1. 1 Department of Geology, University of Tartu, Ravila 14A, 50411 Tartu, Estonia
2. 2 Department of Earth Sciences, The College of Wooster, Wooster, Ohio 44691, USA
3. 3 Borissiak Paleontological Institute, Russian Academy of Sciences, Moscow 117647, Russia
4. 4 Department of Geology, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia