Remains of antiarchs from the Bothriolepididae family widely distributed in the Devonian are often found in the Famennian deposits of the western part of the Tver oblast (Moloshnikov and Linkevich, 2017a, 2017b; 2019). A deep-bodied crested Livnolepis heckeri (Lukševičs) and Bothriolepis sp. with a flattened body shield without a dorsal crest were found in the presumed Bilovo formation, and B. cf. B. ciecere Lyarskaja, in the L’nyanskaya formation. Livnolepis heckeri prevails among the bothriolepidids of the Tver oblast; numerous remains of the species are found near the village of Bilovo on the Malyi Tuder River. This locality was studied in detail by R.F. Gekker (Gekker et al., 1935). He identified the Bilovo sequence of carbonate rocks composed of variegated marls and greenish-gray sandy limestones and clays, which corresponded to the Lebedianian horizon of the Middle Famennian (Reshenie …, 1990).

D.V. Obruchev (Gekker et al., 1935, p. 74) identified the remains of osteo- and porolepiform crossopterygians and placoderms, including the novel species Bothriolepis n. sp., in the Bilovo locality. However, a formal description of the new antiarch species from Bilovo was given by E.V. Lukševičs in 2001 only (Lukševičs, 2001); the author of the description named the species B. heckeri after Gekker. Species description was based on three specimens from Gekker’s collections: one almost intact and one incomplete anterior mediodorsale plate, as well as a part of the lateral, marginal nuchal, and posterior marginal plates joined together. In the description of the species, Lukševičs noted that the material supposedly originated from Bilovo beds (“Bilovo Beds (?)”, Lukševičs, 2001, p. 577). New materials collected after 2011 by employees of the Shimkevich District Museum of Local Lore, Andreapol’ (KMA) from the type locality enabled considerable refinement of the description and clarification of the systematic position of this species. This species was assigned to the genus Livnolepis Moloshnikov (Moloshnikov, 2016; Moloshnikov and Linkevich, 2017a, 2017b) according to a number of morphological features of the head and trunk shield plates. Livnolepis remains have already been encountered in the Lower Famennian deposits of the Tver oblast (Nelidovskaya and Redkinskaya wells) (Moloshnikov, 2008). Most of the L. heckeri remains were collected from the talus, and this precluded the precise assessment of their stratigraphic position. The L. heckeri bones currently known include the plates of the entire head shield and almost the entire body shield, as well as the plates of the proximal segment of the pectoral fin. Specimens from different ontogenetic stages are available for some bones. The holotype and two paratypes of L. heckeri are preserved at the Borissiak Paleontological Institute at the Russian Academy of Sciences (PIN) (Coll. No. 835), and the other materials analyzed are preserved at the KMA and the Museum of Earth Sciences at Moscow State University.

The description of L. heckeri presented below is based on new materials collected in the 2000s from the type locality. The terminology adopted in Russian scientific publications is used in the description. The measurements were carried out according to the schemes proposed by E. Stensiö (1948).

  • SYSTEMATIC PALEONTOLOGY

  • Order Bothriolepiformes

  • Family Bothriolepididae Cope, 1886

  • Subfamily Livnolepidinae Moloshnikov, 2012

  • Genus Livnolepis Moloshnikov, 2008

  • Livnolepis heckeri (Lukševičs, 2001)

  • Plate 8, figs. 1–8; Plate 9, figs. 1–9

Fig. 1.
figure 1

Head shield plates of Livnolepis heckeri (Lukševičs): (a) incomplete left laterale, marginal nuchale, and posterior marginale joined to each other, specimen PIN, no. 835/40, external side; (b, c) right laterale, specimen KMA/HB/5184: (b) external view, (c) internal view; (d) frontal unpaired plate, specimen KMA/HB/5178, internal view; (e) nuchale, specimen KMA/HB/5173, external side; (f) nuchale joined to posterior pineale, specimen KMA/4770-1, external side. Symbols: (cir) semicircular fossal groove, (ifc1) upper infraorbital groove, (ifc.b) posterior oblique cranial fossal groove, (L) laterale, (nm) smooth nuchal marge, (npp) posterior pineal notch on the nuchale, (Nu) nuchale, (orb) orbital (orbitonasal) notch, (PMg) posteriomarginale, (PNu) marginal nuchale, (PP) posterior pineale, (prh) preorbital hollow, (pr.po) posteriolateral angles of the oticooccipital hollow, (vcp) vertical sensory groove. Scale bar 1 cm.

