Lophosteus 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 (4), pp. 1-32 : 19

LOPHOSTEUS SP. CF. L. SUPERBUS

( FIG. 6E–G ; TABLE 1 ; SUPPL. 1, FIGS. 1 , 10, 12)

Referred specimens —Scales assigned to this species occur at levels 318’ (96.9 m), 457’ (139.3 m), 468’ (142.6 m), and possibly 527.25’ (160.7 m): Roberts Mountains Formation.

Description —The rare remains comprise scale and dermal bone fragments ( Fig. 6 E-G), the former ornamented with inclined, elongate ridged tubercles ( Fig. 6E ) with the best example being a broken scale from level 318’ having parallel elongate tubercles extending the length of the rhombic scale. The dermal bone fragments mostly have more stellate tubercles ( Fig. 6F ).

Comparison — The best-preserved scale fragment compares closely with scales of the type species L. superbus from the upper Přidolí Ohesaare Beds , Saaremaa Island, Estonia rather than with scales of other species. (See Schultze and Märss 2004, for examples of Lophosteus spp. From the Baltic, Canada, and Russia).

Figures

Figure 1. Birch Creek II section, central Roberts Mountains, Nevada. A. locality map, topographic map showing locations of sections BC II, BC III, WC I, WC IV after Murphy (2016, appendix 1). B. stratigraphic column through the uppermost Silurian– lowermost Devonian (after Klapper and Murphy 1975, fig. 5; scale on left is in feet; X denotes their proposed Silurian–Devo- nian boundary at approx. 567’=172.8 m level); to the right, stratigraphically significant conodont ranges in red, graptolites in blue (see Murphy 2016, fig. 2).

Figure 6. Chondrichthyan and stem osteichthyan scales from the uppermost Silurian of the Birch Creek II section; A, C–G, light microscope images of whitened specimens; B, ESEM image. A-C. Ellesmereia schultzei. A, scale UCR 10746- 44 (level 430.5’) in crown view (from Suppl. 1, fig. 5); B, UCR 10746-28 (level 430.5’) in anterolateral-crown view; C, scale UCR10746-45 (level 430.5’ in crown and lateral views (from Suppl. 1, fig. 4). D. Polymerolepis sp. scale UCR 10752-1 (level 458.67’) in crown view (from Suppl. 1, fig. 11). E-G. Lophosteus sp. cf. L. superbus. E, dermal bone fragment 10754-1 (level 468’) in external view (from Suppl. 1, fig. 12); F, G, tubercles UCR951-1, 2 (level 457’) in crown views (from Suppl. 1, fig. 10). Scale bars=0.25 mm, anterior of scale is up or to left, otherwise arrow points to anterior. See Table 1 for meterage.