Bothriolepis leptocheira Traquair, 1893

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 : 544-553

Bothriolepis leptocheira Traquair, 1893 ( Figs 32-39 )

Pterichthys major – Geikie 1869: 12-13 (after Miles 1968).

Bothriolepis major Ag. – Traquair 1888: 510 (after Miles 1968).

Bothriolepis leptocheirus Traquair, 1893: 285-286 . — Stensiö 1931: 164.

Bothriolepis leptocheira Traquair – Evans in Miles 1968: 112.

Bothriolepis curonica Gross, 1942: 420 , 421, abb. 10. — Stensiö 1948: 615. — Lukševičs 1987: 90, textfigs 1-6.

For a full list of synonyms before 1965 see Miles (1968).

TYPE SPECIMEN. — Gross (1932: 26) selected the AVL plate RSM 1859.33.19A as a lectotype illustrated by Traquair (1906: pl. 29, fig. 3).

MATERIAL EXAMINED. — Apart from the British material ( Miles 1968), LDM 15/33 ( AMD, PMD), 15/34, 15/121, 65/110-118, 121, 123, 130, 133, 89/1- 15, 89/27, 89/28, 98/1-68, 98/76-89, 98/91,98/94-101: articulated head-shields and pectoral appendages, disarticulated plates of the trunk-armour and pectoral fin. All these specimens come from Latvia.

LOCALITIES AND HORIZON. — The type locality is Bracken Bay , Ayrshire (Heads of Ayr), Scotland ; the

Upper Old Red Sandstone. In western Latvia, it has been collected in the right bank of Imula River near Bienes hamlet (number 3 in Fig. 1 ); stratotype of the Amula Formation and exposure of dolomite marls, clays and siltstones of the Eleja Formation at the right bank of Amula River 1 km upsteam from water-mill Kalnamuiža (number 6 in Fig. 1 ); the Purviņi Member of the Eleja Formation, lowermost upper Famennian. A possible new subspecies of B. leptocheira occurs in the Malyutka Formation of Severnaya Zemlya, outcrops along Matusevich River ( Lukševičs 1999a).

DIAGNOSIS. — Rather large Bothriolepis with a medi- an dorsal armour length of at least 240 mm. B/L index of dorsal wall of trunk-armour about 77. B/L index of the head-shield of 130. Preorbital recess of trifid type. Anterior margin of the head-shield is rounded. Orbital fenestra is relatively small. Prm broad, orbital margin is much shorter than rostral margin. Nu L/B index of 84, with very short orbital facets. Supraoccipital groove long, sometimes fused with a long middle pit-line. AMD relatively narrow, B/L index 83, with the relatively short anterior margin. PMD broad with narrow anterior margin. Median dorsal ridge poorly developed in posterior part of PMD. Dorso-lateral and ventro-lateral ridges are well-marked. Both AVL and PVL are elongated. Proximal segment of the pectoral appendage is long and slender, 5.5 times as longs as it is broad. Ornamentation is fine and basically of reticular type, in quite large individuals becoming smooth.

DESCRIPTION

This species is well-represented in clay of the Kalnamuiža locality by many articulated skulls, some articulated proximal segments of the pectoral fin, as well as disarticulated plates of the trunk-shield and pectoral appendage. Most are from individuals of moderate size. The plates are usually flattened, often deformed. The headshield is moderately broad, with average B/L index 130 (n = 10), slightly narrower than the head-shield (B/L index 142) restored by Miles (1968); the differences in breadth could be explained by difficulties in restoration of a correct shape and proportions of the head-shield from disarticulated plates. As in Scottish material, the rostral margin is convex, rounded, usually slightly longer than the posterior margin. The head-shield is weakly vaulted both rostrocaudally and transversely, as in Scottish material, but the anterior part of the Prm and La is strongly curved. The antero-lateral corner (alc), the prelateral notch and the lateral process are weakly defined, not seen in dorsal view. The orbital fenestra is relatively small, with a B/L index varying from 175 in individuals of moderate size to 150 in largest individuals. The preorbital recess both in Latvian and Scottish material ( Miles 1968: text-fig. 36) is of trifid type, but with the lateral horns less extended laterally than that in B. maxima or B. gigantea , and more broad at their base. The orbital edges of the Prm and La are not thickened (this feature is not seen in Scottish material). The antero-lateral corners of otico-occipital depression on the visceral surface of the head-shield extend forward so that they end just in front of the transverse plane of the anterior margin of the orbital fenestra, as in Scottish material ( Miles 1968: 76).

