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 : 14

NOSTOVICINA SP. CF. N. GUANGXIENSIS

( FIG. 4E–I, K, L ; TABLE 1 ; SUPPL. 1, FIGS. 23, 25–29)

Referred specimens —Scales assigned to this species occur at levels 527.25’ (160.7 m), 562–564’ (171.3–171.9 m), 591.5–600’ (180.3–182.9 m), 674’ (205.4 m), 712’ (217 m), and include UCR 5443-1, UCR 5443-3, UCR 5443-4, UCR 5443-6 and thin section UCR 5443–7 (level 562.6’= 171.5 m); also AMF 97963, 97967 (level 562.6’= 171.5 m), figured by Parkes (1995, fig. 33.13, 33.20, 33.21, captioned as Nostolepis sp. ): Roberts Mountains Formation.

Description —Scales are medium-sized, about 0.5 mm wide, with crown morphologies similar to those in N. laticristata , but with up to nine short ridges along the anterior crown margin ( Fig. 4 E-H). A few scales have an almost circular crown outline ( Fig. 4I ), approaching the morphology of Nostovicina multangula ( Valiukevičius 1994) . Scale bases are strongly convex and deep ( Fig. 4K ), usually lacking a marked rim between the neck and base. Odontocytic mesodentine with tubules directed upwards are just visible in the four crown growth zones, bone cell lacunae are rare or absent in the scale base, and the bases are filled with bundles of Sharpey’s fibers ( Fig. 4K, L ).

Comparison —The oldest occurrence of Palaeozoic scales with this range of morphotypes is on the unique partial articulated holotype of Yealepis douglasi Burrow & Young (1999) from the Ludlow of Victoria, Australia; the youngest occurrence is the type material (scales) of Nostovicina guangxiensis from the early Emsian of Guangxi, China. Scales of N. guangxiensis are the most common acanthodian remains in the earliest Lochkovian section at Utopolu, Czechia (CJB, personal observation), and one of the two most common species in the Lochkovian Connemarra Formation, central New South Wales, Australia ( Burrow 2002). As noted, scales of N. laticristata show the same range of crown morphotypes, but the scales are always smaller than those attributed to N. guangxiensis . The same crown morphotypes are also found on scales of the recent Gulper shark Centrophorus granulosus ( Reif 1985, pl. 5.B1), a demersal deep-water fish. This crown morphology undoubtedly is related to the lifestyle of the fish (see Ferron et al. 2018).

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.