Bothriolepis maxima Gross, 1933

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 : 534-538

Bothriolepis maxima Gross, 1933 ( Figs 23-28)

Bothriolepis maxima – Gross 1932: 25 (nomen nudum).

Bothriolepis maxima Gross, 1933: 41-43 ; taf. 5, fig. 14.

HOLOTYPE. — The head-shield f124 Geologisch- Paläontologische Institut und Museum der Universität Berlin.

MATERIAL EXAMINED. — LDM 43/675, 99/1, 84/67, three articulated head-shields; PIN 1652/2, articulat- ed head-shield and dorsal trunk armour; LDM 15/20, 23, 25-31, 125; 43/676-710, 43/712-721; 84/1-14, 17- 19, 21-30, 33-38, 40-47, 66; 87/1, 3, 4, 7-9, 11, 13, 14, 18; 99/2-44; PIN 89/3; 1491/87, 96-98; 1737/62-64; 1767/61; 2917/21,24-33, 35, 37-39, 41-44, 51-53, disarticulated plates of the head-shield, trunk armour and pectoral fin; LUGM 872, 1105: 2 MV.

LOCALITIES AND HORIZON. — The type locality of Bothriolepis maxima is the outcrop of the Ogre Formation sandstones at Imula River not far from Lankserde hamlet, Latvia; Ogre Formation. Other material came from the other outcrops at Imula River near Kalnarāji hamlet and Vītiņi hamlet, exposure and caves Velna Ala at Abava River, outcrops along Ogre River, outcrop at Mūsa River close to Ceraukste village, the Ogre Formation; exposure at the right bank of Daugava River near Lielvārde castle, exposure at the right bank of Liepna River not far from Katleši village, Kuprava quarry for mining clays, Latvia; Katleši Formation. In Russia, B. maxima have been found by D. Obruchev in the outcrop of sandstone, clay and sand of the Prilovat’ Formation at Lovat’ River close to Kurskoye Gorodische village and at the middle current of Lovat’ River near Luka village. B. maxima was reported from the outcrops along Verkhnyaya Paluitsa and Nizhnyaya Paluitsa River surrounding Shugozero village, Tikhvin district of Leningrad region (Ivanov & Khozatski 1986). In Lithuania, B. maxima is found in outcrops along Nyamunelis River near Didžpanemunis and Pakalniečiai, and from borehole Stačiunai, 139.4- 139.7 m deep, and borehole Petrašičnai, 57.8-58.0 m deep; Pamūšis Formation (Kratajūte-Talimaa pers. comm.). B. maxima is recorded also from the Jēkabpils quarry, the Katleši Formation ( Sorokin 1978). B. maxima zone corresponds to the middle Frasnian gigas conodont zone. Bothriolepis cf. maxima is characteristic for the upper part of the Matusevich Formation of Severnaya Zemlya ( Lukševičs 1999a).

DIAGNOSIS. — A Bothriolepis with the median dorsal length of the armour reaching more than 500 mm. Head-shield short and broad, B/L index about 137- 156, 145 on the average, with almost flat preorbital division. Anterior margin just slightly shorter than the posterior margin, gently convex, sometimes with a rounded rostral angle. Processus obstans relatively short. Preorbital recess of trifid type. La relatively short. Nu broad and short, L/B index of about 68-75. Lateral division of the Pn relatively narrow. Trunk armour relatively low with a moderately flat dorsal wall. Dorso-lateral ridges are gently defined and rounded in their anterior part, dorsal median ridge weakly developed and practically absent in large individuals. Tergal angle situated in the foremost part of the middle third of the AMD. Ventro-lateral ridges rounded. AMD about as long as it is broad, B/L index 86-107, 97 on the average, with narrow anterior margin. PMD usually broader as it is long, B/L index about 96-117, 107 on the average; anterior margin of moderate breadth, posterior corner rounded off. Dorsal lamina of ADL about twice as long as broad, relatively narrow posteriorly the well-defined pronounced postnuchal corner; lateral lamina low. Dorsal lamina of MxL comparatively broad, from about 1.5 to 1.6 time as long as broad; lateral lamina low, about 3.5 times as long as high. Both laminae enclosing an angle about 90°. Ventral lamina of AVL about one and a half times as long as broad. MV is relatively large. Pectoral fin fairly robust, moderately long and narrow. Proximal segment about 4.5 times as long as broad; distal segment narrow, rounded in transverse section. CD5, CV5 and MM5 are present. Lateral and median spines of proximal segment short and gently defined. Ornamentation reticulate, in quite large individuals retaining an on the whole reticular character, with concentrically arranged ridges; tubercular and radially arranged on the head-shield anteriorly the infraorbital sensory groove, anterior and posterior parts of the ventral wall of the trunk armour. The ornament become smooth on the pectoral fin; well-defined only in the anterior part of the CD1, CV1 and ML2.

