Some notes on a variability of Bothriolepidids (Placodermi, Antiarchi): unusual specimen of Livnolepis Heckeri (Luksevics) from the famennian of Tver region, European Russia

The fragment of the skull cap of placoderm Livnolepis heckeri (Luksevics) from the Bilovo Formation (Famennian, Upper Devonian) near the Bilovo Village of Tver Region has been described. The character of the passage of sensory grooves on its external surface is unusual as for this species as for all other bothriolepidids. The oblique cephalic pit-line (or central sensory) groove normally passes from the nuchal on the lateral bones. The left branch of the obhque cephalic pit-line groove on the studied specimen runs from the nuchal onto the paranuchal and only then on the lat­eral. The right branch of this pit-line groove reaches the posterolateral margin of the nuchal, passes along the suture between the nuchal and paranuchal and then transfers into the lateral bone. The branches of the obhque cephalic pit-line groove are subparallel to the posterior margin of the nuchal bone in the Bilovo specimen. The pit-line grooves, which run parallel and subparallel to the posterior margin of the nuchal and anteriorly to the supratemporal (supraoccipital) cross-commissural pit-lines, were earlier determined in some bothriolepidids {Bothriolepis cellulosa (Pander), B. paradoxa (Agassiz) and others) as the middle grooves but not the obhque cephalic. The paranuchalswith the obhque cephalic pit-line grooves were earlier unknown. The unusual character of the passage of the sensory lines is refered to the individual variability in the exoskeleton of L. heckeri. Types of the bothriolepidid exoskeletal variability have been briefly considered. The passage of the pit-line grooves on the external surface of the bothriolepidid and asterolepidid skull roofs has been discussed.

1. Karatayute-Talimaa V.N. Rod Asterolepis iz devonskih otlozhenii nia]. Vilnius, Institute Geol. and Geogr. Publ., 1963, pp. 65—224.

2. Russkoi platformi [The genus Asterolepis from the Devonian of (In Russian). Russian Platform]. Voprosigeologii Litvi [The Geology of Lithua- 2. Lukshevich E.V. Botriolepidi ketlerskoi sviti verkhnego devona Latvii (Pisces, Placodermi) [The bothriolepidids of the Uppe Devonian Ketleri Formation of Latvia (Pisces, Placodermi)]. Priroda i Muzei. Seriya paleontologicheskaya [Nature and Museum. Palaeontological Series], 1991, no. 3, pp. 38—50. (In Russian).

3. Lyarskaya L.A Pantsimie ribi Pribaltiki: Asterolepididae [Placoderms of the Baltic Stages: Asterolepididae], Riga, Zinatne Publ., 1981, 152 p. (In Russian).

4. Moloshnikov S.V., Linkevich V.V. Novie dannie po pozdnedevonskoi ikhtiofaune Tverskoi oblasti (Bilovo, r. Malii Tuder) [New data on the Late Devonian ichthyofauna of Tver Region (Bilovo, Malii Tuder River)]. Integrativnaya paleon-tologiya: perspekttvi razvitiya dlya geologicheskikh tselei. Materiali 63 sessii Paleotologicheskogo obtshestva pri RAN (3—7 aprelya 2017 g., Sankt-Peterburg) [Integrative palaeontology: perspective of a development for geology. Proc. of the 63 Session of the Palaeotological Society at Russian Academy of Sciences (April 3—7, 2017, St.-Petersburg)]. St.-Petersbuig, 2017, pp. 196—198. (In Russian).

5. Moloshnikov S.Y., Linkevich V.V. Sistematicheskoe polozhenie famenskikh antiarch (Vertebrata, Placodermi) [Systematic position of antiarchs (Vertebrata, Placodermi) from the Famen-nian of Tver Region, Russia]. Izvestiya vysshikh uchebnykh zavedeniy. Geologiya i razvedka — [Proceedings of higher educational establishments. Geology and Exploration], 2017, no. 2, pp. 8—14. (In Russian).