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Fig. 2.
figure 2

Trunk shield plates of Livnolepis heckeri (Lukševičs): (a–c) anterior mediodorsale, specimen KMA/4049, external side: (a) dorsal view, (b) lateral view, (c) frontal view, (d, e) posterior mediodorsale, specimen KMA/HB/5172, external side: (d) dorsal view, (e) lateral view; (f, g) incomplete posterior mediodorsale, specimen KMA/4770-8: (f) external side, (g) internal side; (h) right anterior mediodorsale, specimen KMA/HB/5183, external side. Symbols: (cf.MxL) plate overlying the mixilaterale, (cr.d) medial dorsal crest, (cr.tp) posterior transverse trunk rib, (dlg2) posterior oblique trunk groove, (dlm) dorsal plate, (dlr) dorsolateral rib, (lcg) groove of the main lateral line, (llm) lateral plate, (oa.PMD) plate overlapped by the medio-dorsale, (pa) posterior corner, (pnoa) posterior nuchal corner, (pr.ob) processus obstans, (pt2) posterior ventral funnel on the posterior medio-dorsale, (tb) spongy field at the posterior medio-dorsale. Scale bar 1 cm.

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Fig. 3.
figure 3

The most characteristic traits of Livnolepis exoskeleton that distinguish the genus from Bothriolepis: (a, b) unpaired frontal plates, internal side: (a) Bothriolepis canadensis (Whiteaves), narrow slit-shaped preorbital hollow (after Stensiö, 1948); (b) Livnolepis zadonica (H. Obrucheva), large preorbital hollow (specimen PIN 3725/1132); (c, d) lateralia, internal side: (c) Bothriolepis maxima Gross, well-pronounced deep anterolateral corners of the oticooccipital hollow (specimen PIN, n/n); (d) Livnolepis zadonica (H. Obrucheva), inconspicuous shallow anterolateral corners of the oticooccipital hollow (specimen PIN 3525/1005). Symbols: (prh) preorbital hollow, (pr.po) posteriolateral corners of the oticooccipital hollow. Not on scale.

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Bothriolepis heckeri: Lukševičs, 2001, p. 577, text-figs. 60H–60J, 62.

Livnolepis heckeri: Moloshnikov and Linkevich, 2017a, text-figs. 3–8; 2017b, pl. 1, figs. 2, 4–7, pl. 2, figs. 1, 2, pl. 3, figs. 1, 3–5; 2019a, Figs. 1–5; 2019b, Figs. 1, 2a, and 3.

Holotype. PIN, no. 835/42, anterior medio-dorsale; Tver oblast, Malyi Tuder River, near the village of Bilovo; Upper Devonian, Famennian, Bilovo (?) formation.

Description. Bothriolepidids with a relatively large and high shield; head shield length amounted to 12–13 cm. The dorsal wall of the body shield could reach a length of 25 cm and carried a relatively high median dorsal crest (cr.d). Its maximal height observed at the level of the suture between the anterior and posterior medio-dorsale reached 1 cm or even more.

The cranial skeleton. Laterale (L; Figs. 1a–1c; Pl. 8, figs. 1, 2) of the head shield wide, with a wide and almost straight rostral edge. Bone length to width ratio is approximately 1.24. The lateral and posterior-lateral corners of the bone are distinct. The upper infraorbital groove (ifc1) on the external surface runs in the middle of the distance between the lateral and orbital edges and at one-third to half of the distance between the rostral and orbital edges in both adult (specimen KMA/HB/5184) and young individuals (specimen KMA/HB/5182), that is, the laterale has a wide lateral part. The vertical sensory groove (vcp) long, well pronounced on the bones of both young and adult individuals. The posterior oblique cephalic fossa line (ifc.b) on the laterale specimens from adults is poorly discernible or absent (Fig. 1b; Pl. 8, fig. 1b), whereas the line is distinct in the young individuals, in which it extends beyond the midline of the orbital notch, but does not reach its anterior edge (Pl. 8, fig. 2). A semicircular pit groove is also well defined on the bones of young individuals (Pl. 8, fig. 2: cir). The anterolateral corner of the otico-occipital deepening (pr.po) on the inner surface of the right laterale (specimen KMA/HB/5184) is shallow, poorly discernible, and slightly wider at the base than the corresponding corner in L. zadonica. The preorbital hollow (prh) on the laterale of L. heckeri apparently had a similar shape as in L. zadonica (Moloshnikov, 2004, 2008): one lateral corner, as well as the lateral and anterior edges, were developed. Orbital (orbito-nasal: orb) notch shallow.