The Prm is weakly arched, with B/L index 123- 148, broader than Prm in Scottish material ( Miles [1968] has mentioned B/L index of 114, 120 and 128). The rostral margin is convex, it is three times longer than the slightly concave orbital margin in material from both countries (for comparison see Figs 32-34 and Miles 1968: pl. 20, figs 1, 2). Also such characters as the position of the infraorbital sensory groove (ifc1) which crosses the plate close to its rostral margin, and a well-defined anterior section of the supraorbital sensory line (soc), are similar.

The La “is of the short, broad type ” ( Miles 1968: 77). The L/B index of the La of 120-128, 124 on the average in Latvian material. The Pp has L/B index varying from 69 to 83, it is elongated in both material from Scotland ( Miles 1968: pl. 20, fig. 4) and Latvia, e.g., LDM 89/1 ( Fig. 34 ).

The Nu has the L/B index about 84 (Miles mentions L/B index 83). The plate is always broadest across the lateral corners. The anterior division of the lateral margin is usually convex (RSM 1859.33.632A and B, LDM 98/12, 13, 20, 86, Fig. 33 , etc.), and a little shorter than the posterior division.

The Pn is of moderate breadth, L/B index about 86, Miles (1968) has restored it with L/B index of about 80. The lateral division of the Pn is relatively narrower than in B. ciecere and is composing 34-45% (38.7 on the average) of the general breadth of a plate. Long supraoccipital groove (socc) usually is present in Latvian material, it terminates usually at the level of the middle of the plate posterior margin. The middle pit-line groove (mp) is always present, sometimes it is very long (LDM 98/86, Fig. 33B ) or (LDM 98/3, 7, 12, 89/5, Fig. 33A ) it fuses with the supraoccipital groove. This character was not described or drawn by Miles (1968: textfig. 36) and not clearly seen in his illustrations; however RSM 1859.33.632B shows long supraoccipital groove and the middle pit-line groove also on the Pn (pers. obs.).

The trunk-armour is narrow, relatively low, with rather flattened low dorsal wall and the lateral wall more than three times as long as high. Length of the dorsal wall, probably, is more than 240 mm ( Miles [1968] estimated the dorsal wall reached a length of some 140 mm). The ventral wall is narrow, with B/L index about 53 in Latvian material. The subcephalic and subanal divisions are relatively long.

The AMD is weakly arched, narrow, B/L index about 83 in Latvian material, and about 77 in Scottish material ( Miles 1968: 78). The antero-lateral and lateral corners, and the postlevator processes (pr.pl) are well-defined ( Miles 1968: text-fig. 37; Fig. 35A ). The posterior division of the lateral margin is 1.4- 1.6 time shorter than the anterior division. There is no median dorsal ridge neither in Scottish, nor in Latvian material.

The PMD is broad in comparison with the AMD, B/L index about 95 in material from Scotland ( Miles 1968) and varies from 88 to 101, 95 on the average, in material from Latvia. The anterior margin is very narrow, convex and rounded; the posterior margin is well convex, 2- 2.5 times longer than the anterior margin; it is without pronounced posterior corner ( Miles 1968: text-fig. 38; Fig. 35C ; 36D ).

The dorsal lamina of the ADL is of moderate breadth, 3.5 times as long as it is broad in RSM 1859.33.632D ( Miles 1968: pl. 20, fig. 3) or a little broader in LDM 98/58 ( Figs 36B ; 37A ). The postnuchal ornamented corner (pnoa) is large in all studied specimens.

The MxL was not described by Miles (1968) in details as being represented in Scottish material only by poorly preserved specimens. However, the dorsal lamina of the plate was correctly assumed by Miles (1968: 78) being slightly less than twice as long as it is broad. The dorsal corner is clearly seen. The lateral lamina is low, more than three times as long as it is broad. The posterior oblique sensory line groove (dlg2) usually terminates in some distance from the lateral margin; LDM 98/53 shows dlg2 crossing the dorso-lateral ridge. In small specimen LDM 98/54 the dlg2 is connected with the main lateral line groove (lcg). The dorso-lateral ridge (dlr) is well-defined both in the ADL and MxL in material from Latvia; Miles (1968) claimed that “there is no clear development of the dlr on either the MxL or ADL”; in fact dlr is not clearly seen, particularly in MxL, because of preservation of the Scottish material as internal impressions.

