Bothriolepis evaldi Lyarskaja, 1986

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 : 539-544

Bothriolepis evaldi Lyarskaja, 1986 ( Figs 29-31 )

Bothriolepis evaldi Lyarskaja, 1986: 123-130 ; pl. I, fig. 1.

HOLOTYPE. — Articulated head-shield, trunk-armour and pectoral appendages LDM 67 /86.

MATERIAL EXAMINED. — LDM 67 /2-4, 67/6-77, 67/79, 67/80, 67/89-93: 62 articulated head-shields, trunk-armour and pectoral appendages, as well as 18 disarticulated plates of the armour from the type locality ; LDM 280 /1: head-shield, 280/2-27: mostly disarticulated plates of the trunk armour and pectoral fin from the Kaibala River site .

LOCALITIES AND HORIZON. — The type locality Kalnamuiža-1 (number 5 in Fig. 1 ) is cliff at the left bank of Amula River downstream from water-mill Kalnamuiža with grey sandstone and thin layers of blue marls; the Middle Frasnian, the Rembate Member of the Ogre Formation ( Lyarskaja 1986). Other material comes from an outcrop exposing similar deposits at the right bank of Kaibala River (number 12 in Fig. 1 ) 200 m from the estuary, not far from ruins of Lielvārde castle.

DIAGNOSIS. — Small Bothriolepis with a median dorsal armour length reaching about 50 mm. B/L index of trunk armour about 95. B/L index of the headshield 140-157. Rostral margin of the head-shield strongly convex. Orbital fenestra relatively small, broad, slightly less than twice as broad as it is long. Nu arched, moderately broad, L/B index of 69. Trunk-armour of moderate height with broad and high dorsal wall. Dorsal and lateral walls of trunk enclosing an angle about 126° on MxL. Dorso-lateral and ventro-lateral ridges well-marked. Median dorsal ridge well-defined posteriorly the tergal angle. Ventral wall of the trunk-armour relatively narrow, B/L index 43-48. AMD broad, B/L index 84-108, arched, with right and left laminae forming an angle of about 128°. Anterior margin broad, almost straight. Postlevator cristae on the visceral surface of AMD are well-defined. AMD overlaps the MxL by the anterior part of the posterior division of lateral margin in medium-sized individuals. PMD moderately broad with pronounced posterior corner. Dorsal lamina of MxL about 1.6-2.2 times as broad as the lateral lamina is high. The dorso-ventral pit-line groove on the MxL is usually present. Proximal segment of the pectoral appendage moderately long, about 3.6 times as longs as it is broad and less then twice longer than the distal segment. Ornamentation fine reticulate, becoming slightly coarser and sparser in medium-sized individuals.

DESCRIPTION

This species is well-represented at the type locality by many articulated head-shields, trunk-armours and pectoral appendages, as well as some disarticulated plates. Most specimens from this locality are slightly flattened, often deformed. Size range is from a median dorsal trunk-armour (LDM 67/10, Fig. 29G ) less than 17 mm long to an individual with a median dorsal armour length estimated of about 34 mm. Material from the Kaibala site is represented by larger plates, an articulated head-shield LDM 280/1 ( Fig. 30D ) suggests a median dorsal armour length estimated of about 48 mm. The head-shield is well-preserved in 22 specimens. It is relatively broad in small individuals, Lyarskaja (1986) mentions B/L index varying from 118 to 170, but my measurements and estimations show the B/L is 140-157, 145 on the average (n = 8), and reaching only 120 in medium-sized individual. The head-shield is strongly vaulted both rostrocaudally and transversely ( Lyarskaja 1986). The rostral margin is convex, shorter than the posterior margin; the anterolateral corners and a shallow prelateral notch are clearly defined only in individuals of medium size ( Lyarskaja 1986). The obtected nuchal area is short, broadest on the Nu. The orbital fenestra is relatively small, but very broad with a B/L index about 168-196, 185 on the average. A new material (LDM 280/1) allows to identify the shape of the preorbital recess, which is of simple type.