figure a

Explanation of Plate 8

Figs. 1–8 .Livnolepis heckeri (Lukševičs), cranial and postcranial plates: (1) specimen KMA/HB/5184, right laterale: (1a) internal, (1b) external side; (2) specimen KMA/HB/5182, left laterale, external side; (3) specimen KMA/HB/5178, praemediale, internal side; (4–6) nuchalia, external side: (4) specimen KMA/HB/5174, (5) specimen KMA/HB/5173, (6) specimen KMA/3666, fragment; (7) specimen KMA /4770-1, nuchale joined to postpineale, external side; (8) specimen KMA/4049, anterior medio-dorsale, external side: (8a) lateral view, (8b) dorsal view, (8c) lateral view. Tver oblast, near the village of Bilovo, Malyi Tuder River; Upper Devonian, Famennian, Bilovo (?) formation. Scale bar 1 cm.

Symbols: (cir) semicircular fossal groove, (cr.d) medial dorsal ridge, (dlg2) posterior oblique trunk groove, (ifc1) upper infraorbital groove, (ifc.b) posterior oblique trunk fossal groove, (nm) smooth nuchal margin, (Nu) nuchale, (npp) posteriopineal notch, (orb) orbital (orbitonasal) notch, (PP) postpineale, (prh) preorbital hollow, (pr.po) anterolateral corners of the oticooccipital hollow, (vcp) vertical sensory groove.

Praemediale; Fig. 1d; Pl. 8, fig. 3) elongated, with a length to greatest width (along the front edge) ratio of approximately 1.4. The anterior edge 1.2 times as long as the posterior. Anterior edge straight, posterior edge slightly convex. Lateral edges slightly convex. The nasal plate of specimen KMA/HB/5178 was not preserved, but the character of the site of its attachment to the facial plate allows for the assumption that the preorbital recess of the head shield (prh) was large, similarly to that in L. zadonica.L. heckeri had a trapezoid preorbital recess, similarly to L. zadonica, as evident from the shape of depressions on the praemediale and laterale (see above).

Postpineale (PP; Fig. 1f; Pl. 8, fig. 7) broad, with a convex anterior edge, length to width ratio 0.6.

Nuchale (Nu; Figs. 1e, 1f; Pl. 8, figs. 4–7) broad and arched. Bone length to width ratio approximately 0.7; the arching angle at the posterior edge 95°–100°. The bone reaches its greatest width at the level of the lateral and posterolateral corners. A shallow and wide posteriopineal notch (npp) is located in the anterior part of nuchale. Anterolateral edges that border on laterale straight and short, 2–3 times shorter than the posterolateral ones. Posterolateral edges straight or slightly concave. A fairly wide smooth nuchal marge (nm) runs along the posterior edge on the external surface and extends to paranuchalia. The posterior oblique head fossa line (if.b) is well developed on the nuchalia of young individuals. The endolymphatic duct openings on the external surface (d.end2) are small and located close to each other (specimen KMA/3666). The transverse nuchal rib on the internal surface of the nuchale is tall, developed over the entire width of the bone, and extends to the paranuchalia. The part posterior to the transverse nuchal rib is long, with a well-defined, rather low medial nuchal crest, sometimes with two low symmetrical additional ridges running obliquely lateral to this ridge.

The paranuchale (PNu; Fig. 1a) broad. The upper infraorbital groove runs at one-third to half of the bone’s width from the lateral edge, that is, the lateral part is broad, similarly to what is observed for laterale.

Postmarginale (PMg; Fig. 1a). Lukševičs (2001, p. 578, text-fig. 62a) characterized this bone as elongated, with medial edges longer than the lateral, in his original description of the species. However, the posterolateral part is broken in the only specimen of this bone available (PIN, no. 835/40), and therefore it is rather difficult to assess the shape of postmarginale. This bone might have still been broad, as in L. zadonica (see, for example, Moloshnikov, 2008, text-figs. 36j–36m; pl. 8, fig. 5).

