Bittium tschokrakense ( Özsayar, 1977 )

Bittium tschokrakense ( Özsayar, 1977)

Figs 21A–F View FIGURE 21

* Bittium reticulatum tschokrakense — Özsayar, 1977: 62, pl. 10, figs 2–3.

Bittium (Bittium) kamyshlakense L. Iljina View in CoL , sp. nov. — Iljina 1993: 67 (pars), pl. 8, figs 10–11 [non fig. 12 = Bittium agibelicum ( Zhizhchenko, 1936) View in CoL ].

Bittium (Bittium) kamyshlakense View in CoL L. Il’ina sp. nov.— Iljina 1994: 35 (pars), pl. fig. 7 [non fig. 8 = Bittium agibelicum ( Zhizhchenko, 1936) View in CoL ].

Bittium kamyshlakense L. Ilyina— Goncharova et al. 2014: 251 View in CoL .

Bittium kamyshlakense L. Iljina— Guzhov 2015: 84 View in CoL .

Bittium reticulatum tschokrakense Özsayar, 1977 — Guzhov 2022: pl. 4, figs 7–8, 11–12, pl. 5. figs 1–6.

Type material. Holotype, specimen illustrated in Özsayar (1977: pl. 10, fig. 2), stored in the Karadeniz Teknik Üniversitesi , Jeoloji Mühendisliği Bölüm , Trabzon ( Turkey); Demirciköy, Sinop ( Turkey), early Chokrakian, Middle Miocene.

Illustrated material. PIN 4450 View Materials /172, SL: 4 mm, MD: 1.7 mm, holotype of Bittium kamyshlakense Iljina, 1993 , Malyi Kamyshlak ( Crimea ), early Chokrakian, Middle Miocene, Fig. 21F View FIGURE 21 . PIN 5794 View Materials /59, SL: 3.8 mm, MD: 1.7 mm, Malyi Kamyshlak ( Crimea ), early Chokrakian, Middle Miocene, Fig. 21A View FIGURE 21 . PIN 5794 View Materials /60, SL: 4.2 mm, MD: 1.8 mm, Malyi Kamyshlak ( Crimea ), early Chokrakian, Middle Miocene, Fig. 21B View FIGURE 21 . PIN 5794 View Materials /61, SL: 4 mm, MD: 1.8 mm, Malyi Kamyshlak ( Crimea ), early Chokrakian, Middle Miocene, Figs 21C View FIGURE 21 1 –C View FIGURE 1 2 View FIGURE 2 . PIN 5794 View Materials /62, SL: 3.9 mm, MD: 1.8 mm, Malyi Kamyshlak ( Crimea ), early Chokrakian, Middle Miocene, Fig. 21D View FIGURE 21 . PIN 5794 View Materials /52, SL: 3.9 mm, MD: 1.8 mm, Semikolennyi ( Russia), early Chokrakian, Middle Miocene, Figs 21E View FIGURE 21 1 –E View FIGURE 1 2 View FIGURE 2 .

Revised description. Small, stocky shell of about eight teleoconch whorls, attaining 5–6 mm in height; apical angle 31–37°. Protoconch of 2.5 smooth convex whorls, terminating in sinusigera (dp = 250 μm). Early teleoconch whorls bicarinate, angled, later whorls with broad subsutural ramp, distinct angulation, moderately convex below. Suture moderately incised, linear. First teleoconch whorl with two prominent spiral cords placed mid-whorl and partially visible suprasutural cord. Later whorls with large, rounded tubercles on spiral cords. Tubercles become denser and smaller on last whorl or become subobsolete. Presence and appearance of secondary spiral sculpture variable, always adapically to primary cords; typically, with subsutural thread. Last whorl convex, strongly constricted, attaining 46–51% of total height. Base with two prominent, widely spaced peribasal cords, two weaker cords over base and three over fasciole. Aperture wide, ovate. Columella excavated. Columellar callus forming thin, narrow rim. Anal canal indistinct. Outer lip thin. Siphonal canal very short, wide.

Paratethyan synonyms. Bittium (Bittium) kamyshlakense Iljina, 1993 ; holotype PIN 4450 View Materials /172, Paleontological Institute of the Russian Academy of Sciences in Moscow, early Chokrakian, Crimea.

Discussion. The type specimens are poorly preserved, abraded shells. Iljina (1993) had much better-preserved material from the Chokrakian of Crimea at hand, which she described as Bittium kamyshlakense Iljina, 1993 . As shown by Guzhov (2022), these specimens are conspecific with Bittium tschokrakense ( Özsayar, 1977) and already Goncharova et al. (2014) treated both species as synonyms but used Bittium kamyshlakense as name, although this is a subjective junior synonym.

Bittium rossicum sp. nov. occurred in the Tarkanian and earliest Chokrakian, whereas Bittium tschokrakense was restricted to a short phase in the middle early Chokrakian. Morphologically, Bittium tschokrakense is intermediate between Bittium rossicum sp. nov. and B. nabokovorum nom. nov. Thus, Bittium tschokrakense seems to be a shortlived anagenetic transition between Bittium rossicum sp. nov. and Bittium nabokovorum nom. nov., from which it differs in its larger tubercles, and the tuberculate spiral cord on the subsutural ramp, and the usually smaller size.

Miocene specimens from the Eastern Paratethys treated herein as Bittium tschokrakense have been identified as the extant Bittium reticulatum by Iljina (1993) and Guzhov (2022) and especially slender specimens are indeed strikingly similar to that variable species. Despite the convergent morphologies of some specimens, we think that the Miocene shells are not conspecific with the extant species. Shells of modern Bittium reticulatum ( Da Costa, 1778) are generally larger, typically attaining ~ 7–10 mm in height, whereas Bittium tschokrakense ranges around 5– 6 mm and Bittium rossicum ranges around 5–7 mm (exceptionally large specimens, however, may attain up to 8 mm ( Guzhov 2022: 21). Generally, B. reticulatum is also more slender, the suture is more incised, and the last whorl is generally more constricted, resulting in a slightly angulated transition from periphery into base. In B. tschokrakense , the last whorl and the transition into the base are convex and the peribasal cords are much weaker. The tubercles of B. reticulatum are generally larger, more close set and it develops varices, which are absent in B. tschokrakense .

Paleoenvironment. Shallow marine, inner neritic.

Distribution. Early Chokrakian of the Eastern Paratethys.

Eastern Paratethys. Early Chokrakian (Middle Miocene): Turkey: Cape Carta, Demirciköy (Sinop District) ( Özsayar 1977; Goncharova et al. 2014); Crimea: Malyi Kamyshlak, Cape Tarkhan, Yuzmyak, Cape Zyuk ( Guzhov 2022); Ciscaucasia : Belaya River, ravine Semikolennyi (Adygea, Russia) ( Guzhov 2022); Transcaucasia : Dzhgali ( Georgia) (hoc opus).