Nostovicina laticristata, (VALIUKEVIČIUS, 1994)

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 : 13-14

NOSTOVICINA LATICRISTATA (VALIUKEVIČIUS, 1994)

( FIG. 4B–D, 4J ; TABLE 1 ; SUPPL. 1, FIGS. 19)

Nostolepis laticristata Valiukevičius, 1994 , 149, 150, fig. 70.1, pl. 18.9, 19.1–19.3.

Nostovicina laticristata Valiukevičius and Burrow 2005 , 646.

Type material— Holotype LIGG 30-1569 ; Uryum Beds , Tareya River , Taimyr , Russia (Lower Devonian, Lochkovian).

Referred specimens—Scales assigned to this species occur at levels 517–613’ (157.6–186.8 m), and include UCR 10768-6, -10 and thin section UCR 10768-11(level 518.3’= 158 m): Roberts Mountains Formation.

Description—Small scales up to 0.4 mm wide, with crowns mostly conforming to two morphotypes, both of which have a smooth flat subtriangular surface with five or six short, usually smoothly rounded and nonbranching, ridges leading back from the anterior crown margin. Posterolateral edges of the crown are straight or slightly convex and lack denticulations, converging at a slightly obtuse angle. One morphotype has several oblique ridges leading back from the posterior corner along the lateral faces of the crown ( Fig. 4B ), and the other morphotype lacks ridges on the posterolateral sides of the crown ( Fig. 4C, D ). All scales have a short or no neck. The base is convex and about the same height as the crown plus neck, lacking a marked rim between the neck and base. As usual for BC II scales, histology is poorly preserved with scales having extensive hyphal borings. Four wide growth zones form the crown ( Fig. 4J ).

Comparison—This taxon was erected for circa 5000 isolated scales from the Lochkovian of Taimyr by Valiukevičius (1994), who originally assigned the species to Nostolepis ; it was subsequently reassigned to Nostovicina Valiukevičius and Burrow (2005) , based on histological structure. Some scales from Timan–Pechora that Valiukevičius (1994) assigned to this species were reassigned to Nostolepis adzvensis Valiukevičius (2003b) and subsequently by Valiukevičius and Burrow (2005) to Pechoralepis adzvensis , based once again on histological differences. The two species Nostovicina laticristata and Pechoralepis adzvensis are virtually impossible to differentiate on morphology alone, but histological study of scales confirmed that those from BC II are N. laticristata . The latter show a similar range in size and morphology to scales from the Lochkovian of the Arctic Canadian Archipelago, which Vieth (1980) assigned to Gomphonchus sp. cf. G. hoppei , and which have since also been assigned to N. laticristata ( Valiukevičius 1994, Turner and Burrow 1997: CJB, personal observation of scales from GSC localities C-8771, C-67653, C-76085). A partial articulated fish from the Lochkovian MOTH locality of Northwest Territories, Canada ( Hanke 2001, figs. 82–85: captioned as Nostolepis tewonensis ?) is here considered to be Nostovicina laticristata . Lochkovian–Pragian scales from southeastern Australia that are now assigned to Nostovicina guangxiensis ( Wang, 1992) have a very similar or greater range of crown morphotypes ( Burrow 2002, figs. 4E–I, 5J–M, 12A, C, D), but these scales are on average much larger than those of N. laticristata . One of the type scales of Nostolepis tewonensis ( Wang et al. 1998, pl. 1H) from the lower Lochkovian of the Xiaputonggou Formation, Tewo county, China, resembles the simplest variants of Nostovicina laticristata , and it seems possible that the Chinese scales from that level should be reassigned to the latter species. The holotype and other paratype scales of N. tewonensis were from the much older, upper Wenlockian Miaogou Formation. N. laticristata is now recorded from the Lochkovian of arctic Canada, Northwest Territories Canada, Nevada, Taimyr, Podolia, and east Baltic countries ( Valiukevičius 1994, 2000, Turner and Burrow 1997).

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.