Bothriolepis cellulosa (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 : 517-519

Bothriolepis cellulosa (Pander in Keyserling, 1846) ( Fig. 11 )

Pterichthys cellulosa Pander in Keyserling, 1846: 292.

Bothriolepis retinata Hoffman, 1911: 293 , 297, figs 14, 15; pl. 24, fig. 4. — Gross 1931: 58. — Stensiö 1931: 11.

Bothriolepis cellulosa (Pander) – Gross 1932: 24; 1933: 36-39, figs 36-39; pl. 4, figs 1, 9, 10, 12, 15; pl. 5, fig. 12 (in part).

TYPE SPECIMEN. — The head-shield f 147, Museum für Naturkunde, Berlin, chosen by Gross among specimen collected from the type locality ( Gross 1933: taf. 4, fig. 15).

MATERIAL EXAMINED. — (Addition to the descriptions of Gross [1941] and Stensiö [1948]). LDM 43/673: fragment of the AMD; LUGM 6, 9, 10: AMD; LUGM 2, 9, 12, 14: PMD; LUGM 5, 16: MxL; LUGM 2, 9, 13, 17: bones of the pectoral fin; LUGM 2, 4, 8, 15: head-shields; NHM P.17807, 17810, 17813, 17814, 17818, 17826, 17828, 17829, 17836, 17837: Nu, AMD, 2 PMD, 4 MxL, AVL, four fin bones; RSM 1964.26.41 ( SMNH P.3275): impression of the AMD and AVL.

LOCALITIES AND HORIZON. — The type locality is an outcrop of dolomites, dolomite marls and clays at the right bank of Pērse River (right tributary of Daugava River) near Koknese (Kokenhusen). The other studied material comes from Pastamuiža on Daugava River, Latvia; the lower Frasnian Pļaviņas Regional Stage: Snetnaya Gora, Sēlija and Atzele Members of the Pļaviņas Formation; and outcrop at the right bank of Velikaya River in Pskov near Piskovichi, Russia; Snetnaya Gora and Pskov Beds. The remains of this species were found in the Snetnaya Gora Member in several localities in western and eastern Latvia, e.g., outcrops along Daugava River from Kaktiņi to the ruins of Koknese castle, exposures at Amata River near Kārļi and along Mazā Jugla and Lielā Jugla rivers, outcrops at Venta River near Kuldīga and at Riežupe River near Kaļķi hamlet; Lithuania: borehole Berčiunai, 73-76 m deep, borehole Pakapiai, 78.2-80.3 m deep. Additionally, B. cellulosa was correctly reported from more easterly boreholes at the middle reaches of Onega River in Arkhangelsk region of Russia ( Ivanov 1990), in Izborsk (Slavyanskie Klyuchi), at Ostenka River, in the Yam-Tesovo locality (pers. comm., A. Ivanov), borehole 7-Ost.-Staraya Russa, 154.4-152.0 m deep ( Sorokin 1978: determination of D. Obruchev), as well as from Ukhta River, South Timan, Lower Ust’ Yarega Formation, and from Pizhma River of the Middle Timan, the Ust’ Srednyaya Beds and the Srednyaya Beds of the Ust’ Yarega Formation ( Ivanov & Lukševičs 1996).

DIAGNOSIS. — Bothriolepis of moderate size with a median dorsal armour length of at least 190 mm. Head-shield is relatively broad, B/L index of 128-146, 138 on the average, and comparatively flat in its preorbital division. Anterior margin of the head-shield is considerably shorter than posterior margin, slightly convex and rounded with a rostral angle. Preorbital recess of simple type. Prm is broad, posterior margin is much shorter than the anterior margin. Pineal plate broader than long or about as broad as long. Nu is broad, L/B index of 65-81, 70 on the average. Lateral division of Pn is comparatively broad. Dorsal wall of the trunk armour is not high and of moderate width. Tergal angle is situated in the foremost part of the middle third of the AMD. Median dorsal ridge is weakly developed and partly absent in large individuals. Postlevator crest usually present and often very strongly developed in its posterior part, forming there to a certain extent a floor beneath the levator fossa. Ventral tuberosity practically absent. AMD is moderately broad, B/L index 83-94, 89 on the average. PMD comparatively broad with B/L index 82-112, 96 on the average; anterior margin is broad, posterior corner obtuse or rounded off. Pectoral fin fairly robust. Proximal segment is moderately long, 3.5 to 4 times as long as broad. The point contact between MM1 and CV2 plates of pectoral fin results in separation of CV1 from MM2. Lateral spines of proximal segment comparatively short. Medial spines fairly strongly developed and independent; the median spines situat- ed on the CD1 and on the adjacent parts of the MM2 pointing dorsally. Ornamentation typically reticulate, in small and medium-sized individuals of a fairly regular fine-meshed network of anastomosing ridges, narrow and well-defined and with distinct tubercular thickenings and elevations at their points of union. Ornament in quite lagre individuals retaining an on the whole fine-meshed reticular character on the head-shield, but often dissolved into tubercles and nodose tubercular ridges on the dorsal wall of the trunk armour.

REMARKS

Bothriolepis cellulosa is well-described by Gross (1941) and Stensiö (1948) and its diagnosis is to the large extent based on their descriptions, except for the measurements and estimated indices.

DISCUSSION

Bothriolepis cellulosa resembles B. panderi in certain aspects, but differs from it in 1) the shape and proportions of the Prm; 2) the shape of the Pi; 3) the shape and forward extension of the Pn in B. panderi ; 4) the robust and relatively short- er proximal segment of the pectoral fin; 5) character of ornamentation. (For the comparison of B. cellulosa with B. prima and B. obrutschewi , see the descriptions of the latter presented above).

B. cellulosa is most closely resembling B. canadensis (Whiteaves, 1880) in several respects and differs from this species just slightly in its 1) narrower and more flattened head-shield; 2) narrower orbital fenestra; 3) broader lateral division of the Pn; 4) shorter and higher submarginal plate; 5) structure of the visceral surface of the AMD; 6) character of the ornamentation in large individuals. These two species seems to be phylogenetically very closely related.

Figures

FIG. 11. — A, head-shield of Bothriolepis cellulosa (Pander in Keyserling, 1846), lectotype (from Gross 1941: abb. 7 D); B, C, reconstruction of the trunk armour of Bothriolepis cellulosa in dorsal and ventral views (from Gross 1941: abb. 17, 18). Abbreviations: ADL, anterior dorso-lateral plate; AMD, anterior median dorsal plate; AVL, anterior ventro-lateral plate; MV, median ventral plate; MxL, mixilateral plate; PMD, posterior median dorsal plate; PVL, posterior ventro-lateral plate; SM, semilunar plate; dlg2, posterior oblique dorsal sensory line groove; dmr, dorsal median ridge of trunk armour; f.ax, axillary foramen; p.br, processus brachialis; vlr, ventro-lateral ridge of trunk armour. Scale bar: 10 mm.