Brachymetopus (Conimetopus) Hahn and Hahn, 1985

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 : 349-352

Brachymetopus (Conimetopus) Hahn and Hahn, 1985

Type species: Phillipsia ouralica de Verneuil 1845 , from the Bashkirian (Late Carboniferous), Shartimka River, Southern Urals, Russia .

Other species: B. (C.) alekseevi Mychko sp. nov., the upper part of Asselian or the Lower Sakmarian, Lower Permian, Shakhtau locality, Sterlitamak town, Bashkortostan, Russia; B. (C.) arcticus Hahn et Hahn, 1992, Middle Morrowan to Middle Atokan (~Bashkirian), Pennsylvanian, Mariana Islands, Alexander Archipelago, Southeast Alaska; B. (C.) conifrons Gandl, 1987, Namurian C (~Upper Part of the Bashkirian), Pennsylvanian, Province of León, Cantabrian Mountains, Spain; B. (C.) esus Hahn et Hahn, 1982 , Lower Warnantium (~Upper Visean), Mississippian, Vise and Richelle, Belgium; B. (C.) inflatus Weber, 1937; Upper Visean–Serpukhovian, Mississippian, Kizil Formation, Horizon D, Kargaly River, Southern Urals, Russia; B. (C.) ingridae Gandl, 2011, Westfalium D (~Moskovian), Pennsylvanian, near Palencia, Cantabrian Mountains, Spain; B. (C.) latorensis Gandl, 1987, upper part of the Bashkirian, Pennsylvanian, Spain, the quarry near Oviedo, Cantabrian Mountains, Spain; B. (C.) ornatus ( Woodward 1884) , Upper Asbian (~Middle-Upper Visean), Mississippian, Scaleber Knoll reef limestones, Settle, North Yorkshire, England; B. (C.) sagittifer Weber, 1937; Upper Visean–Serpukhovian, Mississippian, Kizil Formation, Horizon D, outcrop no. 494, eastern slopes of the Southern Urals, Russia; B. (C.) ultimus Hahn, Hahn et Yuan, 1989, Kasimovian, Pennsylvanian, Nandan County, Province Guangxi, Southern China; B. (C.) zhenanensis Zhou, 1983, probably Serpukhovian or Bashkirian, Zhenan District, Shanxi Province, China.

Remarks. The subgenus B. (Conimetopus) Hahn and Hahn, 1985, to which the new species described undoubtedly belongs, is comparatively diverse (12 species) and occurs exclusively in Carboniferous deposits of Asia, Europe and North America ( Hahn and Hahn, 1996, p. 120).

There are several main morphological features that are characteristic of B. (Conimetopus). The following can be distinguished: the presence of genal spines, a carapace usually decorated with tubercles, large eyes, the presence of basal glabellar lobes, a smooth edge of the pygidium, ca. 20 rachial rings and 9–11 pairs of pleural ribs on the pygidium. Species assigned to the subgenus are very similar to one another, and the number of diagnostic features of each is comparatively small.

The oldest members of B. (Conimetopus) are known from Middle Visean ( Fig. 4). There are two very closely related species, B. (C.) ornatus ( Woodward, 1884) and B. (C.) esus Hahn and Hahn, 1982 . Brachymetopus (C.) ornatus occurs in the Middle Visean of Europe and has been considered to include three subspecies: B. (C.) ornatus esus Hahn and Hahn, 1982 ; B. (C.) ornatus ornatus ( Woodward, 1884) and B. (C.) ornatus sanctacrucensis Osmólska, 1968 (Hanh and Hahn 1996, pp. 125–126). In this work B. (C.) esus , described from the Lower Warnantium (~Upper Visean) of Belgium ( Hahn and Hahn 1982, p. 93), is considered an independent species. Brachymetopus (C.) ornatus sanctacrucensis from Visean (Substages D 2) of Poland (Holy Cross Mountains) was synonymised with B. (C.) ornatus by Owens (1986, p. 22). Specimens of B. (C.) ornatus and B. (C.) esus have a unique feature for the entire subgenus—a subtriangular shape of the cephalon, which makes them somewhat similar to species of Brachymetopus (Acutimetopus) Hahn and Hahn, 1985 .

