Nikolivia aligera, Karatajūtē-Talimaa, 2002

Karatajūtē-Talimaa, Valentina N., 2002, Lower Devonian (Lochkovian) thelodonts from October Revolution Island (Severnaya Zemlya Archipelago, Russia), Geodiversitas 24 (4), pp. 791-804 : 799-802

Nikolivia aligera n. sp. ( Fig. 6 )

HOLOTYPE. — Transitional(?) scale (LIG 35-474) ( Fig. 6H ).

ETYMOLOGY. — Aligera (Latin): containing wings.

TYPE LOCALITY AND HORIZON. — Sample 4-3 (outcrop 4, bed 3) from the Matusevich River, October Revolution Island, Pod”emnaya Fm., Lochkovian, Lower Devonian.

MATERIAL EXAMINED. — About 80 scales well-preserved.

OCCURRENCE. — N. aligera n. sp. scales are identified only from a single sample (outcrop 4, bed 3) along the Matusevich River (October Revolution Island), Lower Devonian, Lochkovian, Pod’’emnaya Fm.

DIAGNOSIS. — Small and medium-sized scales (0.3- 1.3 mm long). Head scales smaller (0.3-0.5 mm), with high, spine-like crown, composed of concave central area and one to two pairs of laterals. Transitional scales comparatively small (0.4-0.7 mm). Crown consists of widened central area and wing-like laterals. Trunk scales the largest (0.8-1.3 mm), drop-shared or keel-like. Crown composed of wide central area with smooth surface and pair of narrowed laterals (type A), or of narrow groove-like central and one to two pairs of laterals (type B). Base of transitional and trunk scales of type A low, roller-like, displaced anteriorly. Keel-like trunk scales of type B with more convex and higher base.

DESCRIPTION

Division of scales into head and transitional types is rather conventional ( Fig. 6 A-M, O, Q). Head scales smaller, with higher, sometimes spine-like crown ( Fig. 6 A-E) and upward sloping distal area. Crown composed of central area and one or two pairs of laterals, sometimes widened and wing-like ( Fig. 6A ). Crowns of transitional scales distinguished by wing-like lateral areas with sometimes notched margins. Central area keel-like, somewhat highered, with smooth surface and usually not prolonged to the crown edge ( Fig. 6 F-M, O, Q).

As typical trunk scales are recognized large drop- or keel-like examples (type A) with central area having wide, flat and smooth surface ( Fig. 6N , U-Y). Narrow keel-like scales ( Fig. 6U, V, Y ), probably covered the tail area and fins. To type B are conventionally attributed trunk scales with more complicated ridged crowns, having narrow, central area. Lateral areas are not always strongly symmetric and may consist of one pair of widened or several pairs of narrowed members ( Fig. 6P , R-T).

Bases of scales of all types anteriorly vaulted, low, roller-like and only in keel-like variety reaching a larger height. Pulp opening comparatively large even in older scales.

COMPARISON

Scales of N. aligera n. sp. are close to scales of N. gutta Karatajūtē- Talimaa, 1978 in size. Trunk scales of type A do not differ in form from the drop-like scales of N. gutta . N. aligera n. sp. differs from all known species by presence within the morphologic set of transitional scales with wing-like lateral areas and also more distinctly recognizable head scales.

Order FURCACAUDIFORMES Wilson & Caldwell, 1998 Family FURCACAUDIDAE ? Wilson & Caldwell, 1998

Genus Canonia Vieth, 1980

TYPE SPECIES. — Canonia grossi Vieth, 1980 .

Canonia sp. cf. C. grossi Vieth, 1980 ( Figs 4 I-R; 7; 8)

OCCURRENCE. — Scales of Canonia sp. in the Lower Devonian of Severnaya Zemlya are found in samples from the outcrop 4, bed 3 at the Matusevich River and outcrop 69, bed 26 at the Pod’’emnaya River, in the middle and upper parts of the Pod”emnaya Fm., Lochkovian, Lower Devonian.

REMARKS

Vieth (1980) made the following diagnosis of Canonia grossi : small symmetric scales; distal crown area frequently three-pointed; 55% of scales have concave and raised medial area compared with laterals; lateral areas ornamented with longitudinal ridgelets (two or fewer); neck well developed, base high; 45% of scales have flattened crown surface, ornamented with foureight narrow longitudinal ridgelets, and low base; rather smooth linear dentine tubules arise only from the pulp cavity.