The AVL with the ventral lamina is 1.9-2 times as long as it is broad; the anterior margin of the ventral lamina is rounded without clearly defined corners ( Miles 1968: 79, text-fig. 39A; Figs 37F, G ; 38A ). The subcephalic division comprises 21-25% (22.5 on the average) of total length of the ventral lamina (about 20% in Scottish material: Miles 1968). The lateral lamina is not preserved within the material from Scotland. It is low, the ventral lamina 3.8 times as broad as the lateral lamina high in LDM 98/30. The lateral lamina is low. The right AVL overlaps the left AVL by very narrow overlap area.

The PVL has variable proportions. It is relatively narrow, the ventral lamina is 2.4-2.7 times as long as it is broad. The subanal division is narrow, it occupies about one fifth-one third (22- 32%) of the total PVL length ( Miles 1968: 80; Figs 38B, C ; 39C ). The lateral lamina is moderately high, 2.3-2.7 times long as it is high. The ventro-lateral ridge (vlr) is clearly defined both in the AVL and PVL.

The MV is not known, but the shape of the AVL and PVL suggest the small size of the slightly elongated MV.

The pectoral fin is represented in Latvian material by some disarticulated bones, and six specimens showing articulated plates of the proximal segment associated with the AVL. The proximal segment bears small rarely set lateral and mesial spines, the lateral spines are larger than the mesial ones; Miles (1968) suggested the mesial spines perhaps absent. The proximal segment is very long and narrow, it is 4.8-6 (5.5 on the average) times as long as it is broad (5.5 to 6 times as long as broad in Scottish material: Miles 1968: 80). The CD1 is of moderate size with L/B index varying from 2.7 to 3.7 (3.3 on the average). The CV1 is gently longer than the CD1 and slightly more elongate (L/B 3.4). The CD2 is slightly longer than it is broad. Specimen LDM 89/4 is an articulated distal segment. It is not adorned with marginal spines, the lateral spines are sharp and proximally directed. The distal segment is very long and narrow, L/B index 5.7. The CD5 plate is present in material from both countries.

The ornamentation is fine and basically of the reticular type ( Miles 1968: 80), in quite large individuals from Latvia becoming smooth. The network of anastomosing ridges are broken into radially arranged shorter ridges on the headshield plates. On the posterior margin of the PMD, subcephalic and subanal divisions the anastomoses between the ridges reduce and nodose short ridges are present. The ornamentation of the pectoral appendage is reticulate in general, on the anterior part of the CD1 and CV1 the ornament is radially arranged ; in the distal part of the proximal segment the ornamentation became smooth. The longitudinal lineation in the ornament of the distal segment is well shown in LDM 89 /4 .

REMARKS

This species was established by Traquair (1893) and well-described by Stensiö (1948) and Miles (1968). Gross (1942) erected Bothriolepis curonica as a new species from Latvia based on a slightly damaged head-shield LDM 15/32, two AMD and one PMD, and several fragments of pectoral fin bones collected in 1934 in the Bienes locality by student of geology Melderis. This description was repeated by Stensiö (1948) in Addenda to his monograph without further comments. Since then, the remains of this fish were collected by Sorokin & Lyarskaja in 1975, and expeditions of the Latvian Museum of Natural History in 1981-1982 in the Kalnamuiža locality. Later specimens described by Gross (1942), as well as a newly collected material from Kalnamuiža site were briefly described and figured (Lukševičs 1987), stressing the close morphological resemblance of B. curonica with B. leptocheira from Scotland. A direct comparison of the specimens belonging to these species during preparation of this work has indicated that they are conspecific. Nevertheless, there are several features which suggest than the Latvian material is a new subspecies of Bothriolepis leptocheira . Bothriolepis leptocheira curonica Gross, 1942 is morphologically very close to Bothriolepis leptocheira leptocheira from Scotland ( Miles 1968). B. leptocheira curonica differs from the nominal subspecies in its 1) larger size; 2) more elongated AVL; 3) smoother ornamentation. The diagnosis of the species presented here is to the large extent based on that provided by Miles (1968), and description adds some previously not known details and comprises comparison of the material from Latvia with that from Scotland.