The postcranial skeleton. Anterior medio-dorsale (Figs. 2a–2c; Pl. 8, fig. 8; Pl. 9, fig. 1) elongated and arched throughout its length. Arching angle approximately 90° at the anterior edge of the bone and approximately 80° at the posterior. The anterior section of the anterior medio-dorsale is somewhat wider than the posterior one in the young individuals, with a length to width ratio of approximately 1.3 (specimen KMA/4049). Bones of large individuals could have had a wider anterior section and edge (Lukševičs, 2001, text-fig. 62f). Similar age-related changes in the proportions of the anterior medio-dorsale can also occur in other bothriolepids, for example, Bothriolepis sibirica Obruchev from the Frasnian of Southern Siberia (Moloshnikov, 2009, p. 81). The anterior section of the anterior medio-dorsale in L. heckeri is twice as long as the posterior section. The anterior edge of the bone is slightly convex; its length is 1.4 times less than the bone width at the level of the lateral corners. The tergal corner is located at one-third of the bone’s length from the anterior edge. The well-developed tall dorsal crest (cr.d) starts from the tergal corner and attains maximal height by the suture between the anterior and posterior medio-dorsalia. The posterior oblique trunk groove (dlg2) on all the anterior medio-dorsale specimens of L. heckeri found in the collection crosses the posterolateral edge of the bone, that is, extends to the mixilaterale. In contrast, some L. zadonica specimens are characterized by the transition of the posterior oblique trunk groove to the posterior mediodorsale (Moloshnikov, 2004, 2008). The sutures between the anterior mediodorsale and the anterior dorsolaterale and mixilaterale have a structure common for bothriolepids: the anterior medio-dorsale overlies the anterior dorso-laterale and runs under the mixilaterale throughout the area of contact. The type of these sutures in some L. zadonica specimens is uncommon for bothriolepids (Obrucheva 1983; Moloshnikov, 2008).

figure b

Explanation of Plate 9

Figs. 1–9 .Livnolepis heckeri (Lukševičs), postcraniale specimens: (1) specimen KMA/4770-2, anterior medio-dorsale, external side; (2) specimen KMA/HB/5172, posterior medio-dorsale, external side: (2a) lateral view, (2b) dorsal view; (3) specimen KMA/4770-8, incomplete posterior medio-dorsale, external side; (4) specimen KMA/HB/5183, right anterior dorso-laterale, external side; (5) specimen KMA/HB/5175, left mixilaterale, external side; (6) specimen KMA/HB/5177, right anterior ventro-laterale and a proximal segment of the pectoral fin shield, external side, ventral view; (7) specimen KMA/HB/5179, subcephalic section of the left anterior ventro-laterale, internal side; (8) specimen KMA/4770-3, proximal segment of the shield of the right pectoral fin, external side, dorsal view; (9) specimen KMA/HB/5181, left posterior ventro-laterale, external side, lateral view; Tver oblast, near the village of Bilovo, Malyi Tuder River; Upper Devonian, Famennian, Bilovo (?) formation. Scale bar 1 cm.

Symbols: (cit1) anterior internal transverse rib, (cr.d) medial dorsal crest, (cr.ptbr) postbranchial crest, (Cv1) centrale-ventrale 1, (dlg2) posterior oblique trunk groove, (dlm) dorsal plate, (dlr) dorsolateral rib, (lcg) groove of the main lateral line, (llm) lateral plate, (Ml2) marginale-laterale 2, (pa) posterior angle of posterior medio-dorsale, (pnoa) posterior nuchal corner, (pr.br) processus brachialis, (pr.ob) processus obstans, (vg) ventral transverse sensory groove, (vlm) ventral plate.

Posterior medio-dorsale (Figs. 2d–2g; Pl. 9, figs. 2, 3) elongated, arched throughout its length; with a long and narrow anterior part; bone length to width ratio approximately 1.4. Arching angle at the anterior edge of the bone is 120°. Anterolateral corners smoothened, weakly pronounced. The posterior corner of the bone (pa) can protrude backwards to form a posterior process (specimen KMA/HB/5172; Fig. 2d; Pl. 9, fig. 2b) or be weakly discernible (specimen KMA/4770-8; Fig. 2f; Pl. 9, fig. 3). The posterior ventral funnel (pt2) on the inner surface of the posterior medio-dorsale is elongated and deep. A large spongy field (tb) is developed in front of it. The posterior transverse crest (cr.tp) is low, flattened; the bone section posterior to it is short (specimen KMA/4770-8).

Anterior dorso-laterale (Fig. 2h, Pl. 9, fig. 4) wide, with a somewhat narrower lateral plate. The ratio of dorsal plate width to lateral plate width is approximately 1.08. These plates converge at an angle of 145°. The dorsolateral rib (dlr) is flattened and weakly pronounced (specimen KMA/HB/5183). The posterior occipital angle (pnoa) of the bone is narrow and elongated. The groove of the main lateral line (lcg) is distinct. The anterior process of the lateral plate (processus obstans, pr.ob) protrudes slightly forward.