The visceral skull surface shows the normal features as a prominent transverse nuchal crista, well-developed median occipital crista, and a very broad otico-occipital depression which is well-defined by the paramarginal cristae. The median ridge sharing the broad paired pits of Pp is low.

The Prm was not described by Lyarskaja (1986). It is broad, much broader than it is long in small specimens with B/L index 150-182, which decreases to 103 in largest individuals. The Prm is broadest at the infraorbital sensory groove or rostral margin. The rostral margin is convex, it is 1.2-1.4 time longer then the almost straight orbital margin. The nasal notch on the orbital margin can be recognized only slightly in medium-sized specimen LDM 280/1. There is a median elevation inside the rostral margin. The infraorbital sensory groove crosses the plate in its anterior part.

The La is moderately broad with the L/B index 126-143, 134 on the average. The infraorbital sensory groove crosses the plate in its anterior part not far from the orbital and lateral margins ( Lyarskaja 1986). The central sensory line groove (csl) usually is finished at the level of the middle of the orbital fenestra length, sometimes it extends almost to the anterior margin of the orbital fenestra ( Lyarskaja 1986). The semicircular pit-line groove (cir) and branch of infraorbital sensory line diverging on La (ifc2) are welldefined ( Lyarskaja 1986).

The pineal plate is moderately narrow, slightly longer than it is broad, and not quadrate, as has been shown by Lyarskaja (1986). The all four margins of the plate are concave. Position of the pineal pit is marked on the outer surface by the pineal elevation ( Lyarskaja 1986).

The Pp is broad in small individuals and of moderate breadth in maturity, L/B index varies from 44 to 55. Lyarskaja (1986) claimed that the shape of the plate is almost constant, but in fact the anterior margin is strongly convex in small specimens and became more straight with increasing size, as in other species of Bothriolepis . The Nu has L/B index 64-76, 69 on the average. The plate is broadest across the lateral corners ( Lyarskaja 1986). The anterior division of the lateral margin usually is concave and a little shorter than the posterior division. The posteri- or margin usually is almost straight, the posteri- or process is weakly defined. The central sensory line groove is clearly distinct ( Lyarskaja 1986). In some cases there are long supraoccipital grooves (socc), which cross the plate little in front of the obtected nuchal area and extend to the Pn. The external openings for the endolymphatic ducts (d.end) are rather large, closely set one to another. Postorbital crista on the visceral surface is low, clearly seen only in largest individuals ( Lyarskaja 1986). Specimen LDM 67/39 shows very unusual feature, which have not been mentioned by Lyarskaja (1986): the Nu is fused with the Pp ( Fig. 30C ).

The Pn is broad, L/B index 70-83, 76 on the average. The lateral division of the Pn is relatively broad and is composing 33-52% of the general breadth of a plate. The middle pit-line groove (mp) always present.

The Pmg is broad with the lateral margins longer than the median margins ( Lyarskaja 1986).

The sclerotic ring is preserved in some specimens. Its features seem to be similar to that of the ring of Bothriolepis canadensis (see Stensiö 1948) or B. hydrophila (see Miles 1968).

The Sm (extralateral) plate is always badly preserved. It seems to be relatively long and narrow ( Lyarskaja 1986).

The trunk-armour is broad ( Lyarskaja 1986), B/L index 87-99, 95 on the average (n = 10). It is relatively high, with a lateral wall 2.5 times as long as high; the dorsal wall is moderately arched with well-defined median dorsal ridge. Length of the dorsal wall, probably, reaches about 50 mm. The shape and proportions of the ventral wall are similar to that of Bothriolepis prima (see Lyarskaja 1986); B/L index 43-48.