DESCRIPTION

This is the largest known Bothriolepis species (Gross in Stensiö 1948). The largest complete AMD LDM 99/11 is 216 mm long, exceeding the largest British species, B. gigantea . The largest specimens with thick plates comes from Latvia, Imula and Abava River localities; the remains of the same species from the east part of the distribution area are usually smaller and less massive.

The head-shield ( Fig. 23A) has the anterior margin which is only slightly shorter than the posterior margin, unlike all the other Frasnian bothriolepidoids from Baltic area. The anterior portion of the head-shield (anteriorly the orbital fenestra) is slightly elongated in comparison with that in such species as B. obrutschewi or B. cellulosa . Obstantic process is short, ending anteriorly quite well behind the transverse plane of the posterior margin of the orbital fenestra. This feature allows to distinguish B. maxima from B. gigantea which possess a long obstantic margin ( Miles 1968).

The visceral surface of the head-shield ( Fig. 24A ) shows close resemblances with that in B. gigantea . The antero-lateral corner of otico-occipital depression extends forward far over the transverse plane of the anterior margin of the orbital fenestra. The paranuchal crista is straight on the La making the floor under the lateralmost part of the anterior postorbital process of endocranium, and of an irregular shape on the Pn. The transverse lateral groove is broad and shallow. The lateral pit is small, shallow and weakly defined, situated just in front of a prominent anterior crista of the transverse lateral groove, almost equally spaced from an orbital edge of the La and prelateral notch. The lateral margin shows very broad attachment areas for the Sm (Gross in Stensiö 1948). The orbital edges of the Prm and La are just slightly thickened, but not so thick as that in B. ornata .

The Prm ( Figs 24C ; 25A ) is relatively broad, B/L index of about 99-113, 104 on the average. The La is relatively broad with the L/B index 125-134, 131 on the average. The Nu ( Figs 23B; 24B ; 29B ) is relatively broad with the L/B index of about 68-75, 71 on the average. It is usually broadest across the posterior lateral corners or sometimes across the lateral corners, just like as in B. gigantea ( Miles 1968) . The Pn has a L/B index of about 73-83, 79 on the average, with the mesial division slightly broader than long. The lateral division of the Pn is relatively narrow (Gross in Stensiö 1948), composing only 44- 48% of the total breadth of the plate.

The complete trunk armour PIN 1652/2 ( Fig. 27 ) is low and broad with a flat and low dorsal wall ( Obrucheva 1974). Unfortunately it is almost impossible to measure correctly the angles enclosed by the dorsal and lateral wall, as well as the lateral and ventral wall due to the deformation of the trunk-armour plates during fossilization.

The AMD ( Fig. 26 ) is about as long as it is broad with B/L index 86-107, 97 on the average. Its anterior margin is narrow, more than twice (from 2.2 to 3.3 times) as long as the plate is broad (Gross in Stensiö 1948) resembling Bothriolepis ornata in that respect. The proportions of the lateral margin of AMD vary significantly among specimens coming from different localities: the posterior division of the lateral margin is 1.3-1.9 time shorter than the anterior division in specimens from Latvia, and the same index in specimens from Luka locality in Russia reaches 1.7-2.6. Overlap areas for ADL and MxL are normally developed as usually in Bothriolepis in general (Gross in Stensiö 1948), but in one case (LDM 99/11) the sutural connection of AMD with MxL is of Remigolepis type on the right side of the plate: the AMD overlaps the anterior part of the right MxL.

The anterior margin of PMD is of moderate breadth, 1.7-2.1 times as long as the plate totally broad. The ADL is not simply overlapped by the AVL, but also at the same time overlaps that plate posteriorly the processus obstans, as in Bothriolepis ornata and B. groenlandica . The PVL ( Fig. 28B ) is relatively broad, the ventral lamina is from 1.8 to 2.2 times as long as it is broad. The subanal division occupies about 30% of the total PVL length.

REMARKS

Latvian material encounted here have been collected by Gross, Lyarskaja and the author from type locality and other site close to the type area. Russian material from Lovat’ River is collected and illustrated by Obruchev (1947) and Obrucheva (1974), but has never been described in details.

