Brachiopod Gyrosoria Cooper, 1973 – a comparative palaeoecological, stratigraphical and taxonomical study

Sklen&#225; &#345; J; Simon E

Brachiopod Gyrosoria Cooper, 1973 – a comparative palaeoecological, stratigraphical and taxonomical study

2009

Sklen&#225 | &#345 | J | Simon E

Cooper (1973) erected Gyrosoria as a monospecific genus for Terebratulites gracilis von Schlotheim, 1813. G. gracilis from white-chalk facies was studied in detail by Steinich (1965) and its morphological adaptation to the environment was discussed by Surlyk (1972). However, populations of G. gracilis, adapted to a high energy environment remained unnoticed and therefore special attention is paid to them in this paper. "Terebratulina" lata Etheridge, 1881, placed here in the genus Gyrosoria, has often been mentioned within the literature and has been used as a zone fossil for more than a century. However, its morphology and its relation to other reported cancellothyridid species has not been studied in detail since its erection. This paper presents an emended diagnosis of the genus, officially assigns the revised lata species to it and presents a detailed morphological study of the genus. The variability of G. lata, studied here, and compared to that of both, the low- and high-energy-environment forms of G. gracilis, points out a clear evolutionary lineage within the genus. Spicular skeletons have been investigated in some Upper Turonian G. lata shells. Particular attention is given to the shell infrastructure. Moreover this paper shows that the palaeogeographical area of G. lata can now be enlarged but a wider application of this species in biostratigraphy should be refused due to the extension of its stratigraphical range.

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