Grossilepis tuberculata ( Gross, 1941 )

Lukševičs, Erwin, 2001, Bothriolepid antiarchs (Vertebrata, Placodermi) from the Devonian of the north-western part of the East European Platform, Geodiversitas 23 (4), pp. 489-609 : 595-597

Grossilepis tuberculata ( Gross, 1941) ( Figs 79 ; 80 )

Bothriolepis tuberculata Gross 1941: 32-57 , abb. 25, 26A-G, 27A-C, 28-43; taf. 18-28.

Bothriolepis cellulosa (Pander) – Gross 1932: 24 (p.p.); 1933: 36-39, taf. 4, fig. 5 (p.p.). — Obruchev 1947: pl. LV, fig. 4.

Grossilepis tuberculata (Gross) – Stensiö 1948: 524- 534, text-figs 26L, 28E, 35F, 36C-E, 39D, 41D, 43E, 44F, 45H, 47D, 48D, 53D, 266-271.

HOLOTYPE. — AMD kept in SMNH ( Gross 1941: abb. 30F, taf. 21, fig. 1).

MATERIAL EXAMINED. — LDM 65/77, MxL; NHM 17827,La; NHM 17811,17817, 17820,three PMD; NHM 17812, PVL; LUGM, several unnumbered specimens including AMD, PMD, La plates is aaditional to that described by Gross (1941) and Stensiö (1948).

LOCALITIES AND HORIZON. — The type locality is an outcrop of dolomite, dolomite marl and clay at the bank of Pērse River near Koknese, Latvia; The lower Frasnian Pļaviņas Formation. This species was found in the Snetnaya Gora Member in several localities in western and eastern Latvia: outcrops along Daugava River from Kaktiņi to the ruins of Koknese castle, exposures at Amata River not far from Kārļi and along Mazā Jugla and Lielā Jugla Rivers, outcrops at Venta River near Kuldīga and at Riežupe River ( Sorokin 1978), Lithuania: borehole Berčiunai, 73-76 m deep, borehole Pakapiai, 78.2-80.3 m deep, and Pskov region of Russia: outcrop at the right bank of Velikaya River near Piskovichi hamlet, Snetnaya Gora, Pskov and Chudovo Beds of Russia. The remains of G. tuberculata are very rare in the middle part of the Pļaviņas Formation (Atzele and Sēlija Members, which corresponds to the Pskov Beds in Russia) and until now reported only from eastern Latvia ( Sorokin 1978).

DIAGNOSIS. — Relatively small bothriolepidoid with estimated length of dorsal wall of trunk armour reaching about 9 cm. Head-shield moderately vaulted with anterior margin much shorter than total breadth of the plate. Postero-lateral corners of head-shield extends anteriorly to the level of the orbital fenestra posterior margin. Nu of moderate width, L/B index of about 61- 73, usually with concave posterior margin bearing the median process, shallow postpineal notch on the anterior margin, slightly pronounced lateral and posterolateral corners. Pn with broad lateral division. Tergal angle situated between the anterior and middle thirds of the AMD length. Posterior margin of AMD very broad. Dorsal median ridge normally developed from the tergal angle backwards to the posterior corner of PMD. Dorsal corner slightly pronounced or sometimes even not be clearly identifiable. Pectoral fin fairly slender, proximal segment from 4.5 to slightly more than 5 times as long as broad. Lateral spines of the pectoral fin numerous, small, closely set and obtuse. Ornament consists of numerous closely and irregularly set pointed tubercles in well-grown individuals.

REMARKS

This species is well-described by Gross (1941) and Stensiö (1948). Their descriptions are based on a large collection of the placoderm and other fish remains kept at Swedish Museum of Natural History, Stockholm. Although little new material is available that has not been described before, the descriptions of Gross and Stensiö can be added, providing a new definition of this species, as the definition of Grossilepis tuberculata suggested by Stensiö (1948: 523- 524) was the same as that of the genus Grossilepis .

DISCUSSION

The comparison of Grossilepis tuberculata with G. spinosa is provided below the description of the latter. G. tuberculata differs well from G. brandi Miles, 1968 in its relatively narrower Nu and a proportions of the anterior and posterior divisions of the lateral margin of this plate.

Figures

FIG. 79. — Grossilepis tuberculata (Gross, 1941); A, reconstruction of the head-shield; B, C, La; D, E, Pn; F, Nu (from Gross 1941: abb. 29 II, 27A, 27C, 26B, 26A, 25A respectively). Pērse River near Koknese (Kokenhusen), Latvia. Pļaviņas Formation. Abbreviations: La, lateral plate; Nu, nuchal plate; Pn, paranuchal plate. Scale bar: 10 mm.

FIG. 80. — Grossilepis tuberculata (Gross, 1941); A, B, AMD in dorsal (A) and visceral (B) views; C, specimen showing visceral and partly remained dorsal side of the AMD; D, reconstruction of dorsal wall of the trunk armour; E, reconstruction of ventral wall of the trunk armour; F, G, reconstruction of proximal segment of pectoral fin in dorsal and ventral views; H, I, parts of distal segment of pectoral fin in dorsal view. From Gross 1941: abb. 30F, 30A, 30D, 36, 37, 43A, 43B, 43F, 43H respectively.Pērse River near Koknese (Kokenhusen), Latvia. Pļaviņas Formation. Abbreviations: ADL, anterior dorso-lateral plate; AMD, anterior median dorsal plate; AVL, anterior ventro-lateral plate; CD1-4, dorsal central plates 1 to 4; CV1, 2, ventral central plates 1 and 2; ML2-4, lateral marginal plates 2 to 4; MM1, 2, 4, mesial marginal plates 1, 2 and 4; MV, median ventral plate; MxL, mixilateral plate; PMD, posterior median dorsal plate; PVL, posterior ventro-lateral plate; SM, semilunar plate; cf.MxL, area overlapping MxL; f.ax, axillary foramen.