Ripidiorhynchus livonicus ( Buch, 1834 )

Sokiran, Elena V., 2002, Frasnian-Famennian extinction and recovery of rhynchonellid brachiopods from the East European Platform, Acta Palaeontologica Polonica 47 (2), pp. 339-354 : 345-346

Ripidiorhynchus livonicus ( Buch, 1834)

Figs. 8 E–P , 9 .

Terebratula livonica ; Buch 1834: 136, pl. 14: 5.

Camarotoechia pskovensis sp. n.; Nalivkin 1941: 158, pl. 3: 1–4.

Camarotoechia tschudovi sp. n.; Nalivkin 1941: 161, pl. 3: 5–6.

Camarotoechia strugi sp. n.; Nalivkin 1941: 160, pl. 3: 7–10.

Ripidiorhynchus livonicus ; Sartenaer 1966: 7, pl. 1: 1–7.

Emendeddiagnosis.— R.livonicus is characterized by highly variable shell morphology expressed in different height and width of tongue, number of radial ribs, internally by varying deflection of crura. From similar R. huotinus differs by less convex ventral and dorsal valve, depper sulcus, which begins in the first half of the ventral valve and more long septum, while R. huotinus has shallower sulcus beginning in the second half of the ventral valve and short septum. Adult individuals of R. livonicus have a well defined and acute tongue, whileadultindividualsof R.huotinus haveobtusetongueand top of the fold near the anterior commisure, curved toward the ventral valve.

Material.— More than 80 specimens.

Remarks.— Terebratula livonica was described by Buch (1834) from the early Frasnian of the Main Devonian Field. Until 1960, however type material of the species was lost. In the 1930s, Hecker (1933) and Obruchev (1933) lithostratigraphically subdivided the Frasnian strata of the Main Devonian Field. A few years later Nalivkin (1941) described four newspeciesof Camarotoechia fromHecker’sandObruchev’s units: C. aldoga , C. pskovensis , C. tschudovi , and C. strugi ( Fig. 4). He included these species in the livonica group, and consequently C. livonica sensu stricto was abandoned. In 1960 Sartenaer, however, found the type material of T. livonica in the Institut für Paläontologie und Museum der math.− naturwissenschaftlichen Fakultät der Humboldt Universität in Berlin (see Sartenaer 1966, 1997) and erected the genus Ripidiorhynchus , with Terebratula livonica as type species. In addition, he included all of Nalivkin's Camarotoechia species from the Main Devonian Field in Ripidiorhynchus ( Sartenaer, 1966) . Furthermore, he assumed that Ripidiorhynchus pskovensis was a junior synonim of R. livonicus , because they share a high tongue, high and acute median costae strongly indenting the upper part of the tongue, and similar numbers of costae ( Sartenaer 1997). Indeed, the lectotype of Ripidiorhynchus livonicus (see Sartenaer 1966: pl. 1: 1a–e) is very similar to R. pskovensis .

Ripidiorhynchus from the Main Devonian Field shows highly variable features, such as the number of ribs, height and width of tongue, features considered by Nalivkin as diagnostic for his species. For R. pskovensis, Nalivkin (1941) noted that this species had 16–22 ribs on the surface of shell. However, the illustrated paratype of R.pskovensis ( Nalivkin 1941: pl. 3: 1a–d) bears about 40 ribs. The number of ribs on the tongue of R. pskovensis is 2–3, as many as in R. strugi , illustrated by Nalivkin (1941: pl. 3: 7–10). The representatives of Ripidiorhynchus are especially numerous in the upper part of the Chudovo Beds and lower part of the Dubnik Beds in the Izborsk region, but identification of Nalivkin’s species is here practically impossible due to the highly variable morphotypes in sampled populations, expressed in the shape of the tongue and the character of shell ribbing. Biometric investigation of more than 60 complete specimens of Ripidiorhynchus from the lower part of Dubnik Beds of Izborsk locality showed that they have 16 to 45 ribs per 5 mm from the beak, a tongue height from 5.9 to 14.1 mm, and the number of ribs on the tongue varies from 2 to 5. In fact, the specimens could be interpreted as a co−occurence of R. strugi , R. pskovensis and R. tschudovi .

Sartenaer (1997) noted that the type material of R. livonicus originated from four different localities: Gauena on the Gauja River (Central Latvia), Izborsk, Pskov and Chudovo districts (NW Russia). Specimens from these localities are from different levels within the Sargaevo regional stage (i.e., from the Pskov Beds to the Dubnik Beds). The type material of Ripidiorhynchuslivonicus, illustrated by Sartenaer (1966: pl. 1), is also derived from different stratigraphic levels. Thus, it is here considered that R. pskovensis , R. tschudovi and R. strugi are synonyms of the long−ranging form R. livonicus (see Fig. 4).

The oldest representatives of Ripidiorhynchus are known from the Main Devonian Field of the upper part of the Snetogorsk Beds ( Sorokin 1978) and are assigned to R. aldogus ( Nalivkin, 1941) . Ripidiorhynchus aldogus differs from R.livonicus by its more convex shell, obtuse shell margin, low tongue and weakly developed fold. The various species of “ Camarotoechia ” described by Nalivkin (1941) are reillustrated here in Fig. 8 .

Occurrence.—EarlyFrasnian, Pa.transitans Zone,Sargaevo Horizon , northwestern Russia, Latvia, and Lithuania.

Figures

Fig. 8. Early Frasnian (Pa.transitansZone)Ripidiorhynchus from Main Devonian Field, northwestwern Russia. A–D. Ripidiorhynchusaldogus (Nalivkin, 1941), CNIGR 40/6993, ventral, dorsal, anterior, and lateral views. Pskov beds, Sjas River, Konopljankina village. E–P. Ripidiorhynchuslivonicus (Buch, 1834). E–H. CNIGR 45/6993, ventral, dorsal, anterior, and lateral views. Chudovo beds, Velikaya River, Vybuty rapids. I–L. CNIGR 47/6993, ventral, dorsal, anterior, and lateral views. Chudovo beds, Kerest River, Luki village. M–P. CNIGR 37/6993, in ventral, dorsal, anterior, and lateral views. Pskov beds, Velikaya River. All × 1.5

Fig. 9. Transverse serial sections of Ripidiorhynchus livonicus (Buch, 1834) from the early Frasnian of the Main Devonian Field, northwestern Russia. Numbers refer to distances in mm from the top of the ventral umbo. A. CNIGR 1/13076. B. Longitudinal section. CNIGR 2/13076, Chudovo beds, Vybuty rapids, Velikaya River, Pskov region. C. CNIGR 3/13076, Dubnik beds, quarry near town Stary Izborsk, Pechory district.