9/1/2008 - present Interim Director, Don Sundquist Center of Excellence in Paleontology, College of Arts and Sciences, East Tennessee State University, Johnson City, TN, U.S.A
02/2008 - present Curator of fossil plants, East Tennessee State University & General Shale Brick Natural History Museum, Gray, TN, U.S.A
8/2006 - present Assistant Professor, Department of Biological Sciences, East Tennessee State University, Johnson City, TN, U.S.A.
9/2003 - July/2006 Assistant Professor, Department of Biology, University of Wisconsin-Stevens Point, U.S.A.
9/2001 – 8/2003 Collection Manager of Paleobotany, Department of Geology, Field Museum of Natural History, Chicago, U.S.A.
11/1998 – 8/2001 Postdoctoral Fellow, Department of Geological Sciences, University of Saskatchewan, Canada.
01/1997 - 10/1998 Alexander von Humboldt Research Fellow, Museum of Natural History, Humboldt University of Berlin, Germany.
04/1996 - 12/1996 Associate Research Professor, Department of Paleobotany, Nanjing Institute of Geology & Paleontology, Chinese Academy of Sciences.
03/1995 - 03/1996 JSPS (Japan Society for Promotion of Sciences) Postdoctoral Fellow, Laboratory of Forest Ecology, Department of Environmental Studies, Faculty of Horticulture, Chiba University, Japan.
02/1994 - 01/1995 ÖAD (Austrian Foreign Exchange Service) Research Fellow, Laboratory of Paleobotany & Palynology, Institute of Paleontology, University of Vienna, Austria
11/1992 - 01/1994 Assistant Research Professor, Department of Paleobotany, Nanjing Institute of Geology & Paleontology, Chinese Academy of Sciences.