Paralogania consimilis, 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 : 396-400

Paralogania consimilis n. sp. ( Figs 6G ; 11-13 )

HOLOTYPE. — Trunk scale Pi 7515 ( Fig. 11O, P ).

ETYMOLOGY. — From the Latin word consimilis meaning “similar to” to indicate that the new species has some features similar to P. martinssoni and some to P. ludlowiensis .

MATERIAL EXAMINED. — About 250 scales.

TYPE LOCALITY AND HORIZON. — Sample MF 46-23, 32a-208, Ushakov River, October Revolution Island,

upper part of Samojlovich Formation, Wenlock, Lower Silurian.

OCCURRENCE. — Samples MF 46-23 and 32a-204, 32a-208, Ushakov River , October Revolution Island, upper part of Samojlovich Formation, Wenlock, Lower Silurian; (?) sample MF 11-1, Matusevich River , Ust’-Spokojnaya Formation , Ludlow , Upper Silurian. DIAGNOSIS. — Length of scales up to 1.1 mm and width up to 0.4 mm. Anterior head scales with crenulated margins around the crown, transitional scales with two to four notches antero-laterally, trunk scales of two type: with flat crown plate, spines (= thornlets) on the lateral vertical crown portion and high base ; or flattened scales with medial crown portion having a longitudinal groove, lateral rib and up to four spines beneath the rib and one below the posterior crown apex. Scales of the latter type usually have long anterior spur-like projection of base. From the pulp depression spring medial and up to three pairs of lateral pulp canals. Widenings of lateral pulp canals form lacunae arranged in a line in the neck and crown just above the base. Dentine canals and dentine tubules are fine and straight. Branching dentine tubules are distributed in the anterior sprong of the base, irregular aspidine “pegs” are present in base.

DESCRIPTION

Morphology

The anterior head scales ( Figs 11 A-C; 12A-E) are deeply crenulated, with a distinct neck and vertical base that has a thickened anterior part. The posterior margin of a head scale ( Fig. 11C ) is sharply cut with a peg-like projection. Transitional scales ( Figs 11D, G ; 12F, G ) are with two rather deep and some shallow notches antero-laterally. Transitional (or from the leading edges of fins) scales can have a spur-like anterior projection ( Fig. 11G ). They are not numerous in our samples. Trunk scales ( Figs 11E, F , H-T; 12H-P, S, T, X) are up to 1.1 mm long and 0.4 mm wide, the length of the crown being 0.8 mm. Measurements for the holotype ( Fig. 11O, P ): length 0.8 mm, width 0.6 mm. There are two main types of trunk scales. First, they can be with a flat smooth crown plate and with just a few (up to four) spines on the lateral vertical crown portions ( Figs 11H, J ; 12S, T ) with an anteriorly placed base. Their length is 0.6 mm and width 0.3 mm. The crowns of some scales show two to three spines and a short rib anterior to them ( Fig. 11E, K, M, N ) ; anteriorly on the crown plate there is just a very shallow furrow. Secondly, fully formed trunk scales characteristic for the species are flattened, have the crown plate with a medial furrow, carry lateral ribs converging posteriorly a little farther than the crown apex is, and have four to five spines beneath the lateral ribs and one below the posterior apex. The neck is indistinct, and the base is with a peg-like projection anteriorly. Fin scales ( Fig. 12Q, R, U, V ) are short and narrow, some have a tripartite posterior crown portion but most crowns are pointed posteriorly. The smallest spiny scales are 0.5 mm long and 0.2 mm wide; overall, the smallest scales in our collection are 0.3 mm long and 0.15 mm wide. Special scale varieties should be noted. A very few scales (e.g., Fig. 11F ) in the samples are built from a short and narrow medial portion of the crown. It is separated from the lateral ridges by a steep and comparatively deep groove. The ridges converge on the posterior medial apex, and lateral spines (four to five in number) lie

A with their proximal part on the crown margins. A second variety present in the samples is ridged scales with spines ( Fig. 11I ). A sample (MF 11-1) from Matusevich River, Ust’-Spokojnaya Formation, contains some scales that because of the lateral rib above the spines can be identified as P. consimilis n. sp. (see Karatajūtē- Talimaa & Märss 2002: fig. 3G-I).

Histology

See Diagnosis, and Figs 6G and 13. COMPARISON

Paralogania consimilis n. sp. is intermediate between P. martinssoni (Gross, 1967) and P. ludlowiensis (Gross, 1967) . Head and transitional scales are rather similar in the new species and P. martinssoni . Trunk scales differ in these species, P. consimilis n. sp. having a lateral rib and spines beneath it. Such a structure characterizes P. ludlowiensis but the latter has two spines below the posterior crown apex while P. consimilis n. sp. has one like P. martinssoni . Head scales of P. consimilis n. sp. and P. ludlowiensis differ strongly because P. ludlowiensis has a high traquairi - type of head scales but those of P. martinssoni have crenulated crown margins and a smooth central part. An anterior spur-like projection is present in P. consimilis n. sp. while in P. ludlowiensis it is absent. P. kummerowi (Gross, 1967) scales are much bigger than P. consimilis n. sp., and without lateral ribs; the number of spines is greater in P. kummerowi .