Mixilaterale (Pl. 9, fig. 5) short and wide. The dorsal plate is slightly wider than the lateral plate, similarly to what is observed for the anterior dorso-laterale. These plates converge at an angle of 120°–130° in the young L. heckeri individuals. The dorsolateral rib (dlr) is flattened. The posterior edge of the mixilaterale is slightly sloping, almost vertical. The posterior oblique trunk groove (dlg2) and the groove of the main lateral line (lcg) are distinct.

Anterior ventro-laterale (Pl. 9, figs. 6, 7) with a relatively narrow ventral plate (vlm); this plate is about 1.5 times as long as wide. The lateral and ventral plates converge at an angle of 125°. Ventro-lateral rib inconspicuous, flattened. Subcephalic section of the anterior ventro-laterale wide and short; it occupies somewhat less than one third of the bone’s overall length (specimen KMA/HB/5177). The ventral transverse sensory groove (vg) is developed on the external surface of the ventral plate of the anterior ventro-laterale. The post-branchial crest (cr.ptbr) on the internal side of the bone is narrow, well defined in the lateral part of the bone only, runs obliquely from the lateral edge, and does not reach the middle of the width of the ventral plate. The anterior inner transverse rib (cit1) inconspicuous, has the appearance of a smoothened bulge.

Posterior ventro-laterale (Pl. 9, fig. 9) has a relatively wide lateral plate with a wide anterior margin and a relatively narrow ventral plate. The lateral plate almost 2.3 times as long as wide. The lateral and ventral plates converge at an angle of 120°–130°. The ventro-lateral rib (vlr) is distinct in the posterior part of the bone only and flattened in the anterior part.

The proximal segment of the pectoral fin is elongated (Pl. 9, figs. 6, 8), 3.5 times as long as wide. The lateral edge of the segment is convex. Medial-dorsal and lateral edgings can carry small pointed denticles (specimen KMA/4770-3). Medial-ventral edging smoothed. The first bone of the central dorsal row (centrale-dorsale 1) is wide; the ratio of length to width is approximately 1.8.

Ornamentation of the external bone surface in adult L. heckeri individuals is tuberculose. The tubercles are large, with rounded apices, can be flattened on some bones. The tubercles are usually well separated from each other, but they can also adjoin tightly to each other, for example, on some trunk bones. The external surface ornamentation of the bones of young individuals (for example, laterale, specimen KMA/HB/5182; anterior medio-dorsale, specimen KMA/4049; mixilaterale, specimen KMA/HB 5175) is mesh-like, transformed into tuberculose-ribbed and tuberculose in some areas. The ventral wall of the trunk shield and the pectoral fin bones are mostly covered by a mesh-like ornament, with tubercles and ridges formed by merged tubercles located in the nodes of the mesh.

Measurements, mm. Praemediale, specimen KMA/HB/5178: length 30, anterior edge length 21.1, posterior edge length 17.5; laterale, specimen KMA/HB/5184: length 87.1, width 70.5; postpineale, specimen KMA/4770-1: length 11, width 18.5; nuchalia, specimen KMA/4770-1: length—24, width (reconstructed at the level of lateral corners) approx. 31; specimen KMA/HB/5173: length—approx. 25.5, width (reconstructed at the level of lateral corners) approx. 34; anterior medio-dorsale, specimen KMA/4049: length 28, width (at the level of lateral corners) 22; posterior medio-dorsale, specimen KMA/HB/5172: length 57.5, width (at the level of lateral corners) 40.5; anterior dorso-laterale, specimen KMA/HB/5183: length 56.5, width (with pnoa reconstructed) approx. 44.5, dorsal plate width (with pnoa reconstructed) 26, lateral plate width 24; mixilaterale, specimen KMA/HB/5175: length approx. 21, dorsal plate width approx. 15, lateral plate width approx. 13; anterior ventro-laterale, specimen KMA/HB/5177: bone length approx. 100, width approx. 65; posterior ventro-lateralia, specimen KMA/HB/5181: lateral plate length approx. 90, lateral plate width approx. 38; specimen KMA/HB/5180: ventral plate width 42.5; proximal segment of the pectoral fin, specimen KMA/HB/5177: length 110, width 30; centrale-dorsale 1, specimen KMA/HB/5177: length 57, width 31.5.

