ACKNOWLEDGMENTS

Financial support for this study was provided by Natural Sciences and Engineering Research Council (NSERC) Discovery Grants 311727-05/08 and 311726-05/08 awarded to Mángano and Buatois, respectively. Earlier work in northwest Argentina was supported by the Argentinean Research Council (Conicet), the Antorchas Foundation and the Argentinean Agency of Scientific Research. G. Albanesi, R. Astini, C. Moya, G. Ortega, E. Vaccari, and B. Waisfeld shared their knowledge on the Ordovician of northwest Argentina during various field seasons. V. Ramos provided useful comments on the tectonic setting. N. Hamoumi guided us through the Ordovician outcrops of Morocco. A. Seilacher provided access to his trace-fossil collection at the Geological Institute of the University of Tübingen. P. Desjardins made unpublished information on the Gog Group available. R. Pickerill commented on the distribution of Trichophycus in the eastern Newfoundland successions. R. Bromley and S. Jensen helped us with valuable comments to an earlier draft of the manuscript. The two Palaeontologica Electronica reviewers also provided very useful criticism. B. Novakovski assisted us with sample preparation, P. Desjardins with drawings and C. Pirrone with photographs.