GLYPTORTHIS (FOERSTE, 1914) AND BASSETTELLA NEW GENUS (BRACHIOPODA: ORTHIDA) FROM THE LATE ORDOVICIAN OF THE EAST BALTIC

Journal of Paleontology, Jan 2008 by Zuykov, Michael A, Butts, Susan H

INTRODUCTION

THE GENUS Glyptorthis Foerste, 1914 is a rare component of the Late Ordovician to early Silurian brachiopod faunas of the East Baltic. Hints and Roomusoks (1997) reported on the occurrence of Glyptorthis in seven stratigraphic levels within the Upper Caradoc, Ashgill and Llandovery, in a paper summarizing the stratigraphy of Estonia. To date, however, very few of these brachiopods have been studied in detail. Three species from the Ashgill and Llandovery were established by Rubel (1962) and Roomusoks (1970), whereas some unnamed Caradoc taxa were listed only in the latter paper. Collections made since 1987 by S. S. Terentiev and M. A. Zuykov revealed that rare specimens of Glyptorthis-like brachiopods occur in fossiliferous lower Caradocian (Idavere Regional Stage) strata in the western part of the St. Petersburg region, northwestern Russia. These specimens, assigned herein to a new glyptorfhid genus and species Bassettella gracilis, comprise the core of this paper. Moreover, generic affinities of Estonian species from the Ashgill currently assigned to Glyptorthis are discussed. The type specimen of J. Hall (1847) in the American Museum of Natural History (New York) and specimens from the type area in the Schuchert Brachiopod Collection in the Peabody Museum of Natural History, Yale University (New Haven), have been investigated for comparative purposes.

MATERIAL AND LOCALITES

The brachiopods described here were collected from localities in NW Russia, Estonia, and North America (Fig. 1). The Bassettella gracilis n. gen. and sp. fossil localities from the St. Petersburg region (NW Russia) are given in Figure 1, as is a correlation chart with the Estonian stratigraphic position of B. gracilis.

NW Russia.-Forty-one specimens of Bassettella gracilis occur in calcareous clay of the Gryazno Formation in a small quarry situated in the northern outskirts of the village Klyasino in the western part of the St. Petersburg region (Fig. 1). Zuykov and Hints (2001) assigned the Gryazno Formation to the lower Idaverian age because of the occurrence of zonal chitinozoans Eisenackitna rhenana and Lagenochitina dalbyensis, which provides a precise correlation with the Upper Ordovician sequences in Estonia and Scandinavia (Nolvak, 1997). Jaanusson (1995) introduced the Haljala Regional Stage to replace the Idavere and Johvi regional stages in the Baltic region. This new subdivision is used widely in Estonia (Nolvak, 1997, etc.); however, we follow the traditional subdivision of the Ordovician of Baltoscandia as it was presented by Mannil and Meidla (1994) (Fig. 1).

Estonia.-The glyptorthid brachiopods described in this report are from the lower Caradoc (Bassettella new genus) and Ashgill (Glyptorthis) strata of North and West Estonia, respectively (Fig. 1). Two specimens of Bassettella gracilis come from the localities near the Alliku and Kiikla villages (collected by A. Opik and V. K5rvel) where the Kahula Formation (Johvi Stage-see discussion above) is exposed (R55musoks, 1970). The general lithology of the Johvian rocks in the area is argillaceous limestone with K-bentonite beds (Hints, 1997). Four specimens of Glyptorthis plana Roomusoks, 1964 are from the type section of the Korgessaare Formation (Vormsi Regional Stage) situated on the outskirts of the Korgessaare village in the Hiiumaa Island. The latter formation is characterized by argillaceous limestone (Hints and Meidla, 1997). These specimens were collected by A. Roomusoks and D. Kaljo and are part of the type collection of Tartu University, Estonia (TUG).

North America.-General data on the locality and age of Orthis insculpta was provided by Hall (1847) as "Maysville (Kentucky), Cincinnati & Oxford (Ohio), Madison (Indiana)." As recorded on the museum label, the holotype of this species was collected by James Hall from the Upper Ordovician Hudson River Group, Cincinnati, Ohio, USA. 32 specimens of Glyptorthis insculpta from the Schuchert Brachiopod Collection were restudied in the course of our examination of the brachiopods from the Upper Ordovician (Ashgill) of the Ohio Valley. Ordovician stratigraphy and paleontology of this area has been described in detail (for references, see Brett and Algeo, 2001).

Repository of illustrated specimens and abbreviations.-American Museum of Natural History, New York, particularly the J. Hall Collection (AMNH); Peabody Museum of Natural History, Yale University, New Haven, CT, particularly the Schuchert Brachiopod Collection (YPM); Tartu University, Estonia (TUG); Central Scientific-Research Geological Exploration Museum named after F. N. Chernyshev, St. Petersburg, Russia (CNIGR); and National Museum of Wales, Cardiff, UK (NMW).

SYSTEMATIC PALEONTOLOGY

Order ORTHIDA Schuchert and Cooper, 1932

Suborder ORTHIDINA Schuchert and Cooper, 1932

Superfamily ORTHOIDEA Woodward, 1852

Family GLYPTORTHIDAE Schuchert and Cooper, 1931

Genus GLYPTORTHIS Foerste, 1914

Type species.-Orthis insculpta Hall, 1847, from the Richmond Group (Ashgill), Ohio, USA.