DISCUSSION

Within other Bothriolepis from Scotland, Baltic and Russia, Bothriolepis leptocheira is particularly characterized by a very short orbital margin of the Prm, the long and narrow AMD and slender pectoral appendage ( Miles 1968). Among the other species of Bothriolepis , B. leptocheira is morphologically closest to B. jarviki Stensiö, 1948 from Greenland ( Stensiö 1948). Both species are similar in 1) their size; 2) shape and proportions of La and Nu of the headshield; 3) the shape and proportions of the AMD; 4) the slender pectoral fin. However, B. jarviki differs from B. leptocheira in the other shape and proportions of the Prm, Pp, Nu, PMD and the ornamentation. B. leptocheira closely resembles also B. jeremejewi Rohon, 1900 from Timan by 1) the slender pectoral appendage; 2) the shape and proportions of the PMD; 3) smooth reticulate ornamentation. Unfortunately, B. jeremejewi is poorly described and known species, represented in collections of LDM and PIN by some badly preserved specimens showing disarticulated fragments of the PMD and pectoral fin. There is not yet enough information to decide whether these species are closely related or not.

Figures

FIG. 32. — Bothriolepis leptocheira curonica Gross, 1942; A, head-shield LDM 15/32; B, head-shield LDM 98/12; C, D, head-shield LDM 98/108 in dorsal and visceral views; E, head-shield LDM 98/86; F, head-shield LDM 89/1; A, Imula River near Bienes hamlet, Latvia; B-F, Amula River upstream Kalnamuiža watermill, Latvia. Eleja Formation. Scale bars: 10 mm.

FIG. 33. — Bothriolepis leptocheira curonica Gross, 1942; A, B, head-shields in dorsal view; A, LDM 98/12; B, LDM 98/86; C-E, Nu; C, D, LDM 98/20 in visceral and dorsal views; E, LDM 98/13 in dorsal view; F, articulated Pn and Pmg LDM 98/18 in dorsal view. Amula River upstream Kalnamuiža watermill, Latvia. Eleja Formation. Abbreviations: La, lateral plate; Nu, nuchal plate; Pmg, postmarginal plate; Pn, paranuchal plate; Pp, postpineal plate; Prm, premedian plate; cir, semicircular pit-line groove; cr.o, median occipital crista; cr.pto, postorbital crista; cr.tv, transverse nuchal crista; csl, central sensory line groove; ifc1, principal section of infraorbital sensory line; ifc2, branch of infraorbital sensory line diverging on La; mp, middle pit-line groove; nm, obtected nuchal area; soc, anterior section of the supraorbital sensory line; socc, supraoccipital cross-commissural pit-line groove; sot, supraotic thickening. Scale bar: 10 mm.

FIG. 34. — Bothriolepis leptocheira curonica Gross, 1942, attempted reconstruction of the head-shield, based on LDM 89/1. Amula River upstream Kalnamuiža watermill, Latvia. Eleja Formation. Abbreviations: La, lateral plate; Nu, nuchal plate; Pmg, postmarginal plate; Pn, paranuchal plate; Pp, postpineal plate; Prm, premedian plate; alc, antero-lateral angle of headshield; cir, semicircular pit-line groove; csl, central sensory line groove; d.end, opening of canal for endolymphatic duct; ifc1, principal section of infraorbital sensory line; ifc2, branch of infraorbital sensory line diverging on La; mp, middle pit-line groove; mppr, posterior process on Nu; nm, obtected nuchal area; soc, anterior section of the supraorbital sensory line; socc, supraoccipital cross-commissural pit-line groove.Scale bar:10 mm.

FIG. 35. — Bothriolepis leptocheira curonica Gross, 1942; A, AMD LDM 15/121, Imula River near Bienes hamlet, Latvia. Eleja Formation; B, AMD LDM 98/21; C, PMD LDM 98/36. Amula River upstream Kalnamuiža watermill, Latvia. Eleja Formation. Abbreviations: AMD, anterior median dorsal plate; PMD, posterior median dorsal plate. Scale bars: 10 mm.

