INTRODUCTION

A new species of the genus Bellazona is described in this paper. This genus was established by Gordon and Yochelson (1987) based on the type species from the Upper Mississippian of the southwestern USA. Until recently, the genus Bellazona was represented by two species, B. bella (Walcott, 1884) and B. polita Gordon et Yochelson, 1987. According to the correlation scheme proposed by Korn and Titus (2011, text-fig. 4), B. bella occurs in the interval of the Viséan of the Chainman Formation (Utah), and also in the interval above the base of the Serpukhovian in the Diamond Peak Formation (Nevada), whereas B. polita occurs in the Viséan–Lower Serpukhovian interval of the Chainman Formation.

The find of the new species in the Lower Permian of southern Cisuralia essentially broadens the geochronological and geographical boundaries of Bellazona. The geochronological hiatus is around 32 Myr. In this case, the so-called “Lazarus effect” reflects on one hand the incompleteness of the fossil record, and on the other hand shows that the data on the taxonomic diversity of Paleozoic gastropods are clearly insufficient.

In addition, the new species described in this paper allows the diagnosis of the genus Bellazona to be emended.

MATERIAL

This paper is based on specimens collected by the present author in the Shakhtau Mountain open cast mine. Shakhtau Mountain is one in a chain of exposed Early Permian reefs, so-called “Bashkirian shikhans.” A chain of shikhans extends in a north-south direction to the east of Sterlitamak (Fig. 1). Each shikhan is composed of reef limestone and represents a pinnacle reef. Prior to the beginning of the mining, the height of Shakhtau above the ground surface was about 170 m (altitude 360 m). At present, Shakhtau Mountain has been almost completely demolished by the open cast mine.

Fig. 1.
figure 1

Map showing the locality of Bellazona acuta sp. nov.: (a) position of Bashkirian shikhans: Tratau, Shakhtau, Kushtau, and Juraktau; (b) gastropod localities of the Shakhtau Quarry.

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Specimens described in this paper were collected in the southern part of the quarry between the altitude marks 127 and 155 m. The preliminary estimate of the geological age based on geological exploration profiles is Late Asselian.

Aggregations of faunal remains are found sporadically in the body of the patch-reef. Despite the large amount and diversity of fossils in such aggregations, the total number of samples collected during five expeditions (fall of 2015, spring and fall of 2016, and 2017) was low due to poor preservation. Poor preservation is associated either with hard rocks and the impossibility of extracting of shell from the rock matrix, or with filling of voids left by leached shells with various minerals: most commonly crystals or crusts of calcite and/or ozokerite, less commonly aragonite, gypsum, celestine, and sulphur. Gastropods are found as fossilized shells and imprints. Interestingly, specimens of the same species can be preserved differently within the same block of rock. At present, the gastropod collection studied includes around 560 specimens (coll. no. 5538, housed in the Orlov Paleontological Museum of Paleontological Institute, Russian Academy of Sciences). The casts were made using dental latex.

RESULTS AND DISCUSSION

The taxonomy of the genus Bellazona in unresolved because the morphology of its protoconch remains unknown, whereas characters of the teleoconch largely coincide with characters of Cerithioides Haughton, 1859. The species of Bellazona described by Gordon and Yochelson (1987) are distinguished from one another only by the size of the apical angle. Following the logic of the existing uncertainty in the identification of Cerithioides, these taxa could be considered as morphotypes of the same species, which in turn can be considered as a species of Cerithioides. For instance, in contrast to the diagnosis proposed by Knight et al. (1960), Cerithioides, which normally has spiral ornamentation on the basal surface, includes several species with a smooth shell. Bellazona also lacks ornamentation, and thus, differences between the genera (with this broadly understood diagnosis of Cerithioides) are only observed in the position of the selenizone.

For the third genus from this group Glyphodeta Donald, 1895, its type species, Murchisonia zonata Donald, 1887, the position of the selenizone as shown by Knight (1941, pl. 45, fig. 6) to be intermediate in position between Cerithioides and Bellazona, so all three type species of the genera under discussion can be placed in one morphological lineage based on the position of the selenizone.

Knight (1941, p. 132, pl. 45, fig. 6) noted that many characters of Glyphodeta zonata (Donald, 1887) described and figured by Donald (1887) are absent in the type material. Even though Donald (later in life Longstaff) rejected the use of Glyphodeta as a taxon based on “erroneous characters” (Longstaff, 1926, p. 529). Knight et al. (1960) classified it with the family Murchisoniidae. Later Batten (1966, p. 74, pl. 8, fig. 9) described several specimens of Glyphodeta zonata from the Hotwells Limestone. The state of preservation of the specimens he studied was much better than of the type material. They show a basal surface ornamented with wide bands separated by thin grooves. Thus, differences between the type species Glyphodetazonata (Donald, 1887) and Cerithioides telescopium Haughton, 1859, which were also studied in detail and described by Batten (1966) are in my opinion species level characters. Furthermore, they correspond to the species-level characters indicated by Batten for the genus Cerithioides: “whorl and shell shape, sutural contact position and position of the selenizone on the whorl” (Batten, 1966, p. 77). As previously (Mazaev, 2011), I maintain that Glyphodeta is a junior synonym of Cerithioides.