DISCUSSION

As the largest species of the genus, Bothriolepis maxima differs well from all the other representatives of the group from Baltic area first of all in its great size and very thick bones. Smallest specimens of B. maxima are much bigger than B. evaldi (for the comparison of both species see the description of B. evaldi ), and they differ considerably from the other Baltic species in the proportions of the AMD, PMD, MxL and AVL. All the early and middle Frasnian Bothriolepis in this area could be well-recognized by their preorbital recess of a simple type, and only B. maxima among them possess the preorbital recess of a trifid type. B. maxima resembles Bothriolepis gigantea ( Stensiö 1948; Miles 1968) from Scotland in several aspects and these species seems to be very closely related phylogenetically. Nevertheless, as it was pointed out by Gross (in Stensiö 1948), Stensiö (1948) and Miles (1968), there are several features distinguishing these two species. Adding the list of such a features provided by Miles, it is possible to suggest that B. maxima differs from B. gigantea in its 1) shorter obstantic margin; 2) presence of the lateral pit on the visceral surface of the La; 3) well-defined nasal notches on the Prm; 4) other shape of the posterior margin of the head-shield; 5) structure of the transverse nuchal crista; 6) more sharp angle between the dorsal and lateral laminae of the MxL.

Figures

FIG. 24. — Bothriolepis maxima Gross, 1933; A, head-shield LDM 99/1 in visceral view; B, Nu LDM 99/5; C, Prm LDM 99/2. Right bank of Imula River near Kalnarāji hamlet, Latvia. Ogre Formation. Abbreviation: Nu, nuchal plate; Prm, premedian plate. Scale bars: 20 mm.

FIG. 25. — Bothriolepis maxima Gross, 1933; A, Prm PIN 2917/53 in dorsal view; B, Nu and Pp PIN 2917/52. Lovat’ River near Luka village, Russia. Prilovat’ Formation. Abbreviations: Nu, nuchal plate; Pp, postpineal plate; Prm, premedian plate; csl, central sensory line groove; d.end, opening of canal for endolymphatic duct; ifc1, principal section of infraorbital sensory line on head-shield; mc, lateral corner; mppr, posterior process; nm, obtected nuchal area; pc, postero-lateral corner; pnn, nasal notch; soc, anterior section of the supraorbital sensory line. Scale bar: 10 mm.

FIG. 29. — Bothriolepis evaldi Lyarskaja, 1986; A, holotype, articulated head, trunk and pectoral fin armour LDM 67/86 in dorsal view; B, AMD LDM 67/7; C, articulated head and trunk armour LDM 67/14 in dorsal view; D, articulated trunk armour LDM 67/2 in dorsal view; E, articulated head, trunk and pectoral fin armour LDM 67/39; F, head and trunk armour in visceral view with articulated right pectoral fin in ventral view LDM 67/6; G, articulated trunk armour LDM 67/10 in dorsal view. Kalnamuiža 1 locality at Amula River, Latvia. Ogre Formation. Abbreviation: AMD, anterior median dorsal plate. Scale bars: 5 mm.

FIG. 27. — Bothriolepis maxima Gross, 1933, reconstruction of the trunk armour based on specimen PIN 1652/2. Right bank of Lovat’ River near Luka village, Russia. Prilovat’ Formation. Abbreviations: ADL, anterior dorso-lateral plate; AMD, anterior median dorsal plate; MxL, mixilateral plate; PMD, posterior median dorsal plate. Scale bar: 20 mm.

FIG. 26. — Bothriolepis maxima Gross, 1933, AMD; A, PIN 2917/42, slightly deformed; B, PIN 1737/63; C, PIN 1737/64; D, PIN 2917/43; A, D, Lovat’ River near Luka village, Russia. Prilovat’ Formation; B, C, Velna ala (Devil Cave) at the left bank of Abava River, Latvia. Ogre Formation. Abbreviations: AMD, anterior median dorsal plate; MxL, mixilateral plate; PMD, posterior median dorsal plate; dlg2, posterior oblique dorsal sensory line groove; dma, tergal angle; npn, postnuchal notch; oa.MxL, area overlapped by MxL; oa.PMD, area overlapped by PMD; pr.pl, external postlevator process of AMD. Scale bar: 20 mm.

FIG. 28. — Bothriolepis maxima Gross, 1933; A, ADL PIN 1491/98, Velna ala (Devil Cave) at the left bank of Abava River, Latvia. Ogre Formation; B, PVL PIN 1491/88, right bank of Bolshoy Tuder River near Medovo village in vicinity of Cholm town, Russia. Prilovat’ Formation. Abbreviations: ADL, anterior dorso-lateral plate; AMD, anterior median dorsal plate; AVL, anterior ventro-lateral plate; PVL, posterior ventro lateral plate; cm1, anteromesial corner of ventral lamina of PVL; cm2, middle corner of ventral lamina of PVL; dlr, dorso-lateral ridge of trunk armour; lcg, main lateral line groove; oa.AMD, area overlapped by AMD; oa.AVL, area overlapped by AVL; oa.PVL, area overlapped by PVL; pnoa, postnuchal ornamented corner; pro, processus obstans; vlr, ventro-lateral ridge. Scale bars: 20 mm.