Brachymetopus, M'Coy, 1847

Mychko, Eduard V. & Savchuk, Oles V., 2019, A new brachymetopid trilobite from the Early Permian Shakhtau reef complex of the southwestern Urals, Bashkortostan, Russia, Zootaxa 4555 (3), pp. 346-358 : 347-348

Brachymetopus in the Permian of Russia

Permian brachymetopids are rare compared with proetoideans, and are known from only eight Russian localities (including that described in this paper).

A cephalon of a species of Brachymetopus from near the village of Zlatoust (now the village of Klyuchi, Suksun Region, Perm Krai, Russia) was described by Möller (1867, pp. 184–187, Pl. 2, figs. 32–35; 1868, p. 57, Pl. 1, figs 32–35; Fig. 1a herein). The stratigraphic unit in which the cephalon was found belongs to the Sarginian horizon of the Early Permian (Artinskian; Mychko and Alekseev, 2017, p. 58). Hahn and Hahn (1996) assigned this specimen to the Asselian Brachymetopus (Acutimetopus) moelleri Weber, 1932 .

Krasnopolsky (1887, p. 295) reported a trilobite specimen identified as " Brachymetopus uralicus Vern. ," from near the village Kyn on the Talca River, Perm Region, Russia. The age of this specimen is unknown and could potentially range from Middle Carboniferous to Early Permian ( Mychko and Alekseev, 2017, p. 56). Subsequently, from the rocky outcrop of the Upper Carboniferous—Lower Permian limestone reef “Kamen Plakun” on the Chusovaya River, Krasnopolsky (1889, p. 221) reported a specimen also identified as " Brachymetopus uralicus Vern. " No images of these specimens were published and their precise age is unknown. According to Hahn and Hahn's (1996, p. 114) revision, the species B. (Conimetopus) ouralicus (de Verneuil, 1845) is known from the Early and Middle Carboniferous ( Fig. 4). Krasnopolsky's ( 1887, 1889) specimens are unlikely to belong to B. (Conimetopus) ouralicus . Weber (1937, p. 84) assigned a trilobite cephalon and pygidium ( Fig. 1b, c ) from the locality “Kazarmenny Kamen” in the Southern Urals (now “Kazarmenny Greben”, Chelyabinsk Region, Ashinsky District, the right bank of the Sim River near the Asha town) to the species now classified as Brachymetopus (Acutimetopus) moelleri Weber, 1932 . Weber (1937) considered this locality Late Carboniferous. However, the age of “Kazarmenny Greben,” which is a large Bryozoan-Tubiphytes boundstone ( Tolstikhina, 1941, p. 73; Miloradovich and Ilina 1951, pp. 17–20), was revised as Asselian by Mychko and Alekseev (2017, p. 60) based on the occurrence of the Early Permian foraminiferan Sphaeroschwagerina moelleri ( Rauzer-Chernousova, 1936) . Hahn and Hahn (1996, p. 137) assigned these specimens to the Carboniferous subspecies B. (Conimetopus) ouralicus ouralicus (de Verneuil, 1845) . Here they are reassigned to B. (Conimetopus) alekseevi Mychko , sp. nov.

Weber (in Chernov and Chernov [1940]) identified a trilobite fragment from the Terravean-Kozhim Formation (Early Permian; Asselian; Mychko and Alekseev, 2017, p. 54) of the Kozhim River in Komi, Brachymetopus sp. ind. This specimen has never been illustrated.

Brachymetopus (Acutimetopus) caucasicus Licharev (in Weber, 1944, Pl. 2, Fig. 15; Fig. 1d, e herein) is known from a single pygidium from the Northern Caucasus, near the “Nikitinskaya Balka” locality (Krasnodar Krai, Mostovsky District, the Malaya Laba River basin). In this locality, there are deposits of the Nikitin and Urushten Formations that belong to the Dzhulfian (~Wuchiapingian) of the Upper Permian ( Kotlyar et al., 1983). These are the youngest known members of the genus Brachymetopus in Russia.

Figures

FIGURE 1. Some members of the genus Brachymetopus from the Permian of Russia. a—B. (Acutimetopus) moelleri (Weber, 1932); reconstruction of cephalon; presumably kept (possibly lost) in the collections of the St. Petersburg Mining University museum, St. Petersburg; Lower Permian, Artinskian, Sarginian (reproduced from Möller [1868, Pl. 1, Fig. 32]). b, c—B. (Conimetopus) alekseevi Mychko, sp. nov.; b—cephalon, spec. TsNIGR no. 5107/2063; c—pygidium, spec. TsNIGR no. 5107/ 2064; Chelyabinsk Region, Ashinsky District, right bank of the Sim River, the town of Asha, “Kazarmenny Kamen” locality; Lower Permian, Asselian; (reproduced from Weber [1937, Pl. 10, figs 10–11]). d, e—B. (Acutimetopus) caucasicus Likharev, 1944; spec. TsNIGR no. 5217/86, holotype, pygidium; Krasnodar Region, Mostovsky District, the Malaya Laba River basin, “Nikitinskaya Balka” locality; Upper Permian, Dzhulfian (~Wuchiapingian), Urushten or Nikitin Formations; d—view from the dorsal side, e—view from the end of the posterior margin (reproduced from Weber [1944, Pl 2, Fig. 15]). The scale bar is 1 cm.