Concerning size and morphologic features the Severnaya Zemlya specimens insignificantly differ from the Canadian ones. More representative material (about 150 scales) was found in outcrop 4, bed 3 at the Matusevich River. A minority consist of the simplest scales – crown of smooth central and one pair of lateral areas,

dt

separated by deep longitudinal grooves ( Fig. 7A ). Small numbers of scales have more complicated crown morphology: central area slightly concave and laterals ornamented with longitudinal grooves ( Fig. 7B, C ). All scales with three distinctly separated areas have three-pointed posterior crown edge, with the central point significantly longer than the laterals ( Fig. 7C ). The majority consists of large scales (up to 0.5 mm), in which crown shape resembles a quadrangle, comparatively widen and flattened. Proximal crown margin slightly convex or linear, lateral margins linear and distal area three-pointed ( Figs 4 J-O; 7D-F). All scales of that type have developed narrow central area, flat or with longitudinal groovelet, and one to three pairs of lateral areas also narrow, ornamented with shallow longitudinal groovelets. The central area is usually separated from the laterals by deeper and wider grooves. Generally speaking, crowns of scales have well distinctive longitudinal sculpture.

The sample yielded also some scales with asymmetric crown ( Fig. 4I ), base small, displaced anteriorly ( Fig. 4 P-R), comparatively low, only rarely higher, pulp opening in all observed scales large.

Fig. 8A illustrates the extent of the pulp cavity, and also the type of dentine forming the crown ( Fig. 8 ).

Vieth (1980) described for Canonia scales characteristic smooth, linear dentine canals, arising only from the pulp cavity, and also their short branch connecting arcade tubules. Based on drawings ( Vieth 1980: text-fig. 18), they are not dominated by such linear dentine canals, but by comparatively wide and interwoven, lacuna-like structures. Tissue with dentine tubules is developed only superficially, confirmed also by our material ( Fig. 8A ).

Dentine tubules, developed in scales of Canonia sp. from Severnaya Zemlya, have a rather unusual form, not characteristic of orthodentine, forming crowns in representatives of the Nikoliviidae family ( Fig. 8 ). Short linear or slightly curved arcades of branch connect vertically upswept dentine canals. Sometimes they form small lacuna-like widenings. Similar dentine tissue is developed in scales of loganiid thelodonts and is not characteristic of representatives of order Thelodontida . At present, the attribution of the genus Canonia to family Nikoliviidae is rather doubtful.

Figures

FIG. 6. — Nikolivia aligera n. sp., set of scales; A-E, head scales; F-M, O-Q, transitional scales; N, R-Y, trunk scales; all scales in crown view; collection numbers: LIG 35-466-LIG 35-489 (holotype H: LIG 35-474); sample 4-3, Matusevich River, Pod”emnaya Formation, Lochkovian, Lower Devonian. Scale bar: 0.3 mm.

FIG. 4. — A-H, Boreania minima Karatajūtē-Talimaa, 1985; A, B, transitional scales; C-H, trunk scales; A-C, E-G, scales in crown view; D, scale in lateral view; H, scale in base view; collection numbers: LIG 35-808-LIG 35-815; I-R, Canonia sp. cf. C. grossi Vieth, 1980; I-O, scales in crown view; P-R, scales in base view; collection numbers: LIG 35-816-LIG 35-825. Sample 4-3, Matusevich River, Pod”emnaya Formation, Lochkovian, Lower Devonian. Scale bars: A-H, 0.1 mm; I-R, 0.1 mm.

FIG. 7. — Canonia sp. cf. C. grossi Vieth, 1980, set of scales; all scales in crown view; collection numbers: LIG 35-826-LIG 35- 831; sample 4-3, Matusevich River, Pod”emnaya Formation, Lochkovian, Lower Devonian. Scale bar: 0.1 mm.

FIG. 8. — Canonia sp. cf. C. grossi Vieth, 1980, histological structure of scales; A, vertical longitudinal section, No. 1094; B, horizontal section of crown (without anterior part), No. 1095; sample 4-3, Matusevich River, Pod”emnaya Formation, Lochkovian, Lower Devonian. Abbreviations: b, base; cr, crown; dt, dentine tubules; pcv, pulp cavity. Scale bar: 0.1 mm.