Nostolepis Pander, 1856

Burrow, Carole J., 2003, Earliest Devonian gnathostome microremains from central New South Wales (Australia), Geodiversitas 25 (2), pp. 273-288 : 275-276

Genus Nostolepis Pander, 1856

TYPE SPECIES. — Nostolepis striata Pander, 1856 .

HOLOTYPE. — Scale figured by Pander (1856: pl. 6, fig. 7) from the Late Silurian (Pridoli) Ohesaare Formation, Saaremaa, Estonia.

Nostolepis lacrima Valiukevicius, 1994 HOLOTYPE. — Scale GI N 30-1604 (Valiukevic˘ius 1994: pl. XIX, fig. 10) from outcrop 775, layer 47, Lochkovian Urum Beds, Tareya River , Taimyr, Russia.

DIAGNOSIS (after Valiukevic˘ius 1994). — Scales up to 0.6 mm long and 0.3 mm wide; four or five regularlyspaced sub-parallel ridges extending up to half the length of the crown; posterior part of crown narrows to a sharp point; neck low to moderate height; base smaller than crown and weakly convex; crown formed of two to four growth zones filled with simple mesodentine, without any wide canals; numerous lacunae in the embryonic growth zone; abundant fine bone cell cavities in the base.

MATERIAL EXAMINED ( Table 1). — Eight scales from sample C923 including figured specimen MMMC 2551 ( Fig. 4A, B ), 24 scales from C925 including figured specimens MMMC 02555-7 ( Fig. 2 A-D, H), one scale from Y4, possibly one scale from C920.

DESCRIPTION

Morphology ( Figs 2 A-D; 4A, B)

The scales are relatively small, ranging from 0.2-0.4 mm wide and 0.3-0.4 mm long. Scale crowns are simple, with a rounded anterior margin bearing three to five short, sharp ridges which usually rise up directly from the base; on some scales the crown and base are separated by a short neck anteriorly. The ridges are evenly spaced and aligned radially relative to the posterior corner of the crown. The crown plane is horizontal, being smooth behind the ridges and with smooth, sharp postero-lateral edges. Most of the scales have an asymmetrical crown. The base is moderately swollen, with its maximum depth slightly forward of centre; a sharp rim often delineates the base/neck junction.

Histology ( Fig. 2H )

The crown is quite shallow, and the base/crown junction is almost flat. Four growth zones form the crown. Poor preservation and remineralization have destroyed/obscured fine histological structures including dentine tubules and bone cell lacunae (if any); no durodentine or wide vascular canals are discernible.

REMARKS

Morphologically, the scales closely resemble the type material (Valiukevic˘ius 1994: pl. XIX, figs 8-11) from the Uryum beds (mid-Lochkovian, spanning the equivalent of the eurekaensis-delta Conodont zones: Valiukevic˘ius 2000: fig. 9) of Taimyr, northern Russia. The taxon has otherwise only been recorded from a borehole in the Timan-Pechora region of northern Russia (Valiukevic˘ius 1994). The Australian scales resemble the type material in having a relatively flat-topped base and lacking vascular canals and durodentine (Valiukevic˘ius 1994: fig. 64.3-6). However, Valiukevic˘ius (1994) also described them as having a base filled with small bone cell cavities. Bases of the Australian scales are also filled with small “spots” which are possibly equivalent to these structures; however, they could have resulted from remineralization of the fibres penetrating the base rather than infilling of bone cell cavities ( Fig. 2H ). Scales with a comparable morphology have also been reported from the Windellama Limestone (delta CZ: Parkes in Basden et al. 2000: fig. 5.1-6: “ Nostolepis sp. nov. ”) and the Garra Formation (pesavis CZ: Burrow in Basden et al. 2000; Burrow 2002: “ Ischnacanthidae ? nov. gen. et sp.”; Garralepis simplex ), both also in New South Wales, as well as from the Martins Well Limestone (pesavis?/ sulcatus CZ), Broken River region, north Queensland ( Turner et al. 2000: table 1: “ Gomphonchus ? n. sp. 1”; Burrow 2000, 2002: “ Ischnacanthidae ? nov. gen. et sp.”; Garralepis simplex ). Histological structure of the scales from the latter two strata differs from the Nostolepis - type (sensu Gross 1947) in having durodentine extensively developed in the upper centre of the crown growth zones, and in having numerous bundles of Sharpey’s fibres layered through the base; unlike the scales of N. lacrima , the anterior crown margin on scales of Garralepis simplex is not separated from the base by a marked neck/base rim. The histological structure of the Windellama Limestone scales is not known.

Figures

FIG. 4. — Acanthodian scales from sample C923, Cookeys Plains Formation (early Lochkovian), central New South Wales, Australia; A, B, Nostolepis lacrima Valiukevicius, 1994 scale MMMC02551 in crown (anterior edge to right) and lateral (anterior edge to left) views; C, D, Nostolepis sp. scale of “N. applicata”-type MMMC02552 in crown and lateral views (presumed anterior edge to left); E, F, Gomphonchoporus hoppei (Gross, 1947) scale MMMC02553 in crown (anterior edge at bottom) and anterior views; G, H, Trundlelepis sp. scale MMMC02554 in crown and lateral views (anterior edge to right). Abbreviation: ms, median sulcus. Scale bars: 0.1 mm.

FIG. 2. — Acanthodian scales from sample C925, Cookeys Plains Formation (early Lochkovian), central New South Wales, Australia; A-D, H, Nostolepis lacrima Valiukevicius, 1994; A, B, specimen MMMC02555; A, crown view; B, antero-lateral view; C, D, specimen MMMC02556; C, crown view; D, lateral view; H, vertical longitudinal ground thin section MMMC02557; remineralization has obscured histological details; E-G, Nostolepis sp.; E, F, specimen MMMC02558; E, crown view; F, anterolateral view; G,?branchial scale MMMC02559 in crown view. Anterior of scale faces to left in A-D, and to right in E-H. Scale bars: 0.1 mm.