In the United States: Ian Tattersall of the American Museum of Natural History in New York; John Thorstensen, Mary K. Hudson, and David Blanchflower of Dartmouth College in Hanover, New Hampshire; Dr. William Abdu and Dr. Bryan Marsh of Dartmouth-Hitchcock Medical Center in Lebanon, New Hampshire; Ray Anderson and Brian Witzke of the Iowa Department of Natural Resources, Iowa City; Mike Voorhies of the University of Nebraska and Ashfall Fossil Beds State Park near Orchard, Nebraska; Chuck Offenburger of Buena Vista University, Storm Lake, Iowa; Ken Rancourt, director of research, Mount Washington Observatory, Gorham, New Hampshire; Paul Doss, geologist of Yellowstone National Park, and his wife, Heidi, also of the National Park; Frank Asaro of the University of California at Berkeley; Oliver Payne and Lynn Addison of the National Geographic Society; James O. Farlow, Indiana-Purdue University; Roger L. Larson, professor of marine geophysics, University of Rhode Island; Jeff Guinn of the Fort Worth Star-Telegram newspaper; Jerry Kasten of Dallas, Texas; and the staff of the Iowa Historical Society in Des Moines.

In England: David Caplin of Imperial College, London; Richard Fortey, Len Ellis, and Kathy Way of the Natural History Museum; Martin Raff of University College, London; Rosalind Harding of the Institute of Biological Anthropology in Oxford; Dr. Laurence Smaje, formerly of the Wellcome Institute; and Keith Blackmore of The Times.

In Australia: the Reverend Robert Evans of Hazelbrook, New South Wales; Alan Thorne and Victoria Bennett of the Australian National University in Canberra; Louise Burke and John Hawley of Canberra; Anne Milne of the Sydney Morning Herald ; Ian Nowak, formerly of the Geological Society of Western Australia; Thomas H. Rich of Museum Victoria; Tim Flannery, director of the South Australian Museum in Adelaide; and the very helpful staff of the State Library of New South Wales in Sydney.