Two Mississippian species, B. (C.) inflatus Weber, 1937, and B. (C.) sagittifer Weber, 1937, were described only with pygidia, which were discovered in Horizon D of the Kizil Formation (Upper Visean–Serpukhovian) in eastern slopes of the Southern Urals (Kargaly River).

The species B. (C.) conifrons was described from the Upper Part of the Bashkirian (Namurian C) of the Cantabrian Mountains in Spain ( Gandl, 1987, p.52) and is similar to B. (C.) ornatus in the indented marginal rim, whereas all other species of the subgenus species have a flat rim.

Brachymetopus (C.) zhenanensis Zhou, 1983, was described based on a pygidium from the Late Mississippian or Early Pennsylvanian (probably Serpukhovian or Bashkirian) of the Zhenan District, Shaanxi, China.

The type species, B. (Conimetopus) ouralicus (de Verneuil 1845) was described (de Verneuil, 1845, p. 378, Pl. 28, Fig. 16) from a pygidium discovered in Carboniferous deposits on the Shartimka River in the Southern Urals in Russia. The neotype of B. (C.) ouralicus (de Verneuil 1845) was designated by Osmólska (1968, p. 363) from another pygidium from the same locality. According to the recent data ( Mychko and Alekseev, 2017, p. 63), trilobites in this section occur in are of Bashkirian age, and not Visean as previously thought.

The species B. (C.) arcticus Hahn and Hahn, 1992, was described from well-preserved specimens (cephalon and pygidium) from the Carboniferous Ladrones Limestone of the Alexander Archipelago, southeast Alaska ( Hahn and Hahn, 1992, p. 114; Hahn and Hahn, 1996, p. 122). According to conodonts data, these deposits are Middle Morrowan to Middle Atokan ( Savage and Barkeley, 1985), which correlates with the Bashkirian.

The species B. (C.) latorensis Gandl, 1987, was described based on a cephalon from upper part of the Bashkirian of the Cantabrian Mountains, Spain. Hahn and Hahn (1996) considered it a subspecies of B. (C.) ouralicus . In the present work, it is considered an independent species.

Brachymetopus (C.) ouralicus ingridae Gandl, 2011, is based on well-preserved cephala and pygidia from the Moscovian (Westfalium D) near Palencia, Spain. This form is derived from deposits younger than that of B. (C.) ouralicus , and small but significant differences (ingridae has more rachis rings, usually around 25 and the tubercle between the upper part of the eye and glabella not pronounced; and also according to Gandl (2011) the ingridae has a shorter and wider cephalon) exist on the species level with B. (C.) ouralicus . Hence, ingridae is considered a separate species herein.

The species B. (C.) ultimus Hahn, Hahn and Yuan, 1989, was described based on cephala and a pygidium ( Hahn et al., 1989, p. 129) from the Kasimovian of Southern China (Guangxi Zhuang Autonomous Region, Hechi, Nandan, and Ghe-Gang). Later, a pygidium from the Kasimovian of Vaygach Island, Arctic Russia, which was identified by V.N. Weber (1937, p. 84, Fig. 68c) as Brachymetopus (Brachymetopina) moelleri ? was assigned to this species (Hanh and Hahn, 1996, p. 142).

The species B. (C.?) psilus Hahn and Hahn, 1996, is represented by a single fragmentary cephalon from the Lower Carboniferous Richrather Kalk, Sonderland, Germany ( Hahn and Hahn 1996, p. 141). Amler and Herbig (2006, p. 461) have assigned these strata to the Richrath-Subformation (lower part of Heiligenhaus Formation) and considered that they are of Early Visean age. The cephalon of psilus does not have a tuberculate sculpture, which distinguishes it from all other species B. (Conimetopus) and most members of the genus Brachymetopus . Its affinity is uncertain and it is provisionally excluded from Brachymetopus (Conimetopus) herein.

Thus, the species B. (C.) alekseevi Mychko sp. nov. is the youngest member of the subgenus Brachymetopus (Conimetopus) and the third species known from Carboniferous-Permian deposits in Russia.