FIG. 36. — Bothriolepis leptocheira curonica Gross, 1942; A, AMD LDM 98/21 in dorsal view; B, ADL LDM 98/58; C, MxL LDM 98/53; D, PMD LDM 98/35 in visceral view. Amula River upstream Kalnamuiža watermill, Latvia. Eleja Formation. Abbreviations: ADL, anterior dorso-lateral plate; AMD, anterior median dorsal plate; MxL, mixilateral plate; PMD, posterior median dorsal plate; cf.AMD, area overlapping AMD; cf.MxL, area overlapping MxL; d, dorsal corner; dlg2, posterior oblique dorsal sensory line groove; dlr, dorso-lateral ridge; dmr, dorsal median ridge; l, lateral corner; lcg, main lateral line groove; npl, postlevator notch; n.prpl, notch in dorsal margin of ADL for external postlevator process of AMD; oa.ADL, area overlapped by ADL; oa.AMD, area overlapped by AMD; oa.AVL, area overlapped by AVL; oa.MxL, area overlapped by MxL; oa.PMD, area overlapped by PMD; oa.PVL, area overlapped by PVL; plc, postero-lateral corner; pnoa, postnuchal ornamented corner; pro, processus obstans of trunk armour; pr.pl, external postlevator process; pt2, posterior ventral pit. Scale bars: 10 mm.

FIG. 37. — Bothriolepis leptocheira curonica Gross, 1942; A, ADL LDM 98/58; B, ADL LDM 89/12; C, ADL LDM 98/94; D, MxL LDM 98/54; E, MxL LDM 89/2; F, AVL LDM 89/7; G, AVL LDM 98/30. Amula River upstream Kalnamuiža watermill, Latvia. Eleja Formation. Abbreviations: ADL, anterior dorso-lateral plate; AVL, anterior ventro-lateral plate; MxL, mixilateral plate. Scale bars: 10 mm.

FIG. 38. — Bothriolepis leptocheira curonica Gross, 1942; A, AVL in visceral view with articulated proximal segment of pectoral fin LDM 98/78; B, PVL LDM 98/45; C, PVL LDM 98/41; D, ML2 LDM 98/76; E, distal segment of the pectoral fin LDM 89/4; F, CV1 LDM 98/90; G, CV1 LDM 98/77. Amula River upstream Kalnamuiža watermill, Latvia. Eleja Formation. Abbreviations: AVL, anterior ventrolateral plate; CV1, ventral central plate 1; ML2, lateral marginal plate 2; PVL, posterior ventro lateral plate. Scale bars: 10 mm.

FIG. 39. — Bothriolepis leptocheira curonica Gross, 1942; A, MxL LDM 89/2; B, AVL plate in visceral view with articulated proximal segment of the pectoral fin in dorsal view LDM 98/78; C, PVL LDM 98/45 in ventral view; D, CV1 LDM 98/90; E, distal segment of the pectoral fin LDM 89/4. Amula River upstream Kalnamuiža watermill, Latvia. Eleja Formation. Abbreviations: ADL, anterior dorso-lateral plate; AVL, anterior ventro-lateral plate; CD1, dorsal central plate 1; CD2, dorsal central plate 2; CV1, ventral central plate 1; ML2, lateral marginal plate 2; MM2, mesial marginal plate 2; MV, median ventral plate; MxL, mixilateral plate; PMD, posterior medi- an dorsal plate; PVL, posterior ventro lateral plate; cf.AVL, area overlapping AVL; cf.MV, area overlapping MV; cf.PVL, area overlapping PVL; cit2, transverse thickening on the visceral surface of AVL; cu, postero-ventral ornamented corner; d, dorsal corner of MxL; dc, dorsal corner of lateral lamina of PVL; dlg2, posterior oblique dorsal sensory line groove; dlr, dorso-lateral ridge; lcg, main lateral line groove; oa.ADL, area overlapped by ADL; oa.AVL, area overlapped by AVL; oa.PMD, area overlapped by PMD; oa.PVL, area overlapped by PVL; vlr, ventro-lateral ridge. Scale bars: 10 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.