Paralogania menneri, Karatajūtē-Talimaa & Märss, 2002

Karatajūtē-Talimaa, Valentina & Märss, Tiiu, 2002, Upper Silurian thelodonts from Severnaya Zemlya Archipelago (Russia), Geodiversitas 24 (2), pp. 405-443 : 410-418

Paralogania menneri n. sp. ( Figs 7 ; 8 )

HOLOTYPE. — Transitional(?) scale LIG 35-878 ( Fig. 7J, K ).

ETYMOLOGY. — Named in honour of Dr. V.V. Menner, Moscow, Russia, one of the organizers of field work to the October Revolution Island in 1978. SYNONYMY. — P. menneri n. sp. scales were earlier identified as Paralogania sp. nov. 2 (Karatajūtē- Talimaa 1997: fig. 9C, D; Talimaa 2000); and as Paralogania sp. 1 (Märss & Karajūtē- Talimaa 2002: fig. 1).

MATERIAL EXAMINED. — More than 5000 scales of good preservation. Especially rich in different morphological varieties of scales is the sample 14-47 from the Spokojnaya River, October Revolution Island.

TYPE LOCALITY AND AGE. — Samples 47-14, Spokojnaya River, October Revolution Island, Severnaya Zemlya Archipelago, Ust-Spokojnaya Formation, Ludlow, Upper Silurian; 18041-14, Komsomolets Island, Ludlow, Upper Silurian.

DIAGNOSIS. — Head scales rounded or oval with crenulated margins. The length of the scales is between 0.3-0.9 mm. Transitional scales are of two morphological types. Type “A” has characteristic for loganelliid scales. They have rhomboidal or oval crowns with deep notches anteriorly, and with one or several projections (spines) of the posterior margin. The length of the scales represents 0.4-0.8 mm. Among type “B”, the scale crowns have a posterior median spine. In some of such scales the spine can be relatively long, e.g., if the average length of the scales is 0.6-0.8 mm then with the spine it can reach 1.1 mm. The crown is anteriorly wide, rhomboidal or rounded, with a median and one to three lateral areas. The surface of the medial area is smooth and that of the spine is finely striated. Some trunk scales have short rhomboidal crowns with a smooth medial area, and with short base (length 0.5-0.75 mm); postero-laterally of the crown is situated one row of short spines four to five in number, and instead of a posterior spine a longitudinal ridge is present. The main part of trunk scales consists of scales with long (length up to 1.7 mm) but narrow crown and relatively short base, wide in the central part. A lot of scales are with spur-like projection anteriorly of the base. Posteriorly the crowns of many scales are longitudinally finely striated. Histology typical for Paralogania .

DESCRIPTION

Morphology

Head scales small (0.3-0.5 mm), oval, rarely rounded, with finely crenulated crown margins ( Fig. 8A, B ). Larger scales, with length up to

A

B

0.9 mm are rare. The base can be rather high and have small vertical rootlets. Pulp cavity in such scales is deep and opens in the centre of the base. Transitional scales have been divided into two morphological types. Type “A” consists of typical loganelliid scales with oval or rhomboidal smooth flat crown surface and shallow notches on the margins ( Fig. 8C, D ); the posterior part of them is tapering posteriorly into keel-like end, or their crowns have deep notches antero-laterally that divide the crown into medial and lateral areas ( Figs 7A ; 8E, H ). Lateral areas (1-2) are relatively shorter than the medial one. The posterior crown margin bears several projections. The length of the scales of type “A” is usually less than 0.6 mm. In larger scales, with a length of about 0.8 mm, the wide and smooth central crown plate ( Fig. 8F ) is developed, and narrow lateral areas carry four to five short lateral spines. The base is low and a little wider than the crown. Transitional(?) scales of the morphological type “B” ( Figs 7 B-O; 8H-O) are particularly characteristic for the squamation of P. menneri n. sp. The main feature is the presence of a median posterior spine (strongly elongated central crown area) which can reach the length of the anterior, main crown part. The length of transitional(?) scales with a short spine is 0.6-0.8 mm (the length of the spine 0.15-0.25 mm) and that with a long spine is up to 1.1 mm (length of the spine 0.3-0.55 mm). The short medial spine is straight and horizontal, on the same plane as remaining crown plate. The longer spines arise posteriorly, sometimes laterally. The tips of long spines are usually broken; in well preserved scales they are sharp and long ( Fig. 7C, D, F, G ). Upper surface of the spine is covered with fine longitudinal striation ( Fig. 7F, H , J-O), lower surface of it is usually smooth ( Fig. 7G ). The crown of transitional(?) scales of type “A” is rhomboidal or rounded and is divided into central and lateral areas separated by deep longitudinal notches anteriorly; its width reaches 0.45-0.6 mm. Sometimes the central area is situated far forward ( Fig. 7J ). The upper surface of the crown is smooth or with a short medial furrow ( Fig. 7B, J, L ). Laterally there can be one pair ( Fig. 7C, D, F, J ), two pairs ( Fig. 7O, N ) or three pairs ( Fig. 7H, I ) of lateral areas. They are always shorter than the medial one; their margins are smooth or crenulated. Especially distinct crenulation or spines are developed on the outer margin of the most lateral area. The base which is relatively low is anteriorly a little larger than the crown and protrudes over the perimeter of the crown as a narrow strip (e.g., Fig. 7 B-D, F, H, J, L). Pulp depression is elongated or triangular ( Figs 7G ; 8H 2 ).