Anterior margin of the AMD is 1.1-1.6 time as long as the posterior margin. The antero-lateral corner, postnuchal notch (npn) and the postlevator processes (pr.pl) are well-defined, as are the obtuse lateral and postero-lateral corners ( Lyarskaja 1986). The posterior division of the lateral margin is 1.6-2.5 (2.2 on the average) times shorter than the anterior division. The tergal angle (dma) is situated in between the anteri- or third and middle of the plate and is well-marked, the median dorsal ridge (dmr) is strongly developed ( Lyarskaja 1986). Overlap areas for ADL and MxL are developed as usually in Bothriolepis in small individuals, but in specimens of medium size the overlap area for MxL is developed as in Remigolepis ( Lyarskaja 1986) . The anterior oblique dorsal sensory line grooves (dlg1) are well-defined on the plates of small individuals. The posterior oblique dorsal sensory line grooves (dlg2) are also well-defined ( Lyarskaja 1986).

The PMD is arched, moderately broad, B/L index 88-105, 95 on the average. The width of the anterior margin comprises 44-55% of total breadth (50% on the average). The median dorsal ridge is strongly developed ( Lyarskaja 1986). The ADL is slightly longer than the MxL in articulated armour. The dorsal lamina is moderately broad, its breadth exceeds height of the lateral lamina. The dorso-lateral ridge (dlr) is welldefined ( Lyarskaja 1986). The postnuchal ornamented corner (pnoa) is sharp, long and narrow. The dorsal lamina of the MxL is moderately broad, 1.4-1.6 time as long as it is broad. The dorsal lamina is 1.6-2.2 times as broad as the lateral lamina is high. Dorsal and lateral laminae enclosing an angle about 126°. The lateral lamina is moderately high, 2.4-3.2 times as long as it is broad. The dorso-lateral ridge is well-defined ( Lyarskaja 1986). The overlap area for the AMD is restricted to half the length of the anterodorsal margin as in Remigolepis ( Stensiö, 1931) . The posterior oblique sensory line groove (dlg2) in some cases terminates in some distance from the lateral margin, but usually the dorso-ventral pit-line groove (dxp) crossing the dorso-lateral ridge is present ( Lyarskaja 1986).

The AVL is broad, the ventral lamina is 1.4-1.7 time as long as it is broad. The subcephalic division 26-33% of total length of the ventral lamina. The ventral lamina 2.2 times as broad as the lateral lamina high in LDM 67/13 ( Fig. 30E ). The lateral lamina is moderately high, about twice as long as it is high. Ventro-lateral ridge is well-defined. The axillary foramen is rather large and slightly elongated in shape ( Lyarskaja 1986).

The PVL has similar proportions to the AVL, as in most Bothriolepis species. It is of moderate breadth, the ventral lamina is 2-2.3 times as long as it is broad. The subanal division is relatively narrow ( Lyarskaja 1986) and occupies 20-27% of the total PVL length. The lateral lamina is relatively high, 1.9-2.2 times as long as it is high. The ventral lamina is 1.3-1.5 time as broad as the lateral lamina high. The ventro-lateral ridge is well-developed.

The length/ breadth index of the MV is 1.1 in LDM 67/54.

The pectoral fin is represented mostly by articulated bones. The proximal segment is about 1.9 time longer than the distal segment. Both segments bear small lateral and mesial spines in small individuals. Individuals of medium size have the proximal segments bearing prominent lateral spines, which are fused in their base forming well-defined crest. The proximal segment is of moderate breadth, 3.3-4 (3.6 on the average) times as long as it is broad. The CD1 is with L/B index varying from 2.7 to 3.3, 3 on the average. The CV1 is slightly longer than the CD1 and have similar proportions. The ML2 is 4.2-4.6 (4.4 on the average) as long as it is broad. The distal segment shows CD3 and CD4, it is long and relatively narrow.

The ornamentation is typically reticulate, becoming slightly coarser and sparser in mediumsized individuals. The network of anastomosing ridges are broken into shorter ridges along the margins of the plates. The ornamentation of the pectoral appendage is reticulate in general, on the CD1 the ornament is radially arranged, on the distal segment it consists of longitudinal gently defined ridges. The T has almost smooth surface.

REMARKS

The following account is the first full treatment in English, which supplements Lyarskaja’s description (in Russian) of Bothriolepis evaldi (1986) , adding some details. It is based on specimens from Lyarskaja’s collection from the type locality, kept at the Latvian Museum of Natural History, and material from the Kaibala site, gathered by the author.

DISCUSSION

Most part of materials on Bothriolepis evaldi from the type locality shows the following features, which can be considered to indicate immature individuals: 1) the proportionally large orbital fenestra; 2) the breadth of the Prm; 3) the shape of the Pp with strongly convex anterior margin; 4) the relatively broad lateral division of the Pn; 5) the poor development of the median ventral ridge on the visceral surface of the AMD; 6) the strong development of the dorsal median ridge; 7) the presence of the anterior oblique dorsal sensory line groove and dorso-ventral pit-line groove. However the largest specimens from the Kaibala locality seem to be from well-grown individuals. B. evaldi resembles B. maxima by many features: 1) broad Nu; 2) shape and proportions of the AMD and ADL; 3) shape of the postnuchal ornamented corner of the ADL; 4) situation of the tergal angle, etc. Nevertheless, B. evaldi differs from B. maxima in its 1) much smaller size; 2) shape of the preorbital recess; 3) shape and proportions of the PMD; 4) strongly developed dorsal median, dorso-lateral and ventro-lateral ridges. The largest AMD from the Kaibala locality LDM 280/8 which is about 50 mm long and seem to be from well-grown individual, retain the strongly developed dorsal median ridge. Smallest AMD of B. maxima PIN 89/4 is 104 mm long and shows only gently defined dmr. The largest (33.3 mm long) head-shield of B. evaldi LDM 280/1 possess the preorbital recess of simpe type, but smallest (97 mm long) head-shield of B. maxima LDM 84/67 has trifid preorbital recess. Specimens from Kaibala site are important because they lead to evaluate two hypothese: 1) B. evaldi does not comprise juveniles of the larger, contemporaneous species B. maxima , which occurs with B. evaldi in the Ogre Formation; or 2) shape of the preorbital recess changes dramatically during ontogeny. Resemblances and differences between these two species as they have been described by Lyarskaja (1986) could be explained mostly by allometric pattern of growth.

B. evaldi can be distinguished readily from B. obrutschewi (Karatajūte-Talimaa 1966) , B. cellulosa ( Gross 1942) and B. panderi , other Frasnian Bothriolepis representatives from the Main Devonian field.

B. evaldi resembles B. prima from the Main Devonian field and B. hydrophila ( Miles 1968) from Scotland by several features. B. evaldi differs from B. prima in its 1) relatively smaller orbital fenestra; 2) shape of the Prm; 3) strongly developed median dorsal ridge; 4) shape of the postlevator cristae on the visceral surface of the AMD. B. evaldi differs from B. hydrophila in its 1) smaller size; 2) much broader dorsal wall of the trunk-shield; 3) shape and proportions of the AMD; 4) shape of the postnuchal ornamented corner of the ADL; 5) narrower ventral wall of the trunk-shield; 6) shorter proximal segment of the pectoral fin.

Figures

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. 30. — Bothriolepis evaldi Lyarskaja, 1986; A, details of the head-shield of specimen LDM 67/14 in dorsal view; B, details of the head-shield of the holotype, LDM 67/86; C, details of the head-shield of specimen LDM 67/39 in dorsal view; D, head-shield LDM 280/1 in dorsal view; E, somewhat flattened and deformed articulated head, trunk and left pectoral fin armour LDM 67/13 in ventral view; F, articulated head, trunk, left pectoral fin armour and right CV1 LDM 67/3 in ventral view; A-C, E, F, Kalnamuiža 1 locality at Amula River, Latvia; D, Kaibala River not far from Lielvārde, Latvia. Ogre Formation. Abbreviation: CV1, ventral central plate 1. Scale bars: 5 mm.