Loganelliidae gen. et sp. indet. ( Figs 8 J-L; 9E)

Together with Paralogania klubovi n. sp., the sample 2zh from the middle(?) Llandovery of Pioneer Island contained a single well preserved scale that cannot be attributed to either Paralogania or other thelodont genera because of its specific morphological features. It is doubtfully determined as Loganelliidae gen. et sp. indet. (new genus of family Loganelliidae ; see Karatajūtē- Talimaa & Märss 2002). Based on the very large pulp depression and low, wall-like base, it is thought to be a young trunk scale. Its crown is small, wide and short (length of the crown is 0.3 mm); it is composed of an enlarged central area, which is wide at the proximal part and tapered, keel-like, at the distal part of the crown. The central area is furrowed. The distal part of the crown is wider, and composed of wing-like areas that are positioned at different levels (higher or lower) ( Fig. 8I, K ). Each higher area overlaps the lower one, and a notch is situated between them. Each area ends with an independent posterior apex. The posterior end of the central one has two medial, tapered apices beneath it, the lowest being the longest. The crown surface of all areas is covered by fine longitudinal striations ( Fig. 8 J-L). The lower side of the crown ( Fig. 9E ) shows wing-like structures from below; its elongated ribs end with spines. The base is at the anterior of the scale. Openings of pulp canals are observed in the comparatively deep pulp depression, in the bases of the longitudinal ribs.

Order THELODONTIDA Kiaer, 1932

Family COELOLEPIDAE Pander, 1856

TYPE GENUS. — Thelodus Agassiz, 1839 .

Genus Thelodus Agassiz, 1839

TYPE SPECIES. — Thelodus parvidens Agassiz, 1839 .

Figures

FIG. 6. — Microstructure of the scales; A, B, Loganellia matura n. sp.; C-F, Shielia multispinata n. sp.; G, Paralogania consimilis n. sp.; A, Pi 7624; B, Pi 7625; C, Pi 7626; D, Pi 7627; E, Pi 7628; F, Pi 7629; G, Pi 7630; A, B, sample MF 3-8, Srednii Island, Golomyannyj Formation, middle part of Llandovery, Lower Silurian; C-F, sample MF 157-7, Spokojnaya River, upper part of Samojlovich Formation, Wenlock, Lower Silurian; G, sample MF 46-23, Ushakov River, October Revolution Island, upper part of Samojlovich Formation, Wenlock, Lower Silurian. Abbreviations: asp, aspidine “pegs” in the base; b, base; bc, canal in the base; cr, crown; dc, dentine canal; dt, dentine tubules; fpc, fan-shaped pulp canals; lac, lacunae of dentine canals; mpc, main pulp canal; n, neck; pc, pulp canal; pco, pulp canal opening; sp, spine. Scale bars: 0.1 mm.

FIG. 11. — Paralogania consimilis n. sp.; A-C, head scales; D, G, transitional scales; E, F, H-T, trunk scales; A-D, F-M, O, Q, R, scales in crown view; E, N, P, scales in lateral view; A, Pi 7510; B, Pi 6808; C, Pi 7508; D, Pi 7509; E, Pi 7507; F, Pi 6806; G, Pi 7514; H, Pi 7506; I, Pi 6816; J, Pi 6809; K, Pi 7511; L, Pi 6810; M, N, Pi 7512; O, P, holotype Pi 7515; Q, Pi 6813; R, Pi 6817; S, Pi 7513; T, Pi 6811; sample MF 46-23, Ushakov River, October Revolution Island, upper part of Samojlovich Formation, Wenlock, Lower Silurian. Scale bars: 0.1 mm.

FIG. 12. — Set of scales of Paralogania consimilis n. sp.; A-E, head scales; F, G, transitional scales; H-P, S, T, W, trunk scales; Q, R, U, V, fin scales; A, LIG 35-149; B, LIG 35-150; C, LIG 35-151; D, LIG 35-152; E, LIG 35-153; F, LIG 35-154; G, LIG 35-155; H, LIG 35-156; I, LIG 35-163; J, K, LIG 35-168; L, LIG 35-169; M, LIG 35-170; N, LIG 35-171; O, LIG 35-172; P, LIG 35-173; Q, R, LIG 35- 174; S, LIG 35-175; T, LIG 35-176; U, LIG 35-177; V, LIG 35-178; W, LIG 35-179; sample 31-208, Ushakov River, October Revolution Island, upper part of Samojlovich Formation, Wenlock, Lower Silurian. Scale bar: 0.3 mm.

FIG. 13. — Paralogania consimilis n. sp., microstructure of the scales; A, B, vertical longitudinal section; A, Pi 7621; B, Pi 7620; C, horizontal section, Pi 7622; sample 46-23, Ushakov River, October Revolution Island, upper part of Samojlovich Formation, Wenlock, Lower Silurian. Abbreviations: lac, lacunae; mpc, main pulp canal; pc, pulp canal; pd, pulp depression; sh, canals of Sharpey’s fibres; sp, spine. Scale bar: 0.1 mm.

FIG. 8. — A-I, Paralogania klubovi n. sp.; A, B, head scales; C, transitional scale; D-I, trunk scales; A, B, D-F, H, I, scales in crown view; C, a scale in base view; G, a scale (holotype) in lateral view; A, LIG 35-085; B, LIG 35-086; C, LIG 35-832; D, LIG 35-087; E, LIG 35-833; F, LIG 35-088; G, LIG 35-834; H, LIG 35-835; I, LIG 35-836; J-L, Loganelliidae gen. et sp. indet.; J, scale in crown view; K, posterior part of the same scale; L, enlarged part of left posterior section, LIG 35-089; sample 2zh, Pioneer Island, middle(?) Llandovery, Lower Silurian. Scale bars: 0.1 mm

FIG. 9. — A-D, Paralogania klubovi n. sp.; A, B, head scales in base view (see Fig. 8A, B); C, trunk scale of type A in base view (see Fig. 8D); D, trunk scale of type B in base view (see Fig. 8F); A, LIG 35-085; B, LIG 35-086; C, LIG 35-087; D, LIG 35-088; E, Loganelliidae gen. et sp. indet.; scale in base view (see Fig. 8J, K), LIG 35-089; sample 2zh, Pioneer Island, middle(?) Llandovery, Lower Silurian. Scale bar: 0.1 mm.