Now, characterizing the genus Bellazona it is possible to note that firstly, Cerithioides shows variation in the position of the selenizoneFootnote 1, and secondly, species lacking spiral ornamentation on the basal surface should be excluded from this genus. By thus defining the major characters of Cerithioides, it is possible to talk about the separation of Bellazona and emend its diagnosis.

SYSTEMATIC PALEONTOLOGY

  • Family Murchisoniidae Koken, 1896

  • Genus Bellazona Gordon et Yochelson, 1987

Bellazona: Gordon and Yochelson, 1987, p. 80.

Type species. Loxonema bella Walcott, 1884, Mississippian, interval above the base of the Serpukhovian, Diamond Peak Formation, Nevada.

Diagnosis. Shell turriform with no umbilicus. Profile of lateral side in early whorls almost straight or weakly convex; in last whorls rounded; basal surface moderately convex, smooth. Lateral surface smooth, subsutural lira developed to a varying extent or absent. Selenizone wide, smooth, straight or slightly convex in cross-section. Selenizone wide, straight or slightly convex in cross-section, delineated by two thin grooves; lying below point of whorl periphery, lower boundary of the selenizone occurring immediately above or below suture. Growth lines above selenizone inclined prosoclinally, below selenizone opistoclinally.

Composition. Two species from the Mississippian of North America, one species from the Lower Permian of Eastern Europe.

Comparison. This genus is distinguished from Cerithioides Haughton, 1859 by a combination of two characters: low position of the selenizone and smooth basal surface.

  • Bellazona acuta Mazaev, sp. nov.

Etymology. From the Latin acutus (acute).

Holotype. PIN, no. 5538/7-69, shell imprint. Paratypes: nos. 5538/7-146, 5538/6-14, shell imprints; 5538/7-185, fossilized shell: Bashkortostan, open cast mine (quarry) on Shakhtau Mountain (east of Sterlitamak), southern side of the quarry, altitude 150–167 m; Lower Permian, Asselian.

Description. (Fig. 2). The shell is turriform, formed by numerous (at least 12), slowly expanding whorls, with no umbilicus. The suture is thin, channeled, relatively deep. The protoconch is not preserved. The profile of the lateral surface in early whorls is moderately convex. In adult and terminal whorls, the profile of the lateral surface is generally evenly rounded. The transition of the lateral surface to the basal is gradual. The point of the whorl periphery is unstable, at different growth stages is either in mid-whorl, or shifted downward between the mid-flank and the suture. At a gerontic stage, the whorl profile is sharply changed: the distance between the shell axis and selenizone sharply increases, so the last quarter of the whorl, the angle of the upper part of the lateral surface becomes less steep, and the angle of the last half of the whorl changes by 20 degrees. The shell surface is ornamented by a subsutural lira and the selenizone. The substutural lira is formed beginning approximately from the fifth whorl; it is cordlike in profile, with numerous relatively massive, mainly collabrally elongated nodes. Spaces between the nodes are approximately as wide as the nodes. In the last whorl, the nodes are weakly developed or altogether absent. In some specimens, the subsutural lira is absent in the last whorl. The selenizone is wide, straight or slightly convex in cross-section, smooth, delineated by two thin grooves. At the gerontic stage (less than ¼ of the last whorl), it is flat sharply raised over the whorl surface. The lunules are the shape of narrow, deep grooves, separated by very wide spaces. The selenizone lies below the mid-flank, the upper boundary of the selenizone is lower than the periphery point; the lower boundary coincides with the suture. The notch is wide and relatively short. Its length is approximately 1.5 times its width. The basal surface is extended downwards. The columella is long and corkscrew-like. Growth lines are generally absent, but at a gerontic stage they are very sharp, in the shape of thin, deep grooves separated by very wide spaces; above the selenizone they are weakly convex, sharply bent near the selenizone, and are inclined at about 75° to the selenizone. Below the selenizone they are moderately convex, transiting smoothly to the basal surface, and their shape and angle form a mirror-image of the growth lines on the upper surface of the whorl.

Fig. 2.
figure 2

Bellazona acuta sp. nov., x 4: southern wall of the Shakhtau Quarry; Lower Permian, Asselian; (a–c) specimen no. 5538/7-146, paratype, (a) mold with a notch imprint, (b, c) latex casts, imprint of the initial whorls is covered by small calcite crystals; (d, e) specimen no. 5538/6-14, paratype, latex casts; (f, g) specimen no. 5538/7-69, holotype, latex casts; (h) specimen no. 5538/7-185, paratype, fossilized shell. Explanations: (s) selenizone.

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Dimensions in mm:

Specimen no.

Shell height

Maximum diameter

5538/6-14

>16.3

>6.8

5538/7-69

⪢19.8

>7.7

5538/7-146

>16.5

>6.8

5538/7-185

≈27.7

>10.9

Comparison. This species is distinguished from B. bella (Walcott, 1884) and B. polita Gordon et Yochelson, 1987 by the more strongly elongated shell with more numerous whorls, which are more rounded in cross-section, in the presence of the subsutural lira ornamented by nodes.

Occurrence. Type locality.

Material. Altogether 7 specimens: 1 specimen in locality no. 5538/6 and 6 specimens in locality no. 5538/7.