FIG. 31.— Bothriolepis evaldi Lyarskaja, 1986; A, holotype, the articulated head-shield, trunk armour and pectoral fins LDM 67/86 in dorsal view; B, articulated head-shield, trunk armour, left pectoral fin and CD1 LDM 67/3 in ventral view, with dotted space showing the matrix. Kalnamuiža 1 locality at Amula River, Latvia. Ogre Formation. Abbreviations: ADL, anterior dorsolateral plate; AMD, anterior median dorsal plate; AVL, anterior ventro-lateral plate; CD1-3, dorsal central plates 1-3; CV1-3, ventral central plates 1-3; La, lateral plate; ML2-4, lateral marginal plates 2-4; MM1, 3, mesial marginal plates 1, 3; MxL, mixilateral plate; Nu, nuchal plate; Pi, pineal plate; PMD, posterior median dorsal plate; Pmg, postmarginal plate; Pn, paranuchal plate; Pp, postpineal plate; Prm, premedian plate; PVL, posterior ventro lateral plate; Ro, rostral plate; SCLR1, 2, plates 1 and 2 of sclerotic ring; Sm, submarginal plate; T, terminal plate; csl, central sensoty line; dlg1, 2, anterior and posterior oblique dorsal sensory line grooves; socc, supraoccipital cross-commissural pit-line groove. Scale bar: 5 mm.

FIG. 1. — Localities of the Main Devonian Field studied by the author and/or mentioned in the text; 1, Ketleri: Bothriolepis ciecere Lyarskaja in Lyarskaja & Savvaitova, 1974; 2, Pavāri: Bothriolepis ciecere; 3, Bienes: Bothriolepis leptocheira curonica Gross, 1942; 4, Kalnarāji: Bothriolepis maxima Gross, 1933; 5, Kalnamuiža 1: Bothriolepis evaldi Lyarskaja, 1986; 6, Kalnamuiža 2: Bothriolepis sp. (in Amula Formation), Bothriolepis leptocheira curonica (in Eleja Formation); 7, Velna Ala: Bothriolepis maxima, Grossilepis spinosa (Gross, 1942); 8, Klūnas: Bothriolepis ornata Eichwald, 1840, B. jani Luksevics, 1986; 9, Ķurbes: Bothriolepis jani; 10, Ceraukste: Bothriolepis maxima; 11, Lielvārde: Bothriolepis maxima, Bothriolepis sp.; 12, Kaibala: Bothriolepis evaldi; 13, Koknese: Bothriolepis cellulosa (Pander in Keyserling, 1846), Grossilepis tuberculata (Gross, 1941); 14, Pastamuiža: Bothriolepis prima Gross, 1942 and B. obrutschewi Gross, 1942: in Amata Formation; B. cellulosa: in Pļaviņas Formation; 15, Jēkabpils: Bothriolepis sp.; 16, Pelyša: Bothriolepis prima, B. obrutschewi; 17, Vidaga: Bothriolepis traudscholdi Jaekel, 1927; 18, Katleši: Bothriolepis maxima; 19, Kuprava: Bothriolepis cf. maxima; 20, Piskovichi: Bothriolepis obrutschewi; 21, Yam-Tesovo: Bothriolepis prima; 22, Kurskoye Gorodische: Bothriolepis maxima (Obruchev 1947); 23, Luka: Bothriolepis maxima (Obruchev 1947); 24, Bilovo: Bothriolepis sp.; 25, Lyubitino: Bothriolepis ornata (Eichwald 1860); 26, Zarubino: Bothriolepis sp. indet. 1; 27, Paluitsa: Bothriolepis maxima (Ivanov & Khozatsky 1986); 28, Montsevo: Bothriolepis panderi Lahusen, 1880; 29, Stolbovo: Bothriolepis traudscholdi; 30, Andoma Hill: Bothriolepis sp. Dotted line outlines distribution of the Devonian rocks on the subquaternary surface of the Main Devonian Field. The Devonian deposits are not presented to the north of the line, and are covered by the youngest rocks to the south and east.