Nostovicina 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 : 13

NOSTOVICINA SP. CF. N. ELEGANS

( FIG. 4A ; TABLE 1 ; SUPPL. 1, FIG. 13)

Referred specimens—One scale from level 470.2’ (143.3 m): Roberts Mountains Formation.

Description—The solitary medium-sized scale assigned to this species is characterized by having an elevated central area in the elongate crown, with just one or two short ridges leading back from the anterior edge. Narrow lower ledges run along each side of the central crown plane. The base is moderately convex, a neck is lacking, and the crown is inclined anteroposterially.

Comparison—The type material of N. elegans was found in Lower Devonian erratics of the Baltic basin, and the species has been reported from Ludlow to Lochkovian deposits, including from the Přidolí of southern Sweden ( Vergoossen 1999b, pl. 2.16, 2.17), Lithuania (Valiukevičius 2005, figs. 2I, 2J, 7, 8) and Latvia ( Valiukevičius 2004b, table, fig. 5A–M). The work by those authors indicates that Nostovicina elegans is a valid species, countering Gross’ (1947) dismissal of Diplacanthoides elegans as a junior synonym of Nostolepis striata . Certainly, in the BC II section, this is amongst the few Nostolepis -type scales sensu Gross (1947) found in the upper Silurian below the 513’ level, with no scales comparable with the holotype of N. striata found at any level. The scale is only tentatively assigned to N. elegans based on its morphology, because the histological structure was not investigated.

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.