1. Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA
2. Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20013, USA
3. Museo Paleontológico Egidio Feruglio, Consejo Nacional de Investigaciones Científicas y Técnicas, Trelew 9100, Chubut, Argentina
4. Plant Biology Section, School of Integrative Plant Science, Cornell University, Ithaca, New York 14853, USA