6. Moloshnikov S.V., Linkevich V.V. Morfologiya i sistematicheskoe polozhenie nekotorikh famenskikh botriolepidid (Placodermi, Antiarchi) Tverskoi oblasti [Morphology and systematic position of some bothriolepdids (Placodermi, Antiarchi) from the Famennian of Tver Region]. Morfologicheskaya evolutsiya i stratigraficheskie problemi. Materiali 65 sessii Paleontologicheskogo obtshestva pri RAN (1-5 aprelya 2019 g., Sankt-Peterburg) [Morphological evolution and strati-graphical problems. Proc. of the 65 Session of the Palaeotological Society at Russian Academy of Sciences (April 1—5, 2019, St.-Petersburg)]. St.-Petersbuig, Kartfabrika VSEGEI, 2019, pp. 249—251. (In Russian).

7. Reshenie mezhvedomstvennogo regionalnogo stratigraficheskogo savetshaniay po srednemu i verkhnemu paleozoyu Russkoi platformi, s regionalnimi stratigraflcheskimi skhemami. Leningrad, 1988, devonskaya sistema [The decision of the Interdepartmental Regional Stratigraphical Meeting on the Middle and Upper Paleozoic of Russian Platform, with the regional stratigraphical schemes, Leningrad, 1988, Devonian System]. Leningrad, 1990, 58 p. (In Russian).

8. Denison R. Placodermi. Handbook of Palaeoichthyology. Stuttgart, New York, Gustav Fischer Verlag, 1978, 128 p.

9. Gross W. Asterolepis omata Eichw. und das Antiarchi-Problem. Palaeontogr., 1931, Bd. 75, Ss. 1—62.

10. Gross W. Die Fische des Baltischen Devons. Palaeontogr. A., 1933, Bd. 79, Ss. 1-97.

11. Gross W. Uber Knochen-MiBbildungen bei Asterolepiden. Palaontol. Z., 1942, Bd. 23, no. 1/2, pp. 206-218.

12. Luksevics E. Bothriolepid antiarchs (Vertebrata, Placodermi) from the Devonian of the north-western part of the East European platform. Geodiversitas, 2001, vol. 23, no. 4, pp. 489-609.

13. Miles R.S. The Old Red Sandstone Antiarchs of Scotland: family Bothriolepididae. Palaeontogr. Soc. Monogr., 1968, no. 130, pp. 1-130.

14. Moloshnikov S. Crested antiarch Bothriolepis zfldonica H.D. Obrucheva from the Lower Famennian of Central European Russia. Acta Palaeontol. Pol., 2004, vol. 49, no. 1, pp. 135—146.

15. Moloshnikov S.V. Devonian antiarchs (Pisces, Antiarchi) from Central and Southern European Russia. Paleontol. J., 2008, vol. 42, no. 7, pp. 691-773. DOI: 10.U34/S0031030108070010.

16. Pan Zh., Zhu M., Zhu Y., Jia L. A new antiarch placoderm from the Emsian (Early Devonian) of Wuding, Yunnan, China. Alche-ringa: An Austral. J. Palaeontol., 2017, vol. 42, no. 1, pp. 10—21. DOI: 10.1080/03115518.2017.1338357.

17. Stensio E. On the Placodermi of the Upper Devonian of East Greenland II. Antiarchi: subfamily Bothriolepinae. Palaeozool. Groenl., 1948, Bd. 2, pp. 1-622 p.

18. Werdelin L., Long J. Allometry in the placoderm Bothriolepis canadensis and its significance to antiarch evolution. Lethaia, 1986, vol. 19, no. 2, pp. 161-169.

19. Young G.C. Antiarchs (Placoderm fishes) from the Devonian Aztec Siltstone, Southern Victoria Land, Antarctica. Palaeontogr. Abt. A., 1988, Bd. 202, pp. 1-125.