Stroinolepis maenniki, Märss & Karatajūtē-Talimaa, 2002

Märss, Tiiu & Karatajūtē-Talimaa, Valentina, 2002, Ordovician and Lower Silurian thelodonts from Severnaya Zemlya Archipelago (Russia), Geodiversitas 24 (2), pp. 381-404 : 384-387

Stroinolepis maenniki n. sp. ( Figs 2 A-M; 3; 4)

HOLOTYPE. — Trunk scale Pi 7481 ( Fig. 2H, I ).

ETYMOLOGY. — Named after Dr. P. Männik, Institute of Geology at Tallinn Technical University, who found and kindly gave the scales for the study.

TYPE LOCALITY AND HORIZON. — Sample MF 49-9, Strojnaya River section, Strojnaya Formation, Upper Ordovician.

MATERIAL EXAMINED. — 49 scales, mainly broken.

OCCURRENCE. — Sample MF 49-7, Ozernaya Formation, Middle-Upper Ordovician; samples MF 49-9,11, MF 50-3, Strojnaya Formation, Upper Ordovician, Strojnaya River, October Revolution Island, Severnaya Zemlya Archipelago.

DIAGNOSIS. — As for genus, by monotypy.

DESCRIPTION

Morphology

Head scales are rounded or oval ( Fig. 2A ). The crown surface is smooth, slightly concave; the crown margins are gently crenulated. The neck is low and rather distinct. The base is in the shape of a vertical wall around a shallow diamond-shape or oval pulp depression. Transitional scales ( Fig. 2 B-E) are slightly longer than the head scales. They have an oval or elongated diamond-shape configuration of the crown. The latter has the anterior part divided into three with two notches and three ridges, of which the central one is pronounced; the lateral parts are narrow. The central and posterior parts of the crown are rather smooth. The neck is indistinct anteriorly and well developed posteriorly of the scale. The base is low. The pulp depression is diamond-shaped and shallow.

Scales in Fig. 2 F-M are treated here as trunk and fin scales. The set of scales is too small to tell for certain where in the squamation they come from. The scale in Fig. 2G characterizes this type; it is twice as large as other scales, strongly elongated, and its crown has three ridges (the lateral ones being sharper). The crown surface rises backwards, and the posterior crown apex is united with the base by a slanting rib. The neck is not distinct. The base is in a shape of a weak wall. The pulp depression is rhomboidal, and the opening of a pulp canal is not observed. All other scales are small, their crowns having three ridges, medial and lateral ones. The medial part can be flat or divided by a longitudinal furrow. The latter can occur only on the anterior part of the crown or reach the posterior end of it. Elongated ridges or short ridgelets are placed laterally. It is rather characteristic that all elongated ridges have sharp crests. The ridges start in the smoothly rounded antero-lateral corners of the base or in the posterior part of it. The neck is not clear in all scales. The base is concave or convex depending on the growth stage of the scale. The pulp depression in younger scales is rhomboidal. The set of scales shown in Fig. 3 exhibits the different size of the scales, and their crown sculpture.

Histology ( Fig. 4 )

It was mainly studied in anise oil. Dentine canals arising from the pulp depression are extremely fine. In the material available for study of the microstructure, the pulp canal is not present. Instead of the latter, some long dentine canals occur. Dentine canals in the crown branch at some levels and in vertical cross section they form a complicated network.

Genus Loganellia Turner, 1991

TYPE SPECIES. — Loganellia scotica (Traquair, 1898) .

Figures

FIG. 2. — A-M, Stroinolepis maenniki n. gen., n. sp.; A, head scale; B-E, transitional scales; F-M, undivided trunk and fin scales; A-G, I, L, M, scales in crown view; H, lateral oblique view; J, K, lateral view; A, Pi 7476; B, Pi 7479; C, Pi 7477; D, Pi 7484; E, Pi 7480; F, Pi 7472; G, Pi 7478; H, I, Pi 7481; J, Pi 7474, scale is lost; K, Pi 7470; L, Pi 7469; M, Pi 7473; A, C, F, G, J-M, sample MF 49-7, Strojnaya River, Ozernaya Formation, Middle-Upper Ordovician; B, E, H, I, sample MF 49-9; D, sample MF 49-11, Strojnaya River, October Revolution Island, Strojnaya Formation, Upper Ordovician; N-S, Loganellia grossi Fredholm, 1990; N, head scale; O, transitional scale; P-S, trunk scales; N, O, Q-S, scales in crown view; P, a scale in base view; N, Pi 7530; O, Pi 6839; P, Pi 7533; Q, Pi 7532; R, Pi 6837; S, Pi 7535; sample 2-68, Matusevich River, October Revolution Island, upper part of Samojlovich Formation, Wenlock, Lower Silurian. Scale bars: 0.1 mm.

FIG. 3. — Set of scales of Stroinolepis maenniki n. gen., n. sp., the same scales are presented in Fig. 2; A-M, Stroinolepis maenniki n. gen., n. sp.; A, head scale; B-E, transitional scales; F-M, undivided trunk and fin scales; A-G, I, L, M, scales in crown view; H, lateral oblique view; J, K, lateral view; A, Pi 7476; B, Pi 7479; C, Pi 7477; D, Pi 7484; E, Pi 7480; F, Pi 7472; G, Pi 7478; H, I, Pi 7481; J, Pi 7474, scale is lost; K, Pi 7470; L, Pi 7469; M, Pi 7473; A, C, F, G, J-M, sample MF 49-7, Strojnaya River, Ozernaya Formation, Middle-Upper Ordovician; B, E, H, I, sample MF 49-9; D, sample MF 49-11, Strojnaya River, October Revolution Island, Strojnaya Formation, Upper Ordovician. Scale bar: 0.5 mm.

FIG. 4. — Stroinolepis maenniki n. gen., n. sp., microstructure of the scales, Pi 7648, sample MF 49-7, Strojnaya River, October Revolution Island, Ozernaya Formation, Middle-Upper Ordovician. Abbreviations: dt, dentine tubules; lac, lacunae of dentine canals. Scale bar: 0.1 mm.