Shell microstructure of Cornulitessemiapertus Öpik, 1930 and other early cornulitids from the Ordovician of North Estonia

Abstract

The shell microstructure of Ordovician Cornulites species is in general similar to Silurian species. The earliest cornulitid from Baltica, C. semiapertus Öpik, 1930 (Darriwilian), has vesicles, lamellar shell structure, but no pseudopunctae. The earliest Cornulites with pseudopunctae appears in the Katian. The initial shell structure of cornulitids may have been microlamellar, but without pseudopunctae.

Keywords:

• cornulitids
• skeletal microstructure
• Ordovician
• Baltica
• Estonia

Acknowledgements

I am grateful to H. Mutvei from the Swedish Museum of Natural History for help with SEM and useful discussions. P.D. Taylor from Natural History Museum and A. Kouchinsky from Swedish Museum of Natural History are thanked for their constructive reviews. I am also grateful to the European Commission program HIGH LAT at the Swedish Natural History Museum, Stockholm, for a grant to the project “Shell structure, palaeoecology, and systematic position of the problematic fossils cornulitids”. I am indebted to the target financed project (from the Estonian Ministry of Education and Science) SF0180051s08 (Ordovician and Silurian climate changes, as documented from the biotic changes and depositional environments in the Baltoscandian Palaeobasin) for financial support.