The oldest heliolitids from the early Katian of the East Baltic region

Abstract

The earliest heliolitids appeared more or less simultaneously in the Late Ordovician shallow seas of different palaeocontinents. In this paper the early Katian heliolitids, represented by the genus Protaraea, are described from the East Baltic region (North Estonia and north-west Russia) and discussed in detail for the first time. A new species Protaraea procella n. sp. Mõtus is established and a neotype for Protaraea diffluens (Eichwald) is designated. The new species shows a wide intraspecific variability including variably oriented septal trabeculae, which results in corallites commonly being poorly defined or not apparent in transverse sections of coralla. P. procella has much larger coralla than P. diffluens, with predominantly laminar growth forms, whereas the latter species is usually encrusting, suggesting that the two species were adapted to different palaeoenvironmental conditions. The new data indicate that these heliolitids, together with other tabulate corals, were already geographically dispersed in the early Katian and thereby contribute to a better understanding of coral diversification patterns in Baltica.

Keywords:

• Heliolitida
• Coccoserididae
• Protaraea
• Ordovician
• East Baltic region

Acknowledgements

The authors are grateful to Mark Wilson (Department of Geology, The College of Wooster, Ohio, USA) for donating specimens for this study. Professor Dimitri Kaljo, Dr Olle Hints and Dr Linda Hints and (Institute of Geology, Tallinn University of Technology) are thanked for revising and providing useful comments for this manuscript. Professor Gregory E. Webb (School of Earth Sciences, The University of Queensland) is thanked for linguistic improvements. We acknowledge Dr Owen Dixon for reviewing the manuscript and for valuable comments. Many thanks are due to Dr Natsuko Adachi and Dr Yuki Tokuda, Osaka City University, who found two studied specimens from Vasalemma quarry and to Dr Nikolaj Nataljin and Anton Krylov, St Peterburg State University, who donated two specimens from Pechurki quarry. Much gratitude is expressed to Georgij Iskjul (All Russian Geological Research Institute, “VSEGEI”), for his help with measurements of specimens from Pechurki quarry. The study was supported by the target-financed project (from the Estonian Ministry of Education and Science) SF0140020s08.