Trunk scales of different size and form compose more than a half of the whole scale material of this species. The best example is the sample 47- 14 from Spokojnaya River section. Two distinct (extreme) morphological varieties have been distinguished: 1) short rhomboidal; and 2) long and narrow, often with a spur-like projection anteriorly of the base. Besides, there are a lot of scales which length and width proportions of the crown and base are transitional between these two varieties. In Figs 7E and 8P, Q some trunk scales are shown. A relatively wide anterior part of them consists of the central and lateral areas with three to four short marginal spinelets; a spur-like projection of the base is directed anteriorwards and downwards. Such scales have the position between transitional(?) and elongated trunk scales.

Short trunk scales are up to 0.5-0.75 mm long at base width of 0.4-0.55 mm ( Fig. 8W, X ). Their crown is composed from a rhomboidal flat smooth area; postero-laterally of it is situated a row of short spinulets, four to five in number. The base is wider than the crown and expanded anteriorly. Fig. 8T represents a comparatively long trunk scale (length 1.0 mm) that after its features can be situated between short and wide and long and narrow scale types. The number of lateral spines is the largest (five). Beneath the postero-medial point of the crown, a longitudinal medial ridgelet, analogous to the medial spine, is developed. It begins at the posterior end of the base and continues into the posterior crown apex.

Long and narrow trunk scales reach a length up to 1.7 mm. Among them also a lot of fine and narrow scales, still having the same proportions of the crown and base, characteristic of the relatively larger scales, have been found ( Figs 7P, S ; 8R, S, V ). The central area of the crown is as elongated rhomb, relatively wide and flat ( Fig. 8R, S ) or narrow and with a furrow ( Figs 7S ; 8V ). Postero-laterally of the crown, a row of three to four short lateral spinulets ( Fig. 8S ), a longitudinal ridge and a row of spinulets ( Fig. 8R ) or two to three longitudinal ridges ( Figs 7S ; 8V ) can be found. The posterior part of the crown is covered with fine striation. On the lower surface a fine medial longitudinal ridge (analogous to the medial spine) is always present ( Fig. 7P, R ). The remaining surface is covered with longitudinal ridgelets or is smooth. The base of a number of elongated trunk scales is rhomboidal, wider than the crown and often prolongated anteriorly as a spur’s shape; it can be relatively wide ( Fig. 8S ) or narrow ( Figs 7P ; 8R, V ). The pulp depression is narrow and long. In many scales the pulp opening is large and situated in the posterior corner of the base.

Histology

The microstructure of the scales has been studied under anise oil immersion. Arrangement, form and width of dentine tubules are as in Paralogania ex gr. martinssoni from the Ludlow deposits of Severnaya Zemlya (Karatajūtē- Talimaa 1997: fig. 9A, B). The main pulp canal is wide and long in elongated trunk scales of P. menneri n. sp., and short and narrow in short trunk scales (see Karatajūtē- Talimaa 1997: fig. 9C, D). Lateral pulp canals, going into lateral spines, are not always developed.

COMPARISON

Paralogania menneri n. sp. can be attributed to the P. kummerowi - P. martinssoni group after the number and disposition of the postero-lateral spines of the trunk scales crown. Medial spine, being distinct and relatively long (or high as in P. kachanovi n. sp.) in the other representatives of this group, is modified in P. menneri n. sp. into a medial longitudinal ridgelet. Presence of special transitional(?) scales in the morphological variety set of scales of P. menneri n. sp. distinguishes this species from the others of the genus. Perhaps, one characterictic is the fine longitudinal striation of the crown present only for the transitional(?) and most of the elongated trunk scales of P. menneri n. sp. On the scales of the closest species, P. martinssoni , the striation is not present. Some morphological varieties of the scales of P. menneri n. sp., e.g., head scales, transitional scales of type “A” and part of trunk scales (with short, rhomboidal and relatively elongated and flat crown) are present also in the morphological set of P. martinssoni and P. ex gr. martinssoni . Still, the lateral spines in trunk scales of P. menneri n. sp. are always short while in P. martinssoni they can reach a noticeable length.

Figures

FIG. 7. — Paralogania menneri n. sp.; A, transitional scale; B-O, transitional(?) scales; P-T, trunk scales; A-C, E, F, H, J, L, S, scales in crown view; D, a scale in oblique lateral view (posterior end on the left); G, P, scales in base view; N, a scale in lateral view; I, magnified of H; K, magnified of J; M, magnified of L; O, magnified of N; R, magnified of P; T, magnified of S; A, Pi 7618; B, Pi 7607; C, D, Pi 7605; E, Pi 7604; F, LIG 35-871; G, LIG 35-872; H, I, LIG 35-877; J, K, holotype, LIG 35-878; L, M, LIG 35-879; N, O, LIG 35-880; P, R, LIG 35-881; S, T, LIG 35-882; A-E, sample MF 11-1, Matusevich River, October Revolution Island, Ust-Spokojnaya Formation, Ludlow; F, G, sample 18041-14, Komsomolets Island, Ludlow; H, J, L, N, P, S, sample 47-14, Spokojnaya River, October Revolution Island, Ust-Spokojnaya Formation, Ludlow, Upper Silurian. Scale bars: A, H-O, R, T, 0.1 mm; B-G, P, S, 0.2 mm.

FIG. 8. — Paralogania menneri n. sp., morphological set of scales; A, B, head scales; C-G, transitional scales; H-O, transitional(?) scales; P-X, trunk scales; A-H1, I-X, scales in crown view; H2, a scale in base view; A-X, LIG 35-194-LIG 35-217; sample 47-14, Spokojnaya River, October Revolution Island, Ust-Spokojnaya Formation, Ludlow, Upper Silurian. Scale bar: 0.5 mm.

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.