars=0.1 mm, anterior of scale is to right or up, otherwise arrows point to anterior. See Table 1 for meterage.

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 8. A–K. Scales of thelodont Barlowodus sp. cf. B. floralis from the uppermost Silurian of the Birch Creek II section, all level 430.5'. A, UCR 10746-31 in baso-lateral view; B, UCR 10746-35 in crown view; C, UCR 10746-36 in crown view; D, UCR 10746-34 in crown view; E, UCR 10746-42 in crown view; F, UCR 10746-29 in crown view; G, UCR 10746-24 in crown view; H, UCR 10746-38 in crown view; I, UCR 10746-23 in crown view; J, K, UCR 10746-14, in crown view, and close up of dorsal mid-crown showing ultrasculpture and taphonomic effects. Scale bars=0.2 mm; anterior to left except A, D, G, I. See Table 1 for meterage.