Comparison. As evident from the arched shape of the nuchalia, anterior medio-dorsalia, and posterior medio-dorsalia, the shield of L. heckeri was rather tall as compared to those of other bothriolepids, similarly to the L. zadonica shield, but was distinguished from the latter by the dorsal crest (cr.d) being lower and different proportions of the trunk shield. The lateral walls of the trunk shield in L. heckeri were apparently wider than in L. zadonica, whereas the dorsolateral walls were narrower. The ornamentation of the external bone surface in young L. heckeri individuals was mesh-like, whereas the bone ornamentation in the young L. zadonica individuals was tuberculose and tuberculose-ridged.

Material. From the type locality: lateralia—3; paranuchale—1; head shield fragment—2; nuchalia—5; anterior medio-dorsalia—6; posterior medio-dorsalia—4; fragment of a single dorsal crest—1; anterior dorso-lateralia—2; mixilaterale—1; anterior ventro-lateralia—6; posterior ventro-lateralia—5; proximal segment of the pectoral fin shield—8; individual plates from the proximal segment of the pectoral fin—8; numerous fragments of unidentifiable postcranial plates.

CONCLUSIONS

The two species L. zadonica (H. Obrucheva) from the Zadonskian horizon (Lower Famennian) of the Central Devonian Field (CDF) and L. heckeri (Lukševičs) from the middle Famennian of the southwestern margin of the Main Devonian Field are currently included into the genus Livnolepis. A large preorbital recess of the head shield and poorly pronounced imprints of the anterolateral processes of the endocranium on the internal side of the body shield are the most characteristic structural features of the exoskeleton in Livnolepis (Fig. 3). Livnolepis spp. were rather large bothriolepids; the total length of the head and trunk shield sometimes amounted to 40 cm. A high median dorsal crest, which served as a stabilizer of the antiarch’s body during swimming and, probably, also as a keel (Moloshnikov, 2010) was present on the trunk shield in both species. Dorsal crests of this type emerged in the Frasnian representatives of the family Bothriolepididae. For example, they are known for the Australian species Bothriolepis gippslandiensis and B. cullodonensis (Stensiö, 1948; Long, 1983; Long and Werdelin, 1986) and in B. markovskii from the western slope of the Southern Urals (Moloshnikov, 2010). The Famennian bothriolepidids with a high dorsal crest include Livnolepis spp. and B. cristata from Scotland (Stensiö, 1948; Miles, 1968).

The low and wide median dorsal crests of the trunk shield were found in the Scottish species B. wilsoni and B. obesa (Miles, 1968). As mentioned by Miles (Miles, 1968, p. 83), the dorsal crest structure in these species was different from that in B. cristata. Lukševičs (2001, text-fig. 83) placed B. wilsoni near L. zadonica (previously B. zadonica) on the cladogram of the species of the genus Bothriolepis because of the presence of a low and broad dorsal crest. Indeed, the dorsal ridge preserved in the L. zadonica holotype (AMD, PIN 1660/3) was low and broad. However, visual examination of this specimen reveals traces of crest breakage and wear of the crest attachment site. As can be inferred from the examination of numerous mediodorsale specimens from other localities, the dorsal c in L. zadonica was high and narrow (see, for example Moloshnikov, 2004, text-figs. 8c, 8d, D; Moloshnikov, 2008, pl. 9, figs. 3, 5), reminiscent of the crests in B. cristata, B. gippslandiensis, and B. markovskii. The newly described L. heckeri has a crest of a similar type, but not as high. Therefore, the phylogenetic closeness of B. wilsoni to the Zadonskian species inferred from the trait discussed above appears dubious, especially given that the dorsal crests in the trunk shield could have emerged independently and in parallel in various bothriolepid groups and species (Miles, 1968, p. 63; Moloshnikov, 2010, p. 82).

Studies of the new materials from Famennian deposits of the Tver oblast supplement the data on bothriolepid morphology, their systematic composition, and distribution of representatives of the genus Livnolepis, so that the remains of these organisms can be used for the refinement of correlation of the Upper Devonian deposits of the East European platform. The remains of large and deep-bodied bothriolepids similar to Livnolepis are known from the Frasnian of the CDP (Moloshnikov, 2008; unpublished data of one of the authors, M.S.V.) and the Lower Famennian of Central Poland (Szrek, 2004), as well as from the Upper Devonian deposits of the South Siberia (Moloshnikov, 2010; Moloshnikov, 2012).