Bothriolepis heckeri, Lukševičs, 2001

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 : 577-578

Bothriolepis heckeri n. sp. ( Figs 60 H-J; 62)

HOLOTYPE. — AMD PIN 835 /42.

MATERIAL EXAMINED. — PIN 835/41, an incomplete AMD; PIN 835/40, an incomplete La, Pn and Pmg; all gathered by R. Hecker in 1930.

LOCALITY AND HORIZON. — Outcrop at the right bank of Malyi Tuder River not far from Bilovo village, Novgorod region, Russia; Bilovo Beds(?), Famennian.

DIAGNOSIS. — Moderately large Bothriolepis with comparatively narrow and strongly arched AMD (B/L index of about 81) which bears high dorsal median crest arising just anteriorly the tergal angle. La is broad with very long infraorbital sensory groove diverging on La.

DESCRIPTION

PIN 835/42 is a relatively small almost complete AMD with damaged antero-lateral corners ( Figs 60H ; 62 B-D) and PIN 835/41 is an imperfect AMD without the right lateral margin and loosed left postero-lateral margin ( Figs 60I ; 62E ). The AMD is comparatively narrow with B/L index of about 81, with a gently concave anterior margin, which is moderately broad. The posterior margin is relatively narrow, about 1.2 time shorter than the anterior margin. The AMD is strongly arched with the angle between the two laminae about 100°, and bears a 2-3 mm high dorsal median crest (cr.d) which arises just anteriorly the tergal angle. The antero-lateral corner is weakly defined. The tergal angle is situated slightly posteriorly the anterior third of the plate. The posterior oblique dorsal sensory line grooves (dlg2) are well-defined. The ornament is reticular, sometimes with slightly defined ridges.

PIN 835/40 is an incomplete head-shield consisting of the Pn, Pmg and incomplete La which lacks the margin making contact with the Prm ( Figs 60J ; 62A ). The La plate is relatively broad as it is preserved, with gently defined antero-lateral corner. The infraorbital sensory groove crosses the plate far from the lateral and rostral margins. The central sensory line groove (csl) seem to finish at the level of the middle of an orbital fenestra length. The branch of the infraorbital sensory groove diverging on La (ifc2) is well-defined and unusually long. The Pn seems to be relatively broad as it is preserved. The Pmg of unusual shape with the median margins longer than the lateral margins.

DISCUSSION

Bothriolepis heckeri n. sp. differs from all the other known Bothriolepis from the Main Devonian Field in its broad La with unusually situated sensory grooves. B. cristata ( Miles 1968) from the Rosebrae Beds of Scotland also has a strongly developed dorsal median crest, but differs in other shape and general proportions of the AMD.

Figures

FIG. 60. — A-G, Bothriolepis jani Lukševičs, 1986; A, B, AVL LDM 100/98 in ventral and visceral views; C, PVL LDM 100/434; D, CD1 plate LDM 100/144; E, CD1 LDM 100/436; F, ML2 LDM 100/378; G, proximal segment of the pectoral fin LDM 100/435. Skujaine River near Klūnas village, Latvia. Tērvete Formation; H-J, Bothriolepis heckeri n. sp.; H, holotype, AMD plate PIN 835/42 in dorsal view; I, incomplete AMD plate PIN 835/41 in dorsal view; J, incomplete La, Pn and Pmg PIN 835/40 in dorsal view. Malyi Tuder River not far from Bilovo village, Russia. Bilovo Beds(?). Abbreviations: AMD, anterior median dorsal plate; AVL, anterior ventro-lateral plate; CD1, central dorsal plate 1; ML2, lateral marginal plate 2; PVL, posterior ventro lateral plate; La, lateral plate; Pn, paranuchal plate; Pmg, postmarginal plate. Scale bars: 5 mm.

FIG. 62. — Bothriolepis heckeri n. sp.; A, incomplete La, Pn and Pmg PIN 835/40; B-D, holotype, AMD PIN 835/42; B, dorsal view; C, lateral view; D, anterior view; E, incomplete AMD PIN 835/41 in dorsal view. Malyi Tuder River not far from Bilovo village, Novgorod region, Russia. Bilovo Beds(?). Abbreviations: AMD, anterior median dorsal plate; PMD, posterior median dorsal plate; La, lateral plate; Pmg, postmarginal plate; Pn, paranuchal plate; cir, semicircular pit-line groove; crd, dorsal median crista; dlg2, posterior oblique dorsal sensory line groove; dma, tergal angle; ifc1, principal section of infraorbital sensory line; ifc2, branch of infraorbital sensory line diverging on La; lpr, lateral process; oa.PMD, area overlapped by PMD; orb, orbital margin. Scale bar: 10 mm.