Paralogania kachanovi, Karatajūtē-Talimaa & Märss, 2002

Karatajūtē-Talimaa, Valentina & Märss, Tiiu, 2002, Upper Silurian thelodonts from Severnaya Zemlya Archipelago (Russia), Geodiversitas 24 (2), pp. 405-443 : 421-424

Paralogania kachanovi n. sp. ( Fig. 11 )

Paralogania sp. 3 Märss & Karajūtē- Talimaa 2002: fig. 1. HOLOTYPE. — LIG 35-051, trunk scale ( Fig. 11L ).

ETYMOLOGY. — Named in honour of late E. I. Kachanov, Magadan, Russia, who studied the Silurian deposits on the Pioneer Island.

TYPE LOCALITY AND AGE. — Sample 12, Pridoli, Upper Silurian, Pioneer Island, Severnaya Zemlya Archipelago (see Fig. 1 ).

MATERIAL EXAMINED. — Over 200 scales of relatively good preservation but pyritized.

DIAGNOSIS. — Medium-sized scales (0.9-1.3 mm long). Crown margins of the head scales crenulated, crown surface flat and smooth. In the transitional scales the antero-medial crown portion separated from the lateral ones; posterior crown margin notched, crown surface flat. Trunk scales rhomboidal with one wide flat central area on the crown. Posterolateral crown walls bear a row of six to eight spines on each side and one spine beneath the posterior crown apex. Spines are short and low, directed upwards. Posterior crown portion of smaller scales may have shallow medial groove. A short pulp canal is developed in trunk scales.

DESCRIPTION

Morphology

Head scales oval, rounded, rhomboidal, elongated and in rare cases widened ( Fig. 11 A-E). Asymmetric, elongated and comparatively big scales have also been found. The length of the head scales 0.5-0.9 mm, rarely up to 1.2-1.3 mm, width 0.4-0.8 mm and height 0.35-0.55 mm. Anterior crown area is distinguishable in almost all scales. Crown is comparatively monolithic, with flat surface, margins with deep crenulation, especially antero-laterally ( Fig. 11 B-D). Base is rather large and can extend beyond the perimeter of the crown. Juvenile scales with low base have a large but shallow pulp depression.

Transitional scales ( Fig. 11 F-H) are oval to rhomboidal. Their length can reach 0.75- 0.9 mm, width 0.4-0.6 mm and height up to 0.4 mm. Crown is comparatively monolithic, with flat surface of antero-medial area and crenulated postero-lateral margins. Lateral areas of the crown are not always distinct. Base is sometimes wider than crown ( Fig. 11G ).

Trunk scales are rhomboidal with shortened anterior and elongated keel-like posterior areas ( Fig. 11 I-T). Length of the crown 0.5-0.9 mm, width 0.4-0.75 mm, height is rather constant: 0.3-0.5 mm. Height of the base is usually smaller than that of the crown. The crown of trunk scales is monolithic and composed of a smooth and flat central area with smooth margins. Antero-lateral areas of the crown (neck) are separated from the postero-lateral ones with a distinct vertical ridge. Postero-lateral crown walls bear spines, six to eight on each side, and one spine under the posterior crown apex. Spines are situated in longitudinal rows. Spines are low, directed upwards and are formed from several apices on a fused base. In Fig. 11L is drawn the scale chosen as the holotype. Its length is 0.8 mm, width 0.65 mm and height 0.35 mm: its number of spines is eight; beneath the posterior crown point the medial spine is composed of two rounded apices. Base of trunk scales is slightly shifted forwardly. The most protruding part of the base is situated anteriorly from the pulp opening. Scales with spur-like projection of the base have not been found. Triangular pulp depression is placed at the posterior corner of the base ( Fig. 11P, R, T 2 ). Pulp opening is well defined in scales of all stages of development.

Small scales ( Fig. 11S, T 1 , 2 ) having a narrow medial fine groove on the posterior crown surface and less lateral spines (four to six) are also present in the samples.

Histology

Short pulp canal of trunk scales distinct. Dentine tubules rather wide.

COMPARISON

P. kachanovi n. sp. scales differ from the other species of the genus in having a monolithic crown and in lacking the lateral areas of the crown on trunk scales. General proportions and flat smooth crown of trunk scales of Severnaya Zemlya species show similarity with P. borealis from the Pridoli of North Timan. Composition of lateral spines, their form and length/height is a unique characteristic of P. kachanovi n. sp. A large number of spines (up to eight) is also observed in P. kummerowi and P. borealis . P. kachanovi n. sp. differs from P. wilsoni n. sp. in its larger size, the form and width of the medial area of the crown, the number and form of lateral spines and also the form of its base (lacking the spur-like projection). P. kachanovi n. sp. can be attributed to the P. kummerowi - P. martinssoni group because they all have a medial spine beneath the posterior crown apex.

Paralogania sp. cf. Paralogania borealis (Karatajūtē- Talimaa, 1978)

DESCRIPTION AND COMMENTS

A sample from the outcrop 41, bed 1, has yielded about 20 predominantly trunk scales which crowns resembling very much the trunk scales of Paralogania borealis from the Eptarma Formation of North Timan (Karatajūtē- Talimaa 1978: 92-94). Together with them scales of Goniporus alatus and Nikolivia elongata are also represented. The composition of the assemblage with its lack of Thelodus scales and occurrence of Nikolivia elongata testify a completeness of the Silurian-Devonian boundary section in the Krasnaya Bay area.

In the deposits of Krasnaya Bukhta (bukhta means bay in Russian) Formation on October Revolution Island and its analogues on Pioneer Island, three thelodont assemblages characterize different levels of the Pridoli. The first and oldest assemblage, established on Pioneer Island (sample 12) contains P. kachanovi n. sp., Loganellia cuneata and Thelodus parvidens (?). The second assemblage is distributed on the higher level of the Krasnaya Bukhta Formation along the Spokojnaya River (sample 157-2 and a sample “a” from the outcrop 51a). This assemblage is composed of Paralogania wilsoni n. sp., Loganellia cuneata and Goniporus alatus . The third assemblage includes scales of the Late Silurian and Early Devonian thelodonts and characterizes the uppermost Pridoli (or transitional beds to the Lochkov, Early Devonian in age?).

Genus Valiukia n. gen.

TYPE SPECIES. — Valiukia flabellata n. gen., n. sp. (by monotypy).

ETYMOLOGY. — Named after Dr. Juozas Valiukevic˘ ius (Vilnius), a member of the field expedition to October Revolution Island in 1978.

OCCURRENCE. — Matusevich River, October Revolution Island, Severnaya Zemlya Archipelago, Ust-Spokojnaya Formation, Ludlow, Upper Silurian.

DIAGNOSIS. — As for species.

REMARKS

The scales figured in Märss & Karatajūtē- Talimaa 2002: figs 8I-L; 9E, referred to Loganelliidae gen. et sp. indet., belong to Valiukia n. gen.

COMPARISON

Morphological set of scales of genus Valiukia n. gen. differs from those of other genera of the family Loganelliidae ( Loganellia , Paralogania , Shielia Märss, 1998 ) distributed in the Wenlock and Ludlow of Severnaya Zemlya Archipelago in several features; the most important lies on the crown structure of the transitional and trunk scales. Numerous longitudinal areas and spines are developed in the posterior part of the crown. Exclusive to Valiukia n. gen. they are not analogous to the postero-lateral spines of the crown of trunk scales of Paralogania . Some similarities can be found with the structure of the posterior part of the ridged crown of trunk scales of Shielia ( Märss & Ritchie 1998; Märss & Karatajūtē- Talimaa 2002). Transverse ridgelets between the main ridges of different crown areas of transitional scales have not been observed in the scales of other genera. The structure of the base of trunk scales, the position of pulp opening and histological features (size and distribution of dentine tubules, presence of main and lateral pulp canals) are like in scales of the genus Paralogania .

Figures

FIG. 11. — Paralogania kachanovi n. sp., morphological set of the scales; A-E, head scales; F-H, transitional scales; I-T, trunk scales; L, holotype; A-I, J1, K, N, T1, scales in crown view; J2, L, M, O, Q, scales in lateral view; T2, scale in base view; P, R, scales in oblique postero-lateral view; S, scale in oblique lateral view; “×” shows the anterior part of the scale; A-K, LIG 35-039-LIG 35-049; L, LIG 35-050; M-P, LIG 35-051-LIG 35-054; Q-T, LIG 35-873-LIG 35-876; sample 12, Pioneer Island, Pridoli, Upper Silurian. Scale bar: 0.3 mm.

FIG. 1. — Distribution of thelodonts in the Silurian section of Pioneer Island; 1, sandstone; 2, sandstone and silty sandstone; 3, argillite; 4, biomorphic limestone; 5, dolomite; 6, dolomitic limestone; 7, oolitic limestone; 8, stromatoporoidal limestone (after Klubov et al. 1980: fig. 2; modified). Cyrillic letters in fig. 2 of Klubov et al. 1980 are in present paper transliterated as follows: A = a; Б = b; B = v; г = g; д = d; E = e; 3 = zh; и = i; K = k; M = m; H = kh.

FIG. 2. — A-I, Thelodus matukhini n. sp., scales in crown view; A, LIG 35-859; B, holotype, LIG 35-860; C, LIG 35-861; D, LIG 35- 862; E, Pi 7552; F, Pi 7550; G, Pi 7547; H, Pi 7551; I, Pi 7557; A-D, sample 18041-14, Komsomolets Island, Ludlow, Upper Silurian; E-I, sample MF 34-1, cape October (Octyabrskij), October Revolution Island, Ludlow, Upper Silurian; J-Q, Loganellia cuneata (Gross, 1947); J, L, O-Q, scales in crown view; K, M, scales in oblique lateral crown view; N, a scale in lateral view; J-Q, LIG 35-863- LIG 35-870; sample 2-23, Matusevich River, October Revolution Island, Ust-Spokojnaya Formation, Ludlow, Upper Silurian. Scale bars: A, C, E-H, J-P, 0.1 mm; B, D, I, Q